Pull the file writing code for the wallet client into a separate file

so that the srvtab and keytab management can share it.  Write atomically
to a new file and then link and rename to do an atomic update.  Leave a
backup copy of any file that's replaced.

1 files changed, 50 insertions, 0 deletions

diff --git a/client/file.c b/client/file.c
new file mode 100644
index 0000000..621b49d
--- /dev/null
+++ b/client/file.c
@@ -0,0 +1,50 @@
+/*  $Id$
+**
+**  File handling for the wallet client.
+**
+**  Written by Russ Allbery <rra@stanford.edu>
+**  Copyright 2007 Board of Trustees, Leland Stanford Jr. University
+**
+**  See README for licensing terms.
+*/
+
+#include <config.h>
+#include <system.h>
+
+#include <fcntl.h>
+
+#include <client/internal.h>
+#include <util/util.h>
+
+/*
+**  Given a filename, some data, and a length, write that data to the given
+**  file safely and atomically by creating file.new, writing the data, linking
+**  file to file.bak, and then renaming file.new to file.
+*/
+void
+write_file(const char *name, const void *data, size_t length)
+{
+    int fd;
+    ssize_t status;
+    char *temp, *backup;
+
+    temp = concat(name, ".new", (char *) 0);
+    backup = concat(name, ".bak", (char *) 0);
+    fd = open(temp, O_WRONLY | O_CREAT | O_TRUNC, 0600);
+    if (fd < 0)
+        sysdie("open of %s failed", temp);
+    status = write(fd, data, length);
+    if (status < 0)
+        sysdie("write to %s failed", temp);
+    else if (status != (ssize_t) length)
+        die("write to %s truncated", temp);
+    if (close(fd) < 0)
+        sysdie("close of %s failed (file probably truncated)", temp);
+    if (access(name, F_OK) == 0)
+        if (link(name, backup) < 0)
+            sysdie("link of %s to %s failed", name, backup);
+    if (rename(temp, name) < 0)
+        sysdie("rename of %s to %s failed", temp, name);
+    free(temp);
+    free(backup);
+}