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INTEGRATION.md

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Integration scenarios of frob program

By design one should spawn a separate frob instance for each connection. Performance isn't an issue, because normally only few ECRs are connected to the POS terminal at the same time (usually 1 or 2). The most convenient way to do this is to use superserver like s6-tcpserver from s6. If you need to reverse the connection, you can use s6-tcpclient. If you need to use serial port, you can just redirect /dev/ttyS0 to frob's stdin/stdout.

Because of very flexible I/O mechanism (file descriptors) employed by frob it can be integrated into a larger system in many different ways.

Integration with big monolithic payment application

             |
+-------+ TCP|socket      UNIX domain socket +------------------+
| ECR 1 | <--|-----> frob <----------------> |                  |
+-------+    |                               | Large monolithic |
+-------+ TCP|socket      UNIX domain socket | application      |
| ECR 2 | <--|-----> frob <----------------> |                  |
+-------+    |                               +------------------+
             |
             |Physical boundary

For a large application it may be useful to have a single file descriptor for a bidirectional communication, to which all messages are written. This can be done by using a UNIX domain socket, created by socketpair(2) system call. From which one end is passed to frob program, and the other end is passed to the payment application.

Integration with payment applications consisting of multiple processes

                            Named pipes
┌───────┐ TCP|socket      |--ui-------->[1]          ┌─────────────┐
│ ECR 1 │ <--|-----> frob |--payment--->[2]   [1]--->│ GUI process │
└───────┘    |            |--storage--->[3]          └─────────────┘
             |            |<--device----[4]                 ↕
             |                                       ┌─────────────┐
┌───────┐ TCP|socket      |--ui-------->[1]   [2]--->│             │
│ ECR 2 │ <--|-----> frob |--payment--->[2]   [3]--->│ Terminal SW │
└───────┘    |            |--storage--->[3]   [4]<---│             │
             |            |<--device----[4]          └─────────────┘
             |
             |Physical boundary

Frob has 4 distinct I/O channels, which can be assigned different file descriptors and connect to different processes.

Integration with nexo payment application using microservice architecture

                        Named pipes or sockets
+-------+ TCP|socket      |--ui-------->[1]          +-------+
| ECR 1 | <--|-----> frob |--payment--->[2]   [1]--->| SCAP  |
+-------+    |            |--storage--->[3]          +-------+
             |            |<--device----[2]              ↕
             |                                       +--------------+
                                              [2]<-->|     FAST     |
+-------+ TCP|socket      |--ui-------->[1]          +--------------+
| ECR 2 | <--|-----> frob |--payment--->[2]             ↕       ↕
+-------+    |            |--storage--->[3]          +-----+ +------+
             |            |<--device----[2]   [3]--->| HAP | | TMAP |
             |                                       +-----+ +------+
             |Physical boundary

Nexo specifies 3 distinct modules that are responsible for different parts of the payment process. Frob channels are neatly modeled by these modules. Read more about Nexo in Nexo standards. Synchronisation is done by frob, applications don't need to worry about it.

Integration with a proxy

             |
+-------+ TCP|socket      TCP socket +------+
| ECR 1 | <--|-----> frob <--------> |      |     +-------------+
+-------+    |                       | Proxy|<--->| Payment     |
+-------+ TCP|socket      TCP socket |      |     | application |
| ECR 2 | <--|-----> frob <--------> |      |     +-------------+
+-------+    |                       +------+
             |
             |Physical boundary

Conversely you can convert all communication via a proxy to another ECR protocol, eg Nexo retaler protocol.