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

17 files changed, 139 insertions, 19 deletions

diff --git a/docs/cmdline-opts/Makefile.am b/docs/cmdline-opts/Makefile.am
index 925f07fc1..4a10b9e5c 100644
--- a/docs/cmdline-opts/Makefile.am
+++ b/docs/cmdline-opts/Makefile.am
@@ -22,7 +22,8 @@
 
 AUTOMAKE_OPTIONS = foreign no-dependencies
 
-DPAGES = anyauth.d append.d basic.d cacert.d capath.d cert.d		\
+DPAGES = abstract-unix-socket.d anyauth.d 				\
+  append.d basic.d cacert.d capath.d cert.d				\
   cert-status.d cert-type.d ciphers.d compressed.d config.d		\
   connect-timeout.d connect-to.d continue-at.d cookie.d cookie-jar.d	\
   create-dirs.d crlf.d crlfile.d data-ascii.d data-binary.d data.d	\
diff --git a/docs/cmdline-opts/abstract-unix-socket.d b/docs/cmdline-opts/abstract-unix-socket.d
new file mode 100644
index 000000000..bb4467b67
--- /dev/null
+++ b/docs/cmdline-opts/abstract-unix-socket.d
@@ -0,0 +1,9 @@
+Long: abstract-unix-socket
+Arg: <path>
+Help: Connect through an abstract Unix domain socket
+Added: 7.53.0
+Protocols: HTTP
+---
+Connect through an abstract Unix domain socket, instead of using the network.
+Note: netstat shows the path of an abstract socket prefixed with '@', however
+the <path> argument should not have this leading character.
diff --git a/docs/curl.1 b/docs/curl.1
index ce54fb2f1..b930b246f 100644
--- a/docs/curl.1
+++ b/docs/curl.1
@@ -139,6 +139,10 @@ but prefix it with "no-". However, in this list we mostly only list and show
 the --option version of them. (This concept with --no options was added in
 7.19.0. Previously most options were toggled on/off on repeated use of the
 same command line option.)
+.IP "--abstract-unix-socket <path>"
+(HTTP) Connect through an abstract Unix domain socket, instead of using the network.
+
+Added in 7.53.0.
 .IP "--anyauth"
 (HTTP) Tells curl to figure out authentication method by itself, and use the most
 secure one the remote site claims to support. This is done by first doing a
diff --git a/docs/libcurl/curl_easy_setopt.3 b/docs/libcurl/curl_easy_setopt.3
index a130a8a08..66f573464 100644
--- a/docs/libcurl/curl_easy_setopt.3
+++ b/docs/libcurl/curl_easy_setopt.3
@@ -207,6 +207,8 @@ Idle time before sending keep-alive. See \fICURLOPT_TCP_KEEPIDLE(3)\fP
 Interval between keep-alive probes. See \fICURLOPT_TCP_KEEPINTVL(3)\fP
 .IP CURLOPT_UNIX_SOCKET_PATH
 Path to a Unix domain socket. See \fICURLOPT_UNIX_SOCKET_PATH(3)\fP
+.IP CURLOPT_ABSTRACT_UNIX_SOCKET
+Path to an abstract Unix domain socket. See \fICURLOPT_ABSTRACT_UNIX_SOCKET(3)\fP
 .SH NAMES and PASSWORDS OPTIONS (Authentication)
 .IP CURLOPT_NETRC
 Enable .netrc parsing. See \fICURLOPT_NETRC(3)\fP
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                      \
diff --git a/docs/libcurl/symbols-in-versions b/docs/libcurl/symbols-in-versions
index bd5960c2f..89672c5e9 100644
--- a/docs/libcurl/symbols-in-versions
+++ b/docs/libcurl/symbols-in-versions
@@ -317,6 +317,7 @@ CURLOPTTYPE_LONG                7.1
 CURLOPTTYPE_OBJECTPOINT         7.1
 CURLOPTTYPE_OFF_T               7.11.0
 CURLOPTTYPE_STRINGPOINT         7.46.0
+CURLOPT_ABSTRACT_UNIX_SOCKET    7.53.0
 CURLOPT_ACCEPTTIMEOUT_MS        7.24.0
 CURLOPT_ACCEPT_ENCODING         7.21.6
 CURLOPT_ADDRESS_SCOPE           7.19.0
diff --git a/include/curl/curl.h b/include/curl/curl.h
index 9481aca8c..a626caf38 100644
--- a/include/curl/curl.h
+++ b/include/curl/curl.h
@@ -1770,6 +1770,9 @@ typedef enum {
      this option is used only if PROXY_SSL_VERIFYPEER is true */
   CINIT(PROXY_PINNEDPUBLICKEY, STRINGPOINT, 263),
 
