Add memory limited dedicated compressors

src/App.h

@@ -27,19 +27,10 @@
 #include "WebSocket.h"
 #include "WebSocketExtensions.h"
 #include "WebSocketHandshake.h"
+#include "PerMessageDeflate.h"
 
 namespace uWS {
 
-/* Compress options (really more like PerMessageDeflateOptions) */
-enum CompressOptions {
-    /* Compression disabled */
-    DISABLED = 0,
-    /* We compress using a shared non-sliding window. No added memory usage, worse compression. */
-    SHARED_COMPRESSOR = 1,
-    /* We compress using a dedicated sliding window. Major memory usage added, better compression of similarly repeated messages. */
-    DEDICATED_COMPRESSOR = 2
-};
-
 template <bool SSL>
 struct TemplatedApp {
 private:
@@ -130,7 +121,7 @@ public:
             if (!loopData->zlibContext) {
                 loopData->zlibContext = new ZlibContext;
                 loopData->inflationStream = new InflationStream;
-                loopData->deflationStream = new DeflationStream;
+                loopData->deflationStream = new DeflationStream(CompressOptions::DEDICATED_COMPRESSOR);
             }
         }
 
@@ -173,9 +164,10 @@ public:
                     res->writeHeader("Sec-WebSocket-Protocol", secWebSocketProtocol.substr(0, secWebSocketProtocol.find(',')));
                 }
 
-                /* Negotiate compression */
+                /* Negotiate compression, we may use a smaller compression window than we negotiate */
                 bool perMessageDeflate = false;
-                bool slidingDeflateWindow = false;
+                /* We are always allowed to share compressor, if perMessageDeflate */
+                int compressOptions = behavior.compression & SHARED_COMPRESSOR;
                 if (behavior.compression != DISABLED) {
                     std::string_view extensions = req->getHeader("sec-websocket-extensions");
                     if (extensions.length()) {
@@ -205,7 +197,7 @@ public:
 
                         /* Is the server allowed to compress with a sliding window? */
                         if (!(extensionsNegotiator.getNegotiatedOptions() & SERVER_NO_CONTEXT_TAKEOVER)) {
-                            slidingDeflateWindow = true;
+                            compressOptions = behavior.compression;
                         }
                     }
                 }
@@ -231,7 +223,7 @@ public:
 
                 /* Initialize websocket with any moved backpressure intact */
                 httpContext->upgradeToWebSocket(
-                            webSocket->init(perMessageDeflate, slidingDeflateWindow, std::move(backpressure))
+                            webSocket->init(perMessageDeflate, compressOptions, std::move(backpressure))
                             );
 
                 /* Arm idleTimeout */

src/PerMessageDeflate.h

@@ -20,6 +20,28 @@
 #ifndef UWS_PERMESSAGEDEFLATE_H
 #define UWS_PERMESSAGEDEFLATE_H
 
+/* We always define these options no matter if ZLIB is enabled or not */
+namespace uWS {
+    /* Compress options (really more like PerMessageDeflateOptions) */
+    enum CompressOptions : int {
+        /* Compression disabled */
+        DISABLED = 0,
+        /* We compress using a shared non-sliding window. No added memory usage, worse compression. */
+        SHARED_COMPRESSOR = 1,
+        /* We compress using a dedicated sliding window. Major memory usage added, better compression of similarly repeated messages. */
+        DEDICATED_COMPRESSOR = 2,
+        /* Flags for limiting memory usage of dedicated compressor */
+        DEDICATED_COMPRESSOR_2KB = 2 | 4,
+        DEDICATED_COMPRESSOR_4KB = 2 | 8,
+        DEDICATED_COMPRESSOR_8KB = 2 | 16,
+        DEDICATED_COMPRESSOR_16KB = 2 | 32,
+        DEDICATED_COMPRESSOR_32KB = 2 | 64,
+        DEDICATED_COMPRESSOR_64KB = 2 | 128,
+        DEDICATED_COMPRESSOR_128KB = 2 | 256,
+        DEDICATED_COMPRESSOR_256KB = 2 | 512
+    };
+}
+
 #ifndef UWS_NO_ZLIB
 #include <zlib.h>
 #endif
@@ -68,8 +90,42 @@ struct ZlibContext {
 struct DeflationStream {
     z_stream deflationStream = {};
 
