1.5. Merchant Backend API

The */private/* endpoints are only supposed to be exposed to the merchant internally, and must not be exposed on the Internet.

Most endpoints given here can be prefixed by a base URL that includes the specific instance selected (BASE_URL/instances/$INSTANCE/). If /instances/ is missing from the request path, the default instance is used.

1.5.1. Configuration API

The configuration API exposes basic information about a merchant backend, such as the implemented version of the protocol and the currency used.

GET /config

Return the protocol version and currency supported by this merchant backend.

Response:

200 OK:
The exchange accepted all of the coins. The body is a VersionResponse.
interface VersionResponse {
  // libtool-style representation of the Merchant protocol version, see
  // https://www.gnu.org/software/libtool/manual/html_node/Versioning.html#Versioning
  // The format is "current:revision:age".
  version: string;

  // Name of the protocol.
  name: "taler-merchant";

  // Currency supported by this backend.
  currency: string;

}

1.5.2. Wallet API

This section describes (public) endpoints that wallets must be able to interact with directly (without HTTP-based authentication). These endpoints are used to process payments (claiming an order, paying for the order, checking payment/refund status and aborting payments), process refunds (check refund status, obtain refund), and to pickup tips.

Claiming an order

The first step of processing any Taler payment consists of the (authorized) wallet claiming the order for itself. In this process, the wallet provides a wallet-generated nonce that is added into the contract terms. This step prevents two different wallets from paying for the same contract, which would be bad especially if the merchant only has finite stocks.

A claim token can be used to ensure that the wallet claiming an order is actually authorized to do so. This is useful in cases where order IDs are predictable and malicious actors may try to claim orders (say in a case where stocks are limited).

POST /orders/$ORDER_ID/claim

Wallet claims ownership (via nonce) over an order. By claiming an order, the wallet obtains the full contract terms, and thereby implicitly also the hash of the contract terms it needs for the other public APIs to authenticate itself as the wallet that is indeed eligible to inspect this particular order’s status.

Request:

The request must be a ClaimRequest

interface ClaimRequest {
  // Nonce to identify the wallet that claimed the order.
  nonce: string;

  // Token that authorizes the wallet to claim the order.
  // *Optional* as the merchant may not have required it
  // (create_token set to false in PostOrderRequest).
  token?: ClaimToken;
}

Response:

200 OK:
The client has successfully claimed the order. The response contains the contract terms.
404 Not found:
The backend is unaware of the instance or order.
409 Conflict:
The someone else claimed the same order ID with different nonce before.
interface ClaimResponse {
  // Contract terms of the claimed order
  contract_terms: ContractTerms;

  // Signature by the merchant over the contract terms.
  sig: EddsaSignature;
}

Making the payment

POST /orders/$ORDER_ID/pay

Pay for an order by giving a deposit permission for coins. Typically used by the customer’s wallet. Note that this request does not include the usual h_contract argument to authenticate the wallet, as the hash of the contract is implied by the signatures of the coins. Furthermore, this API doesn’t really return useful information about the order.

Request:

The request must be a pay request.

Response:

200 OK:
The exchange accepted all of the coins. The body is a payment response. The frontend should now fulfill the contract. Note that it is possible that refunds have been granted.
400 Bad request:
Either the client request is malformed or some specific processing error happened that may be the fault of the client as detailed in the JSON body of the response.
402 Payment required:
There used to be a sufficient payment, but due to refunds the amount effectively paid is no longer sufficient. (If the amount is generally insufficient, we return “406 Not Acceptable”, only if this is because of refunds we return 402.)
403 Forbidden:
One of the coin signatures was not valid.
404 Not found:
The merchant backend could not find the order or the instance and thus cannot process the payment.
406 Not acceptable:
The payment is insufficient (sum is below the required total amount).
408 Request timeout:
The backend took too long to process the request. Likely the merchant’s connection to the exchange timed out. Try again.
409 Conflict:
The exchange rejected the payment because a coin was already spent before. The response will include the coin_pub for which the payment failed, in addition to the response from the exchange to the /deposit request.
410 Gone:
The offer has expired and is no longer available.
412 Precondition failed:
The given exchange is not acceptable for this merchant, as it is not in the list of accepted exchanges and not audited by an approved auditor.
502 Bad gateway:
The merchant’s interaction with the exchange failed in some way. The client might want to try later again. This includes failures like the denomination key of a coin not being known to the exchange as far as the merchant can tell.
504 Gateway timeout:
The merchant’s interaction with the exchange took too long. The client might want to try later again.

The backend will return verbatim the error codes received from the exchange’s deposit API. If the wallet made a mistake, like by double-spending for example, the frontend should pass the reply verbatim to the browser/wallet. If the payment was successful, the frontend MAY use this to trigger some business logic.

interface PaymentResponse {
  // Signature on TALER_PaymentResponsePS with the public
  // key of the merchant instance.
  sig: EddsaSignature;

}
interface PayRequest {
  // The coins used to make the payment.
  coins: CoinPaySig[];

  // The session for which the payment is made (or replayed).
  // Only set for session-based payments.
  session_id?: string;

}
export interface CoinPaySig {
  // Signature by the coin.
  coin_sig: EddsaSignature;

  // Public key of the coin being spend.
  coin_pub: EddsaPublicKey;

  // Signature made by the denomination public key.
  ub_sig: RsaSignature;

  // The hash of the denomination public key associated with this coin.
  h_denom: HashCode;

  // The amount that is subtracted from this coin with this payment.
  contribution: Amount;

  // URL of the exchange this coin was withdrawn from.
  exchange_url: string;
}

Querying payment status

GET /orders/$ORDER_ID

Query the payment status of an order. This endpoint is for the wallet. When the wallet goes to this URL and it is unpaid, they will be prompted for payment. This endpoint typically also supports requests with the “Accept” header requesting “text/html”. In this case, an HTML response suitable for triggering the interaction with the wallet is returned, with timeout_ms ignored (treated as zero). If the backend installation does not include the required HTML templates, a 406 status code is returned.

In the case that the request was made with a claim token (even the wrong one) and the order was claimed and paid, the server will redirect the client to the fulfillment URL. This redirection will happen with a 302 status code if the “Accept” header specified “text/html”, and with a 202 status code otherwise.

Request:

Query Parameters
  • h_contract=HASH – hash of the order’s contract terms (this is used to authenticate the wallet/customer in case $ORDER_ID is guessable). Required once an order was claimed.
  • token=TOKENOptional. Authorizes the request via the claim token that was returned in the PostOrderResponse. Used with unclaimed orders only. Whether token authorization is required is determined by the merchant when the frontend creates the order.
  • session_id=STRINGOptional. Session ID that the payment must be bound to. If not specified, the payment is not session-bound.
  • timeout_ms=NUMBEROptional. If specified, the merchant backend will wait up to timeout_ms milliseconds for completion of the payment before sending the HTTP response. A client must never rely on this behavior, as the merchant backend may return a response immediately.
  • refund=AMOUNTOptional. Indicates that we are polling for a refund above the given AMOUNT. Only useful in combination with timeout.
  • await_refund_obtained=BOOLEANOptional. If set to “yes”, poll for the order’s pending refunds to be picked up.

Response:

200 OK:
The response is a StatusPaidResponse.
202 Accepted:
The response is a StatusGotoResponse. Only returned if the content type requested was not HTML.
302 Found:
The client should go to the indicated location. Only returned if the content type requested was HTML.
402 Payment required:
The response is a StatusUnpaidResponse.
403 Forbidden:
The h_contract (or the token for unclaimed orders) does not match the order and we have no fulfillment URL in the contract.
410 Gone:
The response is a StatusGoneResponse.
404 Not found:
The merchant backend is unaware of the order.
406 Not acceptable:
The merchant backend could not load the template required to generate a reply in the desired format. (Likely HTML templates were not properly installed.)
interface StatusPaid {
  // Was the payment refunded (even partially, via refund or abort)?
  refunded: boolean;

  // Is any amount of the refund still waiting to be picked up (even partially)
  refund_pending: boolean;

  // Amount that was refunded in total.
  refund_amount: Amount;
}
interface StatusGotoResponse {
  // The client should go to the fulfillment URL, it may be ready or
  // might have some other interesting status.
  fulfillment_url: string;
}
interface StatusUnpaidResponse {
  // URI that the wallet must process to complete the payment.
  taler_pay_uri: string;

  // Status URL, can be used as a redirect target for the browser
  // to show the order QR code / trigger the wallet.
  fulfillment_url?: string;

  // Alternative order ID which was paid for already in the same session.
  // Only given if the same product was purchased before in the same session.
  already_paid_order_id?: string;
}
// The client tried to access the order via the claim
// token (and not a valid h_contract), but the order can't be claimed
// anymore, as it is already paid.
interface StatusGoneResponse {
  // Fulfillment URL for the order.
  fulfillment_url: string;
}

Demonstrating payment

In case a wallet has already paid for an order, this is a fast way of proving to the merchant that the order was already paid. The alternative would be to replay the original payment, but simply providing the merchant’s signature saves bandwidth and computation time.

