From 99f1ac18b8d85a2fb89f2134055e093411649e87 Mon Sep 17 00:00:00 2001
From: sanana <umutinanerdogan@pm.me>
Date: Tue, 28 Jan 2025 15:50:49 +0300
Subject: [PATCH] tests/ansi: add ftell test case

This patch adds a simple test for ftell's functionality which also
acts as a simple reproducible test case for the failing GMP tests
documented in #1221. This test used to fail because our behaviour when
checking ftell after a ungetc doesn't match glibc.
---
 tests/ansi/ftell.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++
 tests/meson.build  |  1 +
 2 files changed, 73 insertions(+)
 create mode 100644 tests/ansi/ftell.c

diff --git a/tests/ansi/ftell.c b/tests/ansi/ftell.c
new file mode 100644
index 0000000000..5d4c501cf2
--- /dev/null
+++ b/tests/ansi/ftell.c
@@ -0,0 +1,72 @@
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#ifdef USE_HOST_LIBC
+#define TEST_FILE "ftell-host-libc.tmp"
+#else
+#define TEST_FILE "ftell.tmp"
+#endif
+
+int main() {
+	FILE *file;
+	char str[] = "mlibc ftell test";
+	size_t str_size = sizeof(str) - 1;
+	char buffer[20];
+
+	// Clear buffer to zero
+	memset(buffer, 0, sizeof(buffer));
+
+	// Open the file for writing in binary mode, because ftell is unspecified
+	// in text mode.
+	file = fopen(TEST_FILE, "wb");
+	assert(file);
+
+	// Write string minus null terminator, flush and close.
+	assert(fwrite(str, 1, str_size, file) == str_size);
+	fflush(file);
+	fclose(file);
+
+	// Open the file for reading in binary mode.
+	file = fopen(TEST_FILE, "rb");
+	assert(file);
+
+	// Check position indicator at the start of the file.
+	assert(ftell(file) == 0);
+
+	// Read 4 bytes and check fread and ftell.
+	assert(fread(buffer, 1, 4, file) == 4);
+	assert(ftell(file) == 4);
+
+	// Rewind and check position indicator at the start of the file.
+	rewind(file);
+	assert(ftell(file) == 0);
+
+	// Read the entire file and check fread and ftell.
+	assert(fread(buffer, 1, str_size, file) == str_size);
+	assert((size_t) ftell(file) == str_size);
+
+	// Rewind and check how ftell interacts with getc.
+	rewind(file);
+	assert(fgetc(file) == 'm');
+	assert(ftell(file) == 1);
+	assert(fgetc(file) == 'l');
+	assert(ftell(file) == 2);
+	assert(fgetc(file) == 'i');
+	assert(ftell(file) == 3);
+
+	// Check whether ftell is decremented after ungetc
+	assert(ungetc('X', file) == 'X');
+	int ftell_after_ungetc = ftell(file);
+	fprintf(stderr, "ftell_after_ungetc: %d\n", ftell_after_ungetc);
+	assert(ftell_after_ungetc == 2);
+	ungetc('Y', file);
+	assert(ftell(file) == 1);
+
+	// Check if rewind undoes ungetc's effects on ftell
+	rewind(file);
+	assert(ftell(file) == 0);
+
+	fclose(file);
+	return 0;
+}
diff --git a/tests/meson.build b/tests/meson.build
index 74c0067be2..edeaea166d 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -30,6 +30,7 @@ all_test_cases = [
 	'ansi/strxfrm',
 	'ansi/calloc',
 	'ansi/fgetpos',
+	'ansi/ftell',
 	'bsd/ns_get_put',
 	'bsd/reallocarray',
 	'bsd/strl',