英文:
Why the length of the slice in http.Header returns 0?
问题
从net/http的源代码中，http.Header的定义是map[string][]string。对吗？
但是为什么运行下面的代码，我得到的结果是：
0
2
func main() {
var header = make(http.Header)
header.Add("hello", "world")
header.Add("hello", "anotherworld")
var t = []string {"a", "b"}
fmt.Printf("%d\n", len(header["hello"]))
fmt.Print(len(t))
}
英文:
From the source code of net/http. The definition of http.Header is map[string][]string. Right?
But why go run below code, I get the result:
> 0
>
> 2
func main() {
var header = make(http.Header)
header.Add("hello", "world")
header.Add("hello", "anotherworld")
var t = []string {"a", "b"}
fmt.Printf("%d\n", len(header["hello"]))
fmt.Print(len(t))
}
答案1
得分: 3
如果你尝试
fmt.Println(header)
你会注意到键已经被大写了。这实际上在net/http的文档中有说明。
// HTTP定义标头名称不区分大小写。
// 请求解析器通过将名称规范化来实现这一点，
// 将连字符后的第一个字符和任何字符都大写，其余字符都小写。
这可以在类型为Request的Header字段的注释中找到。
http://golang.org/pkg/net/http/#Request
不过，注释可能应该被移动。
英文:
if you try
fmt.Println(header)
you'll notice that the key has been capitalized. This is actually noted in the documentation of net/http.
// HTTP defines that header names are case-insensitive.
// The request parser implements this by canonicalizing the
// name, making the first character and any characters
// following a hyphen uppercase and the rest lowercase.
This can be found in the comment on the field Header of type Request.
http://golang.org/pkg/net/http/#Request
Comment should probably be moved though..
答案2
得分: 3
看一下http.Header的参考和Get的代码：
> Get获取与给定键关联的第一个值。如果没有与该键关联的值，则Get返回“”。要访问一个键的多个值，请直接使用CanonicalHeaderKey访问映射。
因此，最好使用http.CanonicalHeaderKey而不是字符串作为键。
package main
import (
"net/http"
"fmt"
)
func main() {
header := make(http.Header)
var key = http.CanonicalHeaderKey("hello")
header.Add(key, "world")
header.Add(key, "anotherworld")
fmt.Printf("%#v\n", header)
fmt.Printf("%#v\n", header.Get(key))
fmt.Printf("%#v\n", header[key])
}
输出结果：
http.Header{"Hello":[]string{"world", "anotherworld"}}
"world"
[]string{"world", "anotherworld"}
英文:
Take a look at the reference of http.Header and the code of Get:
> Get gets the first value associated with the given key. If there are no values associated with the key, Get returns "". To access multiple values of a key, access the map directly with CanonicalHeaderKey.
So it helps to use http.CanonicalHeaderKey instead of strings for keys.
package main
import (
"net/http"
"fmt"
)
func main() {
header := make(http.Header)
var key = http.CanonicalHeaderKey("hello")
header.Add(key, "world")
header.Add(key, "anotherworld")
fmt.Printf("%#v\n", header)
fmt.Printf("%#v\n", header.Get(key))
fmt.Printf("%#v\n", header[key])
}
The output:
http.Header{"Hello":[]string{"world", "anotherworld"}}
"world"
[]string{"world", "anotherworld"}
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