3. GNU Taler Exchange Setup Guide

This setup guide walks a system administrator through all steps required to install an exchange and check that it is functional. For more background, please read the Operator Manual.

3.1. System Requirements

This guide assumes that you are running Ubuntu 20.04 (Focal Fossa).

We recommend the setup of offline signing keys to be done on a second machine that does not have Internet access.

In this guide’s shell-session fragments, the command prompt shows two pieces of information:

  • Who is performing the command ($user vs root, and ending character $ vs #).
  • Host where the command is supposed to be executed (exchange-offline vs exchange-online). It is possible to do the entire setup on one machine, but we do not recommend this for security reasons.

3.2. Before you start

To deploy this with a real bank, you need:

  • IBAN of the bank account to use
  • BIC of the bank
  • EBICS host, user and partner IDs

Information to write down during the installation:

  • LibEuFin Nexus superuser password
  • Taler facade base URL
  • exchange Nexus username and password

3.3. Installation

We assume that the system is a minimal installation of Ubuntu 20.04 LTS. Ideally, you should have two hosts, exchange-online and exchange-offline. It is also possible to run the HTTPS nginx server or the PostgreSQL database on yet another host, but in these instructions we will assume that only two hosts are used. Alas, the instructions will also work if you run everything on one system, but then you have the security drawback of not keeping the high-security private keys disconnected from the Internet.

To install the exchange, first make sure that your system is up-to-date and that the gnupg package has been installed.

[root@exchange-online]# apt-get update
[root@exchange-online]# apt-get upgrade

Next, add the focal-fossa apt repository provided by Taler Systems S.A. to your package sources:

[root@exchange-online]# cat > /etc/apt/sources.list.d/taler.list <<EOF
deb https://deb.taler.net/apt/ubuntu focal-fossa main
EOF
[root@exchange-online]# dpkg --remove-architecture i386

The second command is optional. It tells apt-get update to not bother with the i386 architecture (thus avoiding a warning, later). If you use this, make sure you do not use any 32-bit applications.

Before installing Taler packages, you need to add the Taler Systems S.A. package signing key to your list of trusted keys and update the package index:

[root@exchange-online]# wget -O - https://taler.net/taler-systems.gpg.key | apt-key add -
[root@exchange-online]# apt-get update

Finally, the required packages can be installed:

[root@exchange-online]# apt-get install -y nginx postgresql
[root@exchange-online]# apt-get install -y taler-exchange taler-exchange-offline
[root@exchange-online]# apt-get install -y taler-wallet-cli

By default, all installed services will be disabled. You need to enable and start them later.

While taler-merchant and taler-wallet are not required to operate an exchange, they are useful for testing. When asked about using dbconfig to configure the merchant’s database, select yes.

3.4. Configuration Basics

The configuration for all Taler components uses a single configuration file as entry point: /etc/taler/taler.conf.

System defaults are automatically loaded from files in /usr/share/taler/config.d. These default files should never be modified.

The default configuration taler.conf configuration file also includes all configuration files in /etc/taler/conf.d. The settings from files in conf.d are only relevant to particular components of Taler, while taler.conf contains settings that affect all components.

The directory /etc/taler/secrets contains configuration file snippets with values that should only be readable to certain users. They are included with the @inline-secret@ directive and should end with .secret.conf.

To view the entire configuration annotated with the source of each configuration option, you can use the taler-config helper:

[root@exchange-online]# taler-config --diagnostics
< ... annotated, full configuration ... >

Warning

While taler-config also supports rewriting configuration files, we strongly recommend to edit configuration files manually, as taler-config does not preserve comments and, by default, rewrites /etc/taler/taler.conf.

3.5. Services, users, groups and file system hierarchy

The taler-exchange-httpd package will create several system users to compartmentalize different parts of the system:

  • taler-exchange-httpd: runs the HTTP daemon with the core business logic.
  • taler-exchange-secmod-rsa: manages the RSA private online signing keys.
  • taler-exchange-secmod-eddsa: manages the EdDSA private online signing keys.
  • taler-exchange-closer: closes idle reserves by triggering wire transfers that refund the originator.
  • taler-exchange-aggregator: aggregates deposits into larger wire transfer requests.
  • taler-exchange-wire: performs wire transfers with the bank (via LibEuFin/Nexus).
  • postgres: runs the Postgres database (from postgres package).
  • www-data: runs the frontend HTTPS service with the TLS keys (from nginx package).

