mp: new helper functions for map headers size

Signed-off-by: Eduardo Silva <eduardo@treasure-data.com>

Author: edsiper

include/fluent-bit/flb_mp.h

@@ -21,7 +21,23 @@
 #ifndef FLB_MP_H
 #define FLB_MP_H
 
+#include <msgpack.h>
+
 int flb_mp_count(const void *data, size_t bytes);
 void flb_mp_set_map_header_size(char *buf, int arr_size);
 
+
+/*
+ * Map header handling functions
+ */
+struct flb_mp_map_header {
+    off_t offset;
+    size_t entries;
+    void *data;
+};
+
+int flb_mp_map_header_init(struct flb_mp_map_header *mh, msgpack_packer *mp_pck);
+int flb_mp_map_header_append(struct flb_mp_map_header *mh);
+void flb_mp_map_header_end(struct flb_mp_map_header *mh);
+
 #endif

src/flb_mp.c

@@ -19,6 +19,9 @@
  */
 
 #include <fluent-bit/flb_info.h>
+#include <fluent-bit/flb_utils.h>
+#include <fluent-bit/flb_mp.h>
+
 #include <msgpack.h>
 #include <mpack/mpack.h>
 
@@ -60,3 +63,82 @@ void flb_mp_set_map_header_size(char *buf, int arr_size)
         pack_uint32(tmp, arr_size);
     }
 }
+
+/*
+ * msgpack-c requires to set the number of the entries in a map beforehand. For our
+ * use case this adds some complexity, having developers to count all possible
+ * entries that might be added.
+ *
+ * As a workaround and to avoid map's recomposition over and over, this simple API
+ * allows to initialize the array header, 'register' new entries (as counters) and
+ * finalize, upon finalization the proper array header size is adjusted.
+ *
+ * To make things easier, we make sure msgpack-c always register an array type of
+ * 32 bits (identified by 0xdf, for number of entries >= 65536). Yes, for every
+ * array using this API it will use 2 more bytes, not a big ideal. So whoever
+ * uses this API, use it only if you don't know the exact number of entries to add.
+ *
+ * MANDATORY: make sure to always initialize, register every entry and finalize,
+ * otherwise you will get a corrupted or incomplete msgpack buffer.
+ *
+ * Usage example
+ * =============
+ *
+ *  struct flb_mp_map_head mh;
+ *
+ *  flb_mp_map_header_init(&mh, mp_pck);
+ *
+ *  -- First key/value entry --
+ *  flb_mp_map_header_append(&mh);
+ *  msgpack_pack_str(mp_pck, 4);
+ *  msgpack_pack_str_body(mp_pck, "cool", 4);
+ *  msgpack_pack_true(mp_pck);
+ *
+ *  -- Second key/value entry --
+ *  flb_mp_map_header_append(&mh);
+ *  msgpack_pack_str(mp_pck, 4);
+ *  msgpack_pack_str_body(mp_pck, "slow", 4);
+ *  msgpack_pack_false(mp_pck);
+ *
+ *  -- Finalize Map --
+ *  flb_mp_map_header_end(&mh);
+ */
+int flb_mp_map_header_init(struct flb_mp_map_header *mh, msgpack_packer *mp_pck)
+{
+    msgpack_sbuffer *mp_sbuf;
+
+    mp_sbuf = (msgpack_sbuffer *) mp_pck->data;
+
+    /* map sbuffer */
+    mh->data = mp_pck->data;
+
+    /* Reset entries */
+    mh->entries = 0;
+
+    /* Store the next byte available */
+    mh->offset = mp_sbuf->size;
+
+    /*
+     * Pack a map with size = 65536, so we force the underlaying msgpack-c
+     * to use a 32 bit buffer size (0xdf), reference:
+     *
+     * - https://github.com/msgpack/msgpack/blob/master/spec.md#map-format-family
+     */
+    return msgpack_pack_map(mp_pck, 65536);
+}
+
+int flb_mp_map_header_append(struct flb_mp_map_header *mh)
+{
+    mh->entries++;
+    return mh->entries;
+}
+
+void flb_mp_map_header_end(struct flb_mp_map_header *mh)
+{
+    char *ptr;
+    msgpack_sbuffer *mp_sbuf;
+
+    mp_sbuf = mh->data;
+    ptr = (char *) mp_sbuf->data + mh->offset;
+    flb_mp_set_map_header_size(ptr, mh->entries);
+}