github.com/bgentry/go@v0.0.0-20150121062915-6cf5a733d54d/src/net/http/sniff.go (about)

     1  // Copyright 2011 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  	"bytes"
     9  	"encoding/binary"
    10  )
    11  
    12  // The algorithm uses at most sniffLen bytes to make its decision.
    13  const sniffLen = 512
    14  
    15  // DetectContentType implements the algorithm described
    16  // at http://mimesniff.spec.whatwg.org/ to determine the
    17  // Content-Type of the given data.  It considers at most the
    18  // first 512 bytes of data.  DetectContentType always returns
    19  // a valid MIME type: if it cannot determine a more specific one, it
    20  // returns "application/octet-stream".
    21  func DetectContentType(data []byte) string {
    22  	if len(data) > sniffLen {
    23  		data = data[:sniffLen]
    24  	}
    25  
    26  	// Index of the first non-whitespace byte in data.
    27  	firstNonWS := 0
    28  	for ; firstNonWS < len(data) && isWS(data[firstNonWS]); firstNonWS++ {
    29  	}
    30  
    31  	for _, sig := range sniffSignatures {
    32  		if ct := sig.match(data, firstNonWS); ct != "" {
    33  			return ct
    34  		}
    35  	}
    36  
    37  	return "application/octet-stream" // fallback
    38  }
    39  
    40  func isWS(b byte) bool {
    41  	switch b {
    42  	case '\t', '\n', '\x0c', '\r', ' ':
    43  		return true
    44  	}
    45  	return false
    46  }
    47  
    48  type sniffSig interface {
    49  	// match returns the MIME type of the data, or "" if unknown.
    50  	match(data []byte, firstNonWS int) string
    51  }
    52  
    53  // Data matching the table in section 6.
    54  var sniffSignatures = []sniffSig{
    55  	htmlSig("<!DOCTYPE HTML"),
    56  	htmlSig("<HTML"),
    57  	htmlSig("<HEAD"),
    58  	htmlSig("<SCRIPT"),
    59  	htmlSig("<IFRAME"),
    60  	htmlSig("<H1"),
    61  	htmlSig("<DIV"),
    62  	htmlSig("<FONT"),
    63  	htmlSig("<TABLE"),
    64  	htmlSig("<A"),
    65  	htmlSig("<STYLE"),
    66  	htmlSig("<TITLE"),
    67  	htmlSig("<B"),
    68  	htmlSig("<BODY"),
    69  	htmlSig("<BR"),
    70  	htmlSig("<P"),
    71  	htmlSig("<!--"),
    72  
    73  	&maskedSig{mask: []byte("\xFF\xFF\xFF\xFF\xFF"), pat: []byte("<?xml"), skipWS: true, ct: "text/xml; charset=utf-8"},
    74  
    75  	&exactSig{[]byte("%PDF-"), "application/pdf"},
    76  	&exactSig{[]byte("%!PS-Adobe-"), "application/postscript"},
    77  
    78  	// UTF BOMs.
    79  	&maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFE\xFF\x00\x00"), ct: "text/plain; charset=utf-16be"},
    80  	&maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFF\xFE\x00\x00"), ct: "text/plain; charset=utf-16le"},
    81  	&maskedSig{mask: []byte("\xFF\xFF\xFF\x00"), pat: []byte("\xEF\xBB\xBF\x00"), ct: "text/plain; charset=utf-8"},
    82  
    83  	&exactSig{[]byte("GIF87a"), "image/gif"},
    84  	&exactSig{[]byte("GIF89a"), "image/gif"},
    85  	&exactSig{[]byte("\x89\x50\x4E\x47\x0D\x0A\x1A\x0A"), "image/png"},
    86  	&exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"},
    87  	&exactSig{[]byte("BM"), "image/bmp"},
    88  	&maskedSig{
    89  		mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF"),
    90  		pat:  []byte("RIFF\x00\x00\x00\x00WEBPVP"),
    91  		ct:   "image/webp",
    92  	},
    93  	&exactSig{[]byte("\x00\x00\x01\x00"), "image/vnd.microsoft.icon"},
    94  	&exactSig{[]byte("\x4F\x67\x67\x53\x00"), "application/ogg"},
    95  	&maskedSig{
    96  		mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
    97  		pat:  []byte("RIFF\x00\x00\x00\x00WAVE"),
    98  		ct:   "audio/wave",
    99  	},
   100  	&exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"},
   101  	&exactSig{[]byte("\x52\x61\x72\x20\x1A\x07\x00"), "application/x-rar-compressed"},
   102  	&exactSig{[]byte("\x50\x4B\x03\x04"), "application/zip"},
   103  	&exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"},
   104  
   105  	// TODO(dsymonds): Re-enable this when the spec is sorted w.r.t. MP4.