Demonstrating payment is useful in case a digital good was made available only to clients with a particular session ID: if that session ID expired or if the user is using a different client, demonstrating payment will allow the user to regain access to the digital good without having to pay for it again.

POST /orders/$ORDER_ID/paid

Prove that the client previously paid for an order by providing the merchant’s signature from the payment response. Typically used by the customer’s wallet if it receives a request for payment for an order that it already paid. This is more compact then re-transmitting the full payment details. Note that this request does include the usual h_contract argument to authenticate the wallet and to allow the merchant to verify the signature before checking with its own database.

Request:

The request must be a paid request.

Response:

204 No content:
The merchant accepted the signature. The frontend should now fulfill the contract. Note that it is possible that refunds have been granted.
400 Bad request:
Either the client request is malformed or some specific processing error happened that may be the fault of the client as detailed in the JSON body of the response.
403 Forbidden:
The signature was not valid.
404 Not found:
The merchant backend could not find the order or the instance and thus cannot process the request.
409 Conflict:
The provided contract hash does not match this order.
interface PaidRequest {
  // Signature on TALER_PaymentResponsePS with the public
  // key of the merchant instance.
  sig: EddsaSignature;

  // hash of the order's contract terms (this is used to authenticate the
  // wallet/customer and to enable signature verification without
  // database access).
  h_contract: HashCode;

  // Session id for which the payment is proven.
  session_id: string;
}

Aborting incomplete payments

In rare cases (such as a wallet restoring from an outdated backup) it is possible that a wallet fails to complete a payment because it runs out of e-cash in the middle of the process. The abort API allows the wallet to abort the payment for such an incomplete payment and to regain control over the coins that were spent so far. Aborts are not permitted for payments that completed. In contrast to refunds, aborts do not require approval by the merchant because aborts always are for incomplete payments for an order and never for established contracts.

POST /orders/$ORDER_ID/abort

Abort paying for an order and obtain a refund for coins that were already deposited as part of a failed payment.

Request:

The request must be an abort request. We force the wallet to specify the affected coins as it may only request for a subset of the coins (i.e. because the wallet knows that some were double-spent causing the failure). Also we need to know the coins because there may be two wallets “competing” over the same order and one wants to abort while the other still proceeds with the payment. Here we need to again know which subset of the deposits to abort.

Response:

200 OK:
The merchant accepted the request, and passed it on to the exchange. The body is a a merchant refund response. Note that the exchange MAY still have encountered errors in processing. Those will then be part of the body. Wallets MUST carefully consider errors for each of the coins as returned by the exchange.
400 Bad request:
Either the client request is malformed or some specific processing error happened that may be the fault of the client as detailed in the JSON body of the response.
403 Forbidden:
The h_contract does not match the $ORDER_ID.
404 Not found:
The merchant backend could not find the order or the instance and thus cannot process the abort request.
408 Request timeout:
The merchant backend took too long getting a response from the exchange. The wallet SHOULD retry soon.
412 Precondition failed:
Aborting the payment is not allowed, as the original payment did succeed. It is possible that a different wallet succeeded with the payment. This wallet should thus try to refresh all of the coins involved in the payment.
502 Bad gateway:
The merchant’s interaction with the exchange failed in some way. The error from the exchange is included.
504 Gateway timeout:
The merchant’s interaction with the exchange took too long. The client might want to try later again.

The backend will return an abort response, which includes verbatim the error codes received from the exchange’s refund API. The frontend should pass the replies verbatim to the browser/wallet.

interface AbortRequest {

  // hash of the order's contract terms (this is used to authenticate the
  // wallet/customer in case $ORDER_ID is guessable).
  h_contract: HashCode;

  // List of coins the wallet would like to see refunds for.
  // (Should be limited to the coins for which the original
  // payment succeeded, as far as the wallet knows.)
  coins: AbortingCoin[];
}
interface AbortingCoin {
  // Public key of a coin for which the wallet is requesting an abort-related refund.
  coin_pub: EddsaPublicKey;

  // The amount to be refunded (matches the original contribution)
  contribution: Amount;

  // URL of the exchange this coin was withdrawn from.
  exchange_url: string;
}
interface AbortResponse {

  // List of refund responses about the coins that the wallet
  // requested an abort for.  In the same order as the 'coins'
  // from the original request.
  // The rtransaction_id is implied to be 0.
  refunds: MerchantAbortPayRefundStatus[];
}
// Details about why a refund failed.
interface MerchantAbortPayRefundFailureStatus {
  // Used as tag for the sum type RefundStatus sum type.
  type: "failure"

  // HTTP status of the exchange request, must NOT be 200.
  exchange_status: Integer;

  // Taler error code from the exchange reply, if available.
  exchange_code?: Integer;

  // If available, HTTP reply from the exchange.
  exchange_reply?: Object;
}
// Additional details needed to verify the refund confirmation signature
// (h_contract_terms and merchant_pub) are already known
// to the wallet and thus not included.
interface MerchantAbortPayRefundSuccessStatus {
  // Used as tag for the sum type MerchantCoinRefundStatus sum type.
  type: "success"

  // HTTP status of the exchange request, 200 (integer) required for refund confirmations.
  exchange_status: 200;

  // the EdDSA :ref:signature (binary-only) with purpose
  // TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND using a current signing key of the
  // exchange affirming the successful refund
  exchange_sig: EddsaSignature;

  // public EdDSA key of the exchange that was used to generate the signature.
  // Should match one of the exchange's signing keys from /keys.  It is given
  // explicitly as the client might otherwise be confused by clock skew as to
  // which signing key was used.
  exchange_pub: EddsaPublicKey;
}

Obtaining refunds

Refunds allow merchants to fully or partially restitute e-cash to a wallet, for example because the merchant determined that it could not actually fulfill the contract. Refunds must be approved by the merchant’s business logic.

POST /orders/$ORDER_ID/refund

Obtain refunds for an order. After talking to the exchange, the refunds will no longer be pending if processed successfully.

Request:

The request body is a WalletRefundRequest object.

Response:

200 OK:
The response is a WalletRefundResponse.
204 No content:
There are no refunds for the order.
403 Forbidden:
The h_contract does not match the order.
404 Not found:
The merchant backend is unaware of the order.
interface WalletRefundRequest {
  // hash of the order's contract terms (this is used to authenticate the
  // wallet/customer).
  h_contract: HashCode;
}
interface WalletRefundResponse {
  // Amount that was refunded in total.
  refund_amount: Amount;

  // Successful refunds for this payment, empty array for none.
  refunds: MerchantCoinRefundStatus[];

  // Public key of the merchant.
  merchant_pub: EddsaPublicKey;

}
// Details about why a refund failed.
interface MerchantCoinRefundFailureStatus {
  // Used as tag for the sum type RefundStatus sum type.
  type: "failure";

  // HTTP status of the exchange request, must NOT be 200.
  exchange_status: Integer;

  // Taler error code from the exchange reply, if available.
  exchange_code?: Integer;

  // If available, HTTP reply from the exchange.
  exchange_reply?: Object;

  // Refund transaction ID.
  rtransaction_id: Integer;

  // public key of a coin that was refunded
  coin_pub: EddsaPublicKey;

  // Amount that was refunded, including refund fee charged by the exchange
  // to the customer.
  refund_amount: Amount;
}
// Additional details needed to verify the refund confirmation signature
// (h_contract_terms and merchant_pub) are already known
// to the wallet and thus not included.
interface MerchantCoinRefundSuccessStatus {
  // Used as tag for the sum type MerchantCoinRefundStatus sum type.
  type: "success";

  // HTTP status of the exchange request, 200 (integer) required for refund confirmations.
  exchange_status: 200;

  // the EdDSA :ref:signature (binary-only) with purpose
  // TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND using a current signing key of the
  // exchange affirming the successful refund
  exchange_sig: EddsaSignature;

  // public EdDSA key of the exchange that was used to generate the signature.
  // Should match one of the exchange's signing keys from /keys.  It is given
  // explicitly as the client might otherwise be confused by clock skew as to
  // which signing key was used.
  exchange_pub: EddsaPublicKey;

  // Refund transaction ID.
  rtransaction_id: Integer;

  // public key of a coin that was refunded
  coin_pub: EddsaPublicKey;

  // Amount that was refunded, including refund fee charged by the exchange
  // to the customer.
  refund_amount: Amount;
}

Picking up tips

Tips are a way for wallets to obtain e-cash from a website.

GET /tips/$TIP_ID

Handle request from wallet to provide details about a tip.

This endpoint typically also supports requests with the “Accept” header requesting “text/html”. In this case, an HTML response suitable for triggering the interaction with the wallet is returned. If the backend installation does not include the required HTML templates, a 406 status code is returned.