+  /* Path to an abstract Unix domain socket */
+  CINIT(ABSTRACT_UNIX_SOCKET, STRINGPOINT, 264),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;
 
diff --git a/include/curl/typecheck-gcc.h b/include/curl/typecheck-gcc.h
index 4eb896eaa..3d683152b 100644
--- a/include/curl/typecheck-gcc.h
+++ b/include/curl/typecheck-gcc.h
@@ -219,7 +219,8 @@ _CURL_WARNING(_curl_easy_getinfo_err_curl_slist,
 
 /* evaluates to true if option takes a char* argument */
 #define _curl_is_string_option(option)                                        \
-  ((option) == CURLOPT_ACCEPT_ENCODING ||                                     \
+  ((option) == CURLOPT_ABSTRACT_UNIX_SOCKET ||                                \
+   (option) == CURLOPT_ACCEPT_ENCODING ||                                     \
    (option) == CURLOPT_CAINFO ||                                              \
    (option) == CURLOPT_CAPATH ||                                              \
    (option) == CURLOPT_COOKIE ||                                              \
diff --git a/lib/curl_addrinfo.c b/lib/curl_addrinfo.c
index 61cdaddc1..7182a0066 100644
--- a/lib/curl_addrinfo.c
+++ b/lib/curl_addrinfo.c
@@ -47,6 +47,8 @@
 #  define in_addr_t unsigned long
 #endif
 
+#include <stddef.h>
+
 #include "curl_addrinfo.h"
 #include "inet_pton.h"
 #include "warnless.h"
@@ -483,24 +485,29 @@ Curl_addrinfo *Curl_str2addr(char *address, int port)
  * struct initialized with this path.
  * Set '*longpath' to TRUE if the error is a too long path.
  */
-Curl_addrinfo *Curl_unix2addr(const char *path, int *longpath)
+Curl_addrinfo *Curl_unix2addr(const char *path, bool *longpath, bool abstract)
 {
   Curl_addrinfo *ai;
   struct sockaddr_un *sa_un;
   size_t path_len;
 
+  *longpath = FALSE;
+
   ai = calloc(1, sizeof(Curl_addrinfo));
   if(!ai)
     return NULL;
   ai->ai_addr = calloc(1, sizeof(struct sockaddr_un));
   if(!ai->ai_addr) {
     free(ai);
-    *longpath = FALSE;
     return NULL;
   }
+
+  sa_un = (void *) ai->ai_addr;
+  sa_un->sun_family = AF_UNIX;
+
   /* sun_path must be able to store the NUL-terminated path */
-  path_len = strlen(path);
-  if(path_len >= sizeof(sa_un->sun_path)) {
+  path_len = strlen(path) + 1;
+  if(path_len > sizeof(sa_un->sun_path)) {
     free(ai->ai_addr);
     free(ai);
     *longpath = TRUE;
@@ -509,10 +516,14 @@ Curl_addrinfo *Curl_unix2addr(const char *path, int *longpath)
 
