Add a reference counted buffer implementation.

This implementation introduces the notion of a 'slice'. A slice is
simply a sub-buffer of the original buffer. Slices refer to their
parent buffer so no memory is copied and slice creation becomes an
O(1) operation. Although I'm introducing a new concept, in practice,
a slice is indistinguishable from a buffer (they share a type and
all operations).

I expect slices to be used heavily during packet construction. For
example, an RFCOMM implementation would request a buffer from the
L2CAP layer (which may in turn request a buffer from the HCI layer).
The L2CAP layer would reserve some space in the buffer for its header
and return a slice to the RFCOMM layer.

1 files changed, 56 insertions, 0 deletions

diff --git a/osi/include/buffer.h b/osi/include/buffer.h
new file mode 100644
index 000000000..51d23a537
--- /dev/null
+++ b/osi/include/buffer.h
@@ -0,0 +1,56 @@
+/******************************************************************************
+ *
+ *  Copyright (C) 2014 Google, Inc.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at:
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ ******************************************************************************/
+
+#pragma once
+
+#include <stdbool.h>
+#include <stddef.h>
+
+typedef struct buffer_t buffer_t;
+
+// Returns a new buffer of |size| bytes. Returns NULL if a buffer could not be
+// allocated. |size| must be non-zero. The caller must release this buffer with
+// |buffer_free|.
+buffer_t *buffer_new(size_t size);
+
+// Creates a new reference to the buffer |buf|. A reference is indistinguishable
+// from the original: writes to the original will be reflected in the reference
+// and vice versa. In other words, this function creates an alias to |buf|. The
+// caller must release the returned buffer with |buffer_free|. Note that releasing
+// the returned buffer does not release |buf|. |buf| must not be NULL.
+buffer_t *buffer_new_ref(const buffer_t *buf);
+
+// Creates a new reference to the last |slice_size| bytes of |buf|. See
+// |buffer_new_ref| for a description of references. |slice_size| must be
+// greater than 0 and may be at most |buffer_length|
+// (0 < slice_size <= buffer_length). |buf| must not be NULL.
+buffer_t *buffer_new_slice(const buffer_t *buf, size_t slice_size);
+
+// Frees a buffer object. |buf| may be NULL.
+void buffer_free(buffer_t *buf);
+
+// Returns a pointer to a writeable memory region for |buf|. All references
+// and slices that share overlapping bytes will also be written to when
+// writing to the returned pointer. The caller may safely write up to
+// |buffer_length| consecutive bytes starting at the address returned by
+// this function. |buf| must not be NULL.
+void *buffer_ptr(const buffer_t *buf);
+
+// Returns the length of the writeable memory region referred to by |buf|.
+// |buf| must not be NULL.
+size_t buffer_length(const buffer_t *buf);