enchance error logging

Author: danikula

README.md

@@ -140,7 +140,8 @@ HttpProxyCacheServer proxy = HttpProxyCacheServer.Builder(context)
 See `sample` app.
 
 ## Known problems
-`AndroidVideoCache` [doesn't work](https://github.com/danikula/AndroidVideoCache/issues/28) if wifi or mobile internet connection uses proxy.
+- `AndroidVideoCache` [doesn't work](https://github.com/danikula/AndroidVideoCache/issues/28) if wifi or mobile internet connection uses proxy.
+- In some cases clients [can't connect](https://github.com/danikula/AndroidVideoCache/issues/134) to local proxy server ('Error pinging server' error). May be it is result of previous error. Note in this case video will be played, but without caching.
 
 ## Whats new
 See Release Notes [here](https://github.com/danikula/AndroidVideoCache/releases)

library/src/main/java/com/danikula/videocache/Pinger.java

@@ -5,8 +5,13 @@
 
 import java.io.IOException;
 import java.io.OutputStream;
+import java.net.Proxy;
+import java.net.ProxySelector;
 import java.net.Socket;
+import java.net.URI;
+import java.net.URISyntaxException;
 import java.util.Arrays;
+import java.util.List;
 import java.util.Locale;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
@@ -61,13 +66,23 @@ boolean ping(int maxAttempts, int startTimeout) {
             attempts++;
             timeout *= 2;
         }
-        String error = String.format("Error pinging server (attempts: %d, max timeout: %d). " +
-                "If you see this message, please, email me danikula@gmail.com " +
-                "or create issue here https://github.com/danikula/AndroidVideoCache/issues", attempts, timeout / 2);
+        String error = String.format(Locale.US, "Error pinging server (attempts: %d, max timeout: %d). " +
+                        "If you see this message, please, report at https://github.com/danikula/AndroidVideoCache/issues/134. " +
+                        "Default proxies are: %s"
+                , attempts, timeout / 2, getDefaultProxies());
         LOG.error(error, new ProxyCacheException(error));
         return false;
     }
 
+    private List<Proxy> getDefaultProxies() {
+        ProxySelector proxySelector = ProxySelector.getDefault();
+        try {
+            return proxySelector.select(new URI("https://github.com"));
+        } catch (URISyntaxException e) {
+            throw new IllegalStateException(e);
+        }
+    }
+
     boolean isPingRequest(String request) {
         return PING_REQUEST.equals(request);
     }

library/src/main/java/com/danikula/videocache/ProxyCacheException.java

@@ -7,15 +7,17 @@
  */
 public class ProxyCacheException extends Exception {
 
+    private static final String LIBRARY_VERSION = ". Version: " + BuildConfig.VERSION_NAME;
+
     public ProxyCacheException(String message) {
-        super(message);
+        super(message + LIBRARY_VERSION);
     }
 
     public ProxyCacheException(String message, Throwable cause) {
-        super(message, cause);
+        super(message + LIBRARY_VERSION, cause);
     }
 
     public ProxyCacheException(Throwable cause) {
-        super(cause);
+        super("No explanation error" + LIBRARY_VERSION, cause);
     }
 }