header.go

Documentation: net/http

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package http
     6  
     7  import (
     8  	"io"
     9  	"net/http/httptrace"
    10  	"net/http/internal/ascii"
    11  	"net/textproto"
    12  	"slices"
    13  	"strings"
    14  	"sync"
    15  	"time"
    16  
    17  	"golang.org/x/net/http/httpguts"
    18  )
    19  
    20  // A Header represents the key-value pairs in an HTTP header.
    21  //
    22  // The keys should be in canonical form, as returned by
    23  // [CanonicalHeaderKey].
    24  type Header map[string][]string
    25  
    26  // Add adds the key, value pair to the header.
    27  // It appends to any existing values associated with key.
    28  // The key is case insensitive; it is canonicalized by
    29  // [CanonicalHeaderKey].
    30  func (h Header) Add(key, value string) {
    31  	textproto.MIMEHeader(h).Add(key, value)
    32  }
    33  
    34  // Set sets the header entries associated with key to the
    35  // single element value. It replaces any existing values
    36  // associated with key. The key is case insensitive; it is
    37  // canonicalized by [textproto.CanonicalMIMEHeaderKey].
    38  // To use non-canonical keys, assign to the map directly.
    39  func (h Header) Set(key, value string) {
    40  	textproto.MIMEHeader(h).Set(key, value)
    41  }
    42  
    43  // Get gets the first value associated with the given key. If
    44  // there are no values associated with the key, Get returns "".
    45  // It is case insensitive; [textproto.CanonicalMIMEHeaderKey] is
    46  // used to canonicalize the provided key. Get assumes that all
    47  // keys are stored in canonical form. To use non-canonical keys,
    48  // access the map directly.
    49  func (h Header) Get(key string) string {
    50  	return textproto.MIMEHeader(h).Get(key)
    51  }
    52  
    53  // Values returns all values associated with the given key.
    54  // It is case insensitive; [textproto.CanonicalMIMEHeaderKey] is
    55  // used to canonicalize the provided key. To use non-canonical
    56  // keys, access the map directly.
    57  // The returned slice is not a copy.
    58  func (h Header) Values(key string) []string {
    59  	return textproto.MIMEHeader(h).Values(key)
    60  }
    61  
    62  // get is like Get, but key must already be in CanonicalHeaderKey form.
    63  func (h Header) get(key string) string {
    64  	if v := h[key]; len(v) > 0 {
    65  		return v[0]
    66  	}
    67  	return ""
    68  }
    69  
    70  // has reports whether h has the provided key defined, even if it's
    71  // set to 0-length slice.
    72  func (h Header) has(key string) bool {
    73  	_, ok := h[key]
    74  	return ok
    75  }
    76  
    77  // Del deletes the values associated with key.
    78  // The key is case insensitive; it is canonicalized by
    79  // [CanonicalHeaderKey].
    80  func (h Header) Del(key string) {
    81  	textproto.MIMEHeader(h).Del(key)
    82  }
    83  
    84  // Write writes a header in wire format.
    85  func (h Header) Write(w io.Writer) error {
    86  	return h.write(w, nil)
    87  }
    88  
    89  func (h Header) write(w io.Writer, trace *httptrace.ClientTrace) error {
    90  	return h.writeSubset(w, nil, trace)
    91  }
    92  
    93  // Clone returns a copy of h or nil if h is nil.
    94  func (h Header) Clone() Header {
    95  	if h == nil {
    96  		return nil
    97  	}
    98  
    99  	// Find total number of values.
   100  	nv := 0
   101  	for _, vv := range h {
   102  		nv += len(vv)
   103  	}
   104  	sv := make([]string, nv) // shared backing array for headers' values
   105  	h2 := make(Header, len(h))
   106  	for k, vv := range h {
   107  		if vv == nil {
   108  			// Preserve nil values. ReverseProxy distinguishes
   109  			// between nil and zero-length header values.
   110  			h2[k] = nil
   111  			continue
   112  		}
   113  		n := copy(sv, vv)
   114  		h2[k] = sv[:n:n]
   115  		sv = sv[n:]
   116  	}
   117  	return h2
   118  }
   119  
   120  var timeFormats = []string{
   121  	TimeFormat,
   122  	time.RFC850,
   123  	time.ANSIC,
   124  }
   125  
   126  // ParseTime parses a time header (such as the Date: header),
   127  // trying each of the three formats allowed by HTTP/1.1:
   128  // [TimeFormat], [time.RFC850], and [time.ANSIC].
   129  func ParseTime(text string) (t time.Time, err error) {
   130  	for _, layout := range timeFormats {
   131  		t, err = time.Parse(layout, text)
   132  		if err == nil {
   133  			return
   134  		}
   135  	}
   136  	return
   137  }
   138  
   139  var headerNewlineToSpace = strings.NewReplacer("\n", " ", "\r", " ")
   140  
   141  // stringWriter implements WriteString on a Writer.
   142  type stringWriter struct {
   143  	w io.Writer
   144  }
   145  
   146  func (w stringWriter) WriteString(s string) (n int, err error) {
   147  	return w.w.Write([]byte(s))
   148  }
   149  
   150  type keyValues struct {
   151  	key    string
   152  	values []string
   153  }
   154  
   155  // headerSorter contains a slice of keyValues sorted by keyValues.key.
