fifo_buffer: added buffering library

It is a library which I have written years ago for other projects.
This library is licensed under BSD 2-clause, because it is very
generic.

Makefile.am

@@ -61,6 +61,7 @@ mpd_headers = \
 	src/encoder_plugin.h \
 	src/encoder_list.h \
 	src/encoder_api.h \
+	src/fifo_buffer.h \
 	src/update.h \
 	src/dirvec.h \
 	src/gcc.h \
@@ -177,6 +178,7 @@ src_mpd_SOURCES = \
 	src/directory_print.c \
 	src/database.c \
 	src/dirvec.c \
+	src/fifo_buffer.c \
 	src/update.c \
 	src/client.c \
 	src/listen.c \

src/fifo_buffer.c

@@ -0,0 +1,160 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "fifo_buffer.h"
+
+#include <glib.h>
+
+#include <assert.h>
+#include <string.h>
+
+struct fifo_buffer {
+	size_t size, start, end;
+	unsigned char buffer[sizeof(size_t)];
+};
+
+struct fifo_buffer *
+fifo_buffer_new(size_t size)
+{
+	struct fifo_buffer *buffer;
+
+	assert(size > 0);
+
+	buffer = (struct fifo_buffer *)g_malloc(sizeof(*buffer) -
+						sizeof(buffer->buffer) + size);
+
+	buffer->size = size;
+	buffer->start = 0;
+	buffer->end = 0;
+
+	return buffer;
+}
+
+void
+fifo_buffer_free(struct fifo_buffer *buffer)
+{
+	assert(buffer != NULL);
+
+	g_free(buffer);
+}
+
+void
+fifo_buffer_clear(struct fifo_buffer *buffer)
+{
+	assert(buffer != NULL);
+
+	buffer->start = 0;
+	buffer->end = 0;
+}
+
+const void *
+fifo_buffer_read(const struct fifo_buffer *buffer, size_t *length_r)
+{
+	assert(buffer != NULL);
+	assert(buffer->end >= buffer->start);
+	assert(length_r != NULL);
+
+	if (buffer->start == buffer->end)
+		/* the buffer is empty */
+		return NULL;
+
+	*length_r = buffer->end - buffer->start;
+	return buffer->buffer + buffer->start;
+}
+
+void
+fifo_buffer_consume(struct fifo_buffer *buffer, size_t length)
+{
+	assert(buffer != NULL);
+	assert(buffer->end >= buffer->start);
+	assert(buffer->start + length <= buffer->end);
+
+	buffer->start += length;
+}
+
+/**
+ * Move data to the beginning of the buffer, to make room at the end.
+ */
+static void
+fifo_buffer_move(struct fifo_buffer *buffer)
+{
+	if (buffer->start == 0)
+		return;
+
+	if (buffer->end > buffer->start)
+		memmove(buffer->buffer,
+			buffer->buffer + buffer->start,
+			buffer->end - buffer->start);
+
+	buffer->end -= buffer->start;
+	buffer->start = 0;
+}
+
+void *
+fifo_buffer_write(struct fifo_buffer *buffer, size_t *max_length_r)
+{
+	assert(buffer != NULL);
+	assert(buffer->end <= buffer->size);
+	assert(max_length_r != NULL);
+
+	if (buffer->end == buffer->size) {
+		fifo_buffer_move(buffer);
+		if (buffer->end == buffer->size)
+			return NULL;
+	} else if (buffer->start > 0 && buffer->start == buffer->end) {
+		buffer->start = 0;
+		buffer->end = 0;
+	}
+
+	*max_length_r = buffer->size - buffer->end;
+	return buffer->buffer + buffer->end;
+}
+
+void
+fifo_buffer_append(struct fifo_buffer *buffer, size_t length)
+{
+	assert(buffer != NULL);
+	assert(buffer->end >= buffer->start);
+	assert(buffer->end + length <= buffer->size);
+
+	buffer->end += length;
+}
+
+bool
+fifo_buffer_is_empty(struct fifo_buffer *buffer)
+{
+	return buffer->start == buffer->end;
+}
+
+bool
+fifo_buffer_is_full(struct fifo_buffer *buffer)
+{
+	return buffer->start == 0 && buffer->end == buffer->size;
+}

src/fifo_buffer.h

@@ -0,0 +1,128 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/** \file
+ *
+ * This is a general purpose FIFO buffer library.  You may append data
+ * at the end, while another instance reads data from the beginning.
+ * It is optimized for zero-copy usage: you get pointers to the real
+ * buffer, where you may operate on.
+ *
+ * This library is not thread safe.
+ */
+
+#ifndef MPD_FIFO_BUFFER_H
+#define MPD_FIFO_BUFFER_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+struct fifo_buffer;
+
+/**
+ * Creates a new #fifo_buffer object.  Free this object with
+ * fifo_buffer_free().
+ *
+ * @param size the size of the buffer in bytes
+ * @return the new #fifo_buffer object
+ */
+struct fifo_buffer *
+fifo_buffer_new(size_t size);
+
+/**
+ * Frees the resources consumed by this #fifo_buffer object.
+ */
+void
+fifo_buffer_free(struct fifo_buffer *buffer);
+
+/**
+ * Clears all data currently in this #fifo_buffer object.  This does
+ * not overwrite the actuall buffer; it just resets the internal
+ * pointers.
+ */
+void
+fifo_buffer_clear(struct fifo_buffer *buffer);
+
+/**
+ * Reads from the beginning of the buffer.  To remove consumed data
+ * from the buffer, call fifo_buffer_consume().
+ *
+ * @param buffer the #fifo_buffer object
+ * @param length_r the maximum amount to read is returned here
+ * @return a pointer to the beginning of the buffer, or NULL if the
+ * buffer is empty
+ */
+const void *
+fifo_buffer_read(const struct fifo_buffer *buffer, size_t *length_r);
+
+/**
+ * Marks data at the beginning of the buffer as "consumed".
+ *
+ * @param buffer the #fifo_buffer object
+ * @param length the number of bytes which were consumed
+ */
+void
+fifo_buffer_consume(struct fifo_buffer *buffer, size_t length);
+
+/**
+ * Prepares writing to the buffer.  This returns a buffer which you
+ * can write to.  To commit the write operation, call
+ * fifo_buffer_append().
+ *
+ * @param buffer the #fifo_buffer object
+ * @param max_length_r the maximum amount to write is returned here
+ * @return a pointer to the end of the buffer, or NULL if the buffer
+ * is already full
+ */
+void *
+fifo_buffer_write(struct fifo_buffer *buffer, size_t *max_length_r);
+
+/**
+ * Commits the write operation initiated by fifo_buffer_write().
+ *
+ * @param buffer the #fifo_buffer object
+ * @param length the number of bytes which were written
+ */
+void
+fifo_buffer_append(struct fifo_buffer *buffer, size_t length);
+
+/**
+ * Checks if the buffer is empty.
+ */
+bool
+fifo_buffer_is_empty(struct fifo_buffer *buffer);
+
+/**
+ * Checks if the buffer is full.
+ */
+bool
+fifo_buffer_is_full(struct fifo_buffer *buffer);
+
+#endif