fifo_buffer: add function fifo_buffer_realloc()

For growing FIFO buffers.

src/fifo_buffer.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2010 The Music Player Daemon Project
+ * Copyright (C) 2003-2011 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * Redistribution and use in source and binary forms, with or without
@@ -58,6 +58,39 @@ fifo_buffer_new(size_t size)
 	return buffer;
 }
 
+static void
+fifo_buffer_move(struct fifo_buffer *buffer);
+
+struct fifo_buffer *
+fifo_buffer_realloc(struct fifo_buffer *buffer, size_t new_size)
+{
+	if (buffer == NULL)
+		return new_size > 0
+			? fifo_buffer_new(new_size)
+			: NULL;
+
+	/* existing data must fit in new size */
+	assert(new_size >= buffer->end - buffer->start);
+
+	if (new_size == 0) {
+		fifo_buffer_free(buffer);
+		return NULL;
+	}
+
+	/* compress the buffer when we're shrinking and the tail of
+	   the buffer would exceed the new size */
+	if (buffer->end > new_size)
+		fifo_buffer_move(buffer);
+
+	/* existing data must fit in new size: second check */
+	assert(buffer->end <= new_size);
+
+	buffer = g_realloc(buffer, sizeof(*buffer) - sizeof(buffer->buffer) +
+			   new_size);
+	buffer->size = new_size;
+	return buffer;
+}
+
 void
 fifo_buffer_free(struct fifo_buffer *buffer)
 {

src/fifo_buffer.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2010 The Music Player Daemon Project
+ * Copyright (C) 2003-2011 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * Redistribution and use in source and binary forms, with or without
@@ -56,6 +56,18 @@ struct fifo_buffer;
 struct fifo_buffer *
 fifo_buffer_new(size_t size);
 
+/**
+ * Change the capacity of the #fifo_buffer, while preserving existing
+ * data.
+ *
+ * @param buffer the old buffer, may be NULL
+ * @param new_size the requested new size of the #fifo_buffer; must
+ * not be smaller than the data which is stored in the old buffer
+ * @return the new buffer, may be NULL if the requested new size is 0
+ */
+struct fifo_buffer *
+fifo_buffer_realloc(struct fifo_buffer *buffer, size_t new_size);
+
 /**
  * Frees the resources consumed by this #fifo_buffer object.
  */