feat: extend file transmission API to support file upload via TUS

proto/caosdb/entity/v2/main.proto

@@ -24,6 +24,7 @@ option  java_multiple_files = true;
 option  java_package        = "org.caosdb.api.entity.v2";
 option  cc_enable_arenas    = true;
 package caosdb.entity.v2;
+import "caosdb/file_transmission/v1/main.proto"; // for FileTransmissionId
 
 // Data type for references to other entities.
 message ReferenceDataType {

proto/caosdb/file_transmission/v1/main.proto

@@ -82,8 +82,55 @@ enum TransmissionStatus {
   TRANSMISSION_STATUS_GO_ON = 3;
 }
 
-// Register a file upload.
-message RegisterFileUploadRequest {}
+// TODO: This is very similar to the Hash message in the entity API. We should discuss 
+//       if and how they can be merged.
+enum ChecksumAlgorithm {
+  CHECKSUM_ALGORITHM_UNSPECIFIED = 0;
+  CHECKSUM_ALGORITHM_MD5         = 1;
+  CHECKSUM_ALGORITHM_SHA1        = 2;
+  CHECKSUM_ALGORITHM_SHA256      = 3;
+  CHECKSUM_ALGORITHM_SHA512      = 4;
+}
+
+message Checksum {
+  string            checksum           = 1;
+  ChecksumAlgorithm checksum_algorithm = 2;
+}
+
+// Information about a file which is to be uploaded.
+// TODO: This is very similar to the FileDescriptor message in the entity API with the
+//       difference that it has no relation to an entity and is purely filesystem-oriented. 
+//       Maybe we should re-use FileInformation s part of the entity API?
+message FileInformation {
+  // The local filename is the filename, which is used on the client.
+  string local_filename = 1;
+  // The target filename is the filename which will be used on the server.
+  string target_filename = 2;
+  // Size of the file in bytes.
+  int size_bytes = 3;
+  // Checksum of the file according to the checksum algorithm.
+  Checksum checksum = 4;
+}
+
+// Register a file upload for a list of files. The server will respond with a
+// registration id and URLs to which the files can be uploaded.
+message RegisterFileUploadRequest {
+  repeated FileInformation = 1;
+}
+
+// The URL to which a file should be uploaded using the given LinkAhead
+// UploadProtocolVersion.
+message UploadLocation {
+  string url = 1;
+}
+
+// The version of the LinkAhead upload protocol. This is currently identical to
+// the TUS protocol version.
+message UploadProtocolVersion {
+  int major = 1;
+  int minor = 2;
+  int patch = 3;
+}
 
 // Response of the file server upon an upload registration request.
 message RegisterFileUploadResponse {
@@ -94,6 +141,8 @@ message RegisterFileUploadResponse {
   string registration_id = 2;
   // The server's transmission settings for the upload.
   FileTransmissionSettings upload_settings = 4;
+  UploadProtocolVersion    version         = 5;
+  repeated UploadLocation  locations       = 6;
 }
 
 // Request for a file upload which has been registered previously. Chunks may be