Add Precompress example and basic support

build.c

@@ -9,7 +9,7 @@ int main(int argc, char **argv) {
     char *CXX = strncpy(calloc(1024, 1), or_else(getenv("CXX"), "g++"), 1024);
     char *EXEC_SUFFIX = strncpy(calloc(1024, 1), maybe(getenv("EXEC_SUFFIX")), 1024);
 
-    char *EXAMPLE_FILES[] = {"EchoBody", "HelloWorldThreaded", "Http3Server", "Broadcast", "HelloWorld", "Crc32", "ServerName",
+    char *EXAMPLE_FILES[] = {"Precompress", "EchoBody", "HelloWorldThreaded", "Http3Server", "Broadcast", "HelloWorld", "Crc32", "ServerName",
     "EchoServer", "BroadcastingEchoServer", "UpgradeSync", "UpgradeAsync", "ParameterRoutes"};
 
     strcat(CXXFLAGS, " -march=native -O3 -Wpedantic -Wall -Wextra -Wsign-conversion -Wconversion -std=c++20 -Isrc -IuSockets/src");

examples/Precompress.cpp

@@ -0,0 +1,77 @@
+#include "App.h"
+
+int main() {
+    /* ws->getUserData returns one of these */
+    struct PerSocketData {
+        /* Fill with user data */
+    };
+
+	/* Keeping track of last precompressed message both in original and compressed format */
+	std::string originalMessage;
+	std::string compressedMessage;
+	std::mutex m;
+
+	/* For demo, we create a thread that will update the precompressed message every second */
+	std::thread t2([&originalMessage, &compressedMessage, &m]() {
+		uWS::ZlibContext zlibContext;
+		uWS::DeflationStream compressor(uWS::DEDICATED_COMPRESSOR);
+		int counter = 0;
+
+		while (true) {
+			counter++;
+
+			m.lock();
+			originalMessage = "Hello you are looking at message number " + std::to_string(counter) + " and this text should be precompressed";		
+			compressedMessage = compressor.deflate(&zlibContext, {originalMessage.data(), originalMessage.length()}, true);
+			m.unlock();
+
+			std::this_thread::sleep_for(std::chrono::milliseconds(500));
+		}
+
+	});
+
+    uWS::App().ws<PerSocketData>("/*", {
+        /* You must only use SHARED_COMPRESSOR with precompression (can't use dedicated_compressor) */
+        .compression = uWS::CompressOptions(uWS::SHARED_COMPRESSOR | uWS::DEDICATED_DECOMPRESSOR),
+        /* Handlers */
+        .upgrade = nullptr,
+        .open = [](auto */*ws*/) {
+            /* Open event here, you may access ws->getUserData() which points to a PerSocketData struct */
+
+        },
+        .message = [&originalMessage, &compressedMessage, &m](auto *ws, std::string_view message, uWS::OpCode opCode) {
+
+			/* First respond by echoing what they send us, without compression */
+			ws->send(message, opCode, false);
+
+			/* This should be wrapped up into ws->sendPrepared(PreparedMessage) in the future, experimental for now */
+			m.lock();
+			if (ws->hasNegotiatedCompression() && compressedMessage.length() < originalMessage.length()) {
+				std::cout << "Responding with precompressed message saving " << (originalMessage.length() - compressedMessage.length()) << " bytes" << std::endl;
+				ws->send({compressedMessage.data(), compressedMessage.length()}, uWS::OpCode::TEXT, uWS::CompressFlags::ALREADY_COMPRESSED);
+			} else {
+				ws->send({originalMessage.data(), originalMessage.length()}, uWS::OpCode::TEXT);
+			}
+			m.unlock();
+        },
+        .dropped = [](auto */*ws*/, std::string_view /*message*/, uWS::OpCode /*opCode*/) {
+            /* A message was dropped due to set maxBackpressure and closeOnBackpressureLimit limit */
+        },
+        .drain = [](auto */*ws*/) {
+            /* Check ws->getBufferedAmount() here */
+        },
+        .ping = [](auto */*ws*/, std::string_view) {
+            /* Not implemented yet */
+        },
+        .pong = [](auto */*ws*/, std::string_view) {
+            /* Not implemented yet */
+        },
+        .close = [](auto */*ws*/, int /*code*/, std::string_view /*message*/) {
+            /* You may access ws->getUserData() here */
+        }
+    }).listen(9001, [&t2](auto *listen_socket) {
+        if (listen_socket) {
+            std::cout << "Listening on port " << 9001 << std::endl;
+        }
+    }).run();
+}

src/WebSocket.h

@@ -27,6 +27,13 @@
 
 namespace uWS {
 
+/* Experimental */
+enum CompressFlags : int {
+    NO_ACTION,
+    COMPRESS,
+    ALREADY_COMPRESSED
+};
+
 template <bool SSL, bool isServer, typename USERDATA>
 struct WebSocket : AsyncSocket<SSL> {
     template <bool> friend struct TemplatedApp;
@@ -87,9 +94,15 @@ struct WebSocket : AsyncSocket<SSL> {
         return send(message, CONTINUATION, compress, true);
     }
 
+    /* Experimental */
+    bool hasNegotiatedCompression() {
+        WebSocketData *webSocketData = (WebSocketData *) Super::getAsyncSocketData();
+        return webSocketData->compressionStatus == WebSocketData::ENABLED;
+    }
+
     /* Send or buffer a WebSocket frame, compressed or not. Returns BACKPRESSURE on increased user space backpressure,
      * DROPPED on dropped message (due to backpressure) or SUCCCESS if you are free to send even more now. */
-    SendStatus send(std::string_view message, OpCode opCode = OpCode::BINARY, bool compress = false, bool fin = true) {
+    SendStatus send(std::string_view message, OpCode opCode = OpCode::BINARY, int compress = false, bool fin = true) {
         WebSocketContextData<SSL, USERDATA> *webSocketContextData = (WebSocketContextData<SSL, USERDATA> *) us_socket_context_ext(SSL,
             (us_socket_context_t *) us_socket_context(SSL, (us_socket_t *) this)
         );
@@ -145,12 +158,15 @@ struct WebSocket : AsyncSocket<SSL> {
 
                 /* Check and correct the compress hint. It is never valid to compress 0 bytes */
                 if (message.length() && opCode < 3 && webSocketData->compressionStatus == WebSocketData::ENABLED) {
-                    LoopData *loopData = Super::getLoopData();
-                    /* Compress using either shared or dedicated deflationStream */
-                    if (webSocketData->deflationStream) {
-                        message = webSocketData->deflationStream->deflate(loopData->zlibContext, message, false);
-                    } else {
-                        message = loopData->deflationStream->deflate(loopData->zlibContext, message, true);
+                    /* If compress is 2 (IS_PRE_COMPRESSED), skip this step (experimental) */
+                    if (compress != CompressFlags::ALREADY_COMPRESSED) {
+                        LoopData *loopData = Super::getLoopData();
+                        /* Compress using either shared or dedicated deflationStream */
+                        if (webSocketData->deflationStream) {
+                            message = webSocketData->deflationStream->deflate(loopData->zlibContext, message, false);
+                        } else {
+                            message = loopData->deflationStream->deflate(loopData->zlibContext, message, true);
+                        }
                     }
                 } else {
                     compress = false;