(http server) support gzip compression

ixwebsocket/IXHttpServer.cpp

@@ -12,6 +12,7 @@
 #include <fstream>
 #include <sstream>
 #include <vector>
+#include <zlib.h>
 
 namespace
 {
@@ -38,6 +39,47 @@ namespace
         auto vec = res.second;
         return std::make_pair(res.first, std::string(vec.begin(), vec.end()));
     }
+
+    std::string gzipCompress(const std::string& str)
+    {
+        z_stream zs; // z_stream is zlib's control structure
+        memset(&zs, 0, sizeof(zs));
+
+        // deflateInit2 configure the file format: request gzip instead of deflate
+        const int windowBits = 15;
+        const int GZIP_ENCODING = 16;
+
+        deflateInit2(&zs, Z_DEFAULT_COMPRESSION, Z_DEFLATED,
+                     windowBits | GZIP_ENCODING, 8,
+                     Z_DEFAULT_STRATEGY);
+
+        zs.next_in = (Bytef*) str.data();
+        zs.avail_in = (uInt) str.size(); // set the z_stream's input
+
+        int ret;
+        char outbuffer[32768];
+        std::string outstring;
+
+        // retrieve the compressed bytes blockwise
+        do
+        {
+            zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
+            zs.avail_out = sizeof(outbuffer);
+
+            ret = deflate(&zs, Z_FINISH);
+
+            if(outstring.size() < zs.total_out)
+            {
+                // append the block to the output string
+                outstring.append(outbuffer,
+                                 zs.total_out - outstring.size());
+            }
+        } while(ret == Z_OK);
+
+        deflateEnd(&zs);
+
+        return outstring;
+    }
 } // namespace
 
 namespace ix
@@ -120,6 +162,12 @@ namespace ix
 
                 std::string content = res.second;
 
+                std::string acceptEncoding = request->headers["Accept-encoding"];
+                if (acceptEncoding == "gzip" or acceptEncoding == "*")
+                {
+                    content = gzipCompress(content);
+                }
+
                 // Log request
                 std::stringstream ss;
                 ss << request->method << " " << request->headers["User-Agent"] << " "