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