[tz] [PATCH 5/5] Clean up temp files better

[Paul Eggert]

The previous change causes zic to create temporary output files
or links before renaming them to the final destination.
If zic is interrupted, it would leave these files behind.
This change causes zic to finish writing the temporary file and
rename it to its destination before exiting due to a signal.
Since the temp files are quite small, that’s good enough.
Also, this change fixes a place in close_file where an
error could have left a temp file behind.
* zic.c (close_file): New arg TEMPNAME.  All callers changed.
(got_signal): New static var.
(signal_handler, catch_signals, check_for_signal): New functions.
(main): Catch signals.
(dolink, outzone): At opportune times, check for a signal
and exit.
---
 zic.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 79 insertions(+), 7 deletions(-)

diff --git a/zic.c b/zic.c
index 8298198..f1ae11d 100644
--- a/zic.c
+++ b/zic.c
@@ -550,8 +550,11 @@ warning(const char *const string, ...)
 	warnings = true;
 }
 
+/* Close STREAM.  If it had an I/O error, report it against DIR/NAME,
+   remove TEMPNAME if nonnull, and then exit.  */
 static void
-close_file(FILE *stream, char const *dir, char const *name)
+close_file(FILE *stream, char const *dir, char const *name,
+	   char const *tempname)
 {
   char const *e = (ferror(stream) ? _("I/O error")
 		   : fclose(stream) != 0 ? strerror(errno) : NULL);
@@ -560,6 +563,8 @@ close_file(FILE *stream, char const *dir, char const *name)
 	    dir ? dir : "", dir ? "/" : "",
 	    name ? name : "", name ? ": " : "",
 	    e);
+    if (tempname)
+      remove(tempname);
     exit(EXIT_FAILURE);
   }
 }
@@ -576,7 +581,7 @@ usage(FILE *stream, int status)
 	    "Report bugs to %s.\n"),
 	  progname, progname, REPORT_BUGS_TO);
   if (status == EXIT_SUCCESS)
-    close_file(stream, NULL, NULL);
+    close_file(stream, NULL, NULL, NULL);
   exit(status);
 }
 
@@ -600,6 +605,68 @@ change_directory (char const *dir)
   }
 }
 
+/* Simple signal handling: just set a flag that is checked
+   periodically outside critical sections.  To set up the handler,
+   prefer sigaction if available to close a signal race.  */
+
+static sig_atomic_t got_signal;
+
+static void
+signal_handler(int sig)
+{
+#ifndef SA_SIGINFO
+  signal(sig, signal_handler);
+#endif
+  got_signal = sig;
+}
+
+/* Arrange for SIGINT etc. to be caught by the handler.  */
+static void
+catch_signals(void)
+{
+  static int const signals[] = {
+#ifdef SIGHUP
+    SIGHUP,
+#endif
+    SIGINT,
+#ifdef SIGPIPE
+    SIGPIPE,
+#endif
+    SIGTERM
+  };
+  int i;
+  for (i = 0; i < sizeof signals / sizeof signals[0]; i++) {
+#ifdef SA_SIGINFO
+    struct sigaction act0, act;
+    act.sa_handler = signal_handler;
+    sigemptyset(&act.sa_mask);
+    act.sa_flags = 0;
+    if (sigaction(signals[i], &act, &act0) == 0
+	&& ! (act0.sa_flags & SA_SIGINFO) && act0.sa_handler == SIG_IGN) {
+      sigaction(signals[i], &act0, NULL);
+      got_signal = 0;
+    }
+#else
+    if (signal(signals[i], signal_handler) == SIG_IGN) {
+      signal(signals[i], SIG_IGN);
+      got_signal = 0;
+    }
+#endif
+  }
+}
+
+/* If a signal has arrived, terminate zic with appropriate status.  */
+static void
+check_for_signal(void)
+{
+  int sig = got_signal;
+  if (sig) {
+    signal(sig, SIG_DFL);
+    raise(sig);
+    abort(); /* A bug in 'raise'.  */
+  }
+}
+
 #define TIME_T_BITS_IN_FILE 64
 
 /* The minimum and maximum values representable in a TZif file.  */
@@ -692,7 +759,7 @@ main(int argc, char **argv)
 	for (k = 1; k < argc; k++)
 		if (strcmp(argv[k], "--version") == 0) {
 			printf("zic %s%s\n", PKGVERSION, TZVERSION);
-			close_file(stdout, NULL, NULL);
+			close_file(stdout, NULL, NULL, NULL);
 			return EXIT_SUCCESS;
 		} else if (strcmp(argv[k], "--help") == 0) {
 			usage(stdout, EXIT_SUCCESS);
@@ -815,6 +882,7 @@ _("%s: invalid time range: %s\n"),
 		return EXIT_FAILURE;
 	associate();
 	change_directory(directory);
+	catch_signals();
 	for (i = 0; i < nzones; i = j) {
 		/*
 		** Find the next non-continuation zone entry.
@@ -1058,6 +1126,8 @@ dolink(char const *target, char const *linkname, bool staysymlink)
 	char *tempname = NULL;
 	char const *outname = linkname;
 
+	check_for_signal();
+
 	if (strcmp(target, "-") == 0) {
 	  if (remove(linkname) == 0 || errno == ENOENT || errno == ENOTDIR)
 	    return;
@@ -1132,8 +1202,8 @@ dolink(char const *target, char const *linkname, bool staysymlink)
 	    tp = open_outfile(&outname, &tempname);
 	    while ((c = getc(fp)) != EOF)
 	      putc(c, tp);
-	    close_file(fp, directory, target);
-	    close_file(tp, directory, outname);
+	    close_file(tp, directory, linkname, tempname);
+	    close_file(fp, directory, target, NULL);
 	    if (link_errno != ENOTSUP)
 	      warning(_("copy used because hard link failed: %s"),
 		      strerror(link_errno));
@@ -1323,7 +1393,7 @@ _("%s: panic: Invalid l_value %d\n"),
 		}
 		free(fields);
 	}
-	close_file(fp, NULL, filename);
+	close_file(fp, NULL, filename, NULL);
 	if (wantcont)
 		error(_("expected continuation line not found"));
 }
@@ -2310,7 +2380,7 @@ writezone(const char *const name, const char *const string, char version,
 				putc(ttisuts[i], fp);
 	}
 	fprintf(fp, "\n%s\n", string);
-	close_file(fp, directory, outname);
+	close_file(fp, directory, name, tempname);
 	rename_dest(tempname, name);
 	free(ats);
 }
@@ -2664,6 +2734,8 @@ outzone(const struct zone *zpfirst, ptrdiff_t zonecount)
 	zic_t max_year0;
 	int defaulttype = -1;
 
+	check_for_signal();
+
 	max_abbr_len = 2 + max_format_len + max_abbrvar_len;
 	max_envvar_len = 2 * max_abbr_len + 5 * 9;
 	startbuf = emalloc(max_abbr_len + 1);
-- 
2.27.0