2014年9月1日 15:09:16go评论90阅读模式

英文:

issue with accessing GET parameters net/http in golang

问题

以下是我提供的翻译：

以下是我提取GET参数的Go程序。（URL：/mysql?hostname=example.com）

package main

import (
    "net/http"
    "fmt"
    // "encoding/json"
    // "html"
    "github.com/kr/pretty"
);

func main() {
    http.HandleFunc("/", foo)
    http.ListenAndServe(":80", nil)
}

func foo(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Server", "A Go WebServer")

    w.Header().Set("Content-Type", "text/html")

    hostname := r.URL.Query()["hostname"]
    // w.Write([]byte(hostname[0]))
    fmt.Printf("%#v", pretty.Formatter(hostname[0]))

    w.Write([]byte(hostname))
}

控制台显示的错误信息。

"example.com"2014/09/01 02:57:22 http: panic serving 172.17.92.14:49411: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42dc41)
    _func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f8b5)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410381)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x410228)
/root/go/src/api/main.go:34 (0x400d77)
    foo: fmt.Printf("%#v", pretty.Formatter(hostname[0]))
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421bed)
    HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422a6f)
    (*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x421a00)
    (*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d9bb)
2014/09/01 02:57:22 http: panic serving 172.17.92.14:49412: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42dc41)
    _func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f8b5)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410381)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x410228)
/root/go/src/api/main.go:34 (0x400d77)
    foo: fmt.Printf("%#v", pretty.Formatter(hostname[0]))
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421bed)
    HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422a6f)
    (*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x421a00)
    (*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d9bb)
2014/09/01 02:57:22 http: panic serving 172.17.92.14:49413: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42dc41)
    _func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f8b5)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410381)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x410228)
/root/go/src/api/main.go:34 (0x400d77)
    foo: fmt.Printf("%#v", pretty.Formatter(hostname[0]))
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421bed)
    HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422a6f)
    (*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x421a00)
    (*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d9bb)

我在确定hostname变量的数据类型时遇到了问题。我应该将其作为字符串获取。

当我尝试写入HTTP响应写入器时：

w.Write([]byte(hostname))

会显示以下构建错误：

go/src/api/main.go:38: cannot convert hostname (type []string) to type []byte

如果我将其视为字符串数组，则构建成功，但会出现运行时错误：

newhost := hostname[0]
w.Write([]byte(newhost))

错误信息：

2014/09/01 04:42:40 http: panic serving 172.17.92.14:50404: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42db27)
    _func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f79b)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410267)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x41010e)
/root/go/src/api/main.go:38 (0x400d63)
    foo: newhost := hostname[0]
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421ad3)
    HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422955)
    (*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x4218e6)
    (*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d8a1)

我还按照@VonC的建议检查了newhost的长度，并得到了预期的结果。

fmt.Print("\n")
fmt.Println(len(newhost))

控制台输出：

"example.com"
11
2014/09/01 05:05:15 http: panic serving 172.17.92.14:50779: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42dd33)

英文:

Following is my go program to extract GET parameters. (URL: /mysql?hostname=example.com)

package main

import (
        &quot;net/http&quot;
        &quot;fmt&quot;
        //&quot;encoding/json&quot;
        //&quot;html&quot;
        &quot;github.com/kr/pretty&quot;
);

func main(){
        http.HandleFunc(&quot;/&quot;, foo)
        http.ListenAndServe(&quot;:80&quot;, nil)
}

func foo(w http.ResponseWriter, r * http.Request){
        w.Header().Set(&quot;Server&quot;,&quot;A Go WebServer&quot;)

        w.Header().Set(&quot;Content-Type&quot;, &quot;text/html&quot;)

        hostname := r.URL.Query()[&quot;hostname&quot;]
        //w.Write([]byte(hostname[0]))
        fmt.Printf(&quot;%# v&quot;, pretty.Formatter(hostname[0]))

        
        w.Write([]byte(hostname))
}

Error shown on console.

&quot;example.com&quot;2014/09/01 02:57:22 http: panic serving 172.17.92.14:49411: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42dc41)
	_func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f8b5)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410381)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x410228)
/root/go/src/api/main.go:34 (0x400d77)
	foo: fmt.Printf(&quot;%# v&quot;, pretty.Formatter(hostname[0]))
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421bed)
	HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422a6f)
	(*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x421a00)
	(*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d9bb)
2014/09/01 02:57:22 http: panic serving 172.17.92.14:49412: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42dc41)
	_func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f8b5)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410381)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x410228)
/root/go/src/api/main.go:34 (0x400d77)
	foo: fmt.Printf(&quot;%# v&quot;, pretty.Formatter(hostname[0]))
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421bed)
	HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422a6f)
	(*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x421a00)
	(*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d9bb)
2014/09/01 02:57:22 http: panic serving 172.17.92.14:49413: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42dc41)
	_func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f8b5)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410381)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x410228)
/root/go/src/api/main.go:34 (0x400d77)
	foo: fmt.Printf(&quot;%# v&quot;, pretty.Formatter(hostname[0]))
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421bed)
	HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422a6f)
	(*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x421a00)
	(*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d9bb)

I am having trouble with determining the data type of hostname variable. I should get it as a string.