Note

The taler-merchant-httpd package additionally creates a taler-merchant-httpd user to runs the HTTP daemon with the merchant business logic.

The exchange setup uses the following system groups:

  • taler-exchange-db: group for all Taler users with direct database access, specifically taler-exchange-httpd, taler-exchange-wire, taler-exchange-closer and taler-exchange-aggregator.
  • taler-exchange-secmod: group for processes with access to online signing keys; this group must have three users: taler-exchange-secmod-rsa, taler-exchange-secmod-eddsa and taler-exchange-httpd.
  • taler-exchange-offline: group for the access to the offline private key (only used on the offline host and not used on the online system).

The package will deploy systemd service files in /usr/lib/systemd/system/ for the various components:

  • taler-exchange-aggregator.service: service that schedules wire transfers which combine multiple deposits to the same merchant.
  • taler-exchange-closer.service: service that watches for reserves that have been abandoned and schedules wire transfers to send the money back to the originator.
  • taler-exchange-httpd.service: main Taler exchange logic with the public REST API.
  • taler-exchange-httpd.socket: systemd socket activation for the Taler exchange HTTP daemon.
  • taler-exchange-secmod-eddsa.service: software security module for making EdDSA signatures.
  • taler-exchange-secmod-rsa.service: software security module for making RSA signatures.
  • taler-exchange-transfer.service: service that triggers outgoing wire transfers (pays merchants).
  • taler-exchange-wirewatch.service: service that watches for incoming wire transfers (first step of withdraw).
  • taler-exchange.target: Main target for the Taler exchange to be operational.

The deployment creates the following key locations in the system:

  • /etc/taler/: configuration files.
  • /run/taler/: contains the UNIX domain sockets for inter-process communication (IPC).
  • /var/lib/taler/: serves as the $HOME for all Taler users and contains sub-directories with the private keys; which keys are stored here depends on the host:
    • online system: exchange-secmod-eddsa and exchange-secmod-rsa keys.
    • offline system: exchange-offline keys.

3.6. Setup Linting

The taler-wallet-cli package comes with a experimental tool that runs various checks on the current GNU Taler exchange deployment:

[root@exchange-online]# taler-wallet-cli deployment lint-exchange

You can optionally pass the --debug option to get more verbose output, and --continue to continue with further checks even though a previous one has failed.

3.7. Basic Setup: Currency and Denominations

A Taler exchange only supports a single currency. The currency and the smallest currency unit supported by the bank system must be specified in /etc/taler/taler.conf.

/etc/taler/taler.conf
 [taler]
 CURRENCY = EUR
 CURRENCY_ROUND_UNIT = EUR:0.01

 # ... rest of file ...

Warning

When editing /etc/taler/taler.conf, take care to not accidentally remove the @inline-matching@ directive to include the configuration files in conf.d.

Next, the electronic cash denominations that the exchange offers must be specified. The taler-wallet-cli has a helper command that generates a reasonable denomination structure.

taler-wallet-cli deployment gen-coin-config --min-amount EUR:0.01 --max-amount EUR:100 > /etc/taler/conf.d/exchange-coins.conf

You can manually review and edit the generated configuration file. The main change that is possibly required is updating the various fees.

3.8. Wire Gateway Setup

The Taler Wire Gateway is an API that connects the Taler exchange to the underlying core banking system.

LibEuFin is an implementation of the Wire Gateway API for the EBICS protocol. This section will walk through (1) installing and configuring LibEuFin and (2) connecting the Taler Exchange to LibEuFin.

Note

If you do not have a bank account with EBICS but want to test these instructions, you can use the EBICS sandbox as described in the LibEuFin Tutorial.

3.8.1. Installation and Basic Configuration

First, install the libeufin package. This can be done on the exchange-online machine or a different one.

