golang server.go 处理head请求的一个小坑
虽然是个小坑，可是trace了一个星期，浪费了不少时间，解决方案很简单，思考的过程却是很值得借鉴：）
http web完整代码在：https://github.com/philsong/golang_samples/tree/master/src/emvdecoder
emvdecoder中问题代码片段如下：
func checkError(w http.ResponseWriter, err error) {
if err != nil {
fmt.Fprintf(w,"Fatal error ", err.Error())
os.Exit(1)
}
}
func index(w http.ResponseWriter, r *http.Request) {
r.ParseForm()
t, err := template.ParseFiles("index.html")
checkError(w, err)
err = t.Execute(w, emvdecoder)
checkError(w, err)
}
于是自己就搜索google，发现了这篇文章，Linux 技巧：让进程在后台可靠运行的几种方法http://www.ibm.com/developerworks/cn/linux/l-cn-nohup/
用nohup emvdecoder&运行后，似乎运行良好了（稍后就知道这是巧合。。。），于是发一微博
继续测试发现其实无论用&， nohup还是setsid， 父进程已经变成了init了，所以效果其实一样，于是猜测是代码的bug（其实又是自己的问题...)，但是奇怪为什么没打印出来呢
philsong@compiler:~$ cd go/src/emvdecoder/
philsong@compiler:~/go/src/emvdecoder$ emvdecoder&
[1] 22908
philsong@compiler:~/go/src/emvdecoder$ ps
PID TTY TIME CMD
22729 pts/2 00:00:01 bash
22908 pts/2 00:00:00 emvdecoder
22911 pts/2 00:00:00 ps
philsong@compiler:~/go/src/emvdecoder$ pstree -ps 22908
init(1)---sshd(702)---sshd(22703)---sshd(22728)---bash(22729)---emvdecoder(22908)-+-{emvdecoder}(22909)
`-{emvdecoder}(22910)
断开ssh后，
philsong@compiler:~$ pstree -ps 22908
init(1)---emvdecoder(22908)-+-{emvdecoder}(22909)
|-{emvdecoder}(22910)
|-{emvdecoder}(22916)
`-{emvdecoder}(22917)
，
fuck代码发现
func checkError(w http.ResponseWriter, err error) {
if err != nil {
fmt.Fprintf(w,"Fatal error ", err.Error())
os.Exit(1)
}
}
fmt.Fprintf(w由于copy时默认打印到http 的w句柄，并没有打印道控制台，囧啊，改为
fmt.Println("
继续log大法，并打印堆栈
import "runtime/debug"
debug.PrintStack()
func checkError(w http.ResponseWriter, err error) {
fmt.Println("error: ")
if err != nil {
fmt.Println("Fatal error ", err.Error())
debug.PrintStack()
os.Exit(1)
}
}
func index(w http.ResponseWriter, r *http.Request) {
println("Request ", r.URL.Path, " from ", r.RemoteAddr)
// path := r.URL.Path[1:]
path := "." + r.URL.Path
fmt.Println("path", path)
if path == "./favicon.ico" {
http.NotFound(w, r)
return
}
r.ParseForm()
t, err := template.ParseFiles("index.html")
checkError(w, err)
err = t.Execute(w, emvdecoder)
checkError(w, err)
}
这次捕获到珍贵的输出：
Request / from 208.94.145.109:22492
path ./
error:
error:
Fatal error template: index.html:1:0: executing "index.html" at <"<!DOCTYPE HTML>\r\n...>: http: request method or response status code does not allow body
/home/philsong/go/src/emvdecoder/emvdecoder.go:47 (0x8048d50)
checkError: debug.PrintStack()
/home/philsong/go/src/emvdecoder/emvdecoder.go:69 (0x80490a5)
index: checkError(w, err)
/usr/local/go/src/pkg/net/http/server.go:1149 (0x809936c)
HandlerFunc.ServeHTTP: f(w, r)
/usr/local/go/src/pkg/net/http/server.go:1416 (0x809a39d)
(*ServeMux).ServeHTTP: h.ServeHTTP(w, r)
/usr/local/go/src/pkg/net/http/server.go:1517 (0x809aa21)
serverHandler.ServeHTTP: handler.ServeHTTP(rw, req)
/usr/local/go/src/pkg/net/http/server.go:1096 (0x8099073)
(*conn).serve: serverHandler{c.server}.ServeHTTP(w, w.req)
/usr/local/go/src/pkg/runtime/proc.c:1223 (0x805fd60)
goexit: runtime路goexit(void)
The error is self-explaining:
request method or response status code does not allow body
A HEAD request only allows HTTP headers to be sent back as response.
899 func (w *response) Write(data []byte) (n int, err error) { 900 if w.conn.hijacked() { 901 log.Print("http: response.Write on hijacked connection") 902 return 0, ErrHijacked 903 } 904 if !w.wroteHeader { 905 w.WriteHeader(StatusOK) 906 } 907 if len(data) == 0 { 908 return 0, nil 909 } 910 if !w.bodyAllowed() { 911 return 0, ErrBodyNotAllowed 912 } 913 914 w.written += int64(len(data)) // ignoring errors, for errorKludge 915 if w.contentLength != -1 && w.written > w.contentLength { 916 return 0, ErrContentLength 917 } 918 return w.w.Write(data) 919 }猜测是发起的head请求，不是正常的get和post请求，怪不得，直接用浏览器访问时无法重现这个bug，于是用
curl: (52) Empty reply from server
//os.Exit(1)
HTTP/1.1 200 OK
Date: Tue, 17 Sep 2013 06:31:32 GMT
philsong@compiler:~$ curl -I 192.168.7.14:9090
HTTP/1.1 200 OK
Date: Tue, 17 Sep 2013 06:31:40 GMT