revert missing tests + small fixes

- revert the 4 missing tests, e.g. proxy test from commit 20468f5
- add virtual host name `test.localhost` to embedded jetty server
  (JUnit Tests) since localhost and IP-Addresses are no longer
  supported by the proxy and use this address inside proxy `src`
- add `test-localhost` support for the docker tests. To support
  this the docker hostname need to be set to test.localhost by:
  `--hostname=test.localhost` (only for the docker tests)
- proxy: add file format support for PDF
- proxy: add error messages on "bad request" response
- proxy: remove dead code
- old proxy: add error messages on "bad request" response
- fix incorrect README link to docs
- add `HTTP_PROXY_READ_TIMEOUT` option -- close #240

src/test/java/net/sourceforge/plantuml/servlet/TestOldProxy.java

@@ -0,0 +1,71 @@
+package net.sourceforge.plantuml.servlet;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URL;
+
+import net.sourceforge.plantuml.servlet.utils.WebappTestCase;
+
+
+public class TestOldProxy extends WebappTestCase {
+
+    /**
+     * Verifies the proxified reception of the default Bob and Alice diagram
+     */
+    public void testDefaultProxy() throws IOException {
+        final URL url = new URL(getServerUrl() + "/proxy/" + getTestDiagramUrl());
+        final HttpURLConnection conn = (HttpURLConnection)url.openConnection();
+        // Analyze response
+        // Verifies HTTP status code and the Content-Type
+        assertEquals("Bad HTTP status received", 200, conn.getResponseCode());
+        assertEquals(
+            "Response content type is not PNG",
+            "image/png",
+            conn.getContentType().toLowerCase()
+        );
+        // Get the image and verify its size (~2000 bytes)
+        byte[] inMemoryImage = getContentAsBytes(conn);
+        int diagramLen = inMemoryImage.length;
+        assertTrue(diagramLen > 2000);
+        assertTrue(diagramLen < 3000);
+    }
+
+    public void testProxyWithFormat() throws IOException {
+        final URL url = new URL(getServerUrl() + "/proxy/svg/" + getTestDiagramUrl());
+        final HttpURLConnection conn = (HttpURLConnection)url.openConnection();
+        // Analyze response
+        // Verifies HTTP status code and the Content-Type
+        assertEquals("Bad HTTP status received", 200, conn.getResponseCode());
+        assertEquals(
+            "Response content type is not SVG",
+            "image/svg+xml",
+            conn.getContentType().toLowerCase()
+        );
+        // Get the content and verify its size
+        String diagram = getContentText(conn);
+        int diagramLen = diagram.length();
+        assertTrue(diagramLen > 1000);
+        assertTrue(diagramLen < 3000);
+    }
+
+    /**
+     * Verifies that the HTTP header of a diagram incites the browser to cache it.
+     */
+    public void testInvalidUrl() throws IOException {
+        final URL url = new URL(getServerUrl() + "/proxy/invalidURL");
+        final HttpURLConnection conn = (HttpURLConnection)url.openConnection();
+        // Analyze response
+        // Check if status code is 400
+        assertEquals(
+            "Bad HTTP status received",
+            400,
+            conn.getResponseCode()
+        );
+        // Check error message
+        assertTrue(
+            "Response is not malformed URL",
+            getContentText(conn.getErrorStream()).contains("URL malformed.")
+        );
+    }
+
+}