2 files changed, 236 insertions, 0 deletions

diff --git a/src/regress/lib/libc/stdio/Makefile b/src/regress/lib/libc/stdio/Makefile
new file mode 100644
index 0000000000..ee865013dd
--- /dev/null
+++ b/src/regress/lib/libc/stdio/Makefile
@@ -0,0 +1,11 @@
+# $OpenBSD: Makefile,v 1.1 2025/05/24 11:07:20 yasuoka Exp $
+
+PROGS=          test_fflush
+
+CLEANFILES=     test_fflush.tmp
+WARNINGS=       yes
+
+# until fflush comply POSIX-2008
+REGRESS_EXPECTED_FAILURES=      run-regress-test_fflush
+
+.include <bsd.regress.mk>
diff --git a/src/regress/lib/libc/stdio/test_fflush.c b/src/regress/lib/libc/stdio/test_fflush.c
new file mode 100644
index 0000000000..fe1772bdfc
--- /dev/null
+++ b/src/regress/lib/libc/stdio/test_fflush.c
@@ -0,0 +1,225 @@
+/*      $OpenBSD: test_fflush.c,v 1.1 2025/05/24 11:07:21 yasuoka Exp $ */
+
+/*
+ * Copyright (c) 2025 YASUOKA Masahiko <yasuoka@yasuoka.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+/* we use assert() */
+#undef  NDEBUG
+
+#define TMPFILENAME     "test_fflush.tmp"
+
+void setup(void);
+
+void test_fflush_read0(void);
+void test_fflush_read1(void);
+void test_fflush_read2(void);
+void test_fflush_read3(void);
+void test_fflush_read4(void);
+
+void
+setup(void)
+{
+        FILE    *fp;
+
+        /* common setup */
+        unlink(TMPFILENAME);
+        fp = fopen(TMPFILENAME, "w+");
+        assert(fp != NULL);
+        fputs("Hello world\n", fp);
+        fclose(fp);
+}
+
+/* fflush work with reading file and seekable */
+void
+test_fflush_read0(void)
+{
+        int      r;
+        char     buf[80];
+        FILE    *fp;
+
+        setup();
+
+        /* In POSIX 2008, fflush() must work with the file object for reading */
+        fp = fopen(TMPFILENAME, "r");
+        assert(fp != NULL);
+        assert(fgetc(fp) == 'H');
+        r = fflush(fp);
+        assert(r == 0);
+
+        /* the position is moved to 1 */
+        assert(ftell(fp) == 1);
+
+        /* can read rest of that */
+        fgets(buf, sizeof(buf), fp);
+        assert(strcmp(buf, "ello world\n") == 0);
+        r = fclose(fp);
+        assert(r == 0);
+}
+
+/* fflush work with reading file and seekable + unget */
+void
+test_fflush_read1(void)
+{
+        int      r;
+        char     buf[80];
+        FILE    *fp;
+
+        setup();
+
+        fp = fopen(TMPFILENAME, "r");
+        assert(fp != NULL);
+        assert(fgetc(fp) == 'H');
+        assert(fgetc(fp) == 'e');
+        assert(fgetc(fp) == 'l');
+        assert(fgetc(fp) == 'l');
+        assert(fgetc(fp) == 'o');
+
+        /* push the 'AAAA' back */
+        ungetc('A', fp);
+        ungetc('A', fp);
+        ungetc('A', fp);
+        ungetc('A', fp);
+
+        /* can read rest of that */
+        fgets(buf, sizeof(buf), fp);
+        assert(strcmp(buf, "AAAA world\n") == 0);
+        r = fclose(fp);
+        assert(r == 0);
+
+        /* do the same thing + fflush */
+
+        fp = fopen(TMPFILENAME, "r");
+        assert(fp != NULL);
+        assert(fgetc(fp) == 'H');
+        assert(fgetc(fp) == 'e');
+        assert(fgetc(fp) == 'l');
+        assert(fgetc(fp) == 'l');
+        assert(fgetc(fp) == 'o');
+
+        /* push 'AAAA' back */
+        ungetc('A', fp);
+        ungetc('A', fp);
+        ungetc('A', fp);
+        ungetc('A', fp);
+
+        /* then fflush */
+        r = fflush(fp);
+        assert(r == 0);
+
+        /* fllush() clears the all pushed back chars */
+
+        /* can read rest of that */
+        fgets(buf, sizeof(buf), fp);
+        assert(strcmp(buf, " world\n") == 0);
+        r = fclose(fp);
+        assert(r == 0);
+}
+
+/* fflush() to reading and non-seekable stream */
+void
+test_fflush_read2(void)
+{
+        int      r;
+        FILE    *fp;
+        char     buf[80];
+
+        /* In POSIX-2008, fflush() must work with the file object for reading */
+        fp = popen("echo Hello world", "r");
+        assert(fp != NULL);
+        assert(fgetc(fp) == 'H');
+        r = fflush(fp);
+        assert(r == 0);
+
+        /*
+         * FILE object for read and NOT seekable.  In that case, fflush does
+         * nothing, but must keep the buffer.
+         */
+
+        /* can read rest of that */
+        fgets(buf, sizeof(buf), fp);
+        assert(strcmp(buf, "ello world\n") == 0);
+        r = pclose(fp);
+        assert(r == 0);
+}
+
+/* fflush() to the file which doesn't have any buffer */
+void
+test_fflush_read3(void)
+{
+        int      r;
+        FILE    *fp;
+
+        setup();
+
+        /* In POSIX-2008, fflush() must work with the file object for reading */
+        fp = fopen(TMPFILENAME, "r");
+        assert(fp != NULL);
+        r = fflush(fp);
+        assert(r == 0);
+        r = fclose(fp);
+        assert(r == 0);
+}
+
+/* freopen() should call fflush() internal */
+void
+test_fflush_read4(void)
+{
+        int      r;
+        FILE    *fp;
+        off_t    pos;
+        char     buf[80];
+
+        setup();
+
+        /* In POSIX-2008, fflush() must work with the file object for reading */
+        fp = fopen(TMPFILENAME, "r");
+        assert(fp != NULL);
+
+        assert(fgetc(fp) == 'H');       /* read 1 */
+
+        pos = lseek(fileno(fp), 0, SEEK_CUR);
+        assert(pos >= 1);
+        assert(pos > 1);        /* this test assume the buffer is used */
+
+        /* freopen() should call fflush() internal */
+        fp = freopen(TMPFILENAME, "r", fp);
+        assert(fp != NULL);
+
+        /* can read rest of that on fp */
+        fgets(buf, sizeof(buf), fp);
+        assert(strcmp(buf, "Hello world\n") == 0);
+
+        r = fclose(fp);
+        assert(r == 0);
+}
+
+int
+main(int argc, char *argv[])
+{
+        test_fflush_read0();
+        test_fflush_read1();
+        test_fflush_read2();
+        test_fflush_read3();
+        test_fflush_read4();
+
+        exit(0);
+}