Feat: add non-buffered logging functions

src/log.c

@@ -0,0 +1,43 @@
+#include "log.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdarg.h>
+#include <time.h>
+
+void log_init(void) {
+    setvbuf(stdout, NULL, _IOLBF, 0);
+}
+
+static void ts(char *out, size_t out_sz) {
+    time_t now = time(NULL);
+    struct tm tm;
+    localtime_r(&now, &tm);
+    strftime(out, out_sz, "%Y-%m-%d %H:%M:%S", &tm);
+}
+
+static void vlog(FILE *f, const char *level, const char *fmt, va_list ap) {
+    char t[32];
+    ts(t, sizeof(t));
+    fprintf(f, "%s %s: ", t, level);
+    vfprintf(f, fmt, ap);
+    fputc('\n', f);
+    fflush(f);
+}
+
+void log_info(const char *fmt, ...) {
+    va_list ap; va_start(ap, fmt);
+    vlog(stdout, "INFO", fmt, ap);
+    va_end(ap);
+}
+void log_warn(const char *fmt, ...) {
+    va_list ap; va_start(ap, fmt);
+    vlog(stderr, "WARN", fmt, ap);
+    va_end(ap);
+}
+void log_error(const char *fmt, ...) {
+    va_list ap; va_start(ap, fmt);
+    vlog(stderr, "ERROR", fmt, ap);
+    va_end(ap);
+}
+