read-file: disable buffering if RF_SENSITIVE is set

* lib/read-file.c (read_file): Call setvbuf if RF_SENSITIVE.
Suggested by Glenn Strauss.
(fread_file): Suggest calling setvbuf before calling this
function.  Suggested by Bruno Haible.

1 files changed, 8 insertions, 2 deletions

diff --git a/lib/read-file.c b/lib/read-file.c
index 36780cc157..88bc0070a9 100644
--- a/lib/read-file.c
+++ b/lib/read-file.c
@@ -43,8 +43,11 @@
    *LENGTH.  On errors, *LENGTH is undefined, errno preserves the
    values set by system functions (if any), and NULL is returned.
 
-   If the RF_SENSITIVE flag is set in FLAGS, the memory buffer
-   internally allocated will be cleared upon failure.  */
+   If the RF_SENSITIVE flag is set in FLAGS:
+     - You should control the buffering of STREAM using 'setvbuf'.  Either
+       clear the buffer of STREAM after closing it, or disable buffering of
+       STREAM before calling this function.
+     - The memory buffer internally allocated will be cleared upon failure.  */
 char *
 fread_file (FILE *stream, int flags, size_t *length)
 {
@@ -195,6 +198,9 @@ read_file (const char *filename, int flags, size_t *length)
   if (!stream)
     return NULL;
 
+  if (flags & RF_SENSITIVE)
+    setvbuf (stream, NULL, _IONBF, 0);
+
   out = fread_file (stream, flags, length);
 
   save_errno = errno;