Fix RemoteStore::addToStore() latency

Since 6185d25e52, this was very
latency-bound since it required a round-trip for every 32 KiB. So for
example copying a 514 MiB closure over a virtual ethernet device with
a articial delay of just 1 ms took 343s. Now it takes 2.7s.

Fixes #3372.

src/libstore/daemon.cc

@@ -703,6 +703,64 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (!trusted)
             info.ultimate = false;
 
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 23) {
+
+            struct FramedSource : Source
+            {
+                Source & from;
+                bool eof = false;
+                std::vector<unsigned char> pending;
+                size_t pos = 0;
+
+                FramedSource(Source & from) : from(from)
+                { }
+
+                ~FramedSource()
+                {
+                    if (!eof) {
+                        while (true) {
+                            auto n = readInt(from);
+                            if (!n) break;
+                            std::vector<unsigned char> data(n);
+                            from(data.data(), n);
+                        }
+                    }
+                }
+
+                size_t read(unsigned char * data, size_t len) override
+                {
+                    if (eof) throw EndOfFile("reached end of FramedSource");
+
+                    if (pos >= pending.size()) {
+                        size_t len = readInt(from);
+                        if (!len) {
+                            eof = true;
+                            return 0;
+                        }
+                        pending = std::vector<unsigned char>(len);
+                        pos = 0;
+                        from(pending.data(), len);
+                    }
+
+                    auto n = std::min(len, pending.size() - pos);
+                    memcpy(data, pending.data() + pos, n);
+                    pos += n;
+                    return n;
+                }
+            };
+
+            logger->startWork();
+
+            {
+                FramedSource source(from);
+                store->addToStore(info, source, (RepairFlag) repair,
+                    dontCheckSigs ? NoCheckSigs : CheckSigs);
+            }
+
+            logger->stopWork();
+        }
+
+        else {
             std::unique_ptr<Source> source;
             if (GET_PROTOCOL_MINOR(clientVersion) >= 21)
                 source = std::make_unique<TunnelSource>(from, to);
@@ -721,6 +779,8 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                 dontCheckSigs ? NoCheckSigs : CheckSigs);
 
             logger->stopWork();
+        }
+
         break;
     }
 

src/libstore/remote-store.cc

@@ -503,9 +503,84 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
         conn->to << info.registrationTime << info.narSize
                  << info.ultimate << info.sigs << renderContentAddress(info.ca)
                  << repair << !checkSigs;
-        bool tunnel = GET_PROTOCOL_MINOR(conn->daemonVersion) >= 21;
+
-        if (!tunnel) copyNAR(source, conn->to);
+        if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 23) {
-        conn.processStderr(0, tunnel ? &source : nullptr);
+
+            std::exception_ptr ex;
+
+            struct FramedSink : BufferedSink
+            {
+                ConnectionHandle & conn;
+                std::exception_ptr & ex;
+
+                FramedSink(ConnectionHandle & conn, std::exception_ptr & ex) : conn(conn), ex(ex)
+                { }
+
+                ~FramedSink()
+                {
+                    try {
+                        conn->to << 0;
+                        conn->to.flush();
+                    } catch (...) {
+                        ignoreException();
+                    }
+                }
+
+                void write(const unsigned char * data, size_t len) override
+                {
+                    /* Don't send more data if the remote has
+                       encountered an error. */
+                    if (ex) {
+                        auto ex2 = ex;
+                        ex = nullptr;
+                        std::rethrow_exception(ex2);
+                    }
+                    conn->to << len;
+                    conn->to(data, len);
+                };
+            };
+
+            /* Handle log messages / exceptions from the remote on a
+               separate thread. */
+            std::thread stderrThread([&]()
+            {
+                try {
+                    conn.processStderr(0, nullptr);
+                } catch (...) {
+                    ex = std::current_exception();
+                }
+            });
+
+            Finally joinStderrThread([&]()
+            {
+                if (stderrThread.joinable()) {
+                    stderrThread.join();
+                    if (ex) {
+                        try {
+                            std::rethrow_exception(ex);
+                        } catch (...) {
+                            ignoreException();
+                        }
+                    }
+                }
+            });
+
+            {
+                FramedSink sink(conn, ex);
+                copyNAR(source, sink);
+                sink.flush();
+            }
+
+            stderrThread.join();
+            if (ex)
+                std::rethrow_exception(ex);
+
+        } else if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 21) {
+            conn.processStderr(0, &source);
+        } else {
+            copyNAR(source, conn->to);
+            conn.processStderr(0, nullptr);
+        }
     }
 }
 

src/libstore/worker-protocol.hh

@@ -6,7 +6,7 @@ namespace nix {
 #define WORKER_MAGIC_1 0x6e697863
 #define WORKER_MAGIC_2 0x6478696f
 
-#define PROTOCOL_VERSION 0x116
+#define PROTOCOL_VERSION 0x117
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)