#include <zlib.h>

/* z.msg can be NULL if there's no message, in particular for zero length
   input inflate() returns Z_BUF_ERROR with z.msg==NULL */
Lisp_Object
make_z_stream_msg (z_stream *zp, int ret)
{
  if (zp->msg != NULL)
    return build_string (zp->msg);
  else
    return concat2 (build_string ("Zlib error code "),
                    Fnumber_to_string (make_number (ret)));
}

DEFUN ("zlib-inflate-string", Fzlib_inflate_string, Szlib_inflate_string, 1, 1, 0,
       doc: /* Inflate Zlib or Gzip format compressed data.
STR is a unibyte string of compressed data in either Zlib (RFC 1950)
or Gzip (RFC 1952) format.  The return is a unibyte string of the
decompressed result.  An error is thrown for invalid contents.  */)
     (str)
     Lisp_Object str;
{
  z_stream z;
  int ret;
  char buf[4096];
  Lisp_Object lst = Qnil;

  CHECK_STRING (str);

  z.zalloc = Z_NULL;
  z.zfree = Z_NULL;
  z.opaque = Z_NULL;

  z.next_in = (Bytef *) SDATA (str);
  z.avail_in = SBYTES (str);
  z.next_out = (Bytef *) buf;
  z.avail_out = sizeof (buf);

  /* ask to accept either gzip or zlib header formats */
  ret = inflateInit2 (&z, 32 + 15);
  if (ret != Z_OK)
    xsignal1 (Qerror, concat2 (build_string ("Zlib inflateInit2: "),
                               make_z_stream_msg (&z, ret)));

  for (;;)
    {
      ret = inflate (&z, Z_NO_FLUSH);
      if (ret != Z_OK && ret != Z_STREAM_END)
        {
          Lisp_Object msg = make_z_stream_msg (&z, ret);
          inflateEnd (&z);
          xsignal1 (Qerror, concat2 (build_string ("Zlib inflate: "), msg));
        }

      if (z.avail_out == 0 || ret == Z_STREAM_END)
        {
          lst = Fcons (make_unibyte_string (buf, sizeof (buf) - z.avail_out),
                       lst);
          z.next_out = (Bytef *) buf;
          z.avail_out = sizeof (buf);
        }

      if (ret == Z_STREAM_END)
        break;
    }

  if (z.avail_in != 0)
    {
      ret = inflateEnd (&z);
      error ("Garbage after compressed data");
    }

  ret = inflateEnd (&z);
  if (ret != Z_OK)
    xsignal1 (Qerror, concat2 (build_string ("Zlib inflateEnd: "),
                               make_z_stream_msg (&z, ret)));

  return apply1 (intern ("concat"), Fnreverse (lst));
}