shl: add ring-buffer helpers

The shl_ring helpers manage a dynamically-growing ring-buffer. We need
that for the following RTSP stream parsers, so add them to src/shared/.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

Makefile.am

@@ -77,6 +77,8 @@ libmiracle_shared_la_SOURCES = \
 	src/shared/shl_log.h \
 	src/shared/shl_log.c \
 	src/shared/shl_macro.h \
+	src/shared/shl_ring.h \
+	src/shared/shl_ring.c \
 	src/shared/shl_util.h \
 	src/shared/shl_util.c \
 	src/shared/util.h \

src/shared/shl_ring.c

@@ -0,0 +1,188 @@
+/*
+ * SHL - Ring buffer
+ *
+ * Copyright (c) 2011-2013 David Herrmann <dh.herrmann@gmail.com>
+ * Dedicated to the Public Domain
+ */
+
+/*
+ * Ring buffer
+ */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/uio.h>
+#include "shl_macro.h"
+#include "shl_ring.h"
+
+#define RING_MASK(_r, _v) ((_v) & ((_r)->size - 1))
+
+void shl_ring_flush(struct shl_ring *r)
+{
+	r->start = 0;
+	r->used = 0;
+}
+
+void shl_ring_clear(struct shl_ring *r)
+{
+	free(r->buf);
+	memset(r, 0, sizeof(*r));
+}
+
+/*
+ * Get data pointers for current ring-buffer data. @vec must be an array of 2
+ * iovec objects. They are filled according to the data available in the
+ * ring-buffer. 0, 1 or 2 is returned according to the number of iovec objects
+ * that were filled (0 meaning buffer is empty).
+ *
+ * Hint: "struct iovec" is defined in <sys/uio.h> and looks like this:
+ *     struct iovec {
+ *         void *iov_base;
+ *         size_t iov_len;
+ *     };
+ */
+size_t shl_ring_peek(struct shl_ring *r, struct iovec *vec)
+{
+	if (r->used == 0) {
+		return 0;
+	} else if (r->start + r->used <= r->size) {
+		if (vec) {
+			vec[0].iov_base = &r->buf[r->start];
+			vec[0].iov_len = r->used;
+		}
+		return 1;
+	} else {
+		if (vec) {
+			vec[0].iov_base = &r->buf[r->start];
+			vec[0].iov_len = r->size - r->start;
+			vec[1].iov_base = r->buf;
+			vec[1].iov_len = r->used - (r->size - r->start);
+		}
+		return 2;
+	}
+}
+
+/*
+ * Copy data from the ring buffer into the linear external buffer @buf. Copy
+ * at most @size bytes. If the ring buffer size is smaller, copy less bytes and
+ * return the number of bytes copied.
+ */
+size_t shl_ring_copy(struct shl_ring *r, void *buf, size_t size)
+{
+	size_t l;
+
+	if (size > r->used)
+		size = r->used;
+
+	if (size > 0) {
+		l = r->size - r->start;
+		if (size <= l) {
+			memcpy(buf, &r->buf[r->start], size);
+		} else {
+			memcpy(buf, &r->buf[r->start], l);
+			memcpy((uint8_t*)buf + l, r->buf, size - l);
+		}
+	}
+
+	return size;
+}
+
+/*
+ * Resize ring-buffer to size @nsize. @nsize must be a power-of-2, otherwise
+ * ring operations will behave incorrectly.
+ */
+static int ring_resize(struct shl_ring *r, size_t nsize)
+{
+	uint8_t *buf;
+	size_t l;
+
+	buf = malloc(nsize);
+	if (!buf)
+		return -ENOMEM;
+
+	if (r->used > 0) {
+		l = r->size - r->start;
+		if (r->used <= l) {
+			memcpy(buf, &r->buf[r->start], r->used);
+		} else {
+			memcpy(buf, &r->buf[r->start], l);
+			memcpy(&buf[l], r->buf, r->used - l);
+		}
+	}
+
+	free(r->buf);
+	r->buf = buf;
+	r->size = nsize;
+	r->start = 0;
+
+	return 0;
+}
+
+/*
+ * Resize ring-buffer to provide enough room for @add bytes of new data. This
+ * resizes the buffer if it is too small. It returns -ENOMEM on OOM and 0 on
+ * success.
+ */
+static int ring_grow(struct shl_ring *r, size_t add)
+{
+	size_t need;
+
+	if (r->size - r->used >= add)
+		return 0;
+
+	need = r->used + add;
+	if (need <= r->used)
+		return -ENOMEM;
+	else if (need < 4096)
+		need = 4096;
+
+	need = SHL_ALIGN_POWER2(need);
+	if (need == 0)
+		return -ENOMEM;
+
+	return ring_resize(r, need);
+}
+
+/*
+ * Push @len bytes from @u8 into the ring buffer. The buffer is resized if it
+ * is too small. -ENOMEM is returned on OOM, 0 on success.
+ */
+int shl_ring_push(struct shl_ring *r, const void *u8, size_t size)
+{
+	int err;
+	size_t pos, l;
+
+	if (size == 0)
+		return 0;
+
+	err = ring_grow(r, size);
+	if (err < 0)
+		return err;
+
+	pos = RING_MASK(r, r->start + r->used);
+	l = r->size - pos;
+	if (l >= size) {
+		memcpy(&r->buf[pos], u8, size);
+	} else {
+		memcpy(&r->buf[pos], u8, l);
+		memcpy(r->buf, (const uint8_t*)u8 + l, size - l);
+	}
+
+	r->used += size;
+
+	return 0;
+}
+
+/*
+ * Remove @len bytes from the start of the ring-buffer. Note that we protect
+ * against overflows so removing more bytes than available is safe.
+ */
+void shl_ring_pull(struct shl_ring *r, size_t size)
+{
+	if (size > r->used)
+		size = r->used;
+
+	r->start = RING_MASK(r, r->start + size);
+	r->used -= size;
+}

src/shared/shl_ring.h

@@ -0,0 +1,52 @@
+/*
+ * SHL - Ring buffer
+ *
+ * Copyright (c) 2011-2013 David Herrmann <dh.herrmann@gmail.com>
+ * Dedicated to the Public Domain
+ */
+
+/*
+ * Ring buffer
+ */
+
+#ifndef SHL_RING_H
+#define SHL_RING_H
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/uio.h>
+
+struct shl_ring {
+	uint8_t *buf;		/* buffer or NULL */
+	size_t size;		/* actual size of @buf */
+	size_t start;		/* start position of ring */
+	size_t used;		/* number of actually used bytes */
+};
+
+/* flush buffer so it is empty again */
+void shl_ring_flush(struct shl_ring *r);
+
+/* flush buffer, free allocated data and reset to initial state */
+void shl_ring_clear(struct shl_ring *r);
+
+/* get pointers to buffer data and their length */
+size_t shl_ring_peek(struct shl_ring *r, struct iovec *vec);
+
+/* copy data into external linear buffer */
+size_t shl_ring_copy(struct shl_ring *r, void *buf, size_t size);
+
+/* push data to the end of the buffer */
+int shl_ring_push(struct shl_ring *r, const void *u8, size_t size);
+
+/* pull data from the front of the buffer */
+void shl_ring_pull(struct shl_ring *r, size_t size);
+
+/* return size of occupied buffer in bytes */
+static inline size_t shl_ring_get_size(struct shl_ring *r)
+{
+	return r->used;
+}
+
+#endif  /* SHL_RING_H */