[root@exchange-online]# apt-get install -y libeufin

The main component of LibEuFin is called the Nexus. It implements a Web service that provides a JSON abstraction layer to access bank accounts.

The Nexus currently uses an sqlite3 database as storage by default. We currently recommend to stick with this default. In future versions, there will be a migration path to a PostgreSQL database.

The HTTP port and database connection string can be edited in the configuration:

/etc/libeufin/nexus.env
LIBEUFIN_NEXUS_PORT=5017
LIBEUFIN_NEXUS_DB_CONNECTION=jdbc:sqlite:/var/lib/libeufin/nexus/nexus-db.sqlite3

After configuring the database, you can start the service. The database is initialized automatically.

[root@exchange-online]# systemctl enable libeufin-nexus
[root@exchange-online]# systemctl start libeufin-nexus

You can now create a superuser account. The command to create the superuser needs direct database access, thus the configuration file is sourced first, and the relevant environment variable is exported.

[root@exchange-online]# source /etc/libeufin/nexus.env
[root@exchange-online]# export LIBEUFIN_NEXUS_DB_CONNECTION
[root@exchange-online]# NEXUS_ADMIN_PW=$(tr -dc A-Za-z0-9 </dev/urandom | head -c 13)
[root@exchange-online]# libeufin-nexus superuser admin --password $NEXUS_ADMIN_PW

If you omit --password $NEXUS_ADMIN_PW, you will interactively be asked for a password. For simplicity, a superuser can as well act as a normal user, but an API to create less privileged users is offered.

Note

User and permissions management in LibEuFin is still under development. In particular, permissions for non-superusers are very limited at the moment.

3.8.2. Connecting Nexus with an EBICS account

The command line interface of the LibEuFin Nexus needs the following three values to be defined in the environment: LIBEUFIN_NEXUS_URL, LIBEUFIN_NEXUS_USERNAME, and LIBEUFIN_NEXUS_PASSWORD. In this example, LIBEUFIN_NEXUS_USERNAME should be set to admin, and LIBEUFIN_NEXUS_PASSWORD to the value hold in NEXUS_ADMIN_PW from the previous step (the libeufin-nexus superuser command). The LIBEUFIN_NEXUS_URL could be given as http://localhost:5017/.

Next, we create a EBICS bank connection that Nexus can use to communicate with the bank.

[root@exchange-online]# libeufin-cli \
    connections \
      new-ebics-connection \
        --ebics-url $EBICS_BASE_URL \
        --host-id $EBICS_HOST_ID \
        --partner-id $EBICS_PARTNER_ID \
        --ebics-user-id $EBICS_USER_ID \
        $CONNECTION_NAME

If this step executes correctly, Nexus will have created all the cryptographic material that is needed on the client side; in this EBICS example, it created the signature and identification keys. It is therefore advisable to make a backup copy of such keys.

[root@exchange-online]# libeufin-cli \
    connections \
      export-backup \
        --passphrase $SECRET \
        --output-file $BACKUP_FILE \
        $CONNECTION_NAME

At this point, Nexus needs to both communicate its keys to the bank, and download the bank’s keys. This syncronization happens through the INI, HIA, and finally, HPB message types.

After the electronic synchronization, the subscriber must confirm their keys by sending a physical mail to the bank. The following command helps generating such letter:

[root@exchange-online]# libeufin-cli connections get-key-letter $CONNECTION_NAME out.pdf
[root@exchange-online]# libeufin-cli \
    connections \
      connect \
        $CONNECTION_NAME

Once the connection is synchronized, Nexus needs to import locally the data corresponding to the bank accounts offered by the bank connection just made. The command below downloads the list of the bank accounts offered by $CONNECTION_NAME.

[root@exchange-online]# libeufin-cli \
    connections \
      download-bank-accounts \
        $CONNECTION_NAME

It is now possible to list the accounts offered by the connection.

[root@exchange-online]# libeufin-cli \
    connections \
      list-offered-bank-accounts \
        $CONNECTION_NAME

Note

The nexusBankAccountId field should at this step be null, as we have not yet imported the bank account and thus the account does not yet have a local name.

Nexus now needs an explicit import of the accounts it should manage. This step is needed to let the user pick a custom name for such accounts.

