feat: add symlinks capabilities for S3-compatible systems, and fix multipart copy source-size handling

core/backend.go

@@ -30,6 +30,9 @@ type Capabilities struct {
 	// indicates that the blob store has native support for directories
 	DirBlob bool
 	Name    string
+	// SupportsConditionalWrites indicates the backend supports If-Match/If-None-Match
+	// conditional headers on PutObject (used for optimistic locking of .geesefs_symlinks)
+	SupportsConditionalWrites bool
 }
 
 type HeadBlobInput struct {
@@ -116,10 +119,11 @@ type CopyBlobOutput struct {
 }
 
 type GetBlobInput struct {
-	Key     string
-	Start   uint64
-	Count   uint64
-	IfMatch *string
+	Key         string
+	Start       uint64
+	Count       uint64
+	IfMatch     *string
+	IfNoneMatch *string // For conditional GET - returns 304 if ETag matches
 }
 
 type GetBlobOutput struct {
@@ -138,6 +142,13 @@ type PutBlobInput struct {
 
 	Body io.ReadSeeker
 	Size *uint64
+
+	// IfMatch specifies an ETag; the request succeeds only if the object's ETag matches.
+	// Used for optimistic locking / conditional updates.
+	IfMatch *string
+	// IfNoneMatch specifies that the request should succeed only if the object does not exist.
+	// Set to "*" to prevent overwriting an existing object.
+	IfNoneMatch *string
 }
 
 type PutBlobOutput struct {

core/backend_s3.go

@@ -80,8 +80,9 @@ func NewS3(bucket string, flags *cfg.FlagStorage, config *cfg.S3Config) (*S3Back
 		flags:     flags,
 		config:    config,
 		cap: Capabilities{
-			Name:             "s3",
-			MaxMultipartSize: 5 * 1024 * 1024 * 1024,
+			Name:                      "s3",
+			MaxMultipartSize:          5 * 1024 * 1024 * 1024,
+			SupportsConditionalWrites: true,
 		},
 	}
 
@@ -925,7 +926,14 @@ func (s *S3Backend) GetBlob(param *GetBlobInput) (*GetBlobOutput, error) {
 		}
 		get.Range = &bytes
 	}
-	// TODO handle IfMatch
+
+	if param.IfMatch != nil {
+		get.IfMatch = param.IfMatch
+	}
+
+	if param.IfNoneMatch != nil {
+		get.IfNoneMatch = param.IfNoneMatch
+	}
 
 	req, resp := s.GetObjectRequest(&get)
 	err := req.Send()
@@ -990,6 +998,16 @@ func (s *S3Backend) PutBlob(param *PutBlobInput) (*PutBlobOutput, error) {
 		put.ACL = &s.config.ACL
 	}
 
+	// Conditional write support (S3 feature since August 2024)
+	// IfMatch: only write if ETag matches (optimistic locking for updates)
+	// IfNoneMatch: only write if object doesn't exist (create-if-not-exists)
+	if param.IfMatch != nil {
+		put.IfMatch = param.IfMatch
+	}
+	if param.IfNoneMatch != nil {
+		put.IfNoneMatch = param.IfNoneMatch
+	}
+
 	req, resp := s.PutObjectRequest(put)
 	err := req.Send()
 	if err != nil {