When I try to write to http response writer

w.Write([]byte(hostname))

following build error is shown

go/src/api/main.go:38: cannot convert hostname (type []string) to type []byte

If I treat it as a string array build is successful but there is run time error

        newhost := hostname[0];
        w.Write([]byte(newhost))

Error:

    2014/09/01 04:42:40 http: panic serving 172.17.92.14:50404: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42db27)
	_func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f79b)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410267)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x41010e)
/root/go/src/api/main.go:38 (0x400d63)
	foo: newhost := hostname[0];
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421ad3)
	HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422955)
	(*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x4218e6)
	(*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d8a1)
2014/09/01 04:42:40 http: panic serving 172.17.92.14:50405: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42db27)
	_func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f79b)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410267)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x41010e)
/root/go/src/api/main.go:38 (0x400d63)
	foo: newhost := hostname[0];
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421ad3)
	HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422955)
	(*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x4218e6)
	(*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d8a1)
2014/09/01 04:42:40 http: panic serving 172.17.92.14:50406: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42db27)
	_func_003: buf.Write(debug.Stack())
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:1443 (0x40f79b)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:128 (0x410267)
/home/michael/DPKG/golang/src/pkg/runtime/runtime.c:85 (0x41010e)
/root/go/src/api/main.go:38 (0x400d63)
	foo: newhost := hostname[0];
/usr/lib/go/src/pkg/net/http/server.go:690 (0x421ad3)
	HandlerFunc.ServeHTTP: f(w, r)
/usr/lib/go/src/pkg/net/http/server.go:926 (0x422955)
	(*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/lib/go/src/pkg/net/http/server.go:656 (0x4218e6)
	(*conn).serve: handler.ServeHTTP(w, w.req)
/home/michael/DPKG/golang/src/pkg/runtime/proc.c:271 (0x40d8a1)

I also checked length of newhost as @VonC suggested and it gave expected results.

        fmt.Print(&quot;\n&quot;)
        fmt.Println((len(newhost)))

Output on console

&quot;example.com&quot;
11
2014/09/01 05:05:15 http: panic serving 172.17.92.14:50779: runtime error: index out of range
/usr/lib/go/src/pkg/net/http/server.go:576 (0x42dd33)

答案1

得分: 53

你需要使用url/Values.Get方法，如果值未设置，它将返回空字符串：

hostname := r.URL.Query().Get("hostname")
if len(hostname) != 0 {
    io.WriteString(w, hostname)  // 或者
    w.Write([]byte(hostname))
}

// 编辑

让我们逐步来解释：

go/src/api/main.go:38: cannot convert hostname (type []string) to type []byte：

req.URL.Query["hostname"]返回一个字符串切片([]string)，你不能直接将其转换为[]byte，只有string可以这样转换。

第一个runtime error: index out of range：

在没有检查切片中有多少元素的情况下，你尝试使用hostname[0]，所以在这种情况下没有任何元素。

最后一个runtime error: index out of range很奇怪，我不知道你为什么会得到它，可能是你在代码中做了其他改动。

英文:

You need to use url/Values.Get, it will return the empty string if the value isn't set:

hostname := r.URL.Query().Get(&quot;hostname&quot;)
if len(hostname) != 0 {
    io.WriteString(w, hostname)  // or
    w.Write([]byte(hostname))
}

// edit

Let's take it a step by step:

go/src/api/main.go:38: cannot convert hostname (type []string) to type []byte:

req.URL.Query["hostname"], returns a string slice ([]string) which you can't directly convert to []byte, only string can be converted like that.

The first runtime error: index out of range:

You're trying to use hostname[0] without checking how many elements in the slice, so in that case there weren't any elements.

That last runtime error: index out of range is weird though, I have no idea why you got it, must be something else you changed in the code.

答案2

得分: 7

如果您只关心第一个值，并且不需要区分POST还是GET，您可以考虑使用更简单的Request.FormValue函数。

hostname := r.FormValue("hostname")

英文:

If you only care about the first value, and you don't have to distinguish between POST or GET, you might consider using the simpler Request.FormValue function.

hostname := r.FormValue(&quot;hostname&quot;)

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