Add -rpcbind option to allow binding RPC port on a specific interface

Add -rpcbind command option to specify binding RPC service on one
or multiple specific interfaces.

Functionality if -rpcbind is not specified remains the same as before:

- If no -rpcallowip specified, bind on localhost
- If no -rpcbind specified, bind on any interface

Implements part of #3111.

2 files changed, 62 insertions, 36 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 7007707855..7664988762 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -304,10 +304,11 @@ std::string HelpMessage(HelpMessageMode hmm)
 
     strUsage += "\n" + _("RPC server options:") + "\n";
     strUsage += "  -server                " + _("Accept command line and JSON-RPC commands") + "\n";
+    strUsage += "  -rpcbind=<addr>        " + _("Bind to given address to listen for JSON-RPC connections. Use [host]:port notation for IPv6. This option can be specified multiple times (default: bind to all interfaces)") + "\n";
     strUsage += "  -rpcuser=<user>        " + _("Username for JSON-RPC connections") + "\n";
     strUsage += "  -rpcpassword=<pw>      " + _("Password for JSON-RPC connections") + "\n";
     strUsage += "  -rpcport=<port>        " + _("Listen for JSON-RPC connections on <port> (default: 8332 or testnet: 18332)") + "\n";
-    strUsage += "  -rpcallowip=<ip>       " + _("Allow JSON-RPC connections from specified IP address") + "\n";
+    strUsage += "  -rpcallowip=<ip>       " + _("Allow JSON-RPC connections from specified IP address. This option can be specified multiple times") + "\n";
     strUsage += "  -rpcthreads=<n>        " + _("Set the number of threads to service RPC calls (default: 4)") + "\n";
 
     strUsage += "\n" + _("RPC SSL options: (see the Bitcoin Wiki for SSL setup instructions)") + "\n";
diff --git a/src/rpcserver.cpp b/src/rpcserver.cpp
index d4a229b092..2534a9dcf4 100644
--- a/src/rpcserver.cpp
+++ b/src/rpcserver.cpp
@@ -508,6 +508,14 @@ static void RPCAcceptHandler(boost::shared_ptr< basic_socket_acceptor<Protocol,
     }
 }
 
+static ip::tcp::endpoint ParseEndpoint(const std::string &strEndpoint, int defaultPort)
+{
+    std::string addr;
+    int port = defaultPort;
+    SplitHostPort(strEndpoint, port, addr);
+    return ip::tcp::endpoint(asio::ip::address::from_string(addr), port);
+}
+
 void StartRPCThreads()
 {
     rpc_allow_subnets.clear();
@@ -589,57 +597,74 @@ void StartRPCThreads()
         SSL_CTX_set_cipher_list(rpc_ssl_context->impl(), strCiphers.c_str());
     }
 
-    // Try a dual IPv6/IPv4 socket, falling back to separate IPv4 and IPv6 sockets
-    const bool loopback = !mapArgs.count("-rpcallowip");
-    asio::ip::address bindAddress = loopback ? asio::ip::address_v6::loopback() : asio::ip::address_v6::any();
-    ip::tcp::endpoint endpoint(bindAddress, GetArg("-rpcport", Params().RPCPort()));
-    boost::system::error_code v6_only_error;
+    std::vector<ip::tcp::endpoint> vEndpoints;
+    bool bBindAny = false;
+    int defaultPort = GetArg("-rpcport", Params().RPCPort());
+    if (!mapArgs.count("-rpcallowip")) // Default to loopback if not allowing external IPs
+    {
+        vEndpoints.push_back(ip::tcp::endpoint(asio::ip::address_v6::loopback(), defaultPort));
+        vEndpoints.push_back(ip::tcp::endpoint(asio::ip::address_v4::loopback(), defaultPort));
+        if (mapArgs.count("-rpcbind"))
+        {
+            LogPrintf("WARNING: option -rpcbind was ignored because -rpcallowip was not specified, refusing to allow everyone to connect\n");
+        }
+    } else if (mapArgs.count("-rpcbind")) // Specific bind address
+    {
+        BOOST_FOREACH(const std::string &addr, mapMultiArgs["-rpcbind"])
+        {
+            try {
+                vEndpoints.push_back(ParseEndpoint(addr, defaultPort));
+            }
+            catch(boost::system::system_error &e)
+            {
+                uiInterface.ThreadSafeMessageBox(
+                    strprintf(_("Could not parse -rpcbind value %s as network address"), addr),
+                    "", CClientUIInterface::MSG_ERROR);
+                StartShutdown();
+                return;
+            }
+        }
+    } else { // No specific bind address specified, bind to any
+        vEndpoints.push_back(ip::tcp::endpoint(asio::ip::address_v6::any(), defaultPort));
+        vEndpoints.push_back(ip::tcp::endpoint(asio::ip::address_v4::any(), defaultPort));
+        // Prefer making the socket dual IPv6/IPv4 instead of binding
+        // to both addresses seperately.
+        bBindAny = true;
+    }
 
