[PiotrSikora]

Notable changes:

1. Removed proxy_on_vm_start callback.
2. Split plugin lifecycle from stream context lifecycle.
3. Consolidated proxy_on_done, proxy_on_log, and proxy_on_delete
   into proxy_on_context_finalize.

[PiotrSikora]

This is stacked on #91, so please review only the last commit.

[PiotrSikora]

FWIW, the more I look at this, the more I think that we should implicitly create context as part of "new" callback, which would save one call into VM, and it would match callouts, since we implicitly create new context as part of sending the call.

Change from:

proxy_on_context_create(context_id, context_type, plugin_context_id)
proxy_on_http_request_headers(context_id, end_of_stream)
proxy_on_http_request_body_chunk(context_id, body_size, end_of_stream)
...
proxy_on_context_finalize(context_id)

to:

proxy_on_http_request_headers(context_id, plugin_context_id, end_of_stream)
proxy_on_http_request_body_chunk(context_id, body_size, end_of_stream)
...
proxy_on_http_finalize(context_id)

The main reason for the proxy_on_context_create callback is to bind it to the plugin context, but we also have proxy_context_resume that we'd otherwise have to create for each context.

See previous discussion in #9.

[mpwarres]

Recording discussion elsewhere, we decided that proxy_on_context_create is useful as a "guaranteed" callbacks, since in some integrations (e.g. Service Extensions), customers can choose whether or not to enable/disable headers and body callback events.

[PiotrSikora]

Unstacked after #91 was merged, no other changes were made.