310 lines
8 KiB
Go
310 lines
8 KiB
Go
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package http
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import (
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"bytes"
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"encoding/binary"
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)
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// The algorithm uses at most sniffLen bytes to make its decision.
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const sniffLen = 512
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// DetectContentType implements the algorithm described
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// at https://mimesniff.spec.whatwg.org/ to determine the
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// Content-Type of the given data. It considers at most the
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// first 512 bytes of data. DetectContentType always returns
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// a valid MIME type: if it cannot determine a more specific one, it
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// returns "application/octet-stream".
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func DetectContentType(data []byte) string {
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if len(data) > sniffLen {
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data = data[:sniffLen]
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}
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// Index of the first non-whitespace byte in data.
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firstNonWS := 0
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for ; firstNonWS < len(data) && isWS(data[firstNonWS]); firstNonWS++ {
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}
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for _, sig := range sniffSignatures {
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if ct := sig.match(data, firstNonWS); ct != "" {
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return ct
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}
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}
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return "application/octet-stream" // fallback
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}
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// isWS reports whether the provided byte is a whitespace byte (0xWS)
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// as defined in https://mimesniff.spec.whatwg.org/#terminology.
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func isWS(b byte) bool {
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switch b {
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case '\t', '\n', '\x0c', '\r', ' ':
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return true
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}
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return false
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}
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// isTT reports whether the provided byte is a tag-terminating byte (0xTT)
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// as defined in https://mimesniff.spec.whatwg.org/#terminology.
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func isTT(b byte) bool {
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switch b {
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case ' ', '>':
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return true
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}
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return false
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}
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type sniffSig interface {
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// match returns the MIME type of the data, or "" if unknown.
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match(data []byte, firstNonWS int) string
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}
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// Data matching the table in section 6.
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var sniffSignatures = []sniffSig{
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htmlSig("<!DOCTYPE HTML"),
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htmlSig("<HTML"),
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htmlSig("<HEAD"),
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htmlSig("<SCRIPT"),
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htmlSig("<IFRAME"),
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htmlSig("<H1"),
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htmlSig("<DIV"),
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htmlSig("<FONT"),
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htmlSig("<TABLE"),
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htmlSig("<A"),
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htmlSig("<STYLE"),
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htmlSig("<TITLE"),
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htmlSig("<B"),
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htmlSig("<BODY"),
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htmlSig("<BR"),
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htmlSig("<P"),
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htmlSig("<!--"),
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\xFF"),
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pat: []byte("<?xml"),
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skipWS: true,
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ct: "text/xml; charset=utf-8"},
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&exactSig{[]byte("%PDF-"), "application/pdf"},
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&exactSig{[]byte("%!PS-Adobe-"), "application/postscript"},
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// UTF BOMs.
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&maskedSig{
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mask: []byte("\xFF\xFF\x00\x00"),
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pat: []byte("\xFE\xFF\x00\x00"),
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ct: "text/plain; charset=utf-16be",
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},
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&maskedSig{
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mask: []byte("\xFF\xFF\x00\x00"),
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pat: []byte("\xFF\xFE\x00\x00"),
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ct: "text/plain; charset=utf-16le",
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},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\x00"),
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pat: []byte("\xEF\xBB\xBF\x00"),
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ct: "text/plain; charset=utf-8",
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},
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// Image types
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// For posterity, we originally returned "image/vnd.microsoft.icon" from
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// https://tools.ietf.org/html/draft-ietf-websec-mime-sniff-03#section-7
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// https://codereview.appspot.com/4746042
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// but that has since been replaced with "image/x-icon" in Section 6.2
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// of https://mimesniff.spec.whatwg.org/#matching-an-image-type-pattern
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&exactSig{[]byte("\x00\x00\x01\x00"), "image/x-icon"},
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&exactSig{[]byte("\x00\x00\x02\x00"), "image/x-icon"},
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&exactSig{[]byte("BM"), "image/bmp"},
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&exactSig{[]byte("GIF87a"), "image/gif"},
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&exactSig{[]byte("GIF89a"), "image/gif"},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF"),
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pat: []byte("RIFF\x00\x00\x00\x00WEBPVP"),
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ct: "image/webp",
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},
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&exactSig{[]byte("\x89PNG\x0D\x0A\x1A\x0A"), "image/png"},
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&exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"},
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// Audio and Video types
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// Enforce the pattern match ordering as prescribed in
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// https://mimesniff.spec.whatwg.org/#matching-an-audio-or-video-type-pattern
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF"),
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pat: []byte(".snd"),
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ct: "audio/basic",
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},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
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pat: []byte("FORM\x00\x00\x00\x00AIFF"),
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ct: "audio/aiff",
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},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF"),
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pat: []byte("ID3"),
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ct: "audio/mpeg",
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},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\xFF"),
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pat: []byte("OggS\x00"),
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ct: "application/ogg",
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},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"),
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pat: []byte("MThd\x00\x00\x00\x06"),
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ct: "audio/midi",
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},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
