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package sniff
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// ref: https://mimesniff.spec.whatwg.org
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var imageMIMEs = map[string]Sniffer{
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"image/jpeg": prefixSniffer{0xFF, 0xD8, 0xFF},
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"image/png": prefixSniffer{0x89, 'P', 'N', 'G', '\r', '\n', 0x1A, '\n'},
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"image/bmp": prefixSniffer("BM"),
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"image/webp": prefixSniffer("RIFF"),
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"image/gif": prefixSniffer("GIF8"),
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}
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// ImageMIME sniffs the well-known image types, and returns its MIME.
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func ImageMIME(header []byte) (string, bool) {
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for ext, sniffer := range imageMIMEs {
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if sniffer.Sniff(header) {
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return ext, true
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}
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}
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return "", false
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}
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// ImageExtension is equivalent to ImageMIME, but returns file extension
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func ImageExtension(header []byte) (string, bool) {
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ext, ok := ImageMIME(header)
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if !ok {
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return "", false
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}
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// todo: use mime.ExtensionsByType
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return "." + ext[6:], true // "image/" is 6 bytes
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}
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