   ai->ai_family = AF_UNIX;
   ai->ai_socktype = SOCK_STREAM; /* assume reliable transport for HTTP */
-  ai->ai_addrlen = (curl_socklen_t) sizeof(struct sockaddr_un);
-  sa_un = (void *) ai->ai_addr;
-  sa_un->sun_family = AF_UNIX;
-  memcpy(sa_un->sun_path, path, path_len + 1); /* copy NUL byte */
+  ai->ai_addrlen = offsetof(struct sockaddr_un, sun_path) + path_len;
+
+  /* Abstract Unix domain socket have NULL prefix instead of suffix */
+  if(abstract)
+    memcpy(sa_un->sun_path + 1, path, path_len - 1);
+  else
+    memcpy(sa_un->sun_path, path, path_len); /* copy NUL byte */
+
   return ai;
 }
 #endif
diff --git a/lib/curl_addrinfo.h b/lib/curl_addrinfo.h
index 4f24730af..8f6f3d106 100644
--- a/lib/curl_addrinfo.h
+++ b/lib/curl_addrinfo.h
@@ -80,7 +80,7 @@ Curl_ip2addr(int af, const void *inaddr, const char *hostname, int port);
 Curl_addrinfo *Curl_str2addr(char *dotted, int port);
 
 #ifdef USE_UNIX_SOCKETS
-Curl_addrinfo *Curl_unix2addr(const char *path, int *longpath);
+Curl_addrinfo *Curl_unix2addr(const char *path, bool *longpath, bool abstract);
 #endif
 
 #if defined(CURLDEBUG) && defined(HAVE_GETADDRINFO) && \
diff --git a/lib/url.c b/lib/url.c
index 074289ed4..edae1e3f3 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -2814,6 +2814,12 @@ CURLcode Curl_setopt(struct Curl_easy *data, CURLoption option,
 
 #ifdef USE_UNIX_SOCKETS
   case CURLOPT_UNIX_SOCKET_PATH:
+    data->set.abstract_unix_socket = FALSE;
+    result = setstropt(&data->set.str[STRING_UNIX_SOCKET_PATH],
+                       va_arg(param, char *));
+    break;
+  case CURLOPT_ABSTRACT_UNIX_SOCKET:
+    data->set.abstract_unix_socket = TRUE;
     result = setstropt(&data->set.str[STRING_UNIX_SOCKET_PATH],
                        va_arg(param, char *));
     break;
@@ -3523,6 +3529,8 @@ ConnectionExists(struct Curl_easy *data,
           continue;
         if(strcmp(needle->unix_domain_socket, check->unix_domain_socket))
           continue;
+        if(needle->abstract_unix_socket != check->abstract_unix_socket)
+          continue;
       }
       else if(check->unix_domain_socket)
         continue;
@@ -5863,8 +5871,9 @@ static CURLcode resolve_server(struct Curl_easy *data,
       if(!hostaddr)
         result = CURLE_OUT_OF_MEMORY;
       else {
-        int longpath=0;
-        hostaddr->addr = Curl_unix2addr(path, &longpath);
+        bool longpath = FALSE;
+        hostaddr->addr = Curl_unix2addr(path, &longpath,
+                                        conn->abstract_unix_socket);
         if(hostaddr->addr)
           hostaddr->inuse++;
         else {
@@ -6273,6 +6282,7 @@ static CURLcode create_conn(struct Curl_easy *data,
       result = CURLE_OUT_OF_MEMORY;
       goto out;
     }
+    conn->abstract_unix_socket = data->set.abstract_unix_socket;
   }
 #endif
 
diff --git a/lib/urldata.h b/lib/urldata.h
index 0271d266b..96c0aca19 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1133,6 +1133,7 @@ struct connectdata {
 
 #ifdef USE_UNIX_SOCKETS
   char *unix_domain_socket;
+  bool abstract_unix_socket;
 #endif
 };
 
