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send local response: clarify call sequence #73

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send local response: clarify call sequence #73

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3 changes: 2 additions & 1 deletion abi-versions/v0.2.1/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1156,7 +1156,8 @@ Plugin must return one of the following values:

Sends HTTP response with body (`body_data`, `body_size`) and
[serialized] headers (`serialized_headers_data`,
`serialized_headers_size`).
`serialized_headers_size`). The response is sent after the current
callback completes and triggers response callbacks.
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This is the opposite of the intended behavior (which is that proxy_send_local_response() is always a final call).

We want plugins to do something like this:

proxy_on_request_headers() {
   ...
   return proxy_send_local_response(...);
}

and not something like this:

proxy_on_request_headers() {
   ...
   proxy_send_local_response(...);
   do_something_very_important();
   return Pause;
}

The reason this is deferred in Envoy is because the response callbacks (i.e. proxy_on_response_headers() and friends) are called immediately upon sending local response, which leads to re-entrancy problems, but that's another issue (I don't think that plugins should "receive" the local responses they generated themselves).

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@mpwarres I think we have to specify it one way or another. How does WaaS behave here?


This can be used as long as HTTP response headers were not sent downstream.

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