Add support to proxy outbound requests from Synapse in tests (#18158)

Adds new environment variables that can be used with the Docker image
(`SYNAPSE_HTTP_PROXY`/`SYNAPSE_HTTPS_PROXY`/`SYNAPSE_NO_PROXY`)

Useful for things like the [Secure Border
Gateway](https://element.io/server-suite/secure-border-gateways)


### Why is this necessary?

You can already configure the `HTTP_PROXY`/`HTTPS_PROXY` environment
variables to proxy outbound requests but setting this globally in the
Docker image affects all processes which isn't always desirable or
workable in the case where the proxy is running in the Docker image
itself (because the Debian packages will fail to download because the
proxy isn't up and running yet) . Adding Synapse specific environment
variables
(`SYNAPSE_HTTP_PROXY`/`SYNAPSE_HTTPS_PROXY`/`SYNAPSE_NO_PROXY`) makes
things much more targetable.

changelog.d/18158.docker

@@ -0,0 +1 @@
+Add `SYNAPSE_HTTP_PROXY`/`SYNAPSE_HTTPS_PROXY`/`SYNAPSE_NO_PROXY` environment variables to pass through specifically to the Synapse process (instead of needing to apply [`http_proxy`/`https_proxy`/`no_proxy`](https://element-hq.github.io/synapse/latest/setup/forward_proxy.html) globally).

docker/README.md

@@ -114,6 +114,9 @@ The following environment variables are supported in `run` mode:
   is set via `docker run --user`, defaults to `991`, `991`. Note that this user
   must have permission to read the config files, and write to the data directories.
 * `TZ`: the [timezone](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones) the container will run with. Defaults to `UTC`.
+* `SYNAPSE_HTTP_PROXY`: Passed through to the Synapse process as the `http_proxy` environment variable.
+* `SYNAPSE_HTTPS_PROXY`: Passed through to the Synapse process as the `https_proxy` environment variable.
+* `SYNAPSE_NO_PROXY`: Passed through to the Synapse process as `no_proxy` environment variable.
 
 For more complex setups (e.g. for workers) you can also pass your args directly to synapse using `run` mode. For example like this:
 

docker/conf-workers/synapse.supervisord.conf.j2

@@ -1,5 +1,6 @@
 {% if use_forking_launcher %}
 [program:synapse_fork]
+environment=http_proxy="%(ENV_SYNAPSE_HTTP_PROXY)s",https_proxy="%(ENV_SYNAPSE_HTTPS_PROXY)s",no_proxy="%(ENV_SYNAPSE_NO_PROXY)s"
 command=/usr/local/bin/python -m synapse.app.complement_fork_starter
   {{ main_config_path }}
   synapse.app.homeserver
@@ -20,6 +21,7 @@ exitcodes=0
 
 {% else %}
 [program:synapse_main]
+environment=http_proxy="%(ENV_SYNAPSE_HTTP_PROXY)s",https_proxy="%(ENV_SYNAPSE_HTTPS_PROXY)s",no_proxy="%(ENV_SYNAPSE_NO_PROXY)s"
 command=/usr/local/bin/prefix-log /usr/local/bin/python -m synapse.app.homeserver
   --config-path="{{ main_config_path }}"
   --config-path=/conf/workers/shared.yaml
@@ -36,6 +38,7 @@ exitcodes=0
 
   {% for worker in workers %}
 [program:synapse_{{ worker.name }}]
+environment=http_proxy="%(ENV_SYNAPSE_HTTP_PROXY)s",https_proxy="%(ENV_SYNAPSE_HTTPS_PROXY)s",no_proxy="%(ENV_SYNAPSE_NO_PROXY)s"
 command=/usr/local/bin/prefix-log /usr/local/bin/python -m {{ worker.app }}
   --config-path="{{ main_config_path }}"
   --config-path=/conf/workers/shared.yaml

docker/configure_workers_and_start.py

@@ -1099,6 +1099,13 @@ def main(args: List[str], environ: MutableMapping[str, str]) -> None:
     else:
         log("Could not find %s, will not use" % (jemallocpath,))
 
+    # Empty strings are falsy in Python so this default is fine. We just can't have these
+    # be undefined because supervisord will complain about our
+    # `%(ENV_SYNAPSE_HTTP_PROXY)s` usage.
+    environ.setdefault("SYNAPSE_HTTP_PROXY", "")
+    environ.setdefault("SYNAPSE_HTTPS_PROXY", "")
+    environ.setdefault("SYNAPSE_NO_PROXY", "")
+
     # Start supervisord, which will start Synapse, all of the configured worker
     # processes, redis, nginx etc. according to the config we created above.
     log("Starting supervisord")

synapse/http/proxyagent.py

@@ -150,6 +150,12 @@ class ProxyAgent(_AgentBase):
             http_proxy = proxies["http"].encode() if "http" in proxies else None
             https_proxy = proxies["https"].encode() if "https" in proxies else None
             no_proxy = proxies["no"] if "no" in proxies else None
+            logger.debug(
+                "Using proxy settings: http_proxy=%s, https_proxy=%s, no_proxy=%s",
+                http_proxy,
+                https_proxy,
+                no_proxy,
+            )
 
         self.http_proxy_endpoint, self.http_proxy_creds = http_proxy_endpoint(
             http_proxy, self.proxy_reactor, contextFactory, **self._endpoint_kwargs