From d47260dd13b2aca303934f1c3f1e61ed6c314738 Mon Sep 17 00:00:00 2001
From: Max Wash <mbswash@gmail.com>
Date: Sun, 31 May 2026 17:20:57 +0100
Subject: [PATCH] libc: io: implement (v)fprintf

---
 lib/libc/include/stdio.h     |  1 +
 lib/libc/io/stdio/fprintf.c  |  9 ++++++++-
 lib/libc/io/stdio/printf.c   |  2 +-
 lib/libc/io/stdio/vfprintf.c | 35 +++++++++++++++++++++++++++++++++++
 lib/libc/io/stdio/vprintf.c  | 18 +++---------------
 5 files changed, 48 insertions(+), 17 deletions(-)
 create mode 100644 lib/libc/io/stdio/vfprintf.c

diff --git a/lib/libc/include/stdio.h b/lib/libc/include/stdio.h
index d8327e3..c8ce5f7 100644
--- a/lib/libc/include/stdio.h
+++ b/lib/libc/include/stdio.h
@@ -25,6 +25,7 @@ typedef struct __opaque_file FILE;
 extern int printf(const char *format, ...);
 extern int vprintf(const char *format, va_list arg);
 extern int fprintf(FILE *stream, const char *format, ...);
+extern int vfprintf(FILE *stream, const char *format, va_list arg);
 extern int snprintf(char *buffer, size_t count, const char *format, ...);
 extern int vsnprintf(
 	char *buffer,
diff --git a/lib/libc/io/stdio/fprintf.c b/lib/libc/io/stdio/fprintf.c
index 35e7d36..f4b2f47 100644
--- a/lib/libc/io/stdio/fprintf.c
+++ b/lib/libc/io/stdio/fprintf.c
@@ -1,6 +1,13 @@
 #include "file.h"
 
+#include <stdio.h>
+
 int fprintf(struct __opaque_file *stream, const char *format, ...)
 {
-	return 0;
+	va_list arg;
+	va_start(arg, format);
+	int ret = vfprintf(stream, format, arg);
+	va_end(arg);
+
+	return ret;
 }
diff --git a/lib/libc/io/stdio/printf.c b/lib/libc/io/stdio/printf.c
index 67e4a1c..c6ffa34 100644
--- a/lib/libc/io/stdio/printf.c
+++ b/lib/libc/io/stdio/printf.c
@@ -5,7 +5,7 @@ int printf(const char *format, ...)
 {
 	va_list arg;
 	va_start(arg, format);
-	int ret = vprintf(format, arg);
+	int ret = vfprintf(stdout, format, arg);
 	va_end(arg);
 
 	return ret;
diff --git a/lib/libc/io/stdio/vfprintf.c b/lib/libc/io/stdio/vfprintf.c
new file mode 100644
index 0000000..442b6ce
--- /dev/null
+++ b/lib/libc/io/stdio/vfprintf.c
@@ -0,0 +1,35 @@
+#include "file.h"
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+
+extern int __libc_fctprintf(
+	int (*out)(char character, void *arg),
+	void *arg,
+	const char *format,
+	va_list va);
+extern int __fputc(int c, struct __opaque_file *stream);
+
+static inline int _out_file(char character, void *arg)
+{
+	FILE *fp = arg;
+	return __fputc(character, fp);
+}
+
+int vfprintf(FILE *fp, const char *format, va_list arg)
+{
+	__libc_file_lock(fp);
+
+	int ret = __libc_fctprintf(_out_file, fp, format, arg);
+	if (errno != SUCCESS) {
+		ret = -1;
+	}
+
+	if (ferror(fp)) {
+		ret = -1;
+	}
+
+	__libc_file_unlock(fp);
+	return ret;
+}
diff --git a/lib/libc/io/stdio/vprintf.c b/lib/libc/io/stdio/vprintf.c
index b6a3e07..f3125fe 100644
--- a/lib/libc/io/stdio/vprintf.c
+++ b/lib/libc/io/stdio/vprintf.c
@@ -1,7 +1,7 @@
 #include "file.h"
 
-#include <stddef.h>
 #include <errno.h>
+#include <stddef.h>
 #include <stdio.h>
 
 extern int __libc_fctprintf(
@@ -11,7 +11,7 @@ extern int __libc_fctprintf(
 	va_list va);
 extern int __fputc(int c, struct __opaque_file *stream);
 
-static inline int  _out_file(char character, void *arg)
+static inline int _out_file(char character, void *arg)
 {
 	FILE *fp = arg;
 	return __fputc(character, fp);
@@ -19,17 +19,5 @@ static inline int  _out_file(char character, void *arg)
 
 int vprintf(const char *format, va_list arg)
 {
-	__libc_file_lock(stdout);
-
-	int ret = __libc_fctprintf(_out_file, stdout, format, arg);
-	if (errno != SUCCESS) {
-		ret = -1;
-	}
-
-	if (ferror(stdout)) {
-		ret = -1;
-	}
-
-	__libc_file_unlock(stdout);
-	return ret;
+	return vfprintf(stdout, format, arg);
 }