Add a generic rate-limited log mechanism, and use it in a few places

Incidentally fixes bug 1042.

1 files changed, 28 insertions, 0 deletions

diff --git a/src/common/util.h b/src/common/util.h
index ba38f4c7ed..1e22bd5b1b 100644
--- a/src/common/util.h
+++ b/src/common/util.h
@@ -252,6 +252,34 @@ int ftime_maybe_before(time_t now, time_t when);
 int ftime_definitely_after(time_t now, time_t when);
 int ftime_definitely_before(time_t now, time_t when);
 
+/* Rate-limiter */
+
+/** A ratelim_t remembers how often an event is occurring, and how often
+ * it's allowed to occur.  Typical usage is something like:
+ *
+   <pre>
+    if (possibly_very_frequent_event()) {
+      const int INTERVAL = 300;
+      static ratelim_t warning_limit = RATELIM_INIT(INTERVAL);
+      char *m;
+      if ((m = rate_limit_log(&warning_limit, approx_time()))) {
+        log_warn(LD_GENERAL, "The event occurred!%s", m);
+        tor_free(m);
+      }
+    }
+   </pre>
+ */
+typedef struct ratelim_t {
+  int rate;
+  time_t last_allowed;
+  int n_calls_since_last_time;
+} ratelim_t;
+
+#define RATELIM_INIT(r) { (r), 0, 0 }
+
+int rate_limit_is_ready(ratelim_t *lim, time_t now);
+char *rate_limit_log(ratelim_t *lim, time_t now);
+
 /* File helpers */
 ssize_t write_all(int fd, const char *buf, size_t count, int isSocket);
 ssize_t read_all(int fd, char *buf, size_t count, int isSocket);