debug: add a logging module

src/log.c

@@ -0,0 +1,38 @@
+#include <errno.h>
+#include <stdarg.h>
+#include <string.h>
+
+#include "log.h"
+
+static FILE* logger_out = NULL;
+
+void log_init(FILE* fd) {
+  if (logger_out) (void)fclose(logger_out);
+  logger_out = fd;
+}
+
+void log_puts(const char* msg) {
+  if (!logger_out) return;
+  (void)fputs(msg, logger_out);
+}
+
+void log_printf(const char* fmt, ...) {
+  if (!logger_out) return;
+
+  va_list args;
+  va_start(args, fmt);
+
+  (void)vfprintf(logger_out, fmt, args);
+
+  va_end(args);
+}
+
+// NOLINTNEXTLINE(readability-identifier-length)
+void log_perror(const char* s) {
+  if (!logger_out) return;
+
+  if (s)
+    (void)fprintf(logger_out, "%s: %s", s, strerror(errno));
+  else
+    (void)fprintf(logger_out, "%s", strerror(errno));
+}

src/main.c

@@ -1,11 +1,13 @@
 #include <pwd.h>
 #include <stdbool.h>
+#include <stdio.h>
 #include <sys/ioctl.h>
 #include <sys/types.h>
 #include <unistd.h>
 
 #include "chvt.h"
 #include "config.h"
+#include "log.h"
 #include "sessions.h"
 #include "ui.h"
 #include "users.h"
@@ -14,6 +16,18 @@
 int main(int argc, char* argv[]) {
   if (argc == 2) chvt_str(argv[1]);
 
+  char* log_output = getenv("LIDM_LOG");
+  if (log_output) {
+    FILE* log_fd = fopen(log_output, "w");
+    if (!log_fd) {
+      perror("fopen");
+      (void)fputs("failed to open logfile in write mode", stderr);
+      return -1;
+    }
+
+    log_init(log_fd);
+  }
+
   char* conf_override = getenv("LIDM_CONF");
   struct config* config =
       parse_config(conf_override == NULL ? "/etc/lidm.ini" : conf_override);