Response:

200 OK:
A tip is being returned. The backend responds with a TipInformation.
404 Not found:
The tip identifier is unknown.
406 Not acceptable:
The merchant backend could not load the template required to generate a reply in the desired format. (Likely HTML templates were not properly installed.)
410 Gone:
A tip has been fully claimed. The JSON reply still contains the TipInformation.
interface TipInformation {

  // Exchange from which the tip will be withdrawn. Needed by the
  // wallet to determine denominations, fees, etc.
  exchange_url: string;

  // (remaining) amount of the tip (including fees).
  tip_amount: Amount;

  // Timestamp indicating when the tip is set to expire (may be in the past).
  // Note that tips that have expired MAY also result in a 404 response.
  expiration: Timestamp;
}
POST /tips/$TIP_ID/pickup

Handle request from wallet to pick up a tip.

Request:

The request body is a TipPickupRequest object.

Response:

200 OK:
A tip is being returned. The backend responds with a TipResponse
401 Unauthorized:
The tip amount requested exceeds the tip.
404 Not found:
The tip identifier is unknown.
409 Conflict:
Some of the denomination key hashes of the request do not match those currently available from the exchange (hence there is a conflict between what the wallet requests and what the merchant believes the exchange can provide).
410 Gone:
The tip has expired.
interface TipPickupRequest {

  // List of planches the wallet wants to use for the tip
  planchets: PlanchetDetail[];
}
interface PlanchetDetail {
  // Hash of the denomination's public key (hashed to reduce
  // bandwidth consumption)
  denom_pub_hash: HashCode;

  // coin's blinded public key
  coin_ev: CoinEnvelope;
}
interface TipResponse {

  // Blind RSA signatures over the planchets.
  // The order of the signatures matches the planchets list.
  blind_sigs: BlindSignature[];
}
interface BlindSignature {

  // The (blind) RSA signature. Still needs to be unblinded.
  blind_sig: BlindedRsaSignature;
}

1.5.3. Instance management

Instances allow one merchant backend to be shared by multiple merchants. Every backend must have at least one instance, typcially the “default” instance setup before it can be used to manage inventory or process payments.

Setting up instances

POST /private/instances

This request will be used to create a new merchant instance in the backend.

Request:

The request must be a InstanceConfigurationMessage.

Response:

204 No content:
The backend has successfully created the instance.
409 Conflict:
This instance already exists, but with other configuration options. Use “PATCH” to update an instance configuration.
interface InstanceConfigurationMessage {
  // The URI where the wallet will send coins.  A merchant may have
  // multiple accounts, thus this is an array.  Note that by
  // removing URIs from this list the respective account is set to
  // inactive and thus unavailable for new contracts, but preserved
  // in the database as existing offers and contracts may still refer
  // to it.
  payto_uris: string[];

  // Name of the merchant instance to create (will become $INSTANCE).
  id: string;

  // Merchant name corresponding to this instance.
  name: string;

  // The merchant's physical address (to be put into contracts).
  address: Location;

  // The jurisdiction under which the merchant conducts its business
  // (to be put into contracts).
  jurisdiction: Location;

  // Maximum wire fee this instance is willing to pay.
  // Can be overridden by the frontend on a per-order basis.
  default_max_wire_fee: Amount;

  // Default factor for wire fee amortization calculations.
  // Can be overridden by the frontend on a per-order basis.
  default_wire_fee_amortization: Integer;

  // Maximum deposit fee (sum over all coins) this instance is willing to pay.
  // Can be overridden by the frontend on a per-order basis.
  default_max_deposit_fee: Amount;

  //  If the frontend does NOT specify an execution date, how long should
  // we tell the exchange to wait to aggregate transactions before
  // executing the wire transfer?  This delay is added to the current
  // time when we generate the advisory execution time for the exchange.
  default_wire_transfer_delay: RelativeTime;

  // If the frontend does NOT specify a payment deadline, how long should
  // offers we make be valid by default?
  default_pay_delay: RelativeTime;

}
PATCH /private/instances/$INSTANCE

Update the configuration of a merchant instance.

Request

The request must be a InstanceReconfigurationMessage. Removing an existing payto_uri deactivates the account (it will no longer be used for future contracts).

Response:

204 No content:
The backend has successfully created the instance.
404 Not found:
This instance is unknown and thus cannot be reconfigured.
interface InstanceReconfigurationMessage {
  // The URI where the wallet will send coins.  A merchant may have
  // multiple accounts, thus this is an array.  Note that by
  // removing URIs from this list
  payto_uris: string[];

  // Merchant name corresponding to this instance.
  name: string;

  // The merchant's physical address (to be put into contracts).
  address: Location;

  // The jurisdiction under which the merchant conducts its business
  // (to be put into contracts).
  jurisdiction: Location;

  // Maximum wire fee this instance is willing to pay.
  // Can be overridden by the frontend on a per-order basis.
  default_max_wire_fee: Amount;

  // Default factor for wire fee amortization calculations.
  // Can be overridden by the frontend on a per-order basis.
  default_wire_fee_amortization: Integer;

  // Maximum deposit fee (sum over all coins) this instance is willing to pay.
  // Can be overridden by the frontend on a per-order basis.
  default_max_deposit_fee: Amount;

  //  If the frontend does NOT specify an execution date, how long should
  // we tell the exchange to wait to aggregate transactions before
  // executing the wire transfer?  This delay is added to the current
  // time when we generate the advisory execution time for the exchange.
  default_wire_transfer_delay: RelativeTime;

  // If the frontend does NOT specify a payment deadline, how long should
  // offers we make be valid by default?
  default_pay_delay: RelativeTime;

}

Inspecting instances

GET /private/instances

This is used to return the list of all the merchant instances

Response:

200 OK:
The backend has successfully returned the list of instances stored. Returns a InstancesResponse.
interface InstancesResponse {
  // List of instances that are present in the backend (see Instance)
  instances: Instance[];
}

The Instance object describes the instance registered with the backend. It does not include the full details, only those that usually concern the frontend. It has the following structure:

 interface Instance {
   // Merchant name corresponding to this instance.
   name: string;

   // Merchant instance this response is about ($INSTANCE)
   id: string;

   // Public key of the merchant/instance, in Crockford Base32 encoding.
   merchant_pub: EddsaPublicKey;

   // List of the payment targets supported by this instance. Clients can
   // specify the desired payment target in /order requests.  Note that
   // front-ends do not have to support wallets selecting payment targets.
   payment_targets: string[];

}
GET /private/instances/$INSTANCE

This is used to query a specific merchant instance.

Response:

200 OK:
The backend has successfully returned the list of instances stored. Returns a QueryInstancesResponse.
interface QueryInstancesResponse {
  // The URI where the wallet will send coins.  A merchant may have
  // multiple accounts, thus this is an array.
  accounts: MerchantAccount[];

  // Merchant name corresponding to this instance.
  name: string;

  // Public key of the merchant/instance, in Crockford Base32 encoding.
  merchant_pub: EddsaPublicKey;

  // The merchant's physical address (to be put into contracts).
  address: Location;

  // The jurisdiction under which the merchant conducts its business
  // (to be put into contracts).
  jurisdiction: Location;

  // Maximum wire fee this instance is willing to pay.
  // Can be overridden by the frontend on a per-order basis.
  default_max_wire_fee: Amount;

  // Default factor for wire fee amortization calculations.
  // Can be overridden by the frontend on a per-order basis.
  default_wire_fee_amortization: Integer;

  // Maximum deposit fee (sum over all coins) this instance is willing to pay.
  // Can be overridden by the frontend on a per-order basis.
  default_max_deposit_fee: Amount;

  //  If the frontend does NOT specify an execution date, how long should
  // we tell the exchange to wait to aggregate transactions before
  // executing the wire transfer?  This delay is added to the current
  // time when we generate the advisory execution time for the exchange.
  default_wire_transfer_delay: RelativeTime;

  // If the frontend does NOT specify a payment deadline, how long should
  // offers we make be valid by default?
  default_pay_deadline: RelativeTime;

}
interface MerchantAccount {

  // payto:// URI of the account.
  payto_uri: string;

  // Hash over the wire details (including over the salt)
  h_wire: HashCode;

  // salt used to compute h_wire
  salt: HashCode;

  // true if this account is active,
  // false if it is historic.
  active: boolean;
}

Deleting instances

DELETE /private/instances/$INSTANCE

This request will be used to delete (permanently disable) or purge merchant instance in the backend. Purging will delete all offers and payments associated with the instance, while disabling (the default) only deletes the private key and makes the instance unusable for new orders or payments.

Request:

Query Parameters
  • purgeOptional. If set to YES, the instance will be fully deleted. Otherwise only the private key would be deleted.

Response

204 No content:
The backend has successfully removed the instance. The body is empty.
404 Not found:
The instance is unknown to the backend.
409 Conflict:
The instance cannot be deleted because it has pending offers, or the instance cannot be purged because it has successfully processed payments that have not passed the TAX_RECORD_EXPIRATION time. The latter case only applies if purge was set.

