Add support for multiple hash types.

Add support for multiple hash types with negotiation of common hash types for comparison.

Manually rebased version of #277 (see discussion there)

b2/b2.go

@@ -74,6 +74,7 @@ type Object struct {
 	remote  string    // The remote path
 	info    api.File  // Info from the b2 object if known
 	modTime time.Time // The modified time of the object if known
+	sha1    string    // SHA-1 hash if known
 }
 
 // ------------------------------------------------------------
@@ -580,6 +581,11 @@ func (f *Fs) Purge() error {
 	return errReturn
 }
 
+// Hashes returns the supported hash sets.
+func (f *Fs) Hashes() fs.HashSet {
+	return fs.HashSet(fs.HashSHA1)
+}
+
 // ------------------------------------------------------------
 
 // Fs returns the parent Fs
@@ -600,9 +606,16 @@ func (o *Object) Remote() string {
 	return o.remote
 }
 
-// Md5sum returns the Md5sum of an object returning a lowercase hex string
-func (o *Object) Md5sum() (string, error) {
-	return "", nil
+// Hash returns the Sha-1 of an object returning a lowercase hex string
+// Hash returns the Md5sum of an object returning a lowercase hex string
+func (o *Object) Hash(t fs.HashType) (string, error) {
+	if t != fs.HashSHA1 {
+		return "", fs.ErrHashUnsupported
+	}
+
+	// Error is logged in readFileMetadata
+	_ = o.readFileMetadata()
+	return o.sha1, nil
 }
 
 // Size returns the size of an object in bytes
@@ -652,23 +665,40 @@ func parseTimeString(timeString string) (result time.Time, err error) {
 //
 // It attempts to read the objects mtime and if that isn't present the
 // LastModified returned in the http headers
+//
+// SHA-1 will also be updated once the request has completed.
 func (o *Object) ModTime() (result time.Time) {
-	if !o.modTime.IsZero() {
-		return o.modTime
+	// The error is logged in readFileMetadata
+	_ = o.readFileMetadata()
+	return o.modTime
+}
+
+// readFileMetadata attempts to read the modified time and
+// SHA-1 hash of the remote object.
+//
+// If the objects mtime and if that isn't present the
+// LastModified returned in the http headers.
+//
+// It is safe to call this function multiple times, and the
+// result is cached between calls.
+func (o *Object) readFileMetadata() error {
+	// Return if already know it
+	if !o.modTime.IsZero() && o.sha1 != "" {
+		return nil
 	}
 
-	// Return the current time if can't read metadata
-	result = time.Now()
+	// Set modtime to now, as default value.
+	o.modTime = time.Now()
 
-	// Read metadata (need ID)
+	// Read metadata (we need the ID)
 	err := o.readMetaData()
 	if err != nil {
-		fs.Debug(o, "Failed to read metadata: %v", err)
-		return result
+		fs.Debug(o, "Failed to get file metadata: %v", err)
+		return err
 	}
 
-	// Return the UploadTimestamp if can't get file info
-	result = time.Time(o.info.UploadTimestamp)
+	// Use the UploadTimestamp if can't get file info
+	o.modTime = time.Time(o.info.UploadTimestamp)
 
 	// Now read the metadata for the modified time
 	opts := rest.Opts{
@@ -682,17 +712,20 @@ func (o *Object) ModTime() (result time.Time) {
 	_, err = o.fs.srv.CallJSON(&opts, &request, &response)
 	if err != nil {
 		fs.Debug(o, "Failed to get file info: %v", err)
-		return result
+		return err
 	}
+	o.sha1 = response.SHA1
 
 	// Parse the result
 	timeString := response.Info[timeKey]
 	parsed, err := parseTimeString(timeString)
 	if err != nil {
 		fs.Debug(o, "Failed to parse mod time string %q: %v", timeString, err)
-		return result
+		return err
 	}
-	return parsed
+	o.modTime = parsed
+
+	return nil
 }
 
 // SetModTime sets the modification time of the local fs object
@@ -785,6 +818,9 @@ func (o *Object) Open() (in io.ReadCloser, err error) {
 	} else {
 		o.modTime = parsed
 	}
+	if o.sha1 == "" {
+		o.sha1 = resp.Header.Get(sha1Header)
+	}
 	return newOpenFile(o, resp), nil
 }
 
@@ -939,6 +975,7 @@ func (o *Object) Update(in io.Reader, modTime time.Time, size int64) (err error)
 	o.info.Action = "upload"
 	o.info.Size = response.Size
 	o.info.UploadTimestamp = api.Timestamp(time.Now()) // FIXME not quite right
+	o.sha1 = response.SHA1
 	return nil
 }