Removing hard equality check for gzip encoding header (#245)

Fixes  #242

Author: sumitsharma0999

src/main/java/com/googlecode/jsonrpc4j/JsonRpcServer.java

@@ -174,7 +174,7 @@ private InputStream getRequestStream(HttpServletRequest request) throws IOExcept
 	private int handleRequest0(InputStream input, OutputStream output, String contentEncoding, HttpServletResponse response, ByteArrayOutputStream byteOutput) throws IOException {
 		int result;
 
-		boolean canGzipResponse = contentEncoding != null && GZIP.equalsIgnoreCase(contentEncoding);
+		boolean canGzipResponse = contentEncoding != null && contentEncoding.contains(GZIP);
 		// Use gzip if client's accept-encoding is set to gzip and gzipResponses is enabled.
 		if (gzipResponses && canGzipResponse) {
 			response.addHeader(CONTENT_ENCODING, GZIP);

src/test/java/com/googlecode/jsonrpc4j/server/JsonRpcServerTest.java

@@ -186,6 +186,25 @@ public void testGzipResponse() throws IOException {
 		Assert.assertEquals("gzip", response.getHeader(CONTENT_ENCODING));
 	}
 
+	@Test
+	public void testGzipResponseMultipleAcceptEncoding() throws IOException {
+		MockHttpServletRequest request = new MockHttpServletRequest("POST", "/test-post");
+		request.addHeader(ACCEPT_ENCODING, "gzip,deflate");
+		request.setContentType("application/json");
+		request.setContent("{\"jsonrpc\":\"2.0\",\"id\":123,\"method\":\"testMethod\",\"params\":[\"Whir?inaki\"]}".getBytes(StandardCharsets.UTF_8));
+
+		MockHttpServletResponse response = new MockHttpServletResponse();
+
+		jsonRpcServer = new JsonRpcServer(Util.mapper, mockService, ServiceInterface.class, true);
+		jsonRpcServer.handle(request, response);
+
+		byte[] compressed = response.getContentAsByteArray();
+		String sb = getCompressedResponseContent(compressed);
+
+		Assert.assertEquals(sb, "{\"jsonrpc\":\"2.0\",\"id\":123,\"result\":null}");
+		Assert.assertEquals("gzip", response.getHeader(CONTENT_ENCODING));
+	}
+
 	@Test
 	public void testCorruptRequest() throws Exception {
 		MockHttpServletRequest request = new MockHttpServletRequest("POST", "/test-post");