Add prometheus metrics

Makefile.in

@@ -31,6 +31,8 @@ chrootdir= @chrootdir@
 user = @user@
 DNSTAP_SRC=@DNSTAP_SRC@
 DNSTAP_OBJ=@DNSTAP_OBJ@
+METRICS_SRC=@METRICS_SRC@
+METRICS_OBJ=@METRICS_OBJ@
 
 # override $U variable which is used by autotools for deansification (for
 # K&R C compilers), but causes problems if $U is defined in the env).
@@ -88,7 +90,7 @@ TARGETS=nsd nsd-checkconf nsd-checkzone nsd-control nsd.conf.sample nsd-control-
 MANUALS=nsd.8 nsd-checkconf.8 nsd-checkzone.8 nsd-control.8 nsd.conf.5
 
 COMMON_OBJ=answer.o axfr.o ixfr.o ixfrcreate.o buffer.o configlexer.o configparser.o dname.o dns.o edns.o iterated_hash.o lookup3.o namedb.o nsec3.o options.o packet.o query.o rbtree.o radtree.o rdata.o region-allocator.o rrl.o siphash.o tsig.o tsig-openssl.o udb.o util.o bitset.o popen3.o proxy_protocol.o
-XFRD_OBJ=xfrd-catalog-zones.o xfrd-disk.o xfrd-notify.o xfrd-tcp.o xfrd.o remote.o $(DNSTAP_OBJ)
+XFRD_OBJ=xfrd-catalog-zones.o xfrd-disk.o xfrd-notify.o xfrd-tcp.o xfrd.o remote.o $(METRICS_OBJ) $(DNSTAP_OBJ)
 NSD_OBJ=$(COMMON_OBJ) $(XFRD_OBJ) difffile.o ipc.o mini_event.o netio.o nsd.o server.o dbaccess.o dbcreate.o zonec.o verify.o
 ALL_OBJ=$(NSD_OBJ) nsd-checkconf.o nsd-checkzone.o nsd-control.o nsd-mem.o xfr-inspect.o
 NSD_CHECKCONF_OBJ=$(COMMON_OBJ) nsd-checkconf.o
@@ -408,6 +410,7 @@ configparser.o: configparser.c config.h configparser.h
 options.o: $(srcdir)/options.c config.h configparser.h
 dns.o: $(srcdir)/dns.c config.h
 zonec.o: $(srcdir)/zonec.c config.h
+metrics.o: $(srcdir)/metrics.c config.h
 
 # dnstap
 dnstap.o:	$(srcdir)/dnstap/dnstap.c config.h dnstap/dnstap_config.h \

configlexer.lex

@@ -258,6 +258,10 @@ server-key-file{COLON}	{ LEXOUT(("v(%s) ", yytext)); return VAR_SERVER_KEY_FILE;
 server-cert-file{COLON}	{ LEXOUT(("v(%s) ", yytext)); return VAR_SERVER_CERT_FILE;}
 control-key-file{COLON}	{ LEXOUT(("v(%s) ", yytext)); return VAR_CONTROL_KEY_FILE;}
 control-cert-file{COLON}	{ LEXOUT(("v(%s) ", yytext)); return VAR_CONTROL_CERT_FILE;}
+metrics-enable{COLON}	{ LEXOUT(("v(%s) ", yytext)); return VAR_METRICS_ENABLE;}
+metrics-interface{COLON}	{ LEXOUT(("v(%s) ", yytext)); return VAR_METRICS_INTERFACE;}
+metrics-port{COLON}	{ LEXOUT(("v(%s) ", yytext)); return VAR_METRICS_PORT;}
+metrics-path{COLON}	{ LEXOUT(("v(%s) ", yytext)); return VAR_METRICS_PATH;}
 AXFR			{ LEXOUT(("v(%s) ", yytext)); return VAR_AXFR;}
 UDP			{ LEXOUT(("v(%s) ", yytext)); return VAR_UDP;}
 rrl-size{COLON}		{ LEXOUT(("v(%s) ", yytext)); return VAR_RRL_SIZE;}

configparser.y

@@ -139,6 +139,10 @@ struct component {
 %token VAR_DROP_UPDATES
 %token VAR_XFRD_TCP_MAX
 %token VAR_XFRD_TCP_PIPELINE
+%token VAR_METRICS_ENABLE
+%token VAR_METRICS_INTERFACE
+%token VAR_METRICS_PORT
+%token VAR_METRICS_PATH
 
 /* dnstap */
 %token VAR_DNSTAP
@@ -588,6 +592,40 @@ server_option:
         }
       }
     }
+  | VAR_METRICS_ENABLE boolean
+    {
+#ifdef USE_METRICS
+      cfg_parser->opt->metrics_enable = $2;
+#endif /* USE_METRICS */
+    }
+  | VAR_METRICS_INTERFACE ip_address
+    {
+#ifdef USE_METRICS
+      struct ip_address_option *ip = cfg_parser->opt->metrics_interface;
+      if(ip == NULL) {
+        cfg_parser->opt->metrics_interface = $2;
+      } else {
+        while(ip->next != NULL) { ip = ip->next; }
+        ip->next = $2;
+      }
+#endif /* USE_METRICS */
+    }
+  | VAR_METRICS_PORT number
+    {
+#ifdef USE_METRICS
+      if($2 == 0) {
+        yyerror("metrics port number expected");
+      } else {
+        cfg_parser->opt->metrics_port = (int)$2;
+      }
+#endif /* USE_METRICS */
+    }
+  | VAR_METRICS_PATH STRING
+    {
+#ifdef USE_METRICS
+      cfg_parser->opt->metrics_path = region_strdup(cfg_parser->opt->region, $2);
+#endif /* USE_METRICS */
+    }
   ;
 
 socket_options:

configure.ac

@@ -1157,6 +1157,19 @@ case "$enable_packed" in
 	;;
 esac
 
+AC_ARG_ENABLE(prometheus-metrics, AS_HELP_STRING([--enable-prometheus-metrics],[Enable prometheus metrics support.]))
+case "$enable_prometheus_metrics" in
+	yes)
+		AC_DEFINE_UNQUOTED([USE_METRICS], [], [Define this to expose NSD statistics via a prometheus metrics HTTP endpoint.])
+		AC_DEFINE_UNQUOTED([NSD_METRICS_PORT], [9100], [Define to the default metrics HTTP endpoint port.])
+		AC_SEARCH_LIBS(evhttp_free, [event], , AC_MSG_ERROR(Cannot find libevent, but is needed for prometheus metrics support.))
+        AC_SUBST([METRICS_SRC], ["metrics.c"])
+        AC_SUBST([METRICS_OBJ], ["metrics.o"])
+		;;
+	no|*)
+		;;
+esac
+
 # check for dnstap if requested
 dt_DNSTAP([${localstatedir}/run/nsd-dnstap.sock],
     [