1.5.4. Inventory management

Inventory management is an optional backend feature that can be used to manage limited stocks of products and to auto-complete product descriptions in contracts (such that the frontends have to do less work). You can use the Taler merchant backend to process payments without using its inventory management.

Adding products to the inventory

POST /private/products

This is used to add a product to the inventory.

Request:

The request must be a ProductAddDetail.

Response:

204 No content:
The backend has successfully expanded the inventory.
409 Conflict:
The backend already knows a product with this product ID, but with different details.
interface ProductAddDetail {

  // product ID to use.
  product_id: string;

  // Human-readable product description.
  description: string;

  // Map from IETF BCP 47 language tags to localized descriptions
  description_i18n: { [lang_tag: string]: string };

  // unit in which the product is measured (liters, kilograms, packages, etc.)
  unit: string;

  // The price for one unit of the product. Zero is used
  // to imply that this product is not sold separately, or
  // that the price is not fixed, and must be supplied by the
  // front-end.  If non-zero, this price MUST include applicable
  // taxes.
  price: Amount;

  // An optional base64-encoded product image
  image: ImageDataUrl;

  // a list of taxes paid by the merchant for one unit of this product
  taxes: Tax[];

  // Number of units of the product in stock in sum in total,
  // including all existing sales ever. Given in product-specific
  // units.
  // A value of -1 indicates "infinite" (i.e. for "electronic" books).
  total_stock: Integer;

  // Identifies where the product is in stock.
  address: Location;

  // Identifies when we expect the next restocking to happen.
  next_restock?: Timestamp;

}
PATCH /private/products/$PRODUCT_ID

This is used to update product details in the inventory. Note that the total_stock and total_lost numbers MUST be greater or equal than previous values (this design ensures idempotency). In case stocks were lost but not sold, increment the total_lost number. All fields in the request are optional, those that are not given are simply preserved (not modified). Note that the description_i18n and taxes can only be modified in bulk: if it is given, all translations must be provided, not only those that changed. “never” should be used for the next_restock timestamp to indicate no intention/possibility of restocking, while a time of zero is used to indicate “unknown”.

Request:

The request must be a ProductPatchDetail.

Response:

204 No content:
The backend has successfully expanded the inventory.
interface ProductPatchDetail {

  // Human-readable product description.
  description: string;

  // Map from IETF BCP 47 language tags to localized descriptions
  description_i18n: { [lang_tag: string]: string };

  // unit in which the product is measured (liters, kilograms, packages, etc.)
  unit: string;

  // The price for one unit of the product. Zero is used
  // to imply that this product is not sold separately, or
  // that the price is not fixed, and must be supplied by the
  // front-end.  If non-zero, this price MUST include applicable
  // taxes.
  price: Amount;

  // An optional base64-encoded product image
  image: ImageDataUrl;

  // a list of taxes paid by the merchant for one unit of this product
  taxes: Tax[];

  // Number of units of the product in stock in sum in total,
  // including all existing sales ever. Given in product-specific
  // units.
  // A value of -1 indicates "infinite" (i.e. for "electronic" books).
  total_stock: Integer;

  // Number of units of the product that were lost (spoiled, stolen, etc.)
  total_lost: Integer;

  // Identifies where the product is in stock.
  address: Location;

  // Identifies when we expect the next restocking to happen.
  next_restock?: Timestamp;

}

Inspecting inventory

GET /private/products

This is used to return the list of all items in the inventory.

Response:

200 OK:
The backend has successfully returned the inventory. Returns a InventorySummaryResponse.
interface InventorySummaryResponse {
  // List of products that are present in the inventory
  products: InventoryEntry[];
}

The InventoryEntry object describes an item in the inventory. It has the following structure:

interface InventoryEntry {
  // Product identifier, as found in the product.
  product_id: string;

}
GET /private/products/$PRODUCT_ID

This is used to obtain detailed information about a product in the inventory.

Response:

200 OK:
The backend has successfully returned the inventory. Returns a ProductDetail.
interface ProductDetail {

  // Human-readable product description.
  description: string;

  // Map from IETF BCP 47 language tags to localized descriptions
  description_i18n: { [lang_tag: string]: string };

  // unit in which the product is measured (liters, kilograms, packages, etc.)
  unit: string;

  // The price for one unit of the product. Zero is used
  // to imply that this product is not sold separately, or
  // that the price is not fixed, and must be supplied by the
  // front-end.  If non-zero, this price MUST include applicable
  // taxes.
  price: Amount;

  // An optional base64-encoded product image
  image: ImageDataUrl;

  // a list of taxes paid by the merchant for one unit of this product
  taxes: Tax[];

  // Number of units of the product in stock in sum in total,
  // including all existing sales ever. Given in product-specific
  // units.
  // A value of -1 indicates "infinite" (i.e. for "electronic" books).
  total_stock: Integer;

  // Number of units of the product that have already been sold.
  total_sold: Integer;

  // Number of units of the product that were lost (spoiled, stolen, etc.)
  total_lost: Integer;

  // Identifies where the product is in stock.
  address: Location;

  // Identifies when we expect the next restocking to happen.
  next_restock?: Timestamp;

}

Reserving inventory

POST /private/products/$PRODUCT_ID/lock

This is used to lock a certain quantity of the product for a limited duration while the customer assembles a complete order. Note that frontends do not have to “unlock”, they may rely on the timeout as given in the duration field. Re-posting a lock with a different duration or quantity updates the existing lock for the same UUID and does not result in a conflict.

Unlocking by using a quantity of zero is is optional but recommended if customers remove products from the shopping cart. Note that actually POSTing to /orders with set manage_inventory and using lock_uuid will transition the lock to the newly created order (which may have a different duration and quantity than what was requested in the lock operation). If an order is for fewer items than originally locked, the difference is automatically unlocked.

Request:

The request must be a LockRequest.

Response:

204 No content:
The backend has successfully locked (or unlocked) the requested quantity.
404 Not found:
The backend has does not know this product.
410 Gone:
The backend does not have enough of product in stock.
interface LockRequest {

  // UUID that identifies the frontend performing the lock
  lock_uuid: UUID;

  // How long does the frontend intend to hold the lock
  duration: RelativeTime;

  // How many units should be locked?
  quantity: Integer;

}

Removing products from inventory

DELETE /private/products/$PRODUCT_ID

Delete information about a product. Fails if the product is locked by anyone.

Response:

204 No content:
The backend has successfully deleted the product.
404 Not found:
The backend does not know the instance or the product.
409 Conflict:
The backend refuses to delete the product because it is locked.

1.5.5. Payment processing

To process Taler payments, a merchant must first setup an order with the merchant backend. The order is then claimed by a wallet, and paid by the wallet. The merchant can check the payment status of the order. Once the order is paid, the merchant may (for a limited time) grant refunds on the order.

Creating orders

POST /private/orders

Create a new order that a customer can pay for.

This request is not idempotent unless an order_id is explicitly specified. However, while repeating without an order_id will create another order, that is generally pretty harmless (as long as only one of the orders is returned to the wallet).

Note

This endpoint does not return a URL to redirect your user to confirm the payment. In order to get this URL use :http:get:/orders/$ORDER_ID. The API is structured this way since the payment redirect URL is not unique for every order, there might be varying parameters such as the session id.

Request:

The request must be a PostOrderRequest.

Response:

200 OK:
The backend has successfully created the proposal. The response is a PostOrderResponse.
404 Not found:
The order given used products from the inventory, but those were not found in the inventory. Or the merchant instance is unknown (including possibly the instance being not configured for new orders). Details in the error code. NOTE: no good way to find out which product is not in the inventory, we MAY want to specify that in the reply.
409 Conflict:
A different proposal already exists under the specified order ID.
410 Gone:
The order given used products from the inventory that are out of stock. The response is a OutOfStockResponse.
interface PostOrderRequest {
  // The order must at least contain the minimal
  // order detail, but can override all
  order: Order;

  // if set, the backend will then set the refund deadline to the current
  // time plus the specified delay.  If it's not set, refunds will not be
  // possible.
  refund_delay?: RelativeTime;

  // specifies the payment target preferred by the client. Can be used
  // to select among the various (active) wire methods supported by the instance.
  payment_target?: string;

  // specifies that some products are to be included in the
  // order from the inventory.  For these inventory management
  // is performed (so the products must be in stock) and
  // details are completed from the product data of the backend.
  inventory_products?: MinimalInventoryProduct[];

  // Specifies a lock identifier that was used to
  // lock a product in the inventory.  Only useful if
  // manage_inventory is set.  Used in case a frontend
  // reserved quantities of the individual products while
  // the shopping card was being built.  Multiple UUIDs can
  // be used in case different UUIDs were used for different
  // products (i.e. in case the user started with multiple
  // shopping sessions that were combined during checkout).
  lock_uuids?: UUID[];

