unix_socket: add support for abstract unix domain socket

In addition to unix domain sockets, Linux also supports an
abstract namespace which is independent of the filesystem.

In order to support it, add new CURLOPT_ABSTRACT_UNIX_SOCKET
option which uses the same storage as CURLOPT_UNIX_SOCKET_PATH
internally, along with a flag to specify abstract socket.

On non-supporting platforms, the abstract address will be
interpreted as an empty string and fail gracefully.

Also add new --abstract-unix-socket tool parameter.

Signed-off-by: Isaac Boukris <iboukris@gmail.com>
Reported-by: Chungtsun Li (typeless)
Reviewed-by: Daniel Stenberg
Reviewed-by: Peter Wu
Closes #1197
Fixes #1061

2 files changed, 61 insertions, 0 deletions

diff --git a/docs/libcurl/opts/CURLOPT_ABSTRACT_UNIX_SOCKET.3 b/docs/libcurl/opts/CURLOPT_ABSTRACT_UNIX_SOCKET.3
new file mode 100644
index 000000000..8b61854c0
--- /dev/null
+++ b/docs/libcurl/opts/CURLOPT_ABSTRACT_UNIX_SOCKET.3
@@ -0,0 +1,58 @@
+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
+.\" * are also available at https://curl.haxx.se/docs/copyright.html.
+.\" *
+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
+.\" *
+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLOPT_ABSTRACT_UNIX_SOCKET 3 "08 Jan 2017" "libcurl 7.53.0" "curl_easy_setopt options"
+.SH NAME
+CURLOPT_ABSTRACT_UNIX_SOCKET \- set an abstract Unix domain socket
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ABSTRACT_UNIX_SOCKET, char *path);
+.SH DESCRIPTION
+Enables the use of an abstract Unix domain socket instead of establishing a TCP
+connection to a host. The parameter should be a char * to a zero terminated string
+holding the path of the socket. The path will be set to \fIpath\fP prefixed by a
+NULL byte (this is the convention for abstract sockets, however it should be stressed
+that the path passed to this function should not contain a leading NULL).
+
+On non-supporting platforms, the abstract address will be interpreted as an empty
+string and fail gracefully, generating a run-time error.
+
+This option shares the same semantics as
+.BR CURLOPT_UNIX_SOCKET_PATH "(3)
+in which documentation more details can be found. Internally, these two options share
+the same storage and therefore only one of them can be set per handle.
+
+.SH DEFAULT
+Default is NULL.
+.SH EXAMPLE
+.nf
+    curl_easy_setopt(curl_handle, CURLOPT_ABSTRACT_UNIX_SOCKET, "/tmp/foo.sock");
+    curl_easy_setopt(curl_handle, CURLOPT_URL, "http://localhost/");
+.fi
+
+.SH AVAILABILITY
+Since 7.53.0.
+.SH RETURN VALUE
+Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
+.SH "SEE ALSO"
+.BR CURLOPT_UNIX_SOCKET_PATH "(3), " unix "(7), "
diff --git a/docs/libcurl/opts/Makefile.am b/docs/libcurl/opts/Makefile.am
index eb7ca1bb5..80f28ca9b 100644
--- a/docs/libcurl/opts/Makefile.am
+++ b/docs/libcurl/opts/Makefile.am
@@ -87,6 +87,7 @@ man_MANS =                                      \
  CURLMOPT_SOCKETFUNCTION.3                      \
  CURLMOPT_TIMERDATA.3                           \
  CURLMOPT_TIMERFUNCTION.3                       \
+ CURLOPT_ABSTRACT_UNIX_SOCKET.3                 \
  CURLOPT_ACCEPTTIMEOUT_MS.3                     \
  CURLOPT_ACCEPT_ENCODING.3                      \
  CURLOPT_ADDRESS_SCOPE.3                        \
@@ -397,6 +398,7 @@ HTMLPAGES =                                     \
  CURLMOPT_SOCKETFUNCTION.html                   \
  CURLMOPT_TIMERDATA.html                        \
  CURLMOPT_TIMERFUNCTION.html                    \
+ CURLOPT_ABSTRACT_UNIX_SOCKET.html              \
  CURLOPT_ACCEPTTIMEOUT_MS.html                  \
  CURLOPT_ACCEPT_ENCODING.html                   \
  CURLOPT_ADDRESS_SCOPE.html                     \
@@ -707,6 +709,7 @@ PDFPAGES =                                      \
  CURLMOPT_SOCKETFUNCTION.pdf                    \
  CURLMOPT_TIMERDATA.pdf                         \
  CURLMOPT_TIMERFUNCTION.pdf                     \
+ CURLOPT_ABSTRACT_UNIX_SOCKET.pdf               \
  CURLOPT_ACCEPTTIMEOUT_MS.pdf                   \
  CURLOPT_ACCEPT_ENCODING.pdf                    \
  CURLOPT_ADDRESS_SCOPE.pdf                      \