bsdiffpatch-test.c: New file suitable for AFL fuzzing

TL;DR: Fuzzing passed.

See http://lcamtuf.coredump.cx/afl/

The basic idea is we take an arbitary input file, split it in half.
The first half is the original, the second is the modified.  Then do a
roundtrip diff->patch and verify that it worked.

I ran this for 1.5 days on one core, and didn't find any crashes, and
the hangs appeared to be false positives.

Usage:

```
$ afl-fuzz -i input -o findings -- ./bsdiffpatch-test
```

The `input` directory contained a two byte file with `NUL`s - afl
rapidly found other inputs.

This code should hopefully be useful if we ever decide to change the
code in the future, or for anyone who wants to try variants of fuzzing
now.

bsdiffpatch-test.c

@@ -0,0 +1,130 @@
+/*-
+ * Copyright 2015 Colin Walters <[email protected]>
+ * All rights reserved
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted providing that the following conditions 
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. 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 AUTHOR ``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 AUTHOR 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.
+ */
+
+/* Compile with $(pkg-config --cflags --libs glib-2.0) */
+
+#include "bsdiff.h"
+#undef BSDIFF_EXECUTABLE
+#include "bsdiff.c"
+#include "bspatch.c"
+
+#include <glib.h>
+#include <err.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+
+static int
+bsdiff_write_gstring (struct bsdiff_stream *stream,
+		      const void *buf,
+		      int size)
+{
+  g_string_append_len ((GString*)stream->opaque, buf, size);
+  return 0;
+}
+
+typedef struct {
+  GString *buf;
+  size_t off;
+} GStringInputStream;
+
+static int
+gstringin_read (const struct bspatch_stream* stream, void* buffer, int length)
+{
+  GStringInputStream *gin = stream->opaque;
+  size_t rlen = MIN(gin->buf->len - gin->off, length);
+
+  if (rlen == 0)
+    return 0;
+
+  memcpy (buffer, gin->buf->str + gin->off, rlen);
+  gin->off += rlen;
+
+  return 0;
+}
+
+int main(int argc,char *argv[])
+{
+  const char *original = NULL;
+  size_t original_len;
+  const char *modified = NULL;
+  size_t modified_len;
+  GString *gmembuf = g_string_new (NULL);
+  GString *gpatchbuf = g_string_new (NULL);
+
+  {
+    ssize_t bytes_read;
+    char inbuf[1024];
+    while ((bytes_read = read (0, inbuf, sizeof (inbuf))) != 0)
+    g_string_append_len (gmembuf, inbuf, bytes_read);
+    if (bytes_read < 0)
+      err (1, "read");
+    if (gmembuf->len < 2)
+      errx (1, "Input length is less than 2");
+  }
+
+  original = gmembuf->str;
+  original_len = gmembuf->len / 2;
+  modified = original + original_len;
+  modified_len = gmembuf->len - original_len;
+  g_string_free (gmembuf, FALSE);
+  gmembuf = NULL;
+
+  {
+    struct bsdiff_stream stream;
+
+    stream.malloc = malloc;
+    stream.free = free;
+    stream.write = bsdiff_write_gstring;
+    stream.opaque = gpatchbuf;
+    if (bsdiff (original, original_len, modified, modified_len, &stream))
+      err(1, "bsdiff");
+  }
+
+  {
+    GStringInputStream gin = { gpatchbuf, 0 };
+    struct bspatch_stream pstream;
+    GString *newbuf = g_string_new (NULL);
+
+    pstream.opaque = &gin;
+    pstream.read = gstringin_read;
+
+    g_string_set_size (newbuf, modified_len);
+
+    if (bspatch (original, original_len, newbuf->str, modified_len, &pstream))
+      errx (1, "bspatch failed");
+
+    if (memcmp (modified, newbuf->str, modified_len) != 0)
+      errx (1, "bspatch did not reproduce modified content!");
+
+    g_string_free (newbuf, TRUE);
+  }
+
+  /* Free the memory we used */
+  g_string_free (gpatchbuf, TRUE);
+
+  return 0;
+}