Add a test to verify the fpurge problem doesn't happen. fpurge()

mistaknely made the write buffer usable even if the stream is read
mode.  See the change of lib/libc/stdio/fpurge.c,v 1.11.

1 files changed, 41 insertions, 1 deletions

diff --git a/src/regress/lib/libc/stdio/test___freading.c b/src/regress/lib/libc/stdio/test___freading.c
index 05716f3a38..f74eb78d35 100644
--- a/src/regress/lib/libc/stdio/test___freading.c
+++ b/src/regress/lib/libc/stdio/test___freading.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: test___freading.c,v 1.1 2025/05/25 00:20:54 yasuoka Exp $     */
+/*      $OpenBSD: test___freading.c,v 1.2 2025/06/12 07:39:26 yasuoka Exp $     */
 
 /*
  * Copyright (c) 2025 YASUOKA Masahiko <yasuoka@yasuoka.net>
@@ -21,14 +21,31 @@
 #include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 /* we use assert() */
 #undef  NDEBUG
 
 #define TMPFILENAME     "test___freading.tmp"
 
+void setup(void);
+
 void test___freading0(void);
 void test___freading1(void);
+void test___freading2(void);
+
+void
+setup(void)
+{
+        FILE    *fp;
+
+        /* common setup */
+        unlink(TMPFILENAME);
+        fp = fopen(TMPFILENAME, "w+");
+        assert(fp != NULL);
+        fputs("Hello world\n", fp);
+        fclose(fp);
+}
 
 void
 test___freading0(void)
@@ -75,11 +92,34 @@ test___freading1(void)
         assert(r == 0);
 }
 
+void
+test___freading2(void)
+{
+        int      r;
+        FILE    *fp;
+
+        /*
+         * until v1.10 of fpurge.c mistakenly enables the writing buffer
+         * without _SRD flag set.
+         */
+        fp = fopen(TMPFILENAME, "r+");
+        assert(fp != NULL);
+        assert(fgetc(fp) == 'H');
+        fpurge(fp);
+        fseek(fp, 0, SEEK_CUR);
+        assert(fputc('X', fp) == 'X');
+        assert(__freading(fp) == 0);
+
+        r = fclose(fp);
+        assert(r == 0);
+}
+
 int
 main(int argc, char *argv[])
 {
         test___freading0();
         test___freading1();
+        test___freading2();
 
         exit(0);
 }