Add Crc32 hashing example

examples/Crc32.cpp

@@ -0,0 +1,51 @@
+#include "App.h"
+
+/* This is a good example for testing and showing the POST requests.
+ * Anything you post (either with content-length or using transfer-encoding: chunked) will
+ * be hashed with crc32 and sent back in the response. This example also shows how to deal with
+ * aborted requests. */
+
+/* Note that uWS::SSLApp({options}) is the same as uWS::App() when compiled without SSL support */
+
+#include <zlib.h>
+#include <sstream>
+
+int main() {
+
+	uWS::SSLApp({
+	  .key_file_name = "misc/key.pem",
+	  .cert_file_name = "misc/cert.pem",
+	  .passphrase = "1234"
+	}).post("/*", [](auto *res, auto *req) {
+
+		/* Display the headers */
+		std::cout << " --- " << req->getUrl() << " --- " << std::endl;
+		for (auto [key, value] : *req) {
+			std::cout << key << ": " << value << std::endl;
+		}
+
+		auto isAborted = std::make_shared<bool>(false);
+		uLong crc = crc32(0L, Z_NULL, 0);
+		res->onData([res, isAborted, crc](std::string_view chunk, bool isFin) mutable {
+			if (chunk.length()) {
+				crc = crc32(crc, (const Bytef *) chunk.data(), (uInt) chunk.length());
+			}
+
+			if (isFin && !*isAborted) {
+				std::stringstream s;
+    			s << std::hex << crc;
+				res->end(s.str());
+			}
+		});
+
+		res->onAborted([isAborted]() {
+			*isAborted = true;
+		});
+	}).listen(3000, [](auto *listen_socket) {
+	    if (listen_socket) {
+			std::cerr << "Listening on port " << 3000 << std::endl;
+	    }
+	}).run();
+
+	std::cout << "Failed to listen on port 3000" << std::endl;
+}