[GitHub] [mynewt-mcumgr] nvlsianpu commented on a change in pull request #72: fs_mgmt: Fix file download for Zephyr

[GitBox <gi...@apache.org>]

nvlsianpu commented on a change in pull request #72: fs_mgmt: Fix file download for Zephyr
URL: https://github.com/apache/mynewt-mcumgr/pull/72#discussion_r394293364
 
 

 ##########
 File path: cmd/fs_mgmt/include/fs_mgmt/fs_mgmt_config.h
 ##########
 @@ -30,7 +30,44 @@
 
 #elif defined __ZEPHYR__
 
-#define FS_MGMT_DL_CHUNK_SIZE   CONFIG_FS_MGMT_DL_CHUNK_SIZE
+#define MCUMGR_BUF_SIZE         CONFIG_MCUMGR_BUF_SIZE
+/* File chunk needs to fit into MCUMGR_BUF_SIZE with all required headers
+ * and other data fields; following information takes space off the
+ * MCUMGR_BUF_SIZE, N is CONFIG_FS_MGMT_MAX_OFFSET_LEN
+ *  MGMT_HDR_SIZE - header that is placed in front of buffer and not
+ *    visible for cbod encoder (see smp_handle_single_req);
+ *  9 + 1 -- bytes taken by definition of CBOR undefined length map and map
+ *    terminator (break) character;
+ *  1 + strlen("off") + [1, N] -- CBOR encoded pair of "off" marker and
+ *    offset of the chunk within the file;
+ *  1 + strlen("data") + [1, N] -- CBOR encoded "data" marker; this marker
+ *    will be followed by file chunk of size FS_MGMT_DL_CHUNK_SIZE
+ *  1 + strlen("rc") + 1 -- status code of operation;
+ *  1 + strlen("len") + [1, N] -- CBOR encoded "len" marker and complete
+ *    length of a file; this is only sent once when "off" is 0;
+ *
+ * FS_MGMT_DL_CHUNK_SIZE is calculated with most pessimistic estimations,
+ * that is with headers fields taking most space, i.e. N bytes.
+ */
+#define CBOR_AND_OTHER_HDR \
 
 Review comment:
   +1 for comprehensive description.

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