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pat: []byte("RIFF\x00\x00\x00\x00AVI "),
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ct: "video/avi",
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},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
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pat: []byte("RIFF\x00\x00\x00\x00WAVE"),
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ct: "audio/wave",
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},
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// 6.2.0.2. video/mp4
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mp4Sig{},
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// 6.2.0.3. video/webm
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&exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"},
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// Font types
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&maskedSig{
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// 34 NULL bytes followed by the string "LP"
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pat: []byte("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00LP"),
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// 34 NULL bytes followed by \xF\xF
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mask: []byte("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xFF\xFF"),
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ct: "application/vnd.ms-fontobject",
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},
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&exactSig{[]byte("\x00\x01\x00\x00"), "font/ttf"},
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&exactSig{[]byte("OTTO"), "font/otf"},
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&exactSig{[]byte("ttcf"), "font/collection"},
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&exactSig{[]byte("wOFF"), "font/woff"},
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&exactSig{[]byte("wOF2"), "font/woff2"},
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// Archive types
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&exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"},
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&exactSig{[]byte("PK\x03\x04"), "application/zip"},
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// RAR's signatures are incorrectly defined by the MIME spec as per
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// https://github.com/whatwg/mimesniff/issues/63
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// However, RAR Labs correctly defines it at:
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// https://www.rarlab.com/technote.htm#rarsign
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// so we use the definition from RAR Labs.
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// TODO: do whatever the spec ends up doing.
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&exactSig{[]byte("Rar!\x1A\x07\x00"), "application/x-rar-compressed"}, // RAR v1.5-v4.0
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&exactSig{[]byte("Rar!\x1A\x07\x01\x00"), "application/x-rar-compressed"}, // RAR v5+
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&exactSig{[]byte("\x00\x61\x73\x6D"), "application/wasm"},
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textSig{}, // should be last
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}
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type exactSig struct {
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sig []byte
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ct string
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}
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func (e *exactSig) match(data []byte, firstNonWS int) string {
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if bytes.HasPrefix(data, e.sig) {
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return e.ct
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}
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return ""
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}
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type maskedSig struct {
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mask, pat []byte
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skipWS bool
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ct string
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}
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func (m *maskedSig) match(data []byte, firstNonWS int) string {
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// pattern matching algorithm section 6
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// https://mimesniff.spec.whatwg.org/#pattern-matching-algorithm
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if m.skipWS {
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data = data[firstNonWS:]
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}
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if len(m.pat) != len(m.mask) {
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return ""
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}
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if len(data) < len(m.pat) {
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return ""
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}
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for i, pb := range m.pat {
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maskedData := data[i] & m.mask[i]
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if maskedData != pb {
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return ""
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}
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}
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return m.ct
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}
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type htmlSig []byte
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func (h htmlSig) match(data []byte, firstNonWS int) string {
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data = data[firstNonWS:]
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if len(data) < len(h)+1 {
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return ""
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}
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for i, b := range h {
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db := data[i]
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if 'A' <= b && b <= 'Z' {
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db &= 0xDF
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}
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if b != db {
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return ""
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}
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}
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// Next byte must be a tag-terminating byte(0xTT).
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if !isTT(data[len(h)]) {
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return ""
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}
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return "text/html; charset=utf-8"
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}
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var mp4ftype = []byte("ftyp")
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var mp4 = []byte("mp4")
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type mp4Sig struct{}
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func (mp4Sig) match(data []byte, firstNonWS int) string {
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// https://mimesniff.spec.whatwg.org/#signature-for-mp4
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// c.f. section 6.2.1
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if len(data) < 12 {
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return ""
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}
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boxSize := int(binary.BigEndian.Uint32(data[:4]))
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if len(data) < boxSize || boxSize%4 != 0 {
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return ""
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}
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if !bytes.Equal(data[4:8], mp4ftype) {
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return ""
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}
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for st := 8; st < boxSize; st += 4 {
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if st == 12 {
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// Ignores the four bytes that correspond to the version number of the "major brand".
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continue
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}
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if bytes.Equal(data[st:st+3], mp4) {
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return "video/mp4"
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}
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}
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return ""
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}
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type textSig struct{}
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func (textSig) match(data []byte, firstNonWS int) string {
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// c.f. section 5, step 4.
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for _, b := range data[firstNonWS:] {
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switch {
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case b <= 0x08,
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b == 0x0B,
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0x0E <= b && b <= 0x1A,
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0x1C <= b && b <= 0x1F:
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return ""
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}
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}
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return "text/plain; charset=utf-8"
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}
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