Golang programs that import flag or httptest will panic due to uninitialized os.Args

[StevenACoffman]

When I try to run fastly compute serve with webassembly code that I build with GOARCH=wasm GOOS=wasip1 go build ./... if I have code that even indirectly includes flag then the flag package imports httptest ( _ "net/http/httptest") which will panic when it gets to: https://github.com/golang/go/blob/3ed007d754b685cd8f6011a8e96a3c9303c785db/src/flag/flag.go#L1199

An example piece of code

package main

import (
    "fmt"
    "os"

    _ "bytes"
    _ "context"
    _ "encoding/json"
    _ "net"
    _ "net/http"

    // This causes issues!
    _ "net/http/httptest"

    _ "net/url"
    _ "strconv"
    _ "strings"
)

func main() {
    fmt.Println("FASTLY_SERVICE_VERSION:", os.Getenv("FASTLY_SERVICE_VERSION"))
}

and run fastly compute serve with this fastly.toml file:

# This file describes a Fastly Compute package. To learn more visit:
# https://www.fastly.com/documentation/reference/compute/fastly-toml

authors = ["XXXXacademy.org"]
cloned_from = "https://github.com/fastly/compute-starter-kit-go-default"
description = "fastly compute go service"
language = "go"
manifest_version = 3
name = "fastly-khanacademy-compute"
service_id = "XXXX"

[scripts]
  build = "go build -o bin/main.wasm ./cmd/serve"
  env_vars = ["GOARCH=wasm", "GOOS=wasip1"]
  post_init = "go get github.com/fastly/compute-sdk-go@latest"

# Despite most of the local_server configuration being in the fastly.{env}.toml
# files, this actually needs to be defined in our basic fastly.toml file.
# It MUST be defined as the full semantic version, but without the 'v'.
# The 'fastly' cli must be at version 10.2.0 or later to use this.
[local_server]
  viceroy_version = "0.9.6"

I can reproduce this problem with tinygo, but wasmtime doesn't seem to have the problem directly, so I assume it is a viceroy problem.

I mentioned this in the gophers slack and @dgryski said he passed it on to a colleague, but I didn't want others to duplicate bug reports, so I thought I'd record it here for others to track.

[kpfleming]

Could you try with 0.9.7? It has a newer wasmtime, it's possible there may be some interaction there.

[dgryski]

This still happens with viceroy 0.9.7.

A much smaller reproducer is:

package main

import (
    "fmt"
    "os"
)

func main() {
    fmt.Println(os.Args[0])
}

[ydnar]

Would it be reasonable to supply at least one WASI arg to the guest? Either with some default value like wasm, or the name of the service?

[dgryski]

@ydnar Yes. The baseame of the wasm file I believe is accessible; worst case we just lie.

[StevenACoffman]

@ydnar Do you have a pointer for where this could be plumbed through? I'm not much of a rustacean.