see previous comment

src/org/geometerplus/android/fbreader/network/BookDownloaderService.java

@@ -285,8 +285,7 @@ public class BookDownloaderService extends Service {
 		};
 
 		final ZLNetworkRequest request = new ZLNetworkRequest(urlString, sslCertificate) {
-
+			public void handleStream(URLConnection connection, InputStream inputStream) throws IOException, ZLNetworkException {
-			public String handleStream(URLConnection connection, InputStream inputStream) throws IOException {
 				final int updateIntervalMillis = 1000; // FIXME: remove hardcoded time constant
 
 				final int fileLength = connection.getContentLength();
@@ -299,7 +298,7 @@ public class BookDownloaderService extends Service {
 				try {
 					outStream = new FileOutputStream(file);
 				} catch (FileNotFoundException ex) {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_CREATE_FILE, file.getPath());
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_CREATE_FILE, file.getPath());
 				}
 				try {
 					final byte[] buffer = new byte[8192];
@@ -328,19 +327,19 @@ public class BookDownloaderService extends Service {
 				} finally {
 					outStream.close();
 				}
-				return null;
 			}
 		};
 
 		final Thread downloader = new Thread(new Runnable() {
 			public void run() {
-				final String err = ZLNetworkManager.Instance().perform(request);
+				try {
-				// TODO: show error message to User
+					ZLNetworkManager.Instance().perform(request);
-				final boolean success = (err == null);
+				} catch (ZLNetworkException e) {
-				if (!success) {
+					// TODO: show error message to User
 					file.delete();
+					downloadFinishHandler.sendEmptyMessage(0);
 				}
-				downloadFinishHandler.sendEmptyMessage(success ? 1 : 0);
+				downloadFinishHandler.sendEmptyMessage(1);
 			}
 		});
 		downloader.setPriority(Thread.MIN_PRIORITY);

src/org/geometerplus/android/fbreader/network/ItemsLoadingRunnable.java

@@ -22,13 +22,13 @@ package org.geometerplus.android.fbreader.network;
 import android.os.Message;
 import android.os.Handler;
 
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
+
 import org.geometerplus.fbreader.network.INetworkLink;
 import org.geometerplus.fbreader.network.NetworkOperationData;
 import org.geometerplus.fbreader.network.NetworkLibraryItem;
 
-
 abstract class ItemsLoadingRunnable implements Runnable {
-
 	private final ItemsLoadingHandler myHandler;
 
 	private final long myUpdateInterval; // in milliseconds
@@ -83,7 +83,7 @@ abstract class ItemsLoadingRunnable implements Runnable {
 	}
 
 	public abstract String doBefore();
-	public abstract String doLoading(NetworkOperationData.OnNewItemListener doWithListener);
+	public abstract void doLoading(NetworkOperationData.OnNewItemListener doWithListener) throws ZLNetworkException;
 
 	public abstract String getResourceKey();
 

src/org/geometerplus/android/fbreader/network/NetworkCatalogActions.java

@@ -30,6 +30,7 @@ import android.view.ContextMenu;
 
 import org.geometerplus.zlibrary.core.resources.ZLResource;
 import org.geometerplus.zlibrary.core.util.ZLBoolean3;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 import org.geometerplus.zlibrary.ui.android.dialogs.ZLAndroidDialogManager;
 
@@ -342,7 +343,6 @@ class NetworkCatalogActions extends NetworkTreeActions {
 	}
 
 	private static class ExpandCatalogRunnable extends ItemsLoadingRunnable {
-
 		private final NetworkCatalogTree myTree;
 		private final boolean myCheckAuthentication;
 		private final boolean myResumeNotLoad;
@@ -380,11 +380,13 @@ class NetworkCatalogActions extends NetworkTreeActions {
 			return null;
 		}
 
-		public String doLoading(NetworkOperationData.OnNewItemListener doWithListener) {
+		@Override
+		public void doLoading(NetworkOperationData.OnNewItemListener doWithListener) throws ZLNetworkException {
 			if (myResumeNotLoad) {
-				return myTree.Item.resumeLoading(doWithListener);
+				myTree.Item.resumeLoading(doWithListener);
+			} else {
+				myTree.Item.loadChildren(doWithListener);
 			}
-			return myTree.Item.loadChildren(doWithListener);
 		}
 	}
 

src/org/geometerplus/android/fbreader/network/NetworkSearchActivity.java

@@ -29,6 +29,7 @@ import android.os.Bundle;
 import android.content.Intent;
 
 import org.geometerplus.zlibrary.core.resources.ZLResource;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 import org.geometerplus.fbreader.network.*;
 
