Fix some bugs with how buffer sizes were being calcuated in printbuf_memset and an off-by-one error in printbuf_memappend.

printbuf.c

@@ -47,6 +47,14 @@ struct printbuf* printbuf_new(void)
 }
 
 
+/**
+ * Extend the buffer p so it has a size of at least min_size.
+ *
+ * If the current size is large enough, nothing is changed.
+ *
+ * Note: this does not check the available space!  The caller
+ *  is responsible for performing those calculations.
+ */
 static int printbuf_extend(struct printbuf *p, int min_size)
 {
 	char *t;
@@ -55,11 +63,11 @@ static int printbuf_extend(struct printbuf *p, int min_size)
 	if (p->size >= min_size)
 		return 0;
 
-	new_size = json_max(p->size * 2, p->bpos + min_size + 8);
+	new_size = json_max(p->size * 2, min_size + 8);
 #ifdef PRINTBUF_DEBUG
 	MC_DEBUG("printbuf_memappend: realloc "
-	  "bpos=%d wrsize=%d old_size=%d new_size=%d\n",
-	  p->bpos, size, p->size, new_size);
+	  "bpos=%d min_size=%d old_size=%d new_size=%d\n",
+	  p->bpos, min_size, p->size, new_size);
 #endif /* PRINTBUF_DEBUG */
 	if(!(t = (char*)realloc(p->buf, new_size)))
 		return -1;
@@ -70,8 +78,8 @@ static int printbuf_extend(struct printbuf *p, int min_size)
 
 int printbuf_memappend(struct printbuf *p, const char *buf, int size)
 {
-  if(p->size - p->bpos <= size) {
-    if (printbuf_extend(p, size) < 0)
+  if (p->size <= p->bpos + size + 1) {
+    if (printbuf_extend(p, p->bpos + size + 1) < 0)
       return -1;
   }
   memcpy(p->buf + p->bpos, buf, size);
@@ -87,7 +95,7 @@ int printbuf_memset(struct printbuf *pb, int offset, int charvalue, int len)
 	if (offset == -1)
 		offset = pb->bpos;
 	size_needed = offset + len;
-	if(pb->size - pb->bpos <= size_needed)
+	if (pb->size < size_needed)
 	{
 		if (printbuf_extend(pb, size_needed) < 0)
 			return -1;