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Refactor common code to skip last 128 bytes from ReadSeeker.

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This commit is contained in:
David Howden 2015-06-30 23:07:26 +10:00
parent 52902f61b8
commit 92e6d71ddb
1 changed files with 17 additions and 18 deletions
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35
sum.go
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@ -96,13 +96,25 @@ func SumAtoms(r io.ReadSeeker) (string, error) {
}
}
func sizeToEndOffset(r io.ReadSeeker, offset int64) (int64, error) {
n, err := r.Seek(-128, os.SEEK_END)
if err != nil {
return 0, fmt.Errorf("error seeking end offset (%d bytes): %v", offset, err)
}
_, err = r.Seek(-n, os.SEEK_CUR)
if err != nil {
return 0, fmt.Errorf("error seeking back to original position: %v", err)
}
return n, nil
}
// SumID3v1 constructs a checksum of MP3 audio file data (assumed to have ID3v1 tags) provided
// by the io.ReadSeeker which is metadata invariant.
func SumID3v1(r io.ReadSeeker) (string, error) {
// Need to stop before we hit potential ID3v1 data.
n, err := r.Seek(-128, os.SEEK_END)
n, err := sizeToEndOffset(r, 128)
if err != nil {
return "", fmt.Errorf("error seeking to the end of the file (minus ID3v1 header): %v", err)
return "", fmt.Errorf("error determining read size to ID3v1 header: %v", err)
}
// TODO: improve this check???
@ -110,12 +122,6 @@ func SumID3v1(r io.ReadSeeker) (string, error) {
return "", fmt.Errorf("file size must be greater than 128 bytes (ID3v1 header size) for MP3")
}
// Seek back to the original position now!
_, err = r.Seek(-1*n, os.SEEK_SET)
if err != nil {
return "", fmt.Errorf("error seeking back to the start of the data: %v", err)
}
h := sha1.New()
_, err = io.CopyN(h, r, n)
if err != nil {
@ -137,10 +143,9 @@ func SumID3v2(r io.ReadSeeker) (string, error) {
return "", fmt.Errorf("error seeking to end of ID3V2 header: %v", err)
}
// Need to stop before we hit potential ID3v1 data.
n, err := r.Seek(-128, os.SEEK_END)
n, err := sizeToEndOffset(r, 128)
if err != nil {
return "", fmt.Errorf("error seeking to the end of the file (minus ID3v1 header): %v", err)
return "", fmt.Errorf("error determining read size to ID3v1 header: %v", err)
}
// TODO: remove this check?????
@ -148,12 +153,6 @@ func SumID3v2(r io.ReadSeeker) (string, error) {
return "", fmt.Errorf("file size must be greater than 128 bytes for MP3: %v bytes", n)
}
// Seek back to the original position now!
_, err = r.Seek(-1*n, os.SEEK_SET)
if err != nil {
return "", fmt.Errorf("error seeking back to the start of the data: %v", err)
}
h := sha1.New()
_, err = io.CopyN(h, r, n)
if err != nil {