Add public function gpgme_io_writen.

* src/gpgme.c (gpgme_io_read): New.
--

This is a writen style variant for gpgme_io_write.  It is often easier
to use this one in passphrase and edit callbacks.

doc/gpgme.texi

@@ -2374,9 +2374,10 @@ previous attempts failed, then @var{prev_was_bad} is 1, otherwise it
 will be 0.
 
 The user must write the passphrase, followed by a newline character,
-to the file descriptor @var{fd}.  If the user returns 0 indicating
+to the file descriptor @var{fd}.  The function @code{gpgme_io_writen}
-success, the user must at least write a newline character before
+should be used for the write operation.  Note that if the user returns
-returning from the callback.
+0 to indicate success, the user must at least write a newline
+character before returning from the callback.
 
 If an error occurs, return the corresponding @code{gpgme_error_t}
 value.  You can use the error code @code{GPG_ERR_CANCELED} to abort

src/gpgme.c

@@ -634,6 +634,30 @@ gpgme_io_write (int fd, const void *buffer, size_t count)
   return TRACE_SYSRES (ret);
 }
 
+/* This function provides access to the internal write function.  It
+   is to be used by user callbacks to return data to gpgme.  See
+   gpgme_passphrase_cb_t and gpgme_edit_cb_t.  Note that this is a
+   variant of gpgme_io_write which guarantees that all COUNT bytes are
+   written or an error is return.  Returns: 0 on success or -1 on
+   error and the sets errno. */
+int
+gpgme_io_writen (int fd, const void *buffer, size_t count)
+{
+  int ret = 0;
+  TRACE_BEG2 (DEBUG_GLOBAL, "gpgme_io_writen", fd,
+	      "buffer=%p, count=%u", buffer, count);
+  while (count)
+    {
+      ret = _gpgme_io_write (fd, buffer, count);
+      if (ret < 0)
+        break;
+      buffer += ret;
+      count -= ret;
+      ret = 0;
+    }
+  return TRACE_SYSRES (ret);
+}
+
 
 /* This function returns the callback function for I/O.  */
 void

src/gpgme.def

@@ -204,5 +204,6 @@ EXPORTS
 
     gpgme_set_global_flag                 @156
 
+    gpgme_io_writen                       @157
 ; END
 

src/gpgme.h.in

@@ -1022,6 +1022,7 @@ void gpgme_get_io_cbs (gpgme_ctx_t ctx, gpgme_io_cbs_t io_cbs);
    gpgme_passphrase_cb_t and gpgme_edit_cb_t.  */
 ssize_t gpgme_io_read (int fd, void *buffer, size_t count);
 ssize_t gpgme_io_write (int fd, const void *buffer, size_t count);
+int     gpgme_io_writen (int fd, const void *buffer, size_t count);
 
 /* Process the pending operation and, if HANG is non-zero, wait for
    the pending operation to finish.  */

src/libgpgme.vers

@@ -81,6 +81,8 @@ GPGME_1.1 {
     gpgme_op_passwd;
 
     gpgme_set_global_flag;
+
+    gpgme_io_writen;
 };