Introduce write_str_if_not_equal()

2 files changed, 22 insertions, 0 deletions

diff --git a/src/lib/fs/files.c b/src/lib/fs/files.c
index a0b5a40aac..189d2cb646 100644
--- a/src/lib/fs/files.c
+++ b/src/lib/fs/files.c
@@ -718,6 +718,26 @@ read_file_to_str, (const char *filename, int flags, struct stat *stat_out))
   return string;
 }
 
+/** Attempt to read a file <b>fname</b>. If the file's contents is
+ * equal to the string <b>str</b>, return 0. Otherwise, attempt to
+ * overwrite the file with the contents of <b>str</b> and return
+ * the value of write_str_to_file().
+ */
+int
+write_str_to_file_if_not_equal(const char *fname, const char *str)
+{
+  char *fstr = read_file_to_str(fname, RFTS_IGNORE_MISSING, NULL);
+  int rv;
+
+  if (!fstr || strcmp(str, fstr)) {
+    rv = write_str_to_file(fname, str, 0);
+  } else {
+    rv = 0;
+  }
+  tor_free(fstr);
+  return rv;
+}
+
 #if !defined(HAVE_GETDELIM) || defined(TOR_UNIT_TESTS)
 #include "ext/getdelim.c"
 #endif
diff --git a/src/lib/fs/files.h b/src/lib/fs/files.h
index a109cd6248..62b79c4cd8 100644
--- a/src/lib/fs/files.h
+++ b/src/lib/fs/files.h
@@ -91,6 +91,8 @@ int append_bytes_to_file(const char *fname, const char *str, size_t len,
 int write_bytes_to_new_file(const char *fname, const char *str, size_t len,
                             int bin);
 
+int write_str_to_file_if_not_equal(const char *fname, const char *str);
+
 /** Flag for read_file_to_str: open the file in binary mode. */
 #define RFTS_BIN            1
 /** Flag for read_file_to_str: it's okay if the file doesn't exist. */