[Core] Allow switch_buffer_write() to fill in a buffer with zeros. Add switch_buffer_zero_fill()

src/include/switch_buffer.h

@@ -132,13 +132,15 @@ SWITCH_DECLARE(void) switch_buffer_set_loops(_In_ switch_buffer_t *buffer, _In_
 
 /*! \brief Write data into a switch_buffer_t up to the length of datalen
  * \param buffer any buffer of type switch_buffer_t
- * \param data pointer to the data to be written
+ * \param data pointer to the data to be written or 0 to fill in with datalen zeros
  * \param datalen amount of data to be written
  * \return int amount of buffer used after the write, or 0 if no space available
  */
 SWITCH_DECLARE(switch_size_t) switch_buffer_write(_In_ switch_buffer_t *buffer, _In_bytecount_(datalen)
 												  const void *data, _In_ switch_size_t datalen);
 
+#define switch_buffer_zero_fill(_buffer, _datalen) switch_buffer_write(_buffer, 0, _datalen);
+
 /*! \brief Remove data from the buffer
  * \param buffer any buffer of type switch_buffer_t
  * \param datalen amount of data to be removed

src/switch_buffer.c

@@ -344,7 +344,12 @@ SWITCH_DECLARE(switch_size_t) switch_buffer_write(switch_buffer_t *buffer, const
 		return 0;
 	}
 
-	memcpy(buffer->head + buffer->used, data, datalen);
+	if (data) {
+		memcpy(buffer->head + buffer->used, data, datalen);
+	} else {
+		memset(buffer->head + buffer->used, 0, datalen);
+	}
+
 	buffer->used += datalen;
 	buffer->actually_used += datalen;
 	return buffer->used;