1 files changed, 159 insertions, 0 deletions
diff --git a/ares_expand_name.c b/ares_expand_name.c
new file mode 100644
index 0000000..1d85b94
--- /dev/null
+++ b/ares_expand_name.c
@@ -0,0 +1,159 @@
+/* Copyright 1998 by the Massachusetts Institute of Technology.
+ *
+ * Permission to use, copy, modify, and distribute this
+ * software and its documentation for any purpose and without
+ * fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting
+ * documentation, and that the name of M.I.T. not be used in
+ * advertising or publicity pertaining to distribution of the
+ * software without specific, written prior permission.
+ * M.I.T. makes no representations about the suitability of
+ * this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ */
+
+static const char rcsid[] = "$Id$";
+
+#include <sys/types.h>
+
+#ifdef WIN32
+#include "nameser.h"
+#else
+#include <netinet/in.h>
+#include <arpa/nameser.h>
+#endif
+
+#include <stdlib.h>
+#include "ares.h"
+
+static int name_length(const unsigned char *encoded, const unsigned char *abuf,
+		       int alen);
+
+/* Expand an RFC1035-encoded domain name given by encoded.  The
+ * containing message is given by abuf and alen.  The result given by
+ * *s, which is set to a NUL-terminated allocated buffer.  *enclen is
+ * set to the length of the encoded name (not the length of the
+ * expanded name; the goal is to tell the caller how many bytes to
+ * move forward to get past the encoded name).
+ *
+ * In the simple case, an encoded name is a series of labels, each
+ * composed of a one-byte length (limited to values between 0 and 63
+ * inclusive) followed by the label contents.  The name is terminated
+ * by a zero-length label.
+ *
+ * In the more complicated case, a label may be terminated by an
+ * indirection pointer, specified by two bytes with the high bits of
+ * the first byte (corresponding to INDIR_MASK) set to 11.  With the
+ * two high bits of the first byte stripped off, the indirection
+ * pointer gives an offset from the beginning of the containing
+ * message with more labels to decode.  Indirection can happen an
+ * arbitrary number of times, so we have to detect loops.
+ *
+ * Since the expanded name uses '.' as a label separator, we use
+ * backslashes to escape periods or backslashes in the expanded name.
+ */
+
+int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
+		     int alen, char **s, int *enclen)
+{
+  int len, indir = 0;
+  char *q;
+  const unsigned char *p;
+
+  len = name_length(encoded, abuf, alen);
+  if (len == -1)
+    return ARES_EBADNAME;
+
+  *s = malloc(len + 1);
+  if (!*s)
+    return ARES_ENOMEM;
+  q = *s;
+
+  /* No error-checking necessary; it was all done by name_length(). */
+  p = encoded;
+  while (*p)
+    {
+      if ((*p & INDIR_MASK) == INDIR_MASK)
+	{
+	  if (!indir)
+	    {
+	      *enclen = p + 2 - encoded;
+	      indir = 1;
+	    }
+	  p = abuf + ((*p & ~INDIR_MASK) << 8 | *(p + 1));
+	}
+      else
+	{
+	  len = *p;
+	  p++;
+	  while (len--)
+	    {
+	      if (*p == '.' || *p == '\\')
+		*q++ = '\\';
+	      *q++ = *p;
+	      p++;
+	    }
+	  *q++ = '.';
+	}
+    }
+  if (!indir)
+    *enclen = p + 1 - encoded;
+
+  /* Nuke the trailing period if we wrote one. */
+  if (q > *s)
+    *(q - 1) = 0;
+
+  return ARES_SUCCESS;
+}
+
+/* Return the length of the expansion of an encoded domain name, or
+ * -1 if the encoding is invalid.
+ */
+static int name_length(const unsigned char *encoded, const unsigned char *abuf,
+		       int alen)
+{
+  int n = 0, offset, indir = 0;
+
+  /* Allow the caller to pass us abuf + alen and have us check for it. */
+  if (encoded == abuf + alen)
+    return -1;
+
+  while (*encoded)
+    {
+      if ((*encoded & INDIR_MASK) == INDIR_MASK)
+	{
+	  /* Check the offset and go there. */
+	  if (encoded + 1 >= abuf + alen)
+	    return -1;
+	  offset = (*encoded & ~INDIR_MASK) << 8 | *(encoded + 1);
+	  if (offset >= alen)
+	    return -1;
+	  encoded = abuf + offset;
+
+	  /* If we've seen more indirects than the message length,
+	   * then there's a loop.
+	   */
+	  if (++indir > alen)
+	    return -1;
+	}
+      else
+	{
+	  offset = *encoded;
+	  if (encoded + offset + 1 >= abuf + alen)
+	    return -1;
+	  encoded++;
+	  while (offset--)
+	    {
+	      n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
+	      encoded++;
+	    }
+	  n++;
+	}
+    }
+
+  /* If there were any labels at all, then the number of dots is one
+   * less than the number of labels, so subtract one.
+   */
+  return (n) ? n - 1 : n;
+}