@@ -1754,6 +1755,8 @@ struct UserDefined {
   int stream_weight;
 
   struct Curl_http2_dep *stream_dependents;
+
+  bool abstract_unix_socket;
 };
 
 struct Names {
diff --git a/src/tool_cfgable.h b/src/tool_cfgable.h
index 5db86f4e3..0d2f765d2 100644
--- a/src/tool_cfgable.h
+++ b/src/tool_cfgable.h
@@ -230,6 +230,7 @@ struct OperationConfig {
   bool nonpn;                     /* enable/disable TLS NPN extension */
   bool noalpn;                    /* enable/disable TLS ALPN extension */
   char *unix_socket_path;         /* path to Unix domain socket */
+  bool abstract_unix_socket;      /* path to an abstract Unix domain socket */
   bool falsestart;
   bool path_as_is;
   double expect100timeout;
diff --git a/src/tool_getparam.c b/src/tool_getparam.c
index d8a3c07bc..2777a0a2e 100644
--- a/src/tool_getparam.c
+++ b/src/tool_getparam.c
@@ -183,6 +183,7 @@ static const struct LongShort aliases[]= {
   {"$R", "expect100-timeout",        TRUE},
   {"$S", "tftp-no-options",          FALSE},
   {"$U", "connect-to",               TRUE},
+  {"$W", "abstract-unix-socket",     TRUE},
   {"0",   "http1.0",                 FALSE},
   {"01",  "http1.1",                 FALSE},
   {"02",  "http2",                   FALSE},
@@ -1024,6 +1025,7 @@ ParameterError getparameter(char *flag,    /* f or -long-flag */
 #endif
         break;
       case 'M': /* --unix-socket */
+        config->abstract_unix_socket = FALSE;
         GetStr(&config->unix_socket_path, nextarg);
         break;
       case 'N': /* --path-as-is */
@@ -1054,6 +1056,10 @@ ParameterError getparameter(char *flag,    /* f or -long-flag */
         if(err)
           return err;
         break;
+      case 'W': /* --abstract-unix-socket */
+        config->abstract_unix_socket = TRUE;
+        GetStr(&config->unix_socket_path, nextarg);
+        break;
       }
       break;
     case '#': /* --progress-bar */
diff --git a/src/tool_help.c b/src/tool_help.c
index a21a336d9..5085e542e 100644
--- a/src/tool_help.c
+++ b/src/tool_help.c
@@ -271,7 +271,8 @@ static const char *const helptext[] = {
   "     --tlsuser USER  TLS username",
   "     --tlspassword STRING  TLS password",
   "     --tlsauthtype STRING  TLS authentication type (default: SRP)",
-  "     --unix-socket FILE    Connect through this Unix domain socket",
+  "     --unix-socket PATH    Connect through this Unix domain socket",
+  "     --abstract-unix-socket PATH Connect to an abstract Unix domain socket",
   " -A, --user-agent STRING  Send User-Agent STRING to server (H)",
   " -v, --verbose       Make the operation more talkative",
   " -V, --version       Show version number and quit",
diff --git a/src/tool_operate.c b/src/tool_operate.c
index eff939f8c..db53d0d5a 100644
--- a/src/tool_operate.c
+++ b/src/tool_operate.c
@@ -1393,11 +1393,17 @@ static CURLcode operate_do(struct GlobalConfig *global,
           my_setopt(curl, CURLOPT_SSL_ENABLE_ALPN, 0L);
         }
 
-        /* new in 7.40.0 */
-        if(config->unix_socket_path)
-          my_setopt_str(curl, CURLOPT_UNIX_SOCKET_PATH,
-                        config->unix_socket_path);
-
+        /* new in 7.40.0, abstract support added in 7.53.0 */
+        if(config->unix_socket_path) {
+          if(config->abstract_unix_socket) {
+            my_setopt_str(curl, CURLOPT_ABSTRACT_UNIX_SOCKET,
+                          config->unix_socket_path);
+          }
+          else {
+            my_setopt_str(curl, CURLOPT_UNIX_SOCKET_PATH,
+                          config->unix_socket_path);
+          }
+        }
         /* new in 7.45.0 */
         if(config->proto_default)
           my_setopt_str(curl, CURLOPT_DEFAULT_PROTOCOL, config->proto_default);