87 lines
1.8 KiB
Go
87 lines
1.8 KiB
Go
package ridata
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import (
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"io"
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"os"
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"strings"
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"net/http"
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"github.com/dsoprea/go-logging"
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)
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const (
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// MimetypeLeadBytesCount is the number of bytes to use for detection.
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MimetypeLeadBytesCount = 512
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)
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// GetMimetypeFromContent uses net/http to map from magic-bytes to mime-type.
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func GetMimetypeFromContent(r io.Reader, fileSize int64) (mimetype string, err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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// TODO(dustin): !! Add test.
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leadCount := int64(MimetypeLeadBytesCount)
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if fileSize > 0 && fileSize < leadCount {
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leadCount = fileSize
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}
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buffer := make([]byte, leadCount)
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n, err := io.ReadFull(r, buffer)
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if err != nil {
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// We can return EOF if a) we weren't given a filesize and the file did
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// not haveat least as many bytes as we check by default, or b) the file-
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// size is actually (0).
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if err == io.EOF {
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return "", err
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}
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log.Panic(err)
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}
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buffer = buffer[:n]
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// Always returns a valid mime-type.
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contentType := http.DetectContentType(buffer)
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contentType = strings.TrimRight(contentType, ";")
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return contentType, nil
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}
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// DetectMimetype is a wrapper for GetMimetypeFromContent which returns the
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// mime-type for the given `File`. An empty-string is returned if it is a zero-
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// length file.
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func DetectMimetype(f *os.File) (mimetype string, err error) {
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defer func() {
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if state := recover(); state != nil {
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err = log.Wrap(state.(error))
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}
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}()
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originalOffsetRaw, err := f.Seek(0, os.SEEK_CUR)
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log.PanicIf(err)
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fi, err := f.Stat()
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log.PanicIf(err)
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fileSize := fi.Size()
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if fileSize == 0 {
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return "", nil
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}
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mimetype, err = GetMimetypeFromContent(f, fileSize)
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log.PanicIf(err)
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_, err = f.Seek(originalOffsetRaw, os.SEEK_SET)
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log.PanicIf(err)
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return mimetype, nil
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}
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