serve/docker: allow to customize proxy settings of docker plugin

cmd/serve/docker/contrib/plugin/Dockerfile

@@ -26,6 +26,10 @@ ENV RCLONE_CACHE_DIR=/data/cache
 ENV RCLONE_BASE_DIR=/mnt
 ENV RCLONE_VERBOSE=0
 
+ENV HTTP_PROXY=
+ENV HTTPS_PROXY=
+ENV NO_PROXY=
+
 WORKDIR /data
 ENTRYPOINT ["/usr/local/bin/rclone"]
 CMD ["serve", "docker"]

cmd/serve/docker/contrib/plugin/config.json

@@ -42,6 +42,21 @@
         {
             "name": "RCLONE_BASE_DIR",
             "value": "/mnt"
+        },
+        {
+            "name": "HTTP_PROXY",
+            "value": "",
+            "settable": ["value"]
+        },
+        {
+            "name": "HTTPS_PROXY",
+            "value": "",
+            "settable": ["value"]
+        },
+        {
+            "name": "NO_PROXY",
+            "value": "",
+            "settable": ["value"]
         }
     ],
     "mounts": [

docs/content/docker.md

@@ -347,7 +347,8 @@ swarm services that use them. This is rather tedious so please carefully
 plan in advance.
 
 You can tweak the following settings:
-`args`, `config`, `cache`, and `RCLONE_VERBOSE`.
+`args`, `config`, `cache`, `HTTP_PROXY`, `HTTPS_PROXY`, `NO_PROXY`
+and `RCLONE_VERBOSE`.
 It's _your_ task to keep plugin settings in sync across swarm cluster nodes.
 
 `args` sets command-line arguments for the `rclone serve docker` command
@@ -389,6 +390,8 @@ The plugin output by default feeds the docker daemon log on local host.
 Log entries are reflected as _errors_ in the docker log but retain their
 actual level assigned by rclone in the encapsulated message string.
 
+`HTTP_PROXY`, `HTTPS_PROXY`, `NO_PROXY` customize the plugin proxy settings.
+
 You can set custom plugin options right when you install it, _in one go_:
 ```
 docker plugin remove rclone
@@ -506,6 +509,8 @@ sudo curl -H Content-Type:application/json -XPOST -d {} --unix-socket /run/docke
 ```
 though this is rarely needed.
 
+## Caveats
+
 Finally I'd like to mention a _caveat with updating volume settings_.
 Docker CLI does not have a dedicated command like `docker volume update`.
 It may be tempting to invoke `docker volume create` with updated options