@@ -140,8 +141,8 @@ public class NetworkSearchActivity extends Activity {
 			return null;
 		}
 
-		public String doLoading(NetworkOperationData.OnNewItemListener doWithListener) {
+		public void doLoading(NetworkOperationData.OnNewItemListener doWithListener) throws ZLNetworkException {
-			return NetworkLibrary.Instance().simpleSearch(myPattern, doWithListener);
+			NetworkLibrary.Instance().simpleSearch(myPattern, doWithListener);
 		}
 	}
 

src/org/geometerplus/fbreader/network/ICustomNetworkLink.java

@@ -19,6 +19,8 @@
 
 package org.geometerplus.fbreader.network;
 
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
+
 public interface ICustomNetworkLink extends INetworkLink {
 
 	public static final int INVALID_ID = -1;
@@ -41,7 +43,7 @@ public interface ICustomNetworkLink extends INetworkLink {
 	void setLink(String urlKey, String url);
 	void removeLink(String urlKey);
 
-	String reloadInfo();
+	void reloadInfo() throws ZLNetworkException;
 
 	// returns true if next methods have changed link's data:
 	//   setSiteName, setTitle, setSummary, setIcon, setLink, removeLink

src/org/geometerplus/fbreader/network/NetworkCatalogItem.java

@@ -22,7 +22,7 @@ package org.geometerplus.fbreader.network;
 import java.util.*;
 
 import org.geometerplus.zlibrary.core.util.ZLBoolean3;
-
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 public abstract class NetworkCatalogItem extends NetworkLibraryItem {
 
@@ -90,14 +90,14 @@ public abstract class NetworkCatalogItem extends NetworkLibraryItem {
 		URLByType = new TreeMap<Integer, String>(urlByType);
 	}
 
-	public abstract String loadChildren(NetworkOperationData.OnNewItemListener listener); // returns Error Message
+	public abstract void loadChildren(NetworkOperationData.OnNewItemListener listener) throws ZLNetworkException;
 
 	public boolean supportsResumeLoading() {
 		return false;
 	}
 
-	public String resumeLoading(NetworkOperationData.OnNewItemListener listener) { // returns Error Message
+	public void resumeLoading(NetworkOperationData.OnNewItemListener listener) throws ZLNetworkException {
-		return NetworkErrors.errorMessage(NetworkErrors.ERROR_UNSUPPORTED_OPERATION);
+		throw new ZLNetworkException(NetworkErrors.ERROR_UNSUPPORTED_OPERATION);
 	}
 
 

src/org/geometerplus/fbreader/network/NetworkLibrary.java

@@ -23,8 +23,9 @@ import java.util.*;
 
 import org.geometerplus.zlibrary.core.util.ZLNetworkUtil;
 import org.geometerplus.zlibrary.core.options.ZLStringOption;
-import org.geometerplus.zlibrary.core.network.ZLNetworkRequest;
 import org.geometerplus.zlibrary.core.network.ZLNetworkManager;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
+import org.geometerplus.zlibrary.core.network.ZLNetworkRequest;
 
 import org.geometerplus.fbreader.tree.FBTree;
 import org.geometerplus.fbreader.network.tree.*;
@@ -226,20 +227,20 @@ public class NetworkLibrary {
 		myLinks = new CompositeList(linksList, new LinksComparator());
 	}
 
-	public String initialize() {
+	public void initialize() throws ZLNetworkException {
 		final LinksComparator comparator = new LinksComparator(); 
 
-		final String error = OPDSLinkReader.loadOPDSLinks(OPDSLinkReader.CACHE_LOAD, new OnNewLinkListener() {
+		try {
-			public void onNewLink(INetworkLink link) {
+			OPDSLinkReader.loadOPDSLinks(OPDSLinkReader.CACHE_LOAD, new OnNewLinkListener() {
-				addLinkInternal(myLoadedLinks, link, comparator);
+				public void onNewLink(INetworkLink link) {
-			}
+					addLinkInternal(myLoadedLinks, link, comparator);
-		});
+				}
-
+			});
-		if (error != null) {
+		} catch (ZLNetworkException e) {
 			synchronized (myLinks) {
 				myLoadedLinks.clear();
 			}
-			return error;
+			throw e;
 		}
 