  // Should a token for claiming the order be generated?
  // False can make sense if the ORDER_ID is sufficiently
  // high entropy to prevent adversarial claims (like it is
  // if the backend auto-generates one). Default is 'true'.
  create_token?: boolean;

}

The following fields must be specified in the order field of the request. Other fields from ContractTerms are optional, and will override the defaults in the merchant configuration.

interface MinimalOrderDetail {
  // Amount to be paid by the customer
  amount: Amount;

  // Short summary of the order
  summary: string;

  // URL that will show that the order was successful after
  // it has been paid for.  Optional. When POSTing to the
  // merchant, the placeholder "${ORDER_ID}" will be
  // replaced with the actual order ID (useful if the
  // order ID is generated server-side and needs to be
  // in the URL).
  fulfillment_url?: string;
}

The following fields can be specified if the order is inventory-based. In this case, the backend can compute the amounts from the prices given in the inventory. Note that if the frontend does give more details (towards the ContractTerms), this will override those details (including total price) that would otherwise computed based on information from the inventory.

type ProductSpecification : (MinimalInventoryProduct | Product);
Note that if the frontend does give details beyond these,
it will override those details (including price or taxes)
that the backend would otherwise fill in via the inventory.

interface MinimalInventoryProduct {
  // Which product is requested (here mandatory!)
  product_id: string;

  // How many units of the product are requested
  quantity: Integer;
}
interface PostOrderResponse {
  // Order ID of the response that was just created
  order_id: string;

  // Token that authorizes the wallet to claim the order.
  // Provided only if "create_token" was set to 'true'
  // in the request.
  token?: ClaimToken;
}
interface OutOfStockResponse {

  // Product ID of an out-of-stock item
  product_id: string;

  // Requested quantity
  requested_quantity: Integer;

  // Available quantity (must be below requested_quanitity)
  available_quantity: Integer;

  // When do we expect the product to be again in stock?
  // Optional, not given if unknown.
  restock_expected?: Timestamp;
}

Inspecting orders

GET /private/orders

Returns known orders up to some point in the past.

Request:

Query Parameters
  • paidOptional. If set to yes, only return paid orders, if no only unpaid orders. Do not give (or use “all”) to see all orders regardless of payment status.
  • refundedOptional. If set to yes, only return refunded orders, if no only unrefunded orders. Do not give (or use “all”) to see all orders regardless of refund status.
  • wiredOptional. If set to yes, only return wired orders, if no only orders with missing wire transfers. Do not give (or use “all”) to see all orders regardless of wire transfer status.
  • dateOptional. Time threshold, see delta for its interpretation. Defaults to the oldest or most recent entry, depending on delta.
  • startOptional. Row number threshold, see delta for its interpretation. Defaults to UINT64_MAX, namely the biggest row id possible in the database.
  • deltaOptional. takes value of the form N (-N), so that at most N values strictly older (younger) than start and date are returned. Defaults to -20 to return the last 20 entries (before start and/or date).
  • timeout_msOptional. Timeout in milli-seconds to wait for additional orders if the answer would otherwise be negative (long polling). Only useful if delta is positive. Note that the merchant MAY still return a response that contains fewer than delta orders.

Response:

200 OK:
The response is an OrderHistory.
interface OrderHistory {
  // timestamp-sorted array of all orders matching the query.
  // The order of the sorting depends on the sign of delta.
  orders : OrderHistoryEntry[];
}
interface OrderHistoryEntry {

  // order ID of the transaction related to this entry.
  order_id: string;

  // row ID of the order in the database
  row_id: number;

  // when the order was created
  timestamp: Timestamp;

  // the amount of money the order is for
  amount: Amount;

  // the summary of the order
  summary: string;

  // whether some part of the order is refundable,
  // that is the refund deadline has not yet expired
  // and the total amount refunded so far is below
  // the value of the original transaction.
  refundable: boolean;

  // whether the order has been paid or not
  paid: boolean;
}
GET /private/orders/$ORDER_ID

Merchant checks the payment status of an order. If the order exists but is not paid and not claimed yet, the response provides a redirect URL. When the user goes to this URL, they will be prompted for payment. Differs from the public API both in terms of what information is returned and in that the wallet must provide the contract hash to authenticate, while for this API we assume that the merchant is authenticated (as the endpoint is not public).

Request:

Query Parameters
  • session_idOptional. Session ID that the payment must be bound to. If not specified, the payment is not session-bound.
  • transferOptional. If set to “YES”, try to obtain the wire transfer status for this order from the exchange. Otherwise, the wire transfer status MAY be returned if it is available.
  • timeout_msOptional. Timeout in milli-seconds to wait for a payment if the answer would otherwise be negative (long polling).

Response:

200 OK:
Returns a MerchantOrderStatusResponse, whose format can differ based on the status of the payment.
404 Not found:
The order or instance is unknown to the backend.
502 Bad gateway:
We failed to obtain a response from the exchange (about the wire transfer status).
504 Gateway timeout:
The merchant’s interaction with the exchange took too long. The client might want to try later again.
interface CheckPaymentPaidResponse {
  // the customer paid for this contract
  order_status: "paid";

  // Was the payment refunded (even partially)
  refunded: boolean;

  // True if there are any approved refunds that the wallet has
  // not yet obtained.
  refund_pending: boolean;

  // Did the exchange wire us the funds
  wired: boolean;

  // Total amount the exchange deposited into our bank account
  // for this contract, excluding fees.
  deposit_total: Amount;

  // Numeric error code indicating errors the exchange
  // encountered tracking the wire transfer for this purchase (before
  // we even got to specific coin issues).
  // 0 if there were no issues.
  exchange_ec: number;

  // HTTP status code returned by the exchange when we asked for
  // information to track the wire transfer for this purchase.
  // 0 if there were no issues.
  exchange_hc: number;

  // Total amount that was refunded, 0 if refunded is false.
  refund_amount: Amount;

  // Contract terms
  contract_terms: ContractTerms;

  // The wire transfer status from the exchange for this order if available, otherwise empty array
  wire_details: TransactionWireTransfer[];

  // Reports about trouble obtaining wire transfer details, empty array if no trouble were encountered.
  wire_reports: TransactionWireReport[];

  // The refund details for this order.  One entry per
  // refunded coin; empty array if there are no refunds.
  refund_details: RefundDetails[];

  // Status URL, can be used as a redirect target for the browser
  // to show the order QR code / trigger the wallet.
  order_status_url: string;
}
interface CheckPaymentClaimedResponse {
  // a wallet claimed the order, but did not yet pay for the contract
  order_status: "claimed";

  // Contract terms
  contract_terms: ContractTerms;

}
interface CheckPaymentUnpaidResponse {
  // the order was neither claimed nor paid
  order_status: "unpaid";

  // URI that the wallet must process to complete the payment.
  taler_pay_uri: string;

  // Alternative order ID which was paid for already in the same session.
  // Only given if the same product was purchased before in the same session.
  already_paid_order_id?: string;

  // Fulfillment URL of an already paid order. Only given if under this
  // session an already paid order with a fulfillment URL exists.
  already_paid_fulfillment_url?: string;

  // Status URL, can be used as a redirect target for the browser
  // to show the order QR code / trigger the wallet.
  order_status_url: string;

  // We do we NOT return the contract terms here because they may not
  // exist in case the wallet did not yet claim them.
}
interface RefundDetails {
  // Reason given for the refund
  reason: string;

  // when was the refund approved
  timestamp: Timestamp;

  // Total amount that was refunded (minus a refund fee).
  amount: Amount;
}
interface TransactionWireTransfer {
  // Responsible exchange
  exchange_url: string;

  // 32-byte wire transfer identifier
  wtid: Base32;

  // execution time of the wire transfer
  execution_time: Timestamp;

  // Total amount that has been wire transferred
  // to the merchant
  amount: Amount;

  // Was this transfer confirmed by the merchant via the
  // POST /transfers API, or is it merely claimed by the exchange?
  confirmed: boolean;
}
interface TransactionWireReport {
  // Numerical error code
  code: number;

  // Human-readable error description
  hint: string;

  // Numerical error code from the exchange.
  exchange_ec: number;

  // HTTP status code received from the exchange.
  exchange_hc: number;

  // Public key of the coin for which we got the exchange error.
  coin_pub: CoinPublicKey;
}

Private order data cleanup

Some orders may contain sensitive information that the merchant may not want to retain after fulfillment, such as the customer’s shipping address. By initially labeling these order components as forgettable, the merchant can later tell the backend to forget those details (without changing the hash of the contract!) to minimize risks from information leakage.

PATCH /private/orders/$ORDER_ID/forget

Forget fields in an order’s contract terms that the merchant no longer needs.

Request:

The request must be a forget request. The fields specified must have been marked as forgettable when the contract was created. Fields in the request that are not in the contract terms are ignored.