     bool fListening = false;
     std::string strerr;
-    try
+    BOOST_FOREACH(const ip::tcp::endpoint &endpoint, vEndpoints)
     {
+        asio::ip::address bindAddress = endpoint.address();
+        LogPrintf("Binding RPC on address %s port %i (IPv4+IPv6 bind any: %i)\n", bindAddress.to_string(), endpoint.port(), bBindAny);
+        boost::system::error_code v6_only_error;
         boost::shared_ptr<ip::tcp::acceptor> acceptor(new ip::tcp::acceptor(*rpc_io_service));
         rpc_acceptors.push_back(acceptor);
-        acceptor->open(endpoint.protocol());
-        acceptor->set_option(boost::asio::ip::tcp::acceptor::reuse_address(true));
-
-        // Try making the socket dual IPv6/IPv4 (if listening on the "any" address)
-        acceptor->set_option(boost::asio::ip::v6_only(loopback), v6_only_error);
-
-        acceptor->bind(endpoint);
-        acceptor->listen(socket_base::max_connections);
-
-        RPCListen(acceptor, *rpc_ssl_context, fUseSSL);
-
-        fListening = true;
-    }
-    catch(boost::system::system_error &e)
-    {
-        strerr = strprintf(_("An error occurred while setting up the RPC port %u for listening on IPv6, falling back to IPv4: %s"), endpoint.port(), e.what());
-    }
-    try {
-        // If dual IPv6/IPv4 failed (or we're opening loopback interfaces only), open IPv4 separately
-        if (!fListening || loopback || v6_only_error)
-        {
-            bindAddress = loopback ? asio::ip::address_v4::loopback() : asio::ip::address_v4::any();
-            endpoint.address(bindAddress);
 
-            boost::shared_ptr<ip::tcp::acceptor> acceptor(new ip::tcp::acceptor(*rpc_io_service));
-            rpc_acceptors.push_back(acceptor);
+        try {
             acceptor->open(endpoint.protocol());
             acceptor->set_option(boost::asio::ip::tcp::acceptor::reuse_address(true));
+
+            // Try making the socket dual IPv6/IPv4 when listening on the IPv6 "any" address
+            acceptor->set_option(boost::asio::ip::v6_only(
+                !bBindAny || bindAddress != asio::ip::address_v6::any()), v6_only_error);
+
             acceptor->bind(endpoint);
             acceptor->listen(socket_base::max_connections);
 
             RPCListen(acceptor, *rpc_ssl_context, fUseSSL);
 
             fListening = true;
+            // If dual IPv6/IPv4 bind succesful, skip binding to IPv4 separately
+            if(bBindAny && bindAddress == asio::ip::address_v6::any() && !v6_only_error)
+                break;
+        }
+        catch(boost::system::system_error &e)
+        {
+            LogPrintf("ERROR: Binding RPC on address %s port %i failed: %s\n", bindAddress.to_string(), endpoint.port(), e.what());
+            strerr = strprintf(_("An error occurred while setting up the RPC address %s port %u for listening: %s"), bindAddress.to_string(), endpoint.port(), e.what());
         }
-    }
-    catch(boost::system::system_error &e)
-    {
-        strerr = strprintf(_("An error occurred while setting up the RPC port %u for listening on IPv4: %s"), endpoint.port(), e.what());
     }
 
     if (!fListening) {