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fs/fingerprint.go
54 строки
1 KB
Nick Craig-Wood
fs: add Fingerprint to detect changes in an object
30 июн 2020, 14:01
30 июн 2020, 14:01
79f5d94
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package fs import ( "context" "fmt" "strings" "github.com/rclone/rclone/fs/hash" ) // Fingerprint produces a unique-ish string for an object. // // This is for detecting whether an object has changed since we last // saw it, not for checking object identity between two different // remotes - operations.Equal should be used for that. // // If fast is set then Fingerprint will only include attributes where // usually another operation is not required to fetch them. For // example if fast is set then this won't include hashes on the local // backend. func Fingerprint(ctx context.Context, o ObjectInfo, fast bool) string { var ( out strings.Builder f = o.Fs() features = f.Features() ) fmt.Fprintf(&out, "%d", o.Size()) // Whether we want to do a slow operation or not // // fast true false true false // opIsSlow true true false false // do Op false true true true // // If !fast (slow) do the operation or if !OpIsSlow == // OpIsFast do the operation. // // Eg don't do this for S3 where modtimes are expensive if !fast || !features.SlowModTime { if f.Precision() != ModTimeNotSupported { fmt.Fprintf(&out, ",%v", o.ModTime(ctx).UTC()) } } // Eg don't do this for SFTP/local where hashes are expensive? if !fast || !features.SlowHash { hashType := f.Hashes().GetOne() if hashType != hash.None { hash, err := o.Hash(ctx, hashType) if err == nil { fmt.Fprintf(&out, ",%v", hash) } } } return out.String() }