[root@exchange-online]# libeufin-cli \
    connections \
      import-bank-account \
        --offered-account-id testacct01 \
        --nexus-bank-account-id $LOCAL_ACCOUNT_NAME \
        $CONNECTION_NAME

Once a Nexus user imported a bank account ($LOCAL_ACCOUNT_NAME) under a certain connection ($CONNECTION_NAME), it is possible to accomplish the usual operations for any bank account: asking for the list of transactions, and making a payment.

Testing: Requesting the transaction history

The LibEuFin Nexus keeps a local copy of the bank account’s transaction history. Before querying transactions locally, it is necessary to request transactions for the bank account via the bank connection.

This command asks Nexus to download the latest transaction reports/statements through the bank connection:

[root@exchange-online]# libeufin-cli accounts fetch-transactions $LOCAL_ACCOUNT_NAME

Note

By default, the latest available transactions are fetched. It is also possible to specify a custom date range (or even all available transactions) and the type of transactions to fetch (inter-day statements or intra-day reports).

Once Nexus has stored all the information in the database, the client can ask to actually see the transactions:

[root@exchange-online]# libeufin-cli accounts transactions $LOCAL_ACCOUNT_NAME

Testing: Making payments

Payments pass through two phases: preparation and submission. The preparation phase assigns the payment initiation a unique ID, which prevents accidental double submissions of payments in case of network failures or other disruptions.

The following command prepares a payment:

[root@exchange-online]# libeufin-cli accounts prepare-payment \
        --creditor-iban=$IBAN_TO_SEND_MONEY_TO \
        --creditor-bic=$BIC_TO_SEND_MONEY_TO \
        --creditor-name=$CREDITOR_NAME \
        --payment-amount=$AMOUNT \
        --payment-subject=$SUBJECT \
        $LOCAL_ACCOUNT_NAME

Note: the $AMOUNT value needs the format X.Y:CURRENCY; for example EUR:10, or EUR:1.01.

The previous command should return a value ($UUID) that uniquely identifies the prepared payment in the Nexus system. That is needed in the next step, to send the payment instructions to the bank:

[root@exchange-online]# libeufin-cli accounts submit-payment \
      --payment-uuid $UUID \
      $LOCAL_ACCOUNT_NAME

Automatic scheduling

With an EBICS bank connection, the LibEuFin Nexus needs to regularly query for new transactions and (re-)submit prepared payments.

It is possible to schedule these tasks via an external task scheduler such as cron(8). However, the nexus also has an internal task scheduling mechanism for accounts.

The following three commands create a schedule for submitting payments hourly, fetching transactions (intra-day reports) every 5 minutes, and (inter-day statements) once at 11pm every day:

[root@exchange-online]# libeufin-cli accounts task-schedule $LOCAL_ACCOUNT_NAME \
    --task-type="submit" \
    --task-name='submit-payments-hourly' \
    --task-cronspec='0 0 *'

[root@exchange-online]# libeufin-cli accounts task-schedule $LOCAL_ACCOUNT_NAME \
    --task-type="fetch" \
    --task-name='fetch-5min' \
    --task-cronspec='0 */5 *' \
    --task-param-level=report \
    --task-param-range-type=latest

[root@exchange-online]# libeufin-cli accounts task-schedule $LOCAL_ACCOUNT_NAME \
    --task-type="fetch" \
    --task-name='fetch-daily' \
    --task-cronspec='0 0 23' \
    --task-param-level=statement \
    --task-param-range-type=latest

The cronspec has the following format, which is slightly non-standard due to the SECONDS field

SECONDS MINUTES HOURS DAY-OF-MONTH[optional] MONTH[optional] DAY-OF-WEEK[optional]

Creating a Taler facade

Facades are additional abstraction layers that can serve specific purposes. For example, one application might need a filtered version of the transaction history, or it might want to refuse payments that do not conform to certain rules.