 		NetworkDatabase.Instance().loadCustomLinks(
@@ -273,8 +274,6 @@ public class NetworkLibrary {
 				 new ATOMUpdated(2012,  2, 15, 23, 40,  1,  0,  3, 30));
 		testDate(new ATOMUpdated(2012,  2, 15, 23, 40,  0,  0.001f,  3, 30),
 				 new ATOMUpdated(2012,  2, 15, 23, 40,  0,  0,  3, 30));*/
-
-		return null;
 	}
 
 	/*private void testDate(ATOMDateConstruct date1, ATOMDateConstruct date2) {
@@ -292,25 +291,29 @@ public class NetworkLibrary {
 	private Object myBackgroundLock = new Object();
 
 	// This method must be called from background thread
-	public String runBackgroundUpdate(boolean clearCache) {
+	public void runBackgroundUpdate(boolean clearCache) throws ZLNetworkException {
 		synchronized (myBackgroundLock) {
 			myBackgroundLinks = new ArrayList<INetworkLink>();
 
 			final int cacheMode = clearCache ? OPDSLinkReader.CACHE_CLEAR : OPDSLinkReader.CACHE_UPDATE;
-			final String error = OPDSLinkReader.loadOPDSLinks(cacheMode, new OnNewLinkListener() {
+			try {
-				public void onNewLink(INetworkLink link) {
+				OPDSLinkReader.loadOPDSLinks(cacheMode, new OnNewLinkListener() {
-					myBackgroundLinks.add(link);
+					public void onNewLink(INetworkLink link) {
-				}
+						myBackgroundLinks.add(link);
-			});
+					}
-
+				});
-			if (error != null || myBackgroundLinks.isEmpty()) {
+			} catch (ZLNetworkException e) {
 				myBackgroundLinks = null;
+				throw e;
+			} finally {
+				if (myBackgroundLinks != null) {
+					if (myBackgroundLinks.isEmpty()) {
+						myBackgroundLinks = null;
+					} else {
+						Collections.sort(myBackgroundLinks, new LinksComparator());
+					}
+				}
 			}
-
-			if (myBackgroundLinks != null) {
-				Collections.sort(myBackgroundLinks, new LinksComparator());
-			}
-			return error;
 		}
 	}
 

src/org/geometerplus/fbreader/network/authentication/litres/LitResAuthenticationXMLReader.java

@@ -25,25 +25,9 @@ import org.geometerplus.fbreader.network.NetworkErrors;
 
 
 class LitResAuthenticationXMLReader extends ZLXMLReaderAdapter {
-
 	public final String HostName;
 
-	private String myErrorMessage;
-
-
 	public LitResAuthenticationXMLReader(String hostName) {
 		HostName = hostName;
 	}
-
-	protected void setErrorCode(String code) {
-		myErrorMessage = NetworkErrors.errorMessage(code);
-	}
-
-	protected void setErrorCode(String code, String arg) {
-		myErrorMessage = NetworkErrors.errorMessage(code, arg);
-	}
-
-	public String getErrorMessage() {
-		return myErrorMessage;
-	}
 }

src/org/geometerplus/fbreader/network/authentication/litres/LitResBookshelfItem.java

@@ -22,10 +22,10 @@ package org.geometerplus.fbreader.network.authentication.litres;
 import java.util.*;
 
 import org.geometerplus.zlibrary.core.util.ZLBoolean3;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 import org.geometerplus.fbreader.network.*;
 
-
 public class LitResBookshelfItem extends NetworkCatalogItem {
 
 	private boolean myForceReload;
@@ -49,24 +49,25 @@ public class LitResBookshelfItem extends NetworkCatalogItem {
 	}
 
 	@Override
-	public String loadChildren(NetworkOperationData.OnNewItemListener listener) {
+	public void loadChildren(NetworkOperationData.OnNewItemListener listener) throws