lavu: add av_bprintf and related.

1 files changed, 136 insertions, 0 deletions

diff --git a/libavutil/bprint.h b/libavutil/bprint.h
new file mode 100644
index 0000000000..c5d750df8b
--- /dev/null
+++ b/libavutil/bprint.h
@@ -0,0 +1,136 @@
+/*
+ * Copyright (c) 2012 Nicolas George
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVUTIL_BPRINT_H
+#define AVUTIL_BPRINT_H
+
+#include "attributes.h"
+
+/**
+ * Define a structure with extra padding to a fixed size
+ * This helps ensuring binary compatibility with future versions.
+ */
+#define FF_PAD_STRUCTURE(size, ...) \
+    __VA_ARGS__ \
+    char reserved_padding[size - sizeof(struct { __VA_ARGS__ })];
+
+/**
+ * Buffer to print data progressively
+ *
+ * The string buffer grows as necessary and is always 0-terminated.
+ * The content of the string is never accessed, and thus is
+ * encoding-agnostic and can even hold binary data.
+ *
+ * Small buffers are kept in the structure itself, and thus require no
+ * memory allocation at all (unless the contents of the buffer is needed
+ * after the structure goes out of scope). This is almost as lightweight as
+ * declaring a local "char buf[512]".
+ *
+ * The length of the string can go beyond the allocated size: the buffer is
+ * then truncated, but the functions still keep account of the actual total
+ * length.
+ *
+ * In other words, buf->len can be greater than buf->size and records the
+ * total length of what would have been to the buffer if there had been
+ * enough memory.
+ *
+ * Append operations do not need to be tested for failure: if a memory
+ * allocation fails, data stop being appended to the buffer, but the length
+ * is still updated. This situation can be tested with
+ * av_bprint_is_complete().
+ *
+ * The size_max field determines several possible behaviours:
+ *
+ * size_max = -1 (= UINT_MAX) or any large value will let the buffer be
+ * reallocated as necessary, with an amortized linear cost.
+ *
+ * size_max = 0 prevents writing anything to the buffer: only the total
+ * length is computed. The write operations can then possibly be repeated in
+ * a buffer with exactly the necessary size
+ * (using size_init = size_max = len + 1).
+ *
+ * size_max = 1 is automatically replaced by the exact size available in the
+ * structure itself, thus ensuring no dynamic memory allocation. The
+ * internal buffer is large enough to hold a reasonable paragraph of text,
+ * such as the current paragraph.
+ */
+typedef struct AVBPrint {
+    FF_PAD_STRUCTURE(1024,
+    char *str;         /** string so far */
+    unsigned len;      /** length so far */
+    unsigned size;     /** allocated memory */
+    unsigned size_max; /** maximum allocated memory */
+    char reserved_internal_buffer[1];
+    )
+} AVBPrint;
+
+/**
+ * Init a print buffer.
+ *
+ * @param buf        buffer to init
+ * @param size_init  initial size (including the final 0)
+ * @param size_max   maximum size;
+ *                   0 means do not write anything, just count the length;
+ *                   1 is replaced by the maximum value for automatic storage
+ */
+void av_bprint_init(AVBPrint *buf, unsigned size_init, unsigned size_max);
+
+/**
+ * Convenience macros for special values for size_max.
+ */
+#define AV_BPRINT_SIZE_UNLIMITED  ((unsigned)-1)
+#define AV_BPRINT_SIZE_AUTOMATIC  1
+#define AV_BPRINT_SIZE_COUNT_ONLY 0
+
+/**
+ * Append a formated string to a print buffer.
+ */
+void av_bprintf(AVBPrint *buf, const char *fmt, ...) av_printf_format(2, 3);
+
+/**
+ * Append char c n times to a print buffer.
+ */
+void av_bprint_chars(AVBPrint *buf, char c, unsigned n);
+
+/**
+ * Test if the print buffer is complete (not truncated).
+ *
+ * It may have been truncated due to a memory allocation failure
+ * or the size_max limit (compare size and size_max if necessary).
+ */
+static inline int av_bprint_is_complete(AVBPrint *buf)
+{
+    return buf->len < buf->size;
+}
+
+/**
+ * Finalize a print buffer.
+ *
+ * The print buffer can no longer be used afterwards,
+ * but the len and size fields are still valid.
+ *
+ * @arg[out] ret_str  if not NULL, used to return a permanent copy of the
+ *                    buffer contents, or NULL if memory allocation fails;
+ *                    if NULL, the buffer is discarded and freed
+ * @return  0 for success or error code (probably AVERROR(ENOMEM))
+ */
+int av_bprint_finalize(AVBPrint *buf, char **ret_str);
+
+#endif /* AVUTIL_BPRINT_H */