At this moment, only the Taler facade type is implemented in the Nexus, and the command below instantiates one under a existing bank account / connection pair. You can freely assign an identifier for the $FACADE_NAME below:

[root@exchange-online]# libeufin-cli facades new-taler-wire-gateway-facade \
    --currency EUR \
    --facade-name $FACADE_NAME \
    $CONNECTION_NAME \
    $LOCAL_ACCOUNT_NAME

At this point, the additional taler-wire-gateway API becomes offered by the Nexus. The purpose is to let a Taler exchange rely on Nexus to manage its bank account.

The base URL of the facade that can be used by the Taler exchange as the Taler Wire Gateway base URL can be seen by listing the facades:

[root@exchange-online]# libeufin-cli facades list

Managing Permissions and Users

This guide has so far assumed that a superuser is accessing the LibEuFin Nexus. However, it is advisable that the Nexus is accessed with users that only have a minimal set of permissions.

The Nexus currently only has support for giving non-superusers access to Taler wire gateway facades.

To create a new user, use the users subcommand of the CLI:

[root@exchange-online]# libeufin-cli users list
# [ ... shows available users ... ]

[root@exchange-online]# libeufin-cli users create $USERNAME
# [ ... will prompt for password ... ]

Permissions are managed with the permissions subcommand. The following commands grant permissions to view the transaction history and create payment initiations with a Taler wire gateway facade:

[root@exchange-online]# libeufin-cli permissions grant \
   user $USERNAME \
   facade $FACADENAME \
   facade.talerwiregateway.history

[root@exchange-online]# libeufin-cli permissions grant \
   user $USERNAME \
   facade $FACADENAME \
   facade.talerwiregateway.transfer

The list of all granted permissions can be reviewed:

[root@exchange-online]# libeufin-cli permissions list

3.8.3. Exchange Wire Configuration

The exchange must be configured with the right settings to access the Taler Wire Gateway. An exchange can be configured to use multiple bank accounts by using multiple Wire Gateways. Typically only one Wire Gateway is used.

A Taler Wire Gateway is configured in a configuration section that follows the pattern exchange-account-$id, where $id is an internal identifier for the bank account accessed by the exchange. The basic information for an account should be put in /etc/taler/conf.d/exchange-business.conf. The secret credentials to access the Taler Wire Gateway API should be put into a corresponding exchange-accountcredentials-$id section in /etc/taler/secrets/exchange-accountcredentials.conf. The latter file should already be only readable for the taler-exchange-wire user. Other exchange processes should not have access to this information.

/etc/taler/conf.d/exchange-business.conf
[exchange-account-1]
enable_credit = yes
enable_debit = yes

# Account identifier in the form of an RFC-8905 payto:// URI.
# For SEPA, looks like payto://sepa/$IBAN?receiver-name=$NAME
# Make sure to URL-encode spaces in $NAME!
payto_uri =

@inline-secret@ exchange-accountcredentials-1 ../secrets/exchange-accountcredentials.secret.conf
/etc/taler/secrets/exchange-accountcredentials.secret.conf
[exchange-accountcredentials-1]

# LibEuFin expects basic auth.
wire_gateway_auth_method = basic

# Username and password set in LibEuFin.
username = ...
password = ...

# Base URL of the wire gateway set up with LibEuFin.
wire_gateway_url = ...

The Wire Gateway configuration can be tested with the following command:

[root@exchange-online]# taler-exchange-wire-gateway-client \
  --section exchange-accountcredentials-1 --debit-history
[root@exchange-online]# taler-exchange-wire-gateway-client \
  --section exchange-accountcredentials-1 --credit-history

3.9. Exchange Database Setup

The access credentials for the exchange’s database are configured in /etc/taler/secrets/exchange-db.secret.conf. Currently, only PostgreSQL is supported as a database backend.

The following users must have access to the exchange database:

  • taler-exchange-httpd
  • taler-exchange-wire
  • taler-exchange-aggregator
  • taler-exchange-closer

These users are all in the taler-exchange-db group, and the exchange-db.secret.conf should already be only readable by users in this group.

