Implement socket file redirection.

* configure.ac (AC_CHECK_FUNC): Check for stat.
* src/assuan-socket.c (SUN_LEN): Add.
(eval_redirection): New.
(_assuan_sock_connect) [!W32]: Implement socket file redirection.
(_assuan_sock_set_sockaddr_un): New.
(assuan_sock_set_sockaddr_un): New.
--

This feature is useful to allow sockets with standard names even on
file system which do not supports socket and to help with shared home
directories.  For example to use GnuPG 2.1 with shared home
directories one will be abale to do:

 rm ~/.gnupg/S.gpg-agent || true
 printf "%%Assuan%%\nsocket=${HOME}/.gnupg/S.gpg-agent_${HOSTNAME}\n" \
       > ~/.gnupg/S.gpg-agent

Signed-off-by: Werner Koch <wk@gnupg.org>

1 files changed, 36 insertions, 1 deletions

diff --git a/doc/assuan.texi b/doc/assuan.texi
index ddac37a..b932be0 100644
--- a/doc/assuan.texi
+++ b/doc/assuan.texi
@@ -1935,7 +1935,10 @@ Wrapper around socket.
 
 Wrapper around connect.  For Unix domain sockets under Windows this
 function also does a write immediately after the the connect to send the
-nonce as read from the socket's file.
+nonce as read from the socket's file.  Under Unix this function check
+whether the socket file is a redirection file and connects to the
+redirected socket instead; see @code{assuan_sock_set_sockaddr_un} for
+details on the redirection file format.
 @end deftypefun
 
 
@@ -1948,6 +1951,38 @@ Wrapper around bind.  Under Windows this creates a file and writes the
 port number and a random nonce to this file.
 @end deftypefun
 
+@deftypefun int assuan_sock_set_sockaddr_un ( @
+        @w{const char *@var{fname}}, @
+        @w{struct sockaddr *@var{addr}}, @
+        @w{int *@var{r_redirected}})
+
+This is a helper function to initialize the Unix socket domain address
+structure @var{addr} and store the file name @var{fname} there.  If
+@var{r_redirected} is not NULL the function checks whether @var{fname}
+already exists, is a regular file, and not a socket.  In that case
+@var{fname} is read to see whether this is a redirection to a socket
+file.  If that is the case 1 is stored at @var{r_redirected}.  If the
+file does not look like a redirection file 0 will be stored there and
+@var{fname} will be used in the regular way.
+
+The format of a redirection file is
+
+@example
+%Assuan%
+socket=@var{name}
+@end example
+
+With @var{name} being is the actual socket to use.  No white spaces
+are allowed, both lines must be terminated by a single linefeed, and
+extra lines are not allowed.  Environment variables are interpreted in
+@var{name} if given in @code{$@{VAR@}} notation.  No escape characters
+are defined; if the string @code{$@{} shall be used in file name, an
+environment variable with that content may be used.  The length of the
+redirection file is limited to 511 bytes which is more than sufficient
+for any known implementation of Unix domain sockets.
+@end deftypefun
+
+
 @deftypefun int assuan_sock_get_nonce ( @
         @w{struct sockaddr *@var{addr}}, @
         @w{int @var{addrlen}}, @