Move the "supported compression bitmask" into compress.[ch]

src/common/compress.c

@@ -277,6 +277,26 @@ tor_compress_supports_method(compress_method_t method)
   }
 }
 
+/**
+ * Return a bitmask of the supported compression types, where 1<<m is
+ * set in the bitmask if and only if compression with method <b>m</b> is
+ * supported.
+ */
+unsigned
+tor_compress_get_supported_method_bitmask(void)
+{
+  static unsigned supported = 0;
+  if (supported == 0) {
+    compress_method_t m;
+    for (m = NO_METHOD; m <= UNKNOWN_METHOD; ++m) {
+      if (tor_compress_supports_method(m)) {
+        supported |= (1u << m);
+      }
+    }
+  }
+  return supported;
+}
+
 /** Table of compression method names.  These should have an "x-" prefix,
  * if they are not listed in the IANA content coding registry. */
 static const struct {

src/common/compress.h

@@ -16,12 +16,12 @@
  * functions here. Call tor_compress_supports_method() to check if a given
  * compression schema is supported by Tor. */
 typedef enum {
-  NO_METHOD=0,
+  NO_METHOD=0, // This method must be first.
   GZIP_METHOD=1,
   ZLIB_METHOD=2,
   LZMA_METHOD=3,
   ZSTD_METHOD=4,
-  UNKNOWN_METHOD=5
+  UNKNOWN_METHOD=5, // This method must be last. Add new ones in the middle.
 } compress_method_t;
 
 /**
@@ -48,6 +48,7 @@ compress_method_t detect_compression_method(const char *in, size_t in_len);
 int tor_compress_is_compression_bomb(size_t size_in, size_t size_out);
 
 int tor_compress_supports_method(compress_method_t method);
+unsigned tor_compress_get_supported_method_bitmask(void);
 const char * compression_method_get_name(compress_method_t method);
 compress_method_t compression_method_get_by_name(const char *name);
 

src/or/directory.c

@@ -2814,20 +2814,6 @@ parse_accept_encoding_header(const char *h)
   return result;
 }
 
-/** Bitmask of supported compression types, to use in a bitwise "and"
- * with the results of parse_accept_encoding_header */
-static const unsigned SUPPORTED_COMPRESSION_MASK =
-    (1u << NO_METHOD)
-  | (1u << ZLIB_METHOD)
-  | (1u << GZIP_METHOD)
-#ifdef HAVE_ZSTD
-  | (1u << ZSTD_METHOD)
-#endif
-#ifdef HAVE_LZMA
-  | (1u << LZMA_METHOD)
-#endif
-  ;
-
 /** Decide whether a client would accept the consensus we have.
  *
  * Clients can say they only want a consensus if it's signed by more
@@ -3028,7 +3014,7 @@ directory_handle_command_get,(dir_connection_t *conn, const char *headers,
   }
 
   /* Remove all methods that we don't both support. */
-  compression_methods_supported &= SUPPORTED_COMPRESSION_MASK;
+  compression_methods_supported &= tor_compress_get_supported_method_bitmask();
 
   get_handler_args_t args;
   args.url = url;