Treat the identity transformation as another kind of compression.

This will allow us to treat NO_METHOD as a real compression method,
and to simplify code that currently does

   if (compressing) {
      compress
   } else {
      copy
   }

1 files changed, 53 insertions, 0 deletions

diff --git a/src/common/compress_none.c b/src/common/compress_none.c
new file mode 100644
index 0000000000..b76e6010ec
--- /dev/null
+++ b/src/common/compress_none.c
@@ -0,0 +1,53 @@
+/* Copyright (c) 2004, Roger Dingledine.
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2017, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file compress_lzma.c
+ * \brief Compression backend for identity compression.
+ *
+ * We actually define this backend so that we can treat the identity transform
+ * as another case of compression.
+ *
+ * This module should never be invoked directly. Use the compress module
+ * instead.
+ **/
+
+#include "orconfig.h"
+
+#include "util.h"
+#include "torlog.h"
+#include "compress.h"
+#include "compress_none.h"
+
+/** Transfer some bytes using the identity transformation.  Read up to
+ * *<b>in_len</b> bytes from *<b>in</b>, and write up to *<b>out_len</b> bytes
+ * to *<b>out</b>, adjusting the values as we go.  If <b>finish</b> is true,
+ * we've reached the end of the input.
+ *
+ * Return TOR_COMPRESS_DONE if we've finished the entire
+ * compression/decompression.
+ * Return TOR_COMPRESS_OK if we're processed everything from the input.
+ * Return TOR_COMPRESS_BUFFER_FULL if we're out of space on <b>out</b>.
+ * Return TOR_COMPRESS_ERROR if the stream is corrupt.
+ */
+tor_compress_output_t
+tor_cnone_compress_process(char **out, size_t *out_len,
+                           const char **in, size_t *in_len,
+                           int finish)
+{
+  size_t n_to_copy = MIN(*in_len, *out_len);
+
+  memcpy(*out, *in, n_to_copy);
+  *out += n_to_copy;
+  *in += n_to_copy;
+  *out_len -= n_to_copy;
+  *in_len -= n_to_copy;
+  if (*in_len == 0) {
+    return finish ? TOR_COMPRESS_DONE : TOR_COMPRESS_OK;
+  } else {
+    return TOR_COMPRESS_BUFFER_FULL;
+  }
+}
+