mirror of https://github.com/perkeep/perkeep.git
84 lines
2.5 KiB
Go
84 lines
2.5 KiB
Go
/*
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Copyright 2011 Google Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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nYou may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Package magic implements MIME type sniffing of data based on the
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// well-known "magic" number prefixes in the file.
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package magic
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import (
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"bytes"
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"io"
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"net/http"
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"strings"
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)
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type prefixEntry struct {
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prefix []byte
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mtype string
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}
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var prefixTable = []prefixEntry{
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{[]byte("GIF87a"), "image/gif"},
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{[]byte("GIF89a"), "image/gif"}, // TODO: Others?
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{[]byte("\xff\xd8\xff\xe2"), "image/jpeg"},
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{[]byte("\xff\xd8\xff\xe1"), "image/jpeg"},
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{[]byte("\xff\xd8\xff\xe0"), "image/jpeg"},
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{[]byte("\xff\xd8\xff\xdb"), "image/jpeg"},
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{[]byte("\x49\x49\x2a\x00\x10\x00\x00\x00\x43\x52\x02"), "image/cr2"},
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{[]byte{137, 'P', 'N', 'G', '\r', '\n', 26, 10}, "image/png"},
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{[]byte("-----BEGIN PGP PUBLIC KEY BLOCK---"), "text/x-openpgp-public-key"},
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{[]byte{'I', 'D', '3'}, "audio/mpeg"},
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// TODO(bradfitz): popular audio & video formats at least
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}
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// MIMEType returns the MIME type from the data in the provided header
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// of the data.
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// It returns the empty string if the MIME type can't be determined.
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func MIMEType(hdr []byte) string {
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hlen := len(hdr)
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for _, pte := range prefixTable {
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plen := len(pte.prefix)
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if hlen > plen && bytes.Equal(hdr[:plen], pte.prefix) {
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return pte.mtype
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}
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}
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t := http.DetectContentType(hdr)
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t = strings.Replace(t, "; charset=utf-8", "", 1)
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if t != "application/octet-stream" && t != "text/plain" {
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return t
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}
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return ""
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}
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// MIMETypeFromReader takes a reader, sniffs the beginning of it,
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// and returns the mime (if sniffed, else "") and a new reader
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// that's the concatenation of the bytes sniffed and the remaining
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// reader.
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func MIMETypeFromReader(r io.Reader) (mime string, reader io.Reader) {
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var buf bytes.Buffer
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io.CopyN(&buf, r, 1024)
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mime = MIMEType(buf.Bytes())
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return mime, io.MultiReader(&buf, r)
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}
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// MIMETypeFromReader takes a ReaderAt, sniffs the beginning of it,
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// and returns the MIME type if sniffed, else the empty string.
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func MIMETypeFromReaderAt(ra io.ReaderAt) (mime string) {
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var buf [1024]byte
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n, _ := ra.ReadAt(buf[:], 0)
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return MIMEType(buf[:n])
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}
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