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diff --git a/src/mbuf.h b/src/mbuf.h
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+/*
+ * Copyright (c) 2018 Richard Braun.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ * Upstream site with license notes :
+ * http://git.sceen.net/rbraun/librbraun.git/
+ *
+ *
+ * FIFO message buffer.
+ */
+
+#ifndef MBUF_H
+#define MBUF_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+#include "cbuf.h"
+
+/*
+ * Message buffer.
+ *
+ * Message buffers are built on top of circular byte buffers. They provide
+ * discrete message transfer from a producer to a consumer.
+ */
+struct mbuf {
+    struct cbuf cbuf;
+};
+
+/*
+ * Initialize a message buffer.
+ *
+ * The descriptor is set to use the given buffer for storage. Capacity
+ * must be a power-of-two.
+ */
+void mbuf_init(struct mbuf *mbuf, void *buf, size_t capacity);
+
+/*
+ * Clear a message buffer.
+ */
+void mbuf_clear(struct mbuf *mbuf);
+
+/*
+ * Push a message to a message buffer.
+ *
+ * If the message doesn't fit in the message buffer, either because it is
+ * larger than the capacity, or because the function isn't allowed to erase
+ * old messages and the message buffer doesn't have enough available memory
+ * for the new message, EMSGSIZE is returned.
+ */
+int mbuf_push(struct mbuf *mbuf, const void *buf, size_t size, bool erase);
+
+/*
+ * Pop a message from a message buffer.
+ *
+ * On entry, the sizep argument points to the size of the output buffer.
+ * On return, it is updated to the size of the message. If the message
+ * doesn't fit in the output buffer, it is not popped, EMSGSIZE is
+ * returned, but the sizep argument is updated nonetheless to let the
+ * user know the message size, to potentially retry with a larger buffer.
+ *
+ * If the buffer is empty, EAGAIN is returned, and the size of the output
+ * buffer is unmodified.
+ *
+ * The output buffer may be NULL, in which case this function acts as if
+ * it wasn't, but without writing output data.
+ */
+int mbuf_pop(struct mbuf *mbuf, void *buf, size_t *sizep);
+
+#endif /* MBUF_H */