Feature/mstp extended frames cobs encoding (#183)

* added COBS encode and decode from BACnet standard

* Add unit tests for COBS encoding and decoding

* Improve COBS unit test and API.

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

src/bacnet/datalink/cobs.h

@@ -0,0 +1,84 @@
+/**************************************************************************
+ *
+ * Copyright (C) 2014 Kerry Lynn <kerlyn@ieee.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *********************************************************************/
+#ifndef COBS_H
+#define COBS_H
+
+#include <stddef.h>
+#include <stdint.h>
+#include "bacnet/bacnet_stack_exports.h"
+
+/* number of bytes needed for COBS encoded CRC */
+#define COBS_ENCODED_CRC_SIZE 5
+/* inclusive extra bytes needed for APDU */
+#define COBS_ENCODED_SIZE(a) ((a)+((a)/254)+1)
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+BACNET_STACK_EXPORT
+size_t cobs_encode(
+    uint8_t *buffer,
+    size_t buffer_size,
+    const uint8_t *from,
+    size_t length,
+    uint8_t mask);
+
+BACNET_STACK_EXPORT
+size_t cobs_frame_encode(
+    uint8_t *buffer,
+    size_t buffer_size,
+    const uint8_t *from,
+    size_t length);
+
+BACNET_STACK_EXPORT
+size_t cobs_decode(
+    uint8_t *buffer,
+    size_t buffer_size,
+    const uint8_t *from,
+    size_t length,
+    uint8_t mask);
+
+BACNET_STACK_EXPORT
+size_t cobs_frame_decode(
+    uint8_t *buffer,
+    size_t buffer_size,
+    const uint8_t *from,
+    size_t length);
+
+BACNET_STACK_EXPORT
+uint32_t cobs_crc32k(
+    uint8_t dataValue,
+    uint32_t crc);
+
+BACNET_STACK_EXPORT
+size_t cobs_crc32k_encode(
+    uint8_t *buffer,
+    size_t buffer_size,
+    uint32_t crc);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+#endif