RPC: Introduce 'unix-abstract:' prefix for abstract Unix sockets

Abstract unix socket addresses can now be specified with the
'unix-abstract:' prefix, and the 'unix:' prefix now explicitly
rejects addresses which contain NULL bytes

c++/src/kj/async-io-test.c++

@@ -102,6 +102,9 @@ TEST(AsyncIo, AddressParsing) {
 
 #if !_WIN32
   EXPECT_EQ("unix:foo/bar/baz", tryParse(w, network, "unix:foo/bar/baz"));
+#if __linux__
+  EXPECT_EQ("unix-abstract:foo/bar/baz", tryParse(w, network, "unix-abstract:foo/bar/baz"));
+#endif
 #endif
 
   // We can parse services by name...

c++/src/kj/async-io-unix.c++

@@ -449,8 +449,12 @@ public:
         return str('[', buffer, "]:", ntohs(addr.inet6.sin6_port));
       }
       case AF_UNIX: {
+        if (addr.unixDomain.sun_path[0] == '\0') {
+          return str("unix-abstract:", addr.unixDomain.sun_path + 1);
+        } else {
           return str("unix:", addr.unixDomain.sun_path);
         }
+      }
       default:
         return str("(unknown address family ", addr.generic.sa_family, ")");
     }
@@ -470,12 +474,25 @@ public:
       StringPtr path = str.slice(strlen("unix:"));
       KJ_REQUIRE(path.size() < sizeof(addr.unixDomain.sun_path),
                  "Unix domain socket address is too long.", str);
+      KJ_REQUIRE(path.size() == strlen(path.cStr()),
+                 "Unix domain socket address contains NULL. Use"
+                 " 'unix-abstract:' for the abstract namespace.");
+      result.addr.unixDomain.sun_family = AF_UNIX;
+      strcpy(result.addr.unixDomain.sun_path, path.cStr());
+      result.addrlen = offsetof(struct sockaddr_un, sun_path) + path.size() + 1;
+      auto array = kj::heapArrayBuilder<SocketAddress>(1);
+      array.add(result);
+      return array.finish();
+    }
+
+    if (str.startsWith("unix-abstract:")) {
+      StringPtr path = str.slice(strlen("unix-abstract:"));
+      KJ_REQUIRE(path.size() + 1 < sizeof(addr.unixDomain.sun_path),
+                 "Unix domain socket address is too long.", str);
       result.addr.unixDomain.sun_family = AF_UNIX;
-      memcpy(result.addr.unixDomain.sun_path, path.cStr(), path.size() + 1);
-      result.addrlen = offsetof(struct sockaddr_un, sun_path) + path.size();
-      // Linux-specific: abstract namespace for unix sockets
-      // According to unix(7), addrlen of an abstract socket should not include the NULL terminator
-      if (path[0] != '\0') result.addrlen++;
+      result.addr.unixDomain.sun_path[0] = '\0';
+      memcpy(result.addr.unixDomain.sun_path + 1, path.cStr(), path.size());
+      result.addrlen = offsetof(struct sockaddr_un, sun_path) + path.size() + 1;
       auto array = kj::heapArrayBuilder<SocketAddress>(1);
       array.add(result);
       return array.finish();

doc/cxxrpc.md

@@ -390,7 +390,8 @@ int main(int argc, const char* argv[]) {
 {% endhighlight %}
 
 Note that for the connect address, Cap'n Proto supports DNS host names as well as IPv4 and IPv6
-addresses.  Additionally, a Unix domain socket can be specified as `unix:` followed by a path name.
+addresses.  Additionally, a Unix domain socket can be specified as `unix:` followed by a path name,
+and an abstract Unix domain socket can be specified as `unix-abstract:` followed by an identifier.
 
 For a more complete example, see the
 [calculator client sample](https://github.com/sandstorm-io/capnproto/tree/master/c++/samples/calculator-client.c++).
@@ -429,7 +430,8 @@ int main(int argc, const char* argv[]) {
 Note that for the bind address, Cap'n Proto supports DNS host names as well as IPv4 and IPv6
 addresses.  The special address `*` can be used to bind to the same port on all local IPv4 and
 IPv6 interfaces.  Additionally, a Unix domain socket can be specified as `unix:` followed by a
-path name.
+path name, and an abstract Unix domain socket can be specified as `unix-abstract:` followed by
+an identifier.
 
 For a more complete example, see the
 [calculator server sample](https://github.com/sandstorm-io/capnproto/tree/master/c++/samples/calculator-server.c++).