Warn on zstd header/library version mismatch

If we're going to potentially degrade performance in this case, we
may as well tell people so.

src/common/compress.c

@@ -663,3 +663,13 @@ tor_compress_init(void)
   tor_zstd_init();
 }
 
+/** Warn if we had any problems while setting up our compression libraries.
+ *
+ * (This isn't part of tor_compress_init, since the logs aren't set up yet.)
+ */
+void
+tor_compress_log_init_warnings(void)
+{
+  tor_zstd_warn_if_version_mismatched();
+}
+

src/common/compress.h

@@ -87,6 +87,7 @@ void tor_compress_free_(tor_compress_state_t *state);
 size_t tor_compress_state_size(const tor_compress_state_t *state);
 
 void tor_compress_init(void);
+void tor_compress_log_init_warnings(void);
 
 #endif /* !defined(TOR_COMPRESS_H) */
 

src/common/compress_zstd.c

@@ -58,21 +58,29 @@ tor_zstd_method_supported(void)
 #endif
 }
 
+/** Format a zstd version number as a string in <b>buf</b>. */
+static void
+tor_zstd_format_version(char *buf, size_t buflen, unsigned version_number)
+{
+  tor_snprintf(buf, buflen,
+               "%u.%u.%u",
+               version_number / 10000 % 100,
+               version_number / 100 % 100,
+               version_number % 100);
+}
+
+#define VERSION_STR_MAX_LEN 16 /* more than enough space for 99.99.99 */
+
 /** Return a string representation of the version of the currently running
  * version of libzstd. Returns NULL if Zstandard is unsupported. */
 const char *
 tor_zstd_get_version_str(void)
 {
 #ifdef HAVE_ZSTD
-  static char version_str[16];
-  size_t version_number;
+  static char version_str[VERSION_STR_MAX_LEN];
 
-  version_number = ZSTD_versionNumber();
-  tor_snprintf(version_str, sizeof(version_str),
-               "%d.%d.%d",
-               (int) version_number / 10000 % 100,
-               (int) version_number / 100 % 100,
-               (int) version_number % 100);
+  tor_zstd_format_version(version_str, sizeof(version_str),
+                          ZSTD_versionNumber());
 
   return version_str;
 #else /* !(defined(HAVE_ZSTD)) */
@@ -487,6 +495,27 @@ tor_zstd_init(void)
   atomic_counter_init(&total_zstd_allocation);
 }
 
+/** Warn if the header and library versions don't match. */
+void
+tor_zstd_warn_if_version_mismatched(void)
+{
+#ifdef HAVE_ZSTD
+  if (! tor_zstd_can_use_static_apis()) {
+    char header_version[VERSION_STR_MAX_LEN];
+    char runtime_version[VERSION_STR_MAX_LEN];
+    tor_zstd_format_version(header_version, sizeof(header_version),
+                            ZSTD_VERSION_NUMBER);
+    tor_zstd_format_version(runtime_version, sizeof(runtime_version),
+                            ZSTD_versionNumber());
+
+    log_warn(LD_GENERAL,
+             "Tor was compiled with zstd %s, but is running with zstd %s. "
+             "For safety, we'll avoid using advanced zstd functionality.",
+             header_version, runtime_version);
+  }
+#endif
+}
+
 #ifdef TOR_UNIT_TESTS
 /** Testing only: disable usage of static-only APIs, so we can make sure that
  * we still work without them. */
@@ -496,3 +525,4 @@ tor_zstd_set_static_apis_disabled_for_testing(int disabled)
   static_apis_disable_for_testing = disabled;
 }
 #endif
+

src/common/compress_zstd.h

@@ -43,6 +43,7 @@ size_t tor_zstd_compress_state_size(const tor_zstd_compress_state_t *state);
 size_t tor_zstd_get_total_allocation(void);
 
 void tor_zstd_init(void);
+void tor_zstd_warn_if_version_mismatched(void);
 
 #ifdef TOR_UNIT_TESTS
 void tor_zstd_set_static_apis_disabled_for_testing(int disabled);

src/or/main.c

@@ -3323,6 +3323,8 @@ tor_init(int argc, char *argv[])
     if (strstr(version, "alpha") || strstr(version, "beta"))
       log_notice(LD_GENERAL, "This version is not a stable Tor release. "
                  "Expect more bugs than usual.");
+
+    tor_compress_log_init_warnings();
   }
 
 #ifdef HAVE_RUST