dechunker: Create separate module for dechunking

The code in xrdp_channel.c to handle dechunking on a virtual channel is moved to a separate module to allow for better sharing of logic.
2026-07-17 11:57:30 +01:00
parent de284747ae
commit be95ba3017
5 changed files with 514 additions and 60 deletions
@@ -0,0 +1,100 @@
+/**
+ * xrdp: A Remote Desktop Protocol server.
+ *
+ * Copyright (C) Jay Sorg 2004-2026
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+/**
+ * @file dechunker.h
+ * @brief Dechunker functions for chunks on virtual channels - declarations
+ *
+ * Many places in xrdp need to dechunk data received from virtual channels.
+ * This process is described in [MS-RDPBCGR] 3.1.5.2.1 (sending) and
+ * 3.1.5.2.2.1 (reassembly).
+ *
+ *
+ * @author Matt Burt
+ */
+
+#if !defined(DECHUNKER_H)
+#define DECHUNKER_H
+
+struct stream;
+
+/* Private type */
+struct vc_dechunker;
+
+/**
+ * Returned from dechunker_process_vc_chunk()
+ */
+enum vc_dechunker_status
+{
+    E_VC_INLINE_CHUNK = 0, ///< This chunk is complete in itself
+    E_VC_IN_PROGRESS,      ///< The dechunker is processing chunks
+    E_VC_READY,            ///< A dechunked stream is now complete
+    E_VC_ERROR             ///< An error occurred (logged)
+};
+
+/**
+ * Initialise a virtual channel dechunker
+ *
+ * @param chan_name - Name of channel
+ * @param max_chunk_size - Max size of chunks allowed on channel
+ * @return vc_dechunker
+ */
+struct vc_dechunker *
+vc_dechunker_init(const char *chan_name, int max_chunk_size);
+
+/**
+ * Free a virtual channel dechunker
+ * @param self vc dechunker to free
+ */
+void
+vc_dechunker_free(struct vc_dechunker *self);
+
+/**
+ * Process a virtual channel chunk
+ *
+ * @param self dechunker
+ * @param s Stream for chunk, positioned at start of chunk
+ * @param flags from CHANNEL_PDU_HEADER
+ * @param total_size length from CHANNEL_PDU_HEADER
+ * @return status of dechunker
+ *
+ * If E_VC_ERROR is returned, the dechunker will ignore further PDUs
+ * until the start of the next one is detected. This can be used to
+ * recover from chunking errors without losing the channel entirely. It
+ * is up to the caller whether to treat a dechunking error as fatal for
+ * the channel or not.
+ */
+enum vc_dechunker_status
+vc_dechunker_process_chunk(struct vc_dechunker *self,
+                           struct stream *s, int flags, int total_size);
+/**
+ * Get the stream from a ready dechunker
+ *
+ * @param self virtual channel dechunker
+ * @return input stream containing completed chunk
+ *
+ * Ownership of the stream passes to the caller
+ *
+ * Resets the dechunker state so that further chunks can be processed.
+ */
+struct stream *
+vc_dechunker_get_stream(struct vc_dechunker *self);
+
+
+#endif // DECHUNKER_H