server: minor websocket client handler refactor

Now explicitly closed connections on the client side are
closed with a clean error code. This is motivated by upcoming
work to detect broken websockets and automatically reconnect

src/interface.h

@@ -67,7 +67,6 @@ struct MonitorScope {
 // registerClient and deregisterClient
 struct LaminarClient {
     virtual void sendMessage(std::string payload) = 0;
-    virtual void close(bool now = true) = 0;
     MonitorScope scope;
 };
 

src/server.cpp

@@ -222,7 +222,6 @@ public:
                 // 404
                 c->set_status(websocketpp::http::status_code::not_found);
             }
-            c->lc->close(false);
         });
 
         // Handle new websocket connection. Parse the URL to determine
@@ -262,7 +261,6 @@ public:
         wss.set_close_handler([this](websocketpp::connection_hdl hdl){
             websocket::connection_ptr c = wss.get_con_from_hdl(hdl);
             laminar.deregisterClient(c->lc);
-            c->lc->close();
         });
     }
 
@@ -297,31 +295,29 @@ struct RpcConnection {
 };
 
 // Context for a WebsocketConnection (implements LaminarClient)
-// This object is a streambuf and reimplements xsputn so that it can follow any
-// write the websocketpp library makes to it with a write to the appropriate
-// descriptor in the kj-async context.
-struct Server::WebsocketConnection : public LaminarClient, public std::streambuf {
+// This object maps read and write handlers between the websocketpp library
+// and the corresponding kj async methods
+struct Server::WebsocketConnection : public LaminarClient {
     WebsocketConnection(kj::Own<kj::AsyncIoStream>&& stream, Server::HttpImpl& http) :
         stream(kj::mv(stream)),
-        out(this),
         cn(http.newConnection(this)),
-        writePaf(kj::newPromiseAndFulfiller<void>()),
-        closeOnComplete(false)
+        writePaf(kj::newPromiseAndFulfiller<void>())
     {
-        cn->register_ostream(&out);
+        cn->set_write_handler([this](websocketpp::connection_hdl, const char* s, size_t sz) {
+            outputBuffer.append(std::string(s, sz));
+            writePaf.fulfiller->fulfill();
+            return std::error_code();
+        });
         cn->start();
     }
 
-    ~WebsocketConnection() noexcept(true) {
-        outputBuffer.clear();
-        writePaf.fulfiller->fulfill();
+    virtual ~WebsocketConnection() noexcept(true) {
     }
 
     kj::Promise<void> pend() {
         return stream->tryRead(ibuf, 1, sizeof(ibuf)).then([this](size_t sz){
-            cn->read_all(ibuf, sz);
+            cn->read_some(ibuf, sz);
             if(sz == 0 || cn->get_state() == websocketpp::session::state::closed) {
-                cn->eof();
                 return kj::Promise<void>(kj::READY_NOW);
             }
             return pend();
@@ -335,14 +331,13 @@ struct Server::WebsocketConnection : public LaminarClient, public std::streambuf
             // to send now
             payload.swap(outputBuffer);
             writePaf = kj::newPromiseAndFulfiller<void>();
-            if(payload.empty()) {
-                stream->shutdownWrite();
-                return kj::Promise<void>(kj::READY_NOW);
-            } else {
+            KJ_ASSERT(!payload.empty());
             return stream->write(payload.data(), payload.size()).then([this](){
-                    return closeOnComplete ? stream->shutdownWrite(), kj::Promise<void>(kj::READY_NOW) : writeTask();
-                }).attach(kj::mv(payload));
+                if(cn->get_state() == websocketpp::session::state::closed) {
+                    return kj::Promise<void>(kj::READY_NOW);
                 }
+                return writeTask();
+            }).attach(kj::mv(payload));
         });
     }
 
@@ -350,27 +345,11 @@ struct Server::WebsocketConnection : public LaminarClient, public std::streambuf
         cn->send(payload, websocketpp::frame::opcode::text);
     }
 
-    void close(bool now) override {
-        closeOnComplete = true;
-        if(now) {
-            outputBuffer.clear();
-            writePaf.fulfiller->fulfill();
-        }
-    }
-
-    std::streamsize xsputn(const char* s, std::streamsize sz) override {
-        outputBuffer.append(std::string(s, sz));
-        writePaf.fulfiller->fulfill();
-        return sz;
-    }
-
     kj::Own<kj::AsyncIoStream> stream;
-    std::ostream out;
     websocket::connection_ptr cn;
     std::string outputBuffer;
     kj::PromiseFulfillerPair<void> writePaf;
     char ibuf[131072];
-    bool closeOnComplete;
 };
 
 Server::Server(LaminarInterface& li, kj::StringPtr rpcBindAddress,