metrics: scaffold module with config parsing

Add a new extra module `metrics` that will eventually expose statistics
over HTTP. This first commit only:

  * creates accel-pppd/extra/metrics.c with an init() that parses the
    [metrics] section options `format` (prometheus|json) and
    `address` (host:port);
  * wires the new shared library into the extras CMakeLists.

No listener, no metrics rendering yet — those land in follow-up
commits. With this commit alone, loading the `metrics` module just
logs the configured listen address and format and is otherwise inert.

Signed-off-by: Denys Fedoryshchenko <denys.f@collabora.com>

2 files changed, 76 insertions, 1 deletions

diff --git a/accel-pppd/extra/CMakeLists.txt b/accel-pppd/extra/CMakeLists.txt
index 6badcd5e..6b5beaff 100644
--- a/accel-pppd/extra/CMakeLists.txt
+++ b/accel-pppd/extra/CMakeLists.txt
@@ -8,8 +8,9 @@ ADD_LIBRARY(chap-secrets SHARED chap-secrets.c)
 ADD_LIBRARY(logwtmp SHARED logwtmp.c)
 TARGET_LINK_LIBRARIES(logwtmp util)
 ADD_LIBRARY(connlimit SHARED connlimit.c)
+ADD_LIBRARY(metrics SHARED metrics.c)
 
-INSTALL(TARGETS pppd_compat ippool ipv6pool sigchld chap-secrets logwtmp connlimit
+INSTALL(TARGETS pppd_compat ippool ipv6pool sigchld chap-secrets logwtmp connlimit metrics
 	LIBRARY DESTINATION lib${LIB_SUFFIX}/accel-ppp
 )
 
diff --git a/accel-pppd/extra/metrics.c b/accel-pppd/extra/metrics.c
new file mode 100644
index 00000000..c7a52ed8
--- /dev/null
+++ b/accel-pppd/extra/metrics.c
@@ -0,0 +1,74 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+
+#include "triton.h"
+#include "events.h"
+#include "log.h"
+
+#include "memdebug.h"
+
+enum metrics_format {
+	METRICS_FORMAT_PROMETHEUS,
+	METRICS_FORMAT_JSON,
+};
+
+static enum metrics_format conf_format = METRICS_FORMAT_PROMETHEUS;
+static char *conf_address;
+
+static int parse_format(const char *opt, enum metrics_format *out)
+{
+	if (!strcasecmp(opt, "prometheus")) {
+		*out = METRICS_FORMAT_PROMETHEUS;
+		return 0;
+	}
+	if (!strcasecmp(opt, "json")) {
+		*out = METRICS_FORMAT_JSON;
+		return 0;
+	}
+	return -1;
+}
+
+static int load_config(void)
+{
+	const char *opt;
+	enum metrics_format fmt = METRICS_FORMAT_PROMETHEUS;
+	char *address = NULL;
+
+	opt = conf_get_opt("metrics", "format");
+	if (opt && parse_format(opt, &fmt) < 0) {
+		log_error("metrics: unknown format '%s', expected 'prometheus' or 'json'\n", opt);
+		return -1;
+	}
+
+	opt = conf_get_opt("metrics", "address");
+	if (!opt) {
+		log_emerg("metrics: 'address' option is required (host:port)\n");
+		return -1;
+	}
+	address = _strdup(opt);
+	if (!address) {
+		log_emerg("metrics: out of memory while loading config\n");
+		return -1;
+	}
+
+	conf_format = fmt;
+	if (conf_address)
+		_free(conf_address);
+	conf_address = address;
+
+	return 0;
+}
+
+static void init(void)
+{
+	if (load_config() < 0)
+		return;
+
+	log_info2("metrics: module loaded, listen %s, format %s\n",
+		  conf_address,
+		  conf_format == METRICS_FORMAT_PROMETHEUS ? "prometheus" : "json");
+}
+
+DEFINE_INIT(100, init);