Add mbuf_clear()

PUBLISHED_FROM=754b98b3000b24ad3b3d9cc0b4c480ca005a1c3f

docs/c-api/mbuf.h/intro.md

@@ -4,6 +4,7 @@ symbol_kind: "intro"
 decl_name: "mbuf.h"
 items:
   - { name: mbuf_append.md }
+  - { name: mbuf_clear.md }
   - { name: mbuf_free.md }
   - { name: mbuf_init.md }
   - { name: mbuf_insert.md }

docs/c-api/mbuf.h/mbuf_clear.md

+---
+title: "mbuf_clear()"
+decl_name: "mbuf_clear"
+symbol_kind: "func"
+signature: |
+  void mbuf_clear(struct mbuf *);
+---
+
+Removes all the data from mbuf (if any). 
+

mongoose.c

@@ -1620,6 +1620,11 @@ void mbuf_remove(struct mbuf *mb, size_t n) {
   }
 }
 
+void mbuf_clear(struct mbuf *mb) WEAK;
+void mbuf_clear(struct mbuf *mb) {
+  mb->len = 0;
+}
+
 #endif /* EXCLUDE_COMMON */
 #ifdef MG_MODULE_LINES
 #line 1 "common/mg_str.c"

mongoose.h

@@ -2388,6 +2388,9 @@ void mbuf_remove(struct mbuf *, size_t data_size);
  */
 void mbuf_resize(struct mbuf *, size_t new_size);
 
+/* Removes all the data from mbuf (if any). */
+void mbuf_clear(struct mbuf *);
+
 /* Shrinks an Mbuf by resizing its `size` to `len`. */
 void mbuf_trim(struct mbuf *);