A valid JSON path is defined as a string beginning with $. that follows the dot notation: $.wire_fee, for example. The $ represents the contract terms object, and an identifier following a . represents the field of that identifier belonging to the object preceding the dot. Arrays can be indexed by an non-negative integer within brackets: $.products[1]. An asterisk * can be used to index an array as a wildcard, which expands the path into a list of paths containing one path for each valid array index: $.products[*].description. For a path to be valid, it must end with a reference to a field of an object (it cannot end with an array index or wildcard).

Response:

200 OK:
The merchant deleted the specified fields from the contract of order $ORDER_ID.
400 Bad request:
The request is malformed or one of the paths is invalid.
404 Not found:
The merchant backend could not find the order or the instance and thus cannot process the abort request.
409 Conflict:
The request includes a field that was not marked as forgettable, so the merchant cannot delete that field.
interface ForgetRequest {

  // Array of valid JSON paths to forgettable fields in the order's
  // contract terms.
  fields: string[];
}
DELETE /private/orders/$ORDER_ID

Delete information about an order. Fails if the order was paid in the last 10 years (or whatever TAX_RECORD_EXPIRATION is set to) or was claimed but is unpaid and thus still a valid offer.

Response:

204 No content:
The backend has successfully deleted the order.
404 Not found:
The backend does not know the instance or the order.
409 Conflict:
The backend refuses to delete the order.

1.5.6. Giving Refunds

POST /private/orders/$ORDER_ID/refund

Increase the refund amount associated with a given order. The user should be redirected to the taler_refund_uri to trigger refund processing in the wallet.

Request:

The request body is a RefundRequest object.

Response:

200 OK:
The refund amount has been increased, the backend responds with a MerchantRefundResponse
403 Forbidden:
For the given order, the refund delay was zero and thus refunds are categorically not allowed.
404 Not found:
The order is unknown to the merchant
410 Gone:
It is too late for aborting, the exchange may have already wired the funds to the merchant.
409 Conflict:
The refund amount exceeds the amount originally paid
interface RefundRequest {
  // Amount to be refunded
  refund: Amount;

  // Human-readable refund justification
  reason: string;
}
interface MerchantRefundResponse {

  // URL (handled by the backend) that the wallet should access to
  // trigger refund processing.
  // taler://refund/...
  taler_refund_uri: string;

  // Contract hash that a client may need to authenticate an
  // HTTP request to obtain the above URI in a wallet-friendly way.
  h_contract: HashCode;
}

1.5.7. Tracking Wire Transfers

This API is used by merchants that want to track the payments from the exchange to be sure that they have been paid on time. By telling the merchant backend about all incoming wire transfers, the backend can detect if an exchange failed to perform a wire transfer that was due.

Informing the backend about incoming wire transfers

POST /private/transfers

Inform the backend over an incoming wire transfer. The backend should inquire about the details with the exchange and mark the respective orders as wired. Note that the request will fail if the WTID is not unique (which should be guaranteed by a correct exchange). This request is idempotent and should also be used to merely re-fetch the transfer information from the merchant’s database (assuming we got a non-error response from the exchange before).

Request:

The request must provide transfer information.

Response:

200 OK:
The wire transfer is known to the exchange, details about it follow in the body. The body of the response is a MerchantTrackTransferResponse.
202 Accepted:
The exchange provided conflicting information about the transfer. Namely, there is at least one deposit among the deposits aggregated by wtid that accounts for a coin whose details don’t match the details stored in merchant’s database about the same keyed coin. The response body contains the ExchangeConflictDetails. This is indicative of a malicious exchange that claims one thing, but did something else. (With respect to the HTTP specficiation, it is not precisely that we did not act upon the request, more that the usual action of filing the transaction as ‘finished’ does not apply. In the future, this is a case where the backend actually should report the bad behavior to the auditor – and then hope for the auditor to resolve it. So in that respect, 202 is the right status code as more work remains to be done for a final resolution.)
404 Not found:
The instance is unknown to the exchange.
409 Conflict:
The wire transfer identifier is already known to us, but for a different amount, wire method or exchange.
502 Bad gateway:
The exchange returned an error when we asked it about the “GET /transfer” status for this wire transfer. Details of the exchange error are returned.
504 Gateway timeout:
The merchant’s interaction with the exchange took too long. The client might want to try later again.

Details:

interface TransferInformation {
  // how much was wired to the merchant (minus fees)
  credit_amount: Amount;

  // raw wire transfer identifier identifying the wire transfer (a base32-encoded value)
  wtid: WireTransferIdentifierRawP;

  // target account that received the wire transfer
  payto_uri: string;

  // base URL of the exchange that made the wire transfer
  exchange_url: string;
}
interface MerchantTrackTransferResponse {
  // Total amount transferred
  total: Amount;

  // Applicable wire fee that was charged
  wire_fee: Amount;

  // Time of the execution of the wire transfer by the exchange, according to the exchange
  execution_time: Timestamp;

  // details about the deposits
  deposits_sums: MerchantTrackTransferDetail[];
}
interface MerchantTrackTransferDetail {
  // Business activity associated with the wire transferred amount
  // deposit_value.
  order_id: string;

  // The total amount the exchange paid back for order_id.
  deposit_value: Amount;

  // applicable fees for the deposit
  deposit_fee: Amount;
}
type ExchangeConflictDetails = WireFeeConflictDetails | TrackTransferConflictDetails
// Note: this is not the full 'proof' of missbehavior, as
// the bogus message from the exchange with a signature
// over the 'different' wire fee is missing.
//
// This information is NOT provided by the current implementation,
// because this would be quite expensive to generate and is
// hardly needed _here_. Once we add automated reports for
// the Taler auditor, we need to generate this data anyway
// and should probably return it here as well.
interface WireFeeConflictDetails {
  // Numerical error code:
  code: "TALER_EC_MERCHANT_PRIVATE_POST_TRANSFERS_BAD_WIRE_FEE";

  // Text describing the issue for humans.
  hint: string;


  // Wire fee (wrongly) charged by the exchange, breaking the
  // contract affirmed by the exchange_sig.
  wire_fee: Amount;

  // Timestamp of the wire transfer
  execution_time: Timestamp;

  // The expected wire fee (as signed by the exchange)
  expected_wire_fee: Amount;

  // Expected closing fee (needed to verify signature)
  expected_closing_fee: Amount;

  // Start date of the expected fee structure
  start_date: Timestamp;

  // End date of the expected fee structure
  end_date: Timestamp;

  // Signature of the exchange affirming the expected fee structure
  master_sig: EddsaSignature;

  // Master public key of the exchange
  master_pub: EddsaPublicKey;
}
interface TrackTransferConflictDetails {
  // Numerical error code
  code: "TALER_EC_MERCHANT_PRIVATE_POST_TRANSFERS_CONFLICTING_REPORTS";

  // Text describing the issue for humans.
  hint: string;

  // Offset in the exchange_transfer where the
  // exchange's response fails to match the exchange_deposit_proof.
  conflict_offset: number;

  // The response from the exchange which tells us when the
  // coin was returned to us, except that it does not match
  // the expected value of the coin.
  //
  // This field is NOT provided by the current implementation,
  // because this would be quite expensive to generate and is
  // hardly needed _here_. Once we add automated reports for
  // the Taler auditor, we need to generate this data anyway
  // and should probably return it here as well.
  exchange_transfer?: TrackTransferResponse;

  // Public key of the exchange used to sign the response to
  // our deposit request.
  deposit_exchange_pub: EddsaPublicKey;

  // Signature of the exchange signing the (conflicting) response.
  // Signs over a struct TALER_DepositConfirmationPS.
  deposit_exchange_sig: EddsaSignature;

  // Hash of the merchant's bank account the wire transfer went to
  h_wire: HashCode;

  // Hash of the contract terms with the conflicting deposit.
  h_contract_terms: HashCode;

  // At what time the exchange received the deposit.  Needed
  // to verify the \exchange_sig\.
  deposit_timestamp: Timestamp;

  // At what time the refund possibility expired (needed to verify exchange_sig).
  refund_deadline: Timestamp;

  // Public key of the coin for which we have conflicting information.
  coin_pub: EddsaPublicKey;

  // Amount the exchange counted the coin for in the transfer.
  amount_with_fee: Amount;

  // Expected value of the coin.
  coin_value: Amount;

  // Expected deposit fee of the coin.
  coin_fee: Amount;

  // Expected deposit fee of the coin.
  deposit_fee: Amount;

}
interface TrackTransferProof {
  // signature from the exchange made with purpose
  // TALER_SIGNATURE_EXCHANGE_CONFIRM_WIRE_DEPOSIT
  exchange_sig: EddsaSignature;

  // public EdDSA key of the exchange that was used to generate the signature.
  // Should match one of the exchange's signing keys from /keys.  Again given
  // explicitly as the client might otherwise be confused by clock skew as to
  // which signing key was used.
  exchange_pub: EddsaSignature;

  // hash of the wire details (identical for all deposits)
  // Needed to check the exchange_sig
  h_wire: HashCode;
}

Querying known wire transfers

GET /private/transfers

Obtain a list of all wire transfers the backend has checked. Note that when filtering by timestamp (using “before” and/or “after”), we use the time reported by the exchange and thus will ONLY return results for which we already have a response from the exchange. This should be virtually all transfers, however it is conceivable that for some transfer the exchange responded with a temporary error (i.e. HTTP status 500+) and then we do not yet have an execution time to filter by. Thus, IF timestamp filters are given, transfers for which we have no response from the exchange yet are automatically excluded.