To create a database for the Taler exchange on the local system, run:

[root@exchange-online]# su - postgres
[postgres@exchange-online]# createuser taler-exchange-httpd
[postgres@exchange-online]# createuser taler-exchange-wire
[postgres@exchange-online]# createuser taler-exchange-aggregator
[postgres@exchange-online]# createuser taler-exchange-closer
[postgres@exchange-online]# createdb -O taler-exchange-httpd taler-exchange
[postgres@exchange-online]# exit

This will create a taler-exchange database owned by the taler-exchange-httpd user. We will use that user later to perform database maintenance operations.

Assuming the above database setup, the database credentials to configure in the configuration file would simply be:

/etc/taler/secrets/exchange-db.secret.conf
[exchangedb-postgres]
CONFIG=postgres:///taler-exchange

If the database is run on a different host, please follow the instructions from the PostgreSQL manual for configuring remote access.

After configuring the database credentials, the exchange database needs to be initialized with the following command:

[root@exchange-online]# sudo -u taler-exchange-httpd taler-exchange-dbinit

Finally we need to grant the other accounts limited access:

[root@exchange-online]# sudo -u taler-exchange-httpd bash
[taler-exchange-httpd@exchange-online]# echo 'GRANT SELECT,INSERT,UPDATE ON ALL TABLES IN SCHEMA public TO "taler-exchange-aggregator";' \
  | psql taler-exchange
[taler-exchange-httpd@exchange-online]# echo 'GRANT SELECT,INSERT,UPDATE ON ALL TABLES IN SCHEMA public TO "taler-exchange-closer";' \
  | psql taler-exchange
[taler-exchange-httpd@exchange-online]# echo 'GRANT SELECT,INSERT,UPDATE ON ALL TABLES IN SCHEMA public TO "taler-exchange-wire";' \
  | psql taler-exchange
[taler-exchange-httpd@exchange-online]# echo 'GRANT USAGE ON ALL SEQUENCES IN SCHEMA public TO "taler-exchange-aggregator";' \
  | psql taler-exchange
[taler-exchange-httpd@exchange-online]# echo 'GRANT USAGE ON ALL SEQUENCES IN SCHEMA public TO "taler-exchange-closer";' \
  | psql taler-exchange
[taler-exchange-httpd@exchange-online]# echo 'GRANT USAGE ON ALL SEQUENCES IN SCHEMA public TO "taler-exchange-wire";' \
  | psql taler-exchange
[taler-exchange-httpd@exchange-online]# exit

Note

The above instructions for changing database permissions only work after having initialized the database with taler-exchange-dbinit, as the tables to exist before permissions can be granted on them. The taler-exchange-dbinit tool cannot setup these permissions, as it does not know which users will be used for which processes.

3.10. Offline Signing Setup

The offline signing keys of the exchange should be stored on a different machine. The responsibilities of this offline signing machine are:

  • Generation of the exchange’s offline master signing key.
  • Secure storage of the exchange’s offline master signing key.
  • Generation of certificates (signed with the offline master signing key) that will be imported by the exchange.
[root@exchange-offline]# sudo -u taler-exchange-offline taler-exchange-offline setup
< ... prints the exchange master public key >

The public key printed as the output of this command must be put into the configuration of the online machine:

/etc/taler/conf.d/exchange-business.conf
 [exchange]
 MASTER_PUBLIC_KEY = YE6Q6TR1ED...

 # ... rest of file ...

3.11. Exchange Web service / API Setup

By default, the taler-exchange-httpd service listens for HTTP connections on a UNIX domain socket. To make the service publicly available, a reverse proxy such as nginx should be used. We strongly recommend to configure nginx to use TLS.

The public URL that the exchange will be served under should be put in /etc/taler/conf.d/exchange-business.conf configuration file.

/etc/taler/conf.d/exchange-business.conf
 [exchange]
 BASE_URL = https://example.com/

 # ... rest of file ...

The taler-exchange package ships with a sample configuration that can be enabled in nginx:

[root@exchange-online]# vim /etc/nginx/sites-available/taler-exchange
< ... customize configuration ... >
[root@exchange-online]# ln -s /etc/nginx/sites-available/taler-exchange \
                              /etc/nginx/sites-enabled/taler-exchange
[root@exchange-online]# systemctl reload nginx

The exchange HTTP service can now be started:

[root@exchange-online]# systemctl start taler-exchange.target

Note

At this point, the exchange service is not yet fully operational.

