ABI vNEXT: generic vs specialized context functions #9
Description
The current version of the ABI defines generic proxy_on_context_create() and proxy_on_context_finalize() functions which are used for VM and plugin lifecycle, as well as for per-stream lifecycle, which makes "context" a bit overloaded and confusing.
For VM context:
proxy_on_context_create(VmContext, ...)
proxy_on_vm_start(...)
proxy_on_context_finalize(...)
For plugin context:
proxy_on_context_create(PluginContext, ...)
proxy_on_plugin_start(...)
proxy_on_context_finalize(...)
For HTTP per-stream context:
proxy_on_context_create(HttpContext, ...)
proxy_on_http_request_headers(...)
proxy_on_http_request_body(...)
proxy_on_http_response_headers(...)
proxy_on_http_response_body(...)
proxy_on_context_finalize(...)
Instead, we could have specialized "finalize" functions for each context type, and create context implicitly as part of each "start" function:
For VM context:
proxy_on_vm_start(...)
proxy_on_vm_shutdown(...)
For plugin context:
proxy_on_plugin_start(...)
proxy_on_plugin_shutdown(...)
For HTTP per-stream context:
proxy_on_http_request_headers(...)
proxy_on_http_request_body(...)
proxy_on_http_response_headers(...)
proxy_on_http_response_body(...)
proxy_on_http_finalize(...)
In case proxy_on_http_finalize() returns Action::Pause, the host would wait until proxy_resume() is called before calling proxy_on_http_finalize() again (which matches the behavior of other callbacks that have the ability to pause/resume processing).
@mattklein123 @htuch @yskopets @yuval-k @gbrail @jplevyak @kyessenov any thoughts?
Activity
htuch commentedon Aug 26, 2020
Seems a slam dunk interface improvement.
mattklein123 commentedon Aug 26, 2020
Huge +1 from me. I think this is one of the things that I initially commented on.
kyessenov commentedon Aug 26, 2020
+1 as a user. Using the same callback is really problematic when one plugin serves in different roles (which might be common to save on resources by reusing the VM/module).
I think this will need pausable access log extensions in envoy.
PiotrSikora commentedon May 21, 2026
As discussed in the Proxy-Wasm meeting on 2/19, we're going to keep the generic interface with added
context_typeto avoid overloading "context" everywhere and to keep the ABI extensible with other context types in the future.Related: #80 (Consistent style in the ABI (expanded vs minimal)).
cc @mpwarres @leonm1