Support for reflect package in TinyGo

[srikarrao]

Is the reflect package implemented in the latest version of Tinygo? I'm trying to decode the JSON in Go WASM and I have been getting the below error that reflect.Type.NumMethod() is unimplemented. I found a couple of issues reported earlier, I'm not sure if this is implemented. However, the TinyGo's supported libs document says it does allow importing encoding/json package.

Previous Issues:
#907
#575

Versions used:

> go version 
	go1.17.6 darwin/amd64
> tinygo version
	tinygo version 0.22.0 darwin/amd64 (using go version go1.17.6 and LLVM version 13.0.0)
> proxy-wasm-go-sdk version
	github.com/tetratelabs/proxy-wasm-go-sdk v0.16.0

Error logs:

proxy_1        | [2022-03-02 02:08:03.668][1][info][wasm] [source/extensions/common/wasm/context.cc:1170] wasm log: panic: unimplemented: (reflect.Type).NumMethod()
proxy_1        | [2022-03-02 02:08:03.668][1][error][wasm] [source/extensions/common/wasm/wasm_vm.cc:38] Function: proxy_on_tick failed: Uncaught RuntimeError: unreachable
proxy_1        | Proxy-Wasm plugin in-VM backtrace:
proxy_1        |   0:  0x170f - runtime._panic
proxy_1        |   1:  0x326d - (reflect.rawType).NumMethod
proxy_1        |   2:  0x6c23a - (*gopkg.in/square/go-jose.v2/json.decodeState).indirect
proxy_1        |   3:  0x696e5 - (*gopkg.in/square/go-jose.v2/json.decodeState).object
proxy_1        |   4:  0x687dc - (*gopkg.in/square/go-jose.v2/json.decodeState).value
proxy_1        |   5:  0x2af8b - gopkg.in/square/go-jose.v2/json.Unmarshal
proxy_1        |   6:  0x65be4 - (*gopkg.in/square/go-jose.v2.JSONWebKey).UnmarshalJSON
proxy_1        |   7:  0x64cef - proxy_on_tick

[dkegel-fastly]

Only a subset of reflect is implemented. The supported package page is overdue to have a "passes tests" column, see
tinygo-org/tinygo-site#110

Work is ongoing to improve reflect, see #2640.

[joeblew99]

Hey @srikarrao

I know that https://github.com/buger/jsonparser is used with tinygo where you need to do JSON serialisation.

You can find the entry point here at https://github.com/genjidb/genji.js/blob/master/scripts/buildgo.sh#L27, which compiles the golang code using tinygo to wasm

[johnkeates]

I ran into the same issue with golang-jwt in a WASI target, it tries to do a (reflect.rawType).NumMethod during JSON decoding and that panics because it's simply not there (yet).

Edit: I tried to see if this is something I can implement but it seems much more complicated than expected, especially when referring to to 'full' go reflect package and all the additional functions that it needs to get this method in rtype.

[dgryski]

encoding/json "should" be working once my last few reflect fixes are in. Please let me know if you're still encountering issues. I will try to test with golang-jwt.

[dgryski]

The next release of tinygo will support validating jwt: (I had to disable the http listener example)

~/go/src/github.com/golang-jwt/jwt $ tinygo test -tags="purego noasm" -target=wasi
ok  	github.com/golang-jwt/jwt/v5	1.766s

[ricardbejarano]

Thank you so much! When can we expect that release to happen?