Request:

Query Parameters
  • payto_uriOptional. Filter for transfers to the given bank account (subject and amount MUST NOT be given in the payto URI)
  • beforeOptional. Filter for transfers executed before the given timestamp
  • afterOptional. Filter for transfers executed after the given timestamp
  • limitOptional. At most return the given number of results. Negative for descending in execution time, positive for ascending in execution time. Default is -20.
  • offsetOptional. Starting transfer_serial_id for an iteration.
  • verifiedOptional. Filter transfers by verification status.

Response:

200 OK:
The body of the response is a TransferList.
interface TransferList {
   // list of all the transfers that fit the filter that we know
   transfers : TransferDetails[];
}
interface TransferDetails {
  // how much was wired to the merchant (minus fees)
  credit_amount: Amount;

  // raw wire transfer identifier identifying the wire transfer (a base32-encoded value)
  wtid: WireTransferIdentifierRawP;

  // target account that received the wire transfer
  payto_uri: string;

  // base URL of the exchange that made the wire transfer
  exchange_url: string;

  // Serial number identifying the transfer in the merchant backend.
  // Used for filgering via offset.
  transfer_serial_id: number;

  // Time of the execution of the wire transfer by the exchange, according to the exchange
  // Only provided if we did get an answer from the exchange.
  execution_time?: Timestamp;

  // True if we checked the exchange's answer and are happy with it.
  // False if we have an answer and are unhappy, missing if we
  // do not have an answer from the exchange.
  verified?: boolean;

  // True if the merchant uses the POST /transfers API to confirm
  // that this wire transfer took place (and it is thus not
  // something merely claimed by the exchange).
  confirmed?: boolean;
}

1.5.8. Backend: Giving tips

Tips are a way for websites to give small amounts of e-cash to visitors (for example as a financial reward for providing information or watching advertisements). Tips are non-contractual: neither merchant nor consumer have any contractual information about the other party as a result of the tip.

Create reserve

Reserves are basically funds a merchant has provided to an exchange for a tipping campaign. Each reserve has a limited lifetime (say 2–4 weeks). Any funds not used to tip customers will automatically be wired back from the exchange to the originating account.

To begin tipping, a merchant must tell the backend to setup a reserve. The backend will return a reserve public key which must be used as the wire transfer subject when wiring the tipping campaign funds to the exchange.

POST /private/reserves

Create a reserve for tipping.

This request is not idempotent. However, while repeating it will create another reserve, that is generally pretty harmless (assuming only one of the reserves is filled with a wire transfer). Clients may want to eventually delete the unused reserves to avoid clutter.

Request:

The request body is a ReserveCreateRequest object.

Response:

200 OK:
The backend is waiting for the reserve to be established. The merchant must now perform the wire transfer indicated in the ReserveCreateConfirmation.
408 Request timeout:
The exchange did not respond on time.
409 Conflict:
The exchange does not support the requested wire method.
502 Bad gateway:
We could not obtain /wire details from the specified exchange base URL.
504 Gateway timeout:
The merchant’s interaction with the exchange took too long. The client might want to try later again.
interface ReserveCreateRequest {
  // Amount that the merchant promises to put into the reserve
  initial_balance: Amount;

  // Exchange the merchant intends to use for tipping
  exchange_url: string;

  // Desired wire method, for example "iban" or "x-taler-bank"
  wire_method: string;
}
interface ReserveCreateConfirmation {
  // Public key identifying the reserve
  reserve_pub: EddsaPublicKey;

  // Wire account of the exchange where to transfer the funds
  payto_uri: string;
}
GET /private/reserves

Obtain list of reserves that have been created for tipping.

Request:

Query Parameters
  • afterOptional. Only return reserves created after the given timestamp in milliseconds
  • activeOptional. Only return active/inactive reserves depending on the boolean given
  • failuresOptional. Only return reserves where we disagree with the exchange about the initial balance.

Response:

200 OK:
Returns a list of known tipping reserves. The body is a TippingReserveStatus.
interface TippingReserveStatus {
  // Array of all known reserves (possibly empty!)
  reserves: ReserveStatusEntry[];
}
 interface ReserveStatusEntry {
  // Public key of the reserve
  reserve_pub: EddsaPublicKey;

  // Timestamp when it was established
  creation_time: Timestamp;

  // Timestamp when it expires
  expiration_time: Timestamp;

  // Initial amount as per reserve creation call
  merchant_initial_amount: Amount;

  // Initial amount as per exchange, 0 if exchange did
  // not confirm reserve creation yet.
  exchange_initial_amount: Amount;

  // Amount picked up so far.
  pickup_amount: Amount;

  // Amount approved for tips that exceeds the pickup_amount.
  committed_amount: Amount;

  // Is this reserve active (false if it was deleted but not purged)
  active: boolean;
}

Query funds remaining

GET /private/reserves/$RESERVE_PUB

Obtain information about a specific reserve that have been created for tipping.

Request:

Query Parameters
  • tipsOptional. If set to “yes”, returns also information about all of the tips created

Response:

200 OK:
Returns the ReserveDetail.
404 Not found:
The tipping reserve is not known.
502 Bad gateway:
We are having trouble with the request because of a problem with the exchange. Likely returned with an “exchange_code” in addition to a “code” and an “exchange_http_status” in addition to our own HTTP status. Also usually includes the full exchange reply to our request under “exchange_reply”. This is only returned if there was actual trouble with the exchange, not if the exchange merely did not respond yet or if it responded that the reserve was not yet filled.
504 Gateway timeout:
The merchant’s interaction with the exchange took too long. The client might want to try later again.
interface ReserveDetail {
  // Timestamp when it was established
  creation_time: Timestamp;

  // Timestamp when it expires
  expiration_time: Timestamp;

  // Initial amount as per reserve creation call
  merchant_initial_amount: Amount;

  // Initial amount as per exchange, 0 if exchange did
  // not confirm reserve creation yet.
  exchange_initial_amount: Amount;

  // Amount picked up so far.
  pickup_amount: Amount;

  // Amount approved for tips that exceeds the pickup_amount.
  committed_amount: Amount;

  // Array of all tips created by this reserves (possibly empty!).
  // Only present if asked for explicitly.
  tips?: TipStatusEntry[];

  // Is this reserve active (false if it was deleted but not purged)
  active: boolean;
}
interface TipStatusEntry {

  // Unique identifier for the tip
  tip_id: HashCode;

  // Total amount of the tip that can be withdrawn.
  total_amount: Amount;

  // Human-readable reason for why the tip was granted.
  reason: string;
}

Authorizing tips

POST /private/reserves/$RESERVE_PUB/authorize-tip

Authorize creation of a tip from the given reserve.

Request:

The request body is a TipCreateRequest object.

Response:

200 OK:
A tip has been created. The backend responds with a TipCreateConfirmation
404 Not found:
The instance or the reserve is unknown to the backend.
412 Precondition failed:
The tip amount requested exceeds the available reserve balance for tipping.
interface TipCreateRequest {
  // Amount that the customer should be tipped
  amount: Amount;

  // Justification for giving the tip
  justification: string;

  // URL that the user should be directed to after tipping,
  // will be included in the tip_token.
  next_url: string;
}
interface TipCreateConfirmation {
  // Unique tip identifier for the tip that was created.
  tip_id: HashCode;

  // taler://tip URI for the tip
  taler_tip_uri: string;

  // URL that will directly trigger processing
  // the tip when the browser is redirected to it
  tip_status_url: string;

  // when does the tip expire
  tip_expiration: Timestamp;
}
POST /private/tips

Authorize creation of a tip from the given reserve, except with automatic selection of a working reserve of the instance by the backend. Intentionally otherwise identical to the /authorize-tip endpoint given above.

Request:

The request body is a TipCreateRequest object.

Response:

200 OK:
A tip has been created. The backend responds with a TipCreateConfirmation
404 Not found:
The instance is unknown to the backend.
412 Precondition failed:
The tip amount requested exceeds the available reserve balance for tipping in all of the reserves of the instance.

Deleting reserves

DELETE /private/reserves/$RESERVE_PUB

Delete information about a reserve. Fails if the reserve still has committed to tips that were not yet picked up and that have not yet expired.

Request:

Query Parameters
  • purgeOptional. If set to YES, the reserve and all information about tips it issued will be fully deleted. Otherwise only the private key would be deleted.