-    DeflationStream() {
-        deflateInit2(&deflationStream, 1, Z_DEFLATED, -15, 8, Z_DEFAULT_STRATEGY);
+    DeflationStream(int compressOptions) {
+
+        /* Sliding inflator should be about 44kb by default, less than compressor */
+
+        /* Memory usage is given by 2 ^ (windowBits + 2) + 2 ^ (memLevel + 9) */
+        int windowBits = -15, memLevel = 8;
+
+        if (compressOptions == DEDICATED_COMPRESSOR_2KB) {
+            windowBits = -8;
+            memLevel = 1;
+        } else if (compressOptions == DEDICATED_COMPRESSOR_4KB) {
+            windowBits = -9;
+            memLevel = 2;
+        } else if (compressOptions == DEDICATED_COMPRESSOR_8KB) {
+            windowBits = -10;
+            memLevel = 3;
+        } else if (compressOptions == DEDICATED_COMPRESSOR_16KB) {
+            windowBits = -11;
+            memLevel = 4;
+        } else if (compressOptions == DEDICATED_COMPRESSOR_32KB) {
+            windowBits = -12;
+            memLevel = 5;
+        } else if (compressOptions == DEDICATED_COMPRESSOR_64KB) {
+            windowBits = -13;
+            memLevel = 6;
+        } else if (compressOptions == DEDICATED_COMPRESSOR_128KB) {
+            windowBits = -14;
+            memLevel = 7;
+        } else if (compressOptions == DEDICATED_COMPRESSOR_256KB) {
+            windowBits = -15;
+            memLevel = 8;
+        }
+
+        /* DEDICATED_COMPRESSOR_256KB is the same as DEDICATED_COMPRESSOR */
+
+        deflateInit2(&deflationStream, 1, Z_DEFLATED, windowBits, memLevel, Z_DEFAULT_STRATEGY);
     }
 
     /* Deflate and optionally reset */

src/WebSocket.h

@@ -33,8 +33,8 @@ struct WebSocket : AsyncSocket<SSL> {
 private:
     typedef AsyncSocket<SSL> Super;
 
-    void *init(bool perMessageDeflate, bool slidingCompression, std::string &&backpressure) {
-        new (us_socket_ext(SSL, (us_socket_t *) this)) WebSocketData(perMessageDeflate, slidingCompression, std::move(backpressure));
+    void *init(bool perMessageDeflate, int compressOptions, std::string &&backpressure) {
+        new (us_socket_ext(SSL, (us_socket_t *) this)) WebSocketData(perMessageDeflate, compressOptions, std::move(backpressure));
         return this;
     }
 public:

src/WebSocketData.h

@@ -45,12 +45,12 @@ private:
     /* We could be a subscriber */
     Subscriber *subscriber = nullptr;
 public:
-    WebSocketData(bool perMessageDeflate, bool slidingCompression, std::string &&backpressure) : AsyncSocketData<false>(std::move(backpressure)), WebSocketState<true>() {
+    WebSocketData(bool perMessageDeflate, int compressOptions, std::string &&backpressure) : AsyncSocketData<false>(std::move(backpressure)), WebSocketState<true>() {
         compressionStatus = perMessageDeflate ? ENABLED : DISABLED;
 
         /* Initialize the dedicated sliding window */
-        if (perMessageDeflate && slidingCompression) {
-            deflationStream = new DeflationStream;
+        if (perMessageDeflate && (compressOptions & CompressOptions::DEDICATED_COMPRESSOR)) {
+            deflationStream = new DeflationStream(compressOptions);
         }
     }