Source: header.go in package net/http


package http

import (
	"io"
	"net/http/httptrace"
	"net/textproto"
	"sort"
	"strings"
	"sync"
	"time"
)

A Header represents the key-value pairs in an HTTP header. The keys should be in canonical form, as returned by CanonicalHeaderKey.

type Header map[string][]string

Add adds the key, value pair to the header. It appends to any existing values associated with key. The key is case insensitive; it is canonicalized by CanonicalHeaderKey.

func (h Header) Add(key, value string) {
	textproto.MIMEHeader(h).Add(key, value)
}

Set sets the header entries associated with key to the single element value. It replaces any existing values associated with key. The key is case insensitive; it is canonicalized by textproto.CanonicalMIMEHeaderKey. To use non-canonical keys, assign to the map directly.

func (h Header) Set(key, value string) {
	textproto.MIMEHeader(h).Set(key, value)
}

Get gets the first value associated with the given key. If there are no values associated with the key, Get returns "". It is case insensitive; textproto.CanonicalMIMEHeaderKey is used to canonicalize the provided key. To use non-canonical keys, access the map directly.

func (h Header) Get(key string) string {
	return textproto.MIMEHeader(h).Get(key)
}

Values returns all values associated with the given key. It is case insensitive; textproto.CanonicalMIMEHeaderKey is used to canonicalize the provided key. To use non-canonical keys, access the map directly. The returned slice is not a copy.

func (h Header) Values(key string) []string {
	return textproto.MIMEHeader(h).Values(key)
}

get is like Get, but key must already be in CanonicalHeaderKey form.

func (h Header) get(key string) string {
	if v := h[key]; len(v) > 0 {
		return v[0]
	}
	return ""
}

has reports whether h has the provided key defined, even if it's set to 0-length slice.

func (h Header) has(key string) bool {
	_, ok := h[key]
	return ok
}

Del deletes the values associated with key. The key is case insensitive; it is canonicalized by CanonicalHeaderKey.

func (h Header) Del(key string) {
	textproto.MIMEHeader(h).Del(key)
}

Write writes a header in wire format.

func (h Header) Write(w io.Writer) error {
	return h.write(w, nil)
}

func (h Header) write(w io.Writer, trace *httptrace.ClientTrace) error {
	return h.writeSubset(w, nil, trace)
}

Clone returns a copy of h or nil if h is nil.

func (h Header) Clone() Header {
	if h == nil {
		return nil
	}

Find total number of values.

	nv := 0
	for _, vv := range h {
		nv += len(vv)
	}
	sv := make([]string, nv) // shared backing array for headers' values
	h2 := make(Header, len(h))
	for k, vv := range h {
		n := copy(sv, vv)
		h2[k] = sv[:n:n]
		sv = sv[n:]
	}
	return h2
}

var timeFormats = []string{
	TimeFormat,
	time.RFC850,
	time.ANSIC,
}

ParseTime parses a time header (such as the Date: header), trying each of the three formats allowed by HTTP/1.1: TimeFormat, time.RFC850, and time.ANSIC.

func ParseTime(text string) (t time.Time, err error) {
	for _, layout := range timeFormats {
		t, err = time.Parse(layout, text)
		if err == nil {
			return
		}
	}
	return
}

var headerNewlineToSpace = strings.NewReplacer("\n", " ", "\r", " ")

stringWriter implements WriteString on a Writer.

type stringWriter struct {
	w io.Writer
}

func (w stringWriter) WriteString(s string) (n int, err error) {
	return w.w.Write([]byte(s))
}

type keyValues struct {
	key    string
	values []string
}

A headerSorter implements sort.Interface by sorting a []keyValues by key. It's used as a pointer, so it can fit in a sort.Interface interface value without allocation.

type headerSorter struct {
	kvs []keyValues
}

func (s *headerSorter) Len() int           { return len(s.kvs) }
func (s *headerSorter) Swap(i, j int)      { s.kvs[i], s.kvs[j] = s.kvs[j], s.kvs[i] }
func (s *headerSorter) Less(i, j int) bool { return s.kvs[i].key < s.kvs[j].key }

var headerSorterPool = sync.Pool{
	New: func() interface{} { return new(headerSorter) },
}

sortedKeyValues returns h's keys sorted in the returned kvs slice. The headerSorter used to sort is also returned, for possible return to headerSorterCache.

func (h Header) sortedKeyValues(exclude map[string]bool) (kvs []keyValues, hs *headerSorter) {
	hs = headerSorterPool.Get().(*headerSorter)
	if cap(hs.kvs) < len(h) {
		hs.kvs = make([]keyValues, 0, len(h))
	}
	kvs = hs.kvs[:0]
	for k, vv := range h {
		if !exclude[k] {
			kvs = append(kvs, keyValues{k, vv})
		}
	}
	hs.kvs = kvs
	sort.Sort(hs)
	return kvs, hs
}

WriteSubset writes a header in wire format. If exclude is not nil, keys where exclude[key] == true are not written. Keys are not canonicalized before checking the exclude map.

func (h Header) WriteSubset(w io.Writer, exclude map[string]bool) error {
	return h.writeSubset(w, exclude, nil)
}

func (h Header) writeSubset(w io.Writer, exclude map[string]bool, trace *httptrace.ClientTrace) error {
	ws, ok := w.(io.StringWriter)
	if !ok {
		ws = stringWriter{w}
	}
	kvs, sorter := h.sortedKeyValues(exclude)
	var formattedVals []string
	for _, kv := range kvs {
		for _, v := range kv.values {
			v = headerNewlineToSpace.Replace(v)
			v = textproto.TrimString(v)
			for _, s := range []string{kv.key, ": ", v, "\r\n"} {
				if _, err := ws.WriteString(s); err != nil {
					headerSorterPool.Put(sorter)
					return err
				}
			}
			if trace != nil && trace.WroteHeaderField != nil {
				formattedVals = append(formattedVals, v)
			}
		}
		if trace != nil && trace.WroteHeaderField != nil {
			trace.WroteHeaderField(kv.key, formattedVals)
			formattedVals = nil
		}
	}
	headerSorterPool.Put(sorter)
	return nil
}

CanonicalHeaderKey returns the canonical format of the header key s. The canonicalization converts the first letter and any letter following a hyphen to upper case; the rest are converted to lowercase. For example, the canonical key for "accept-encoding" is "Accept-Encoding". If s contains a space or invalid header field bytes, it is returned without modifications.

func CanonicalHeaderKey(s string) string { return textproto.CanonicalMIMEHeaderKey(s) }

hasToken reports whether token appears with v, ASCII case-insensitive, with space or comma boundaries. token must be all lowercase. v may contain mixed cased.

func hasToken(v, token string) bool {
	if len(token) > len(v) || token == "" {
		return false
	}
	if v == token {
		return true
	}

Check that first character is good. The token is ASCII, so checking only a single byte is sufficient. We skip this potential starting position if both the first byte and its potential ASCII uppercase equivalent (b|0x20) don't match. False positives ('^' => '~') are caught by EqualFold.

		if b := v[sp]; b != token[0] && b|0x20 != token[0] {
			continue

Check that start pos is on a valid token boundary.

		if sp > 0 && !isTokenBoundary(v[sp-1]) {
			continue

Check that end pos is on a valid token boundary.

		if endPos := sp + len(token); endPos != len(v) && !isTokenBoundary(v[endPos]) {
			continue
		}
		if strings.EqualFold(v[sp:sp+len(token)], token) {
			return true
		}
	}
	return false
}

func isTokenBoundary(b byte) bool {
	return b == ' ' || b == ',' || b == '\t'