Logging improvements: add tracing, level check

* Add WEBDIS_TRACE log level for internal operations
* Warn when verbosity config is invalid
* Add slog_enabled to bypass buffer allocations if the level is filtered

src/conf.c

@@ -159,9 +159,11 @@ conf_read(const char *filename) {
 			}
 		} else if(strcmp(json_object_iter_key(kv),"verbosity") == 0 && json_typeof(jtmp) == JSON_INTEGER){
 			int tmp = json_integer_value(jtmp);
-			if(tmp < 0) conf->verbosity = WEBDIS_ERROR;
-			else if(tmp > (int)WEBDIS_DEBUG) conf->verbosity = WEBDIS_DEBUG;
-			else conf->verbosity = (log_level)tmp;
+			if(tmp < 0 || tmp > (int)WEBDIS_TRACE) {
+				fprintf(stderr, "Invalid log verbosity: %d. Acceptable range: [%d .. %d]\n",
+					tmp, WEBDIS_ERROR, WEBDIS_TRACE);
+			}
+			conf->verbosity = (tmp < 0 ? WEBDIS_ERROR : (tmp > WEBDIS_TRACE ? WEBDIS_TRACE : (log_level)tmp));
 		} else if(strcmp(json_object_iter_key(kv), "daemonize") == 0 && json_typeof(jtmp) == JSON_TRUE) {
 			conf->daemonize = 1;
 		} else if(strcmp(json_object_iter_key(kv), "daemonize") == 0 && json_typeof(jtmp) == JSON_STRING) {

src/slog.c

@@ -76,6 +76,14 @@ slog_fsync_init(struct server *s) {
 	}
 }
 
+/**
+ * Returns whether this log level is enabled.
+ */
+int
+slog_enabled(struct server *s, log_level level) {
+	return level <= s->cfg->verbosity ? 1 : 0;
+}
+
 /**
  * Write log message to disk, or stderr.
  */
@@ -83,6 +91,8 @@ void
 slog(struct server *s, log_level level,
 		const char *body, size_t sz) {
 
+	if(level > s->cfg->verbosity) return; /* too verbose */
+
 	const char *c = "EWNID";
 	time_t now;
 	struct tm now_tm, *lt_ret;
@@ -91,8 +101,6 @@ slog(struct server *s, log_level level,
 	char line[256]; /* bounds are checked. */
 	int line_sz, ret;
 
-	if(level > s->cfg->verbosity) return; /* too verbose */
-
 	if(!s->log.fd) return;
 
 	/* limit message size */

src/slog.h

@@ -6,7 +6,8 @@ typedef enum {
 	WEBDIS_WARNING,
 	WEBDIS_NOTICE,
 	WEBDIS_INFO,
-	WEBDIS_DEBUG
+	WEBDIS_DEBUG,
+	WEBDIS_TRACE
 } log_level;
 
 typedef enum {
@@ -26,6 +27,9 @@ slog_init(struct server *s);
 void
 slog_fsync_init(struct server *s);
 
+int
+slog_enabled(struct server *s, log_level level);
+
 void slog(struct server *s, log_level level,
 		const char *body, size_t sz);