go: plugin: add test (was encoding/asn1 error when using plugin)

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.8beta2 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/fsenart/projects"
GORACE=""
GOROOT="/home/fsenart/tools/go"
GOTOOLDIR="/home/fsenart/tools/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build746500890=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

If possible, provide a recipe for reproducing the error. A complete runnable program is good. A link on play.golang.org is best.

// main.go

package main

import (
	"plugin"
	"reflect"
)

func main() {
	p, err := plugin.Open("plugin.so")
	if err != nil {
		panic(err)
	}
	f, err := p.Lookup("F")
	if err != nil {
		panic(err)
	}

	// f.(func())()
	reflect.ValueOf(f).Call(nil)
}

// plugin.go

package main

import "C"
import "net/http"

func F() {
	_, err := http.Get("https://example.com")
	if err != nil {
		panic(err)
	}
}

# Makefile

test: build
	@./main

build: clean
	@go build -buildmode=plugin -o plugin.so plugin.go
	@go build -o main main.go

clean:
	@rm -rf main *.so

What did you expect to see?

I don’t expect any panic to happen.

What did you see instead?

I see a panic happen.

panic: Get https://example.com: tls: failed to parse certificate from server: asn1: structure error: tags don't match (4 vs {class:0 tag:16 length:1242 isCompound:true}) {optional:false explicit:false application:false defaultValue:<nil> tag:<nil> stringType:0 timeType:0 set:false omitEmpty:false} RawContent @4

goroutine 1 [running]:
plugin/unnamed-4ad3198f73971e7223d350ce7ae956cd80d817d9.F()
	/home/fsenart/projects/src/github.com/alsanium/issue_asn1/plugin.go:9 +0x65
reflect.Value.call(0x4d3820, 0xc42000f728, 0x13, 0x4ef099, 0x4, 0x0, 0x0, 0x0, 0xc42000c2e0, 0x4d3820, ...)
	/home/fsenart/tools/go/src/reflect/value.go:434 +0x91f
reflect.Value.Call(0x4d3820, 0xc42000f728, 0x13, 0x0, 0x0, 0x0, 0xc42004df68, 0x4be551, 0x0)
	/home/fsenart/tools/go/src/reflect/value.go:302 +0xa4
main.main()
	/home/fsenart/projects/src/github.com/alsanium/issue_asn1/main.go:19 +0xed
Makefile:2: recipe for target 'test' failed

---

Observations

• If I don’t use the reflect package, and instead make type assertion manually, then no error happens.

  f.(func())()
  // reflect.ValueOf(f).Call(nil)
  

• If I don’t use the plugin package, then no error happens.

  package main
  
  import (
      "net/http"
      "reflect"
  )
  
  var f interface{} = func() {
      _, err := http.Get("https://example.com")
      if err != nil {
          panic(err)
      }
  }
  
  func main() {
      //f.(func())()
      reflect.ValueOf(f).Call(nil)
  }