/
detect.go
50 lines (41 loc) · 1.06 KB
/
detect.go
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package media
import (
"bytes"
"io"
)
const bytesToRead = 32
type detector interface {
match(data []byte) (ContentType, error)
}
var mediaSignatures = []detector{
&mediaSignature{[]byte("BM"), BMPType},
&mediaSignature{[]byte("GIF87a"), GIFType},
&mediaSignature{[]byte("GIF89a"), GIFType},
&mediaSignature{[]byte("\x89PNG\x0D\x0A\x1A\x0A"), PNGType},
&mediaSignature{[]byte("\xFF\xD8\xFF"), JPEGType},
}
type mediaSignature struct {
sig []byte
mediaType ContentType
}
func (e *mediaSignature) match(data []byte) (ContentType, error) {
if bytes.HasPrefix(data, e.sig) {
return e.mediaType, nil
}
return "", ErrUnknownContentType
}
// DetectContentType returns the ContentType from the first 32 bytes
func DetectContentType(r io.Reader) (ContentType, []byte, error) {
readBytes := make([]byte, bytesToRead)
_, err := r.Read(readBytes)
if err != nil {
return "", readBytes, err
}
for _, sig := range mediaSignatures {
mt, err := sig.match(readBytes)
if err == nil {
return mt, readBytes, nil
}
}
return "", readBytes, ErrUnknownContentType
}