go.talks/pkg/socket: fix go-tour non-main package wrong message
Fixes golang/go#5871.
R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/11200044
diff --git a/pkg/socket/socket.go b/pkg/socket/socket.go
index df573d7..87655bf 100644
--- a/pkg/socket/socket.go
+++ b/pkg/socket/socket.go
@@ -16,6 +16,9 @@
import (
"bytes"
"encoding/json"
+ "errors"
+ "go/parser"
+ "go/token"
"io"
"io/ioutil"
"log"
@@ -24,6 +27,7 @@
"path/filepath"
"runtime"
"strconv"
+ "strings"
"unicode/utf8"
"code.google.com/p/go.net/websocket"
@@ -190,6 +194,12 @@
cmd.Env = append(cmd.Env, "GOMAXPROCS=2")
}
if err := cmd.Start(); err != nil {
+ // If we failed to exec, that might be because they built
+ // a non-main package instead of an executable.
+ // Check and report that.
+ if name, err := packageName(body); err == nil && name != "main" {
+ return errors.New(`executable programs must use "package main"`)
+ }
return err
}
p.run = cmd
@@ -227,6 +237,15 @@
return cmd
}
+func packageName(body string) (string, error) {
+ f, err := parser.ParseFile(token.NewFileSet(), "prog.go",
+ strings.NewReader(body), parser.PackageClauseOnly)
+ if err != nil {
+ return "", err
+ }
+ return f.Name.String(), nil
+}
+
// messageWriter is an io.Writer that converts all writes to Message sends on
// the out channel with the specified id and kind.
type messageWriter struct {