Response:

204 No content:
The backend has successfully deleted the reserve.
404 Not found:
The backend does not know the instance or the reserve.
409 Conflict:
The backend refuses to delete the reserve (committed tips awaiting pickup).

Checking tip status

GET /private/tips/$TIP_ID

Obtain information about a particular tip.

Request:

Query Parameters
  • pickups – if set to “yes”, returns also information about all of the pickups

Response:

200 OK:
The tip is known. The backend responds with a TipDetails message
404 Not found:
The tip is unknown to the backend.
interface TipDetails {
  // Amount that we authorized for this tip.
  total_authorized: Amount;

  // Amount that was picked up by the user already.
  total_picked_up: Amount;

  // Human-readable reason given when authorizing the tip.
  reason: string;

  // Timestamp indicating when the tip is set to expire (may be in the past).
  expiration: Timestamp;

  // Reserve public key from which the tip is funded
  reserve_pub: EddsaPublicKey;

  // Array showing the pickup operations of the wallet (possibly empty!).
  // Only present if asked for explicitly.
  pickups?: PickupDetail[];
}
interface PickupDetail {
  // Unique identifier for the pickup operation.
  pickup_id: HashCode;

  // Number of planchets involved.
  num_planchets: Integer;

  // Total amount requested for this pickup_id.
  requested_amount: Amount;
}
GET /private/tips

Return the list of all tips.

Request:

Query Parameters
  • include_expiredOptional. If set to “yes”, the result includes expired tips also. Otherwise, only active tips are returned.
  • limitOptional. At most return the given number of results. Negative for descending in database row id, positive for ascending in database row id.
  • offsetOptional. Starting row_id for an iteration.

Response:

200 OK:
The backend has successfully found the list of tips. The backend responds with a TipsResponse.
interface TipsResponse {

  // List of tips that are present in the backend.
  tips: Tip[];
}
interface Tip {

  // id of the tip in the backend database
  row_id: number;

  // Unique identifier for the tip.
  tip_id: HashCode;

  // (remaining) amount of the tip (including fees).
  tip_amount: Amount;
}

1.5.9. The Contract Terms

This section describes the overall structure of the contract terms that are the foundation for Taler payments.

FIXME: the “forgettable” attribute is not properly specified here!

The contract terms must have the following structure:

interface ContractTerms {
  // Human-readable description of the whole purchase
  summary: string;

  // Map from IETF BCP 47 language tags to localized summaries
  summary_i18n?: { [lang_tag: string]: string };

  // Unique, free-form identifier for the proposal.
  // Must be unique within a merchant instance.
  // For merchants that do not store proposals in their DB
  // before the customer paid for them, the order_id can be used
  // by the frontend to restore a proposal from the information
  // encoded in it (such as a short product identifier and timestamp).
  order_id: string;

  // Total price for the transaction.
  // The exchange will subtract deposit fees from that amount
  // before transferring it to the merchant.
  amount: Amount;

  // The URL for this purchase.  Every time is is visited, the merchant
  // will send back to the customer the same proposal.  Clearly, this URL
  // can be bookmarked and shared by users.
  fulfillment_url?: string;

  // Maximum total deposit fee accepted by the merchant for this contract
  max_fee: Amount;

  // Maximum wire fee accepted by the merchant (customer share to be
  // divided by the 'wire_fee_amortization' factor, and further reduced
  // if deposit fees are below 'max_fee').  Default if missing is zero.
  max_wire_fee: Amount;

  // Over how many customer transactions does the merchant expect to
  // amortize wire fees on average?  If the exchange's wire fee is
  // above 'max_wire_fee', the difference is divided by this number
  // to compute the expected customer's contribution to the wire fee.
  // The customer's contribution may further be reduced by the difference
  // between the 'max_fee' and the sum of the actual deposit fees.
  // Optional, default value if missing is 1.  0 and negative values are
  // invalid and also interpreted as 1.
  wire_fee_amortization: number;

  // List of products that are part of the purchase (see Product).
  products: Product[];

  // Time when this contract was generated
  timestamp: Timestamp;

  // After this deadline has passed, no refunds will be accepted.
  refund_deadline: Timestamp;

  // After this deadline, the merchant won't accept payments for the contact
  pay_deadline: Timestamp;

  // Transfer deadline for the exchange.  Must be in the
  // deposit permissions of coins used to pay for this order.
  wire_transfer_deadline: Timestamp;

  // Merchant's public key used to sign this proposal; this information
  // is typically added by the backend Note that this can be an ephemeral key.
  merchant_pub: EddsaPublicKey;

  // Base URL of the (public!) merchant backend API.
  // Must be an absolute URL that ends with a slash.
  merchant_base_url: string;

  // More info about the merchant, see below
  merchant: Merchant;

  // The hash of the merchant instance's wire details.
  h_wire: HashCode;

  // Wire transfer method identifier for the wire method associated with h_wire.
  // The wallet may only select exchanges via a matching auditor if the
  // exchange also supports this wire method.
  // The wire transfer fees must be added based on this wire transfer method.
  wire_method: string;

  // Any exchanges audited by these auditors are accepted by the merchant.
  auditors: Auditor[];

  // Exchanges that the merchant accepts even if it does not accept any auditors that audit them.
  exchanges: Exchange[];

  // Delivery location for (all!) products.
  delivery_location?: Location;

  // Time indicating when the order should be delivered.
  // May be overwritten by individual products.
  delivery_date?: Timestamp;

  // Nonce generated by the wallet and echoed by the merchant
  // in this field when the proposal is generated.
  nonce: string;

  // Specifies for how long the wallet should try to get an
  // automatic refund for the purchase. If this field is
  // present, the wallet should wait for a few seconds after
  // the purchase and then automatically attempt to obtain
  // a refund.  The wallet should probe until "delay"
  // after the payment was successful (i.e. via long polling
  // or via explicit requests with exponential back-off).
  //
  // In particular, if the wallet is offline
  // at that time, it MUST repeat the request until it gets
  // one response from the merchant after the delay has expired.
  // If the refund is granted, the wallet MUST automatically
  // recover the payment.  This is used in case a merchant
  // knows that it might be unable to satisfy the contract and
  // desires for the wallet to attempt to get the refund without any
  // customer interaction.  Note that it is NOT an error if the
  // merchant does not grant a refund.
  auto_refund?: RelativeTime;

  // Extra data that is only interpreted by the merchant frontend.
  // Useful when the merchant needs to store extra information on a
  // contract without storing it separately in their database.
  extra?: any;
}

The wallet must select a exchange that either the merchant accepts directly by listing it in the exchanges array, or for which the merchant accepts an auditor that audits that exchange by listing it in the auditors array.

The Product object describes the product being purchased from the merchant. It has the following structure:

interface Product {
  // merchant-internal identifier for the product.
  product_id?: string;

  // Human-readable product description.
  description: string;

  // Map from IETF BCP 47 language tags to localized descriptions
  description_i18n?: { [lang_tag: string]: string };

  // The number of units of the product to deliver to the customer.
  quantity?: Integer;

  // The unit in which the product is measured (liters, kilograms, packages, etc.)
  unit?: string;

  // The price of the product; this is the total price for quantity times unit of this product.
  price?: Amount;

  // An optional base64-encoded product image
  image?: ImageDataUrl;

  // a list of taxes paid by the merchant for this product. Can be empty.
  taxes?: Tax[];

  // time indicating when this product should be delivered
  delivery_date?: Timestamp;
}
interface Tax {
  // the name of the tax
  name: string;

  // amount paid in tax
  tax: Amount;
}
interface Merchant {
  // label for a location with the business address of the merchant
  address: Location;

  // the merchant's legal name of business
  name: string;

  // label for a location that denotes the jurisdiction for disputes.
  // Some of the typical fields for a location (such as a street address) may be absent.
  jurisdiction: Location;
}
// Delivery location, loosely modeled as a subset of
// ISO20022's PostalAddress25.
interface Location {
  // Nation with its own government.
  country?: string;

  // Identifies a subdivision of a country such as state, region, county.
  country_subdivision?: string;

  // Identifies a subdivision within a country sub-division.
  district?: string;

  // Name of a built-up area, with defined boundaries, and a local government.
  town?: string;

  // Specific location name within the town.
  town_location?: string;

  // Identifier consisting of a group of letters and/or numbers that
  // is added to a postal address to assist the sorting of mail.
  post_code?: string;

  // Name of a street or thoroughfare.
  street?: string;

  // Name of the building or house.
  building_name?: string;

  // Number that identifies the position of a building on a street.
  building_number?: string;

  // Free-form address lines, should not exceed 7 elements.
  address_lines?: string[];
}
interface Auditor {
  // official name
  name: string;

  // Auditor's public key
  auditor_pub: EddsaPublicKey;

  // Base URL of the auditor
  url: string;
}
interface Exchange {
  // the exchange's base URL
  url: string;

  // master public key of the exchange
  master_pub: EddsaPublicKey;
}