Add uc_mbuf_extend_headroom function, for growing an mbuf

src/mbuf.c

@@ -1,4 +1,5 @@
 #include <string.h>
+#include <assert.h>
 #include <stdlib.h>
 #include "ucore/mbuf.h"
 
@@ -119,3 +120,81 @@ struct MBuf *uc_mbuf_copy_data(struct MBuf *mbuf)
     return copy;
 }
 
+int uc_mbuf_extend_tailroom(struct MBuf *mbuf, uint32_t len)
+{
+    uint32_t tot_len;
+    uint32_t headroom_len;
+    uint32_t data_len;
+    uint32_t tailroom_len;
+    uint8_t *new_data;
+    uint32_t p1_off;
+    uint32_t p2_off;
+    uint32_t p3_off;
+    uint32_t p4_off;
+
+    if ((mbuf->flags & (UC_MBUF_FL_MALLOC | UC_MBUF_FL_MALLOC_BUF)) == 0) {
+        return -1;
+    }
+    
+    headroom_len = uc_mbuf_headroom(mbuf);
+    data_len     = uc_mbuf_len(mbuf);
+    tailroom_len = uc_mbuf_tailroom(mbuf);
+    tot_len = headroom_len +
+                  data_len     +
+                  tailroom_len;
+
+    if (tot_len + len < tot_len) {
+        //overflowed
+        return -2;
+    }
+    
+    tot_len += len;
+    
+    //need to re-adjust p1-p4 after the realloc
+    //This assumes the user controlled p1-p4 really are
+    //set to point into the data, but we document they have
+    //to be.
+    if (mbuf->p1 != NULL) {
+        p1_off = (uint32_t)(mbuf->p1 - mbuf->bufstart);
+    }
+    if (mbuf->p2 != NULL) {
+        p2_off = (uint32_t)(mbuf->p2 - mbuf->bufstart);
+    }
+    if (mbuf->p3 != NULL) {
+        p3_off = (uint32_t)(mbuf->p3 - mbuf->bufstart);
+    }
+    if (mbuf->p4 != NULL) {
+        p4_off = (uint32_t)(mbuf->p4 - mbuf->bufstart);
+    }
+
+    assert(tot_len >= mbuf->allocated);
+
+    new_data = realloc(mbuf->bufstart, tot_len);
+    if (new_data == NULL) {
+        return -3;
+    }
+
+    mbuf->allocated = tot_len;
+    mbuf->bufstart = new_data;
+    mbuf->head = mbuf->bufstart + headroom_len;
+    mbuf->tail = mbuf->bufstart + headroom_len + data_len;
+
+    assert(uc_mbuf_len(mbuf) == data_len);
+    assert(uc_mbuf_tailroom(mbuf) >= tailroom_len);
+
+    if (mbuf->p1 != NULL) {
+        mbuf->p1 = mbuf->bufstart + p1_off;
+    }
+    if (mbuf->p2 != NULL) {
+        mbuf->p2 = mbuf->bufstart + p2_off;
+    }
+    if (mbuf->p3 != NULL) {
+        mbuf->p3 = mbuf->bufstart + p3_off;
+    }
+    if (mbuf->p4 != NULL) {
+        mbuf->p4 = mbuf->bufstart + p4_off;
+    }
+
+    return 0;
+
+}