   106  	//mp4Sig(0),
   107  
   108  	textSig(0), // should be last
   109  }
   110  
   111  type exactSig struct {
   112  	sig []byte
   113  	ct  string
   114  }
   115  
   116  func (e *exactSig) match(data []byte, firstNonWS int) string {
   117  	if bytes.HasPrefix(data, e.sig) {
   118  		return e.ct
   119  	}
   120  	return ""
   121  }
   122  
   123  type maskedSig struct {
   124  	mask, pat []byte
   125  	skipWS    bool
   126  	ct        string
   127  }
   128  
   129  func (m *maskedSig) match(data []byte, firstNonWS int) string {
   130  	if m.skipWS {
   131  		data = data[firstNonWS:]
   132  	}
   133  	if len(data) < len(m.mask) {
   134  		return ""
   135  	}
   136  	for i, mask := range m.mask {
   137  		db := data[i] & mask
   138  		if db != m.pat[i] {
   139  			return ""
   140  		}
   141  	}
   142  	return m.ct
   143  }
   144  
   145  type htmlSig []byte
   146  
   147  func (h htmlSig) match(data []byte, firstNonWS int) string {
   148  	data = data[firstNonWS:]
   149  	if len(data) < len(h)+1 {
   150  		return ""
   151  	}
   152  	for i, b := range h {
   153  		db := data[i]
   154  		if 'A' <= b && b <= 'Z' {
   155  			db &= 0xDF
   156  		}
   157  		if b != db {
   158  			return ""
   159  		}
   160  	}
   161  	// Next byte must be space or right angle bracket.
   162  	if db := data[len(h)]; db != ' ' && db != '>' {
   163  		return ""
   164  	}
   165  	return "text/html; charset=utf-8"
   166  }
   167  
   168  var mp4ftype = []byte("ftyp")
   169  
   170  type mp4Sig int
   171  
   172  func (mp4Sig) match(data []byte, firstNonWS int) string {
   173  	// c.f. section 6.1.
   174  	if len(data) < 8 {
   175  		return ""
   176  	}
   177  	boxSize := int(binary.BigEndian.Uint32(data[:4]))
   178  	if boxSize%4 != 0 || len(data) < boxSize {
   179  		return ""
   180  	}
   181  	if !bytes.Equal(data[4:8], mp4ftype) {
   182  		return ""
   183  	}
   184  	for st := 8; st < boxSize; st += 4 {
   185  		if st == 12 {
   186  			// minor version number
   187  			continue
   188  		}
   189  		seg := string(data[st : st+3])
   190  		switch seg {
   191  		case "mp4", "iso", "M4V", "M4P", "M4B":
   192  			return "video/mp4"
   193  			/* The remainder are not in the spec.
   194  			case "M4A":
   195  				return "audio/mp4"
   196  			case "3gp":
   197  				return "video/3gpp"
   198  			case "jp2":
   199  				return "image/jp2" // JPEG 2000
   200  			*/
   201  		}
   202  	}
   203  	return ""
   204  }
   205  
   206  type textSig int
   207  
   208  func (textSig) match(data []byte, firstNonWS int) string {
   209  	// c.f. section 5, step 4.
   210  	for _, b := range data[firstNonWS:] {
   211  		switch {
   212  		case 0x00 <= b && b <= 0x08,
   213  			b == 0x0B,
   214  			0x0E <= b && b <= 0x1A,
   215  			0x1C <= b && b <= 0x1F:
   216  			return ""
   217  		}
   218  	}
   219  	return "text/plain; charset=utf-8"
   220  }