feat(proxy-wasm) foreign function support

[casimiro]

Foreign Function Support

The Proxy-Wasm spec defines the function proxy_call_foreign_function and the callback proxy_on_foreign_function that filter developers can use to invoke host specific functions, a.k.a. foreign functions, and receive callbacks.

A foreign function invoked with proxy_call_foreign_function may return its value immediately -- as part of the returned value of the proxy_call_foreign_function call; or it can return it later, writing it to the FOREIGN_FUNCTION_ARGUMENTS buffer, and invoking proxy_on_foreign_function with an id identifying the function initially called.

This PR adds support for the mechanism described above; and although the spec doesn't restrict when foreign functions can be called, in ngx_wasm_module they cannot be invoked from proxy_on_configure or proxy_on_vm_start.

DNS resolution

This PR also exposes the Lua DNS resolver through the resolve_lua foreign function.

This function expects the name to be resolved as its single argument. If the name can be resolved without performing any IO, the resolved address is put in the returned value of proxy_call_foreign_function.

If the resolver needs to forward the resolution request to a DNS server, the resolved address and the name itself are written to the FOREIGN_FUNCTION_ARGUMENTS buffer and the proxy_on_foreign_function callback is invoked with function_id 0, as soon as the address is returned from the server.

TODO

• on_tick support
• update docs
• general review

[codecov]

Codecov Report

Attention: Patch coverage is 82.97872% with 48 lines in your changes missing coverage. Please review.

Project coverage is 90.71034%. Comparing base (004ae21) to head (a03e4b4).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/common/proxy_wasm/ngx_proxy_wasm_foreign_call.c	76.00000%	36 Missing ⚠️
src/common/proxy_wasm/ngx_proxy_wasm_host.c	87.50000%	3 Missing ⚠️
src/http/ngx_http_wasm_util.c	80.00000%	3 Missing ⚠️
src/http/proxy_wasm/ngx_http_proxy_wasm.c	84.21053%	3 Missing ⚠️
src/http/proxy_wasm/ngx_http_proxy_wasm_dispatch.c	93.75000%	2 Missing ⚠️
src/common/proxy_wasm/ngx_proxy_wasm.c	96.15385%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main        #626         +/-   ##
===================================================
- Coverage   90.82100%   90.71034%   -0.11066%     
===================================================
  Files             53          54          +1     
  Lines          11352       11572        +220     
  Branches        1691        1713         +22     
===================================================
+ Hits           10310       10497        +187     
- Misses          1036        1069         +33     
  Partials           6           6                 

Files with missing lines	Coverage Δ
src/common/proxy_wasm/ngx_proxy_wasm.h	92.30769% <ø> (ø)
src/common/proxy_wasm/ngx_proxy_wasm_maps.c	94.01042% <100.00000%> (ø)
src/common/proxy_wasm/ngx_proxy_wasm_util.c	94.25287% <100.00000%> (ø)
src/common/proxy_wasm/ngx_proxy_wasm.c	92.69603% <96.15385%> (-0.01345%)	⬇️
src/http/proxy_wasm/ngx_http_proxy_wasm_dispatch.c	91.74528% <93.75000%> (+0.31671%)	⬆️
src/common/proxy_wasm/ngx_proxy_wasm_host.c	93.61233% <87.50000%> (-0.18699%)	⬇️
src/http/ngx_http_wasm_util.c	86.95652% <80.00000%> (-0.27752%)	⬇️
src/http/proxy_wasm/ngx_http_proxy_wasm.c	92.99065% <84.21053%> (-0.88690%)	⬇️
...rc/common/proxy_wasm/ngx_proxy_wasm_foreign_call.c	76.00000% <76.00000%> (ø)

... and 2 files with indirect coverage changes

Flag	Coverage Δ
unit	90.65053% <90.36145%> (+0.08790%)	⬆️
valgrind	81.00649% <29.41176%> (-1.47085%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[casimiro]

Codecov is playing games with me. It's reporting lines that are definitely covered by tests as uncovered.