head(1): check for stdio errors

- Output errors are terminal.

- Input errors yield a warning and cause head(1) to fail
  gracefully.

Tweaked by millert@.

Thread: https://marc.info/?l=openbsd-tech&m=164419238123928&w=2

ok millert@

diff --git a/usr.bin/head/head.c b/usr.bin/head/head.c
index 90b07a0..7367062 100644 (file)
--- a/usr.bin/head/head.c
+++ b/usr.bin/head/head.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: head.c,v 1.23 2022/01/29 00:19:04 cheloha Exp $       */
+/*     $OpenBSD: head.c,v 1.24 2022/02/07 17:19:57 cheloha Exp $       */
 
 /*
  * Copyright (c) 1980, 1987 Regents of the University of California.
@@ -96,30 +96,43 @@ main(int argc, char *argv[])
 int
 head_file(const char *path, long count, int need_header)
 {
+       const char *name;
        FILE *fp;
-       int ch;
+       int ch, status = 0;
        static int first = 1;
 
        if (path != NULL) {
-               fp = fopen(path, "r");
+               name = path;
+               fp = fopen(name, "r");
                if (fp == NULL) {
-                       warn("%s", path);
+                       warn("%s", name);
                        return 1;
                }
                if (need_header) {
-                       printf("%s==> %s <==\n", first ? "" : "\n", path);
+                       printf("%s==> %s <==\n", first ? "" : "\n", name);
+                       if (ferror(stdout))
+                               err(1, "stdout");
                        first = 0;
                }
-       } else
+       } else {
+               name = "stdin";
                fp = stdin;
+       }
+
+       while ((ch = getc(fp)) != EOF) {
+               if (putchar(ch) == EOF)
+                       err(1, "stdout");
+               if (ch == '\n' && --count == 0)
+                       break;
+       }
+       if (ferror(fp)) {
+               warn("%s", name);
+               status = 1;
+       }
 
-       for (; count > 0 && !feof(fp); --count)
-               while ((ch = getc(fp)) != EOF)
-                       if (putchar(ch) == '\n')
-                               break;
        fclose(fp);
 
-       return 0;
+       return status;
 }