   156  type headerSorter struct {
   157  	kvs []keyValues
   158  }
   159  
   160  var headerSorterPool = sync.Pool{
   161  	New: func() any { return new(headerSorter) },
   162  }
   163  
   164  // sortedKeyValues returns h's keys sorted in the returned kvs
   165  // slice. The headerSorter used to sort is also returned, for possible
   166  // return to headerSorterCache.
   167  func (h Header) sortedKeyValues(exclude map[string]bool) (kvs []keyValues, hs *headerSorter) {
   168  	hs = headerSorterPool.Get().(*headerSorter)
   169  	if cap(hs.kvs) < len(h) {
   170  		hs.kvs = make([]keyValues, 0, len(h))
   171  	}
   172  	kvs = hs.kvs[:0]
   173  	for k, vv := range h {
   174  		if !exclude[k] {
   175  			kvs = append(kvs, keyValues{k, vv})
   176  		}
   177  	}
   178  	hs.kvs = kvs
   179  	slices.SortFunc(hs.kvs, func(a, b keyValues) int { return strings.Compare(a.key, b.key) })
   180  	return kvs, hs
   181  }
   182  
   183  // WriteSubset writes a header in wire format.
   184  // If exclude is not nil, keys where exclude[key] == true are not written.
   185  // Keys are not canonicalized before checking the exclude map.
   186  func (h Header) WriteSubset(w io.Writer, exclude map[string]bool) error {
   187  	return h.writeSubset(w, exclude, nil)
   188  }
   189  
   190  func (h Header) writeSubset(w io.Writer, exclude map[string]bool, trace *httptrace.ClientTrace) error {
   191  	ws, ok := w.(io.StringWriter)
   192  	if !ok {
   193  		ws = stringWriter{w}
   194  	}
   195  	kvs, sorter := h.sortedKeyValues(exclude)
   196  	var formattedVals []string
   197  	for _, kv := range kvs {
   198  		if !httpguts.ValidHeaderFieldName(kv.key) {
   199  			// This could be an error. In the common case of
   200  			// writing response headers, however, we have no good
   201  			// way to provide the error back to the server
   202  			// handler, so just drop invalid headers instead.
   203  			continue
   204  		}
   205  		for _, v := range kv.values {
   206  			v = headerNewlineToSpace.Replace(v)
   207  			v = textproto.TrimString(v)
   208  			for _, s := range []string{kv.key, ": ", v, "\r\n"} {
   209  				if _, err := ws.WriteString(s); err != nil {
   210  					headerSorterPool.Put(sorter)
   211  					return err
   212  				}
   213  			}
   214  			if trace != nil && trace.WroteHeaderField != nil {
   215  				formattedVals = append(formattedVals, v)
   216  			}
   217  		}
   218  		if trace != nil && trace.WroteHeaderField != nil {
   219  			trace.WroteHeaderField(kv.key, formattedVals)
   220  			formattedVals = nil
   221  		}
   222  	}
   223  	headerSorterPool.Put(sorter)
   224  	return nil
   225  }
   226  
   227  // CanonicalHeaderKey returns the canonical format of the
   228  // header key s. The canonicalization converts the first
   229  // letter and any letter following a hyphen to upper case;
   230  // the rest are converted to lowercase. For example, the
   231  // canonical key for "accept-encoding" is "Accept-Encoding".
   232  // If s contains a space or invalid header field bytes, it is
   233  // returned without modifications.
   234  func CanonicalHeaderKey(s string) string { return textproto.CanonicalMIMEHeaderKey(s) }
   235  
   236  // hasToken reports whether token appears with v, ASCII
   237  // case-insensitive, with space or comma boundaries.
   238  // token must be all lowercase.
   239  // v may contain mixed cased.
   240  func hasToken(v, token string) bool {
   241  	if len(token) > len(v) || token == "" {
   242  		return false
   243  	}
   244  	if v == token {
   245  		return true
   246  	}
   247  	for sp := 0; sp <= len(v)-len(token); sp++ {
   248  		// Check that first character is good.
   249  		// The token is ASCII, so checking only a single byte
   250  		// is sufficient. We skip this potential starting
   251  		// position if both the first byte and its potential
   252  		// ASCII uppercase equivalent (b|0x20) don't match.
   253  		// False positives ('^' => '~') are caught by EqualFold.
   254  		if b := v[sp]; b != token[0] && b|0x20 != token[0] {
   255  			continue
   256  		}
   257  		// Check that start pos is on a valid token boundary.
   258  		if sp > 0 && !isTokenBoundary(v[sp-1]) {
   259  			continue
   260  		}
   261  		// Check that end pos is on a valid token boundary.
   262  		if endPos := sp + len(token); endPos != len(v) && !isTokenBoundary(v[endPos]) {
   263  			continue
   264  		}
   265  		if ascii.EqualFold(v[sp:sp+len(token)], token) {
   266  			return true
   267  		}
   268  	}
   269  	return false
   270  }
   271  
   272  func isTokenBoundary(b byte) bool {
   273  	return b == ' ' || b == ',' || b == '\t'
   274  }
   275
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