The Electrum QR Payment Partner Interface is an HTTP RESTFul interface.

Terminology

The Electrum QR Payment Partner Interface documentation utilises several specific terms which for clarity are defined below.

Upstream And Downstream Entities

Upstream and downstream impart a convention for the direction for a request and its response. A request message (such as a payment request) typically originates at a retailer location and must be sent to the partner for processing. When a message is sent from a merchant to a partner it is said to be sent upstream. Conversely, when a message is sent from a partner vendor to a Electrum it is said to be sent downstream. Thus, ‘upstream entity’ is a relative term and is any entity located between the entity under discussion and the partner (including the partner itself). Likewise, ‘downstream entity’ is also a relative term and is any entity located between the entity under discussion and the retailer (including the retailer itself).

Server vs Client

Servers typically host an application and, in the context of the RESTful Electrum QR Payment Partner Interface, a server would host the QR payments service application responsible for servicing requests received from downstream entities and providing a response. A server is the entity which receives requests and returns responses. A client therefore is the entity responsible for sending requests to a server and expects responses from the server.

Security

All communication shall be secured by establishing an SSL encrypted transport. SSL provides a manner for client and server systems to identify themselves to each other as well as to establish an encrypted channel over which they may securely communicate. SSL provides security at a network level and identifies entities who communicate to each other.

Since the Electrum QR Payment Partner Interface is a RESTful service, server implementations are typically hosted on web servers. Using the HTTP Basic Authentication headers over and above SSL allows the sender of a message to be identified at an application level and any appropriate processing to take place on a per-sender basis.

Failures

The failure outcome of a request shall be determined in the first instance by examining the HTTP status code of the response. The HTTP status types and their associated meanings convey information about the possible reasons for a failure response. Where possible, a failure response will also contain further information about the nature of the failure in an ErrorDetail object.

Status type

Three basic types of outcomes are possible for transactions, namely: successful, unknown, and failed. HTTP status types are mapped to one of the possible outcomes as indicated below.

HTTP Status Codes	Status type
200, 201, 202, 404*	successful
500, 504, timeout	unknown
400, 404*, 501, 503, all others	failed

A timeout occurs when the client has not received a response to a request after an agreed upon interval. Unless otherwise agreed, this interval shall be 60 seconds. Any response received after the timeout should be logged but ignored.

*Note that an HTTP status type of 404 could indicate either a success or a failure; this is dependent on the context of the response. This is covered in more detail in the section on Message Flows