11.1. Nexus Manual¶
LibEuFin Nexus is an EBICS facilitator. It offers a command line interface to setup EBICS access, download banking records, and submit payments. Future versions will offer a Web API to allow Taler Exchanges to talk to their banks.
In this manual, we explain how to setup an EBICS subscriber. We assume that the bank had already granted EBICS access to the subscriber.
11.1.1. Installing Nexus¶
The following section was tested on an OpenJDK 17 environment.
11.1.1.1. Building from source¶
Nexus belongs to the LibEuFin project, and can be downloaded via Git:
$ git clone git://git.taler.net/libeufin
Note that Kotlin and Gradle should already work on the host system.
Navigate into the libeufin local repository, and from top-level run:
$ ./bootstrap
$ ./configure --prefix=$PREFIX
$ make install-nexus
If the previous steps succeeded, the libeufin-nexus command should
be found in the $PATH.
11.1.2. Setting up the EBICS subscriber¶
When you sign up for an EBICS-enabled bank account, the bank will provide you
with various credentials. Those must be provided in the
/etc/libeufin/libeufin-nexus.conf configuration file together with the
name of the fiat currency.
The following snippet shows the mandatory configuration values:
[nexus-ebics]
CURRENCY = CHF
# Bank
HOST_BASE_URL = http://bank.example.com/
BANK_DIALECT = postfinance
# EBICS IDs
HOST_ID = mybank
USER_ID = myuser
PARTNER_ID = myorg
# Key files
BANK_PUBLIC_KEYS_FILE = ${LIBEUFIN_HOME}/bank-keys.json
CLIENT_PRIVATE_KEYS_FILE = ${LIBEUFIN_HOME}/subscriber-keys.json
# Account information
IBAN = myiban
BIC = mybic
NAME = myname
Note
Refer to the manpage libeufin-nexus.conf(5)
for the full array of configuration values.
Assuming that the configuration file exists at $config_file, the following
command would start the EBICS setup process. The files CLIENT_PRIVATE_KEYS_FILE
and BANK_PUBLIC_KEYS_FILE would be created at the CWD. Adjust their path to your
setup (‘$HOME’ is currently not supported along paths).
libeufin-nexus ebics-setup -c $config_file
If the previous command succeeded, the subscriber keys reached the bank, but the setup
should fail with an EBICS_INVALID_USER_STATE error code. That happens because
the client tries to download the bank keys before having confirmed the subscriber keys
via the traditional post service.
To that purpose, the previous run should have left a PDF document that the subscriber can
print, sign, and send to the bank to confirm their subscriber keys. Look for the message
looking like PDF file with keys hex encoding created at: /tmp/libeufin-nexus-keys-$timestamp.pdf.
Once the bank received and approved such printed document, run the same command again, in order to download the bank keys and let the user accept them.
libeufin-nexus ebics-setup -c $config_file
The setup is considered finished once the user accepts the bank keys.
11.1.3. Sending payments¶
Sending payments must follow a successful EBICS subscriber setup,
where the bank obtained the subscriber keys, and the subscriber accepted the
bank keys. The responsible subcommand for sending payments is ebics-submit,
and its configuration is a superset of core-config. On top of that, it
expects the database connection string, and optionally a frequency to check
for submittable payments in the database.
The connection string is specified as
[nexus-postgres]
config = postgres:///nexus
The frequency may be specified as
[nexus-submit]
frequency = 5m
# Optional, but useful to check what Nexus sends to the bank
submissions_log_directory = $LIBEUFIN_DATA_HOME/uploads
The supported time units are s (seconds), m (minutes), h (hours).
Before delving into the following sections, the database schema must be created, therefore run the following command:
libeufin-nexus dbinit -c $config_file
Where $config_file is the path to a configuration path that contains at
least the [nexus-postgres] section.
11.1.3.1. For testing¶
The ebics-submit subcommand is not suitable to send arbitrary
payments, but rather to submit initiated payments that may be found
in the database.
Such initiated payments may be refunds of incoming payments with a subject that would be invalid for a Taler withdrawal, or from a Taler exchange in the attempt to pay a merchant.
For testing purposes, however, it is possible to artificially initiate
a payment into the database with the contrib/payment_initiation_debug.sh
script, found in the libeufin repository. The script pays always one Swiss
Franc to an IBAN and subject pair of choice.
The following invocation pays 1 CHF to the CH987654321 with an “Hello, Nexus!” subject.
./payment_initiation_debug.sh $config_file CH987654321 "Hello, Nexus!"
$config_file is the path to Nexus’ configuration file and it does not need
the FREQUENCY value. If the previous command worked, now the database should
contain a new row in the initiated_outgoing_transactions table, with an
unsubmitted submission state.
The following command would now pick such an unsubmitted initiated payment and send it to the bank.
libeufin-nexus ebics-submit -c $config_file --transient
The --transient flag instructs the software to perform only one pass on
the database, submit what is submittable, and return.
Alternatively, the --debug flag makes ebics-submit accept data from STDIN,
and submit it to the bank.
11.1.3.2. For production¶
The ebics-submit subcommand can run in fixed frequency, or transient mode.
The fixed frequency mode causes the command to check the database every time the
frequency period expires. To activate this mode, and – for example – set a frequency
of five minutes, set the configuration value FREQUENCY to 5m. Assuming that
$config_fixed_frequency is set as described above, the following invocation would
make ebics-submit check the database every five minutes, and submit any initiated
payment according to their submission state.
libeufin-nexus ebics-submit -c $config_fixed_frequency
Transient mode causes ebics-submit to check the database only once, submit any
initiated payment according to their submission state, and return.
libeufin-nexus ebics-submit -c $config
11.1.4. Downloading records¶
Downloading records must follow a successful EBICS subscriber setup, where the bank obtained the subscriber keys, and the subscriber accepted the bank keys.
The configuration file must contain all the [ebics-setup] sections, plus the following
values to set the database connection and a log directory where any downloaded record would
be stored.
[nexus-postgres]
config = postgres:///nexus
[nexus-fetch]
# Optional, but usfeful against data loss.
statement_log_directory = $LIBEUFIN_DATA_HOME/downloads
Assuming that $config_file contains any required option, the following command
would download any unseen notifications (as camt.054 files).
libeufin-nexus ebics-fetch -c $config_file --transient
The --transient flag makes the command to download only once and return. If the
bank returned any records, look in $LIBEUFIN_DATA_HOME/camt/YYYY-MM-DD to find them.
YYYY-MM-DD is the date when the download took place.
To activate periodic downloads, add the following setting to the nexus-fetch
configuration section in $config_file:
frequency = 5m
The following invocation would then download records every five minutes, asking the bank to only return documents that are timestamped from (inclusive) the last incoming transaction.
libeufin-nexus ebics-fetch -c $config_file
11.1.4.1. Testing¶
If the bank account history has transactions that are useful for testing, it is
possible to redownload them via the --pinned-start argument. Note: if the Nexus
database contains already the bank account history, you might need to reset it,
in order to have the redownloaded transactions ingested.
Note
double-check the configuration: resetting the wrong database might cause DATA LOSS!
For example, say that three back on the 2023-06-01 an handful of incoming transactions got booked at the bank account watched by Nexus. After such day, the following command would redownload them (and ingest them, if the database doesn’t have them):
libeufin-nexus ebics-fetch -c $config_file --pinned-start 2023-06-01
Note: the command redownloads transactions from the pinned start until the present.