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Document internal APIs and Application Services component (#499)

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* Document internal APIs, app services in WIRING.md

* Add application services component to WIRING diagram

* Fix typo and clarify what mode internal APIs use HTTP
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Andrew Morgan 2018-07-06 02:33:53 -07:00 committed by GitHub
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WIRING.md
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@ -36,7 +36,11 @@ Diagram:
| | | | | | | |
| | | |>==========================>| | | |
| | | | +----------+ | |
| | | | | |
| | | | +---+ | |
| | | | +-------------| R | | |
| | | |>=====>| Application +---+ | |
| | | | | Services | | |
| | | | +--------------+ | |
| | | | +---+ | |
| | | | +--------| R | | |
| | | | | Client +---+ | |
@ -190,3 +194,36 @@ choke-point to implement ratelimiting and backoff correctly.
* Reads new events and the current state of the rooms from logs writeen by the Room Server.
* Reads the position of the read marker from the Receipts Server.
* Makes outbound HTTP hits to the push server for the client device.
## Application Service
* Receives events from the Room Server.
* Filters events and sends them to each registered application service.
* Runs a separate goroutine for each application service.
# Internal Component API
Some dendrite components use internal APIs to communicate information back
and forth between each other. There are two implementations of each API, one
that uses HTTP requests and one that does not. The HTTP implementation is
used in multi-process mode, so processes on separate computers may still
communicate, whereas in single-process or Monolith mode, the direct
implementation is used. HTTP is preferred here to kafka streams as it allows
for request responses.
Running `dendrite-monolith-server` will set up direct connections between
components, whereas running each individual component (which are only run in
multi-process mode) will set up HTTP-based connections.
The functions that make HTTP requests to internal APIs of a component are
located in `/<component name>/api/<name>.go`, named according to what
functionality they cover. Each of these requests are handled in `/<component
name>/<name>/<name>.go`.
As an example, the `appservices` component allows other Dendrite components
to query external application services via its internal API. A component
would call the desired function in `/appservices/api/query.go`. In
multi-process mode, this would send an internal HTTP request, which would
be handled by a function in `/appservices/query/query.go`. In single-process
mode, no internal HTTP request occurs, instead functions are simply called
directly, thus requiring no changes on the calling component's end.