To check whether the exchange is running correctly under the advertized base URL, run:

[root@exchange-online]# export BASE_URL=$(taler-config -s exchange -o base_url)
[root@exchange-online]# wget ${BASE_URL}management/keys

The request might take some time to complete on slow machines, because a lot of key material will be generated.

3.12. Offline Signing Procedure

The exchange HTTP service should be running now, but is not yet completely operational. To make the exchange HTTP service operational, the following steps involving the offline signing machine must be completed:

  1. The public keys of various online keys used by the exchange service are exported via a management HTTP API.
  2. The offline signing system validates this request and signs it. Additionally, the offline signing system signs policy messages to configure the exchange’s bank accounts and associated fees.
  3. The messages generated by the offline signing system are uploaded via the management API of the exchange HTTP service.
[root@exchange-online]# taler-exchange-offline \
  download > sig-request.json

[root@exchange-offline]# taler-exchange-offline \
  sign < sig-request.json > sig-response.json
[root@exchange-offline]# taler-exchange-offline \
  enable-account payto://sepa/$IBAN?receiver-name=$NAME > acct-response.json
[root@exchange-offline]# taler-exchange-offline \
  wire-fee 2021 sepa EUR:0 EUR:0 > fee-response.json
[root@exchange-online]# taler-exchange-offline upload < sig-response.json
[root@exchange-online]# taler-exchange-offline upload < acct-response.json
[root@exchange-online]# taler-exchange-offline upload < fee-response.json

3.13. Testing and Troubleshooting

The following shell session illustrates how the wallet can be used to withdraw electronic cash from the exchange and subsequently spend it. For these steps, a merchant backend is not required, as the wallet acts as a merchant.

# This will now output a payto URI that money needs to be sent to in order to allow withdrawal
# of taler coins.
$ taler-wallet-cli advanced withdraw-manually --exchange $EXCHANGE_URL --amount EUR:10.50

Show the status of the manual withdrawal operation.

$ taler-wallet-cli transactions

At this point, a bank transfer to the exchange’s bank account needs to be made with the correct subject / remittance information as instructed by the wallet after the first step. With the above configuration, it should take about 5 minutes after the wire transfer for the incoming transfer to be observed by the Nexus.

Run the following command to check whether the exchange received an incoming bank transfer:

[root@exchange-online]# taler-exchange-wire-gateway-client \
   --section exchange-accountcredentials-1 --credit-history

Once the transfer has been made, try completing the withdrawal using:

$ taler-wallet-cli run-pending

Afterwards, check the status of transactions and show the current wallet balance:

$ taler-wallet-cli transactions
$ taler-wallet-cli balance

Now, we can directly deposit coins via the exchange into a target account. (Usually, a payment is made via a merchant. The wallet provides this functionality for testing.)

$ taler-wallet-cli deposit create EUR:5 \
  payto://sepa/$IBAN?receiver-name=Name
$ taler-wallet-cli run-pending

Check if this transaction was successful (from the perspective of the wallet):

$ taler-wallet-cli transactions

If the transaction failed, fix any open issue(s) with the exchange and run the “run-pending” command.

The wallet can also track if the exchange wired the money to the merchant account. The “deposit group id” can be found in the output of the transactions list.

$ taler-wallet-cli deposit track $DEPOSIT_GROUP_ID

You can also check using the exchange-tools whether the exchange sent the an outgoing transfer:

[root@exchange-online]# taler-exchange-wire-gateway-client \
  --section exchange-accountcredentials-1 --debit-history

After enough time has passed, the money should arrive at the specified IBAN.

3.14. FIXMEs

  • We should have some summary with the inventory of services that should be running. Systemd by default doesn’t show this nicely. Maybe suggest running “systemd list-dependencies taler-exchange.target”?
  • When multiple TWGs are configured, which one will be used by the taler-exchange-transfer? CG: ALL!
    • FD: Sure, for incoming transactions. But how does taler-exchange-transfer decide which TWG to use for an outgoing transaction?
  • What happens when the TWG doesn’t like one particular outgoing transaction? How to recover from that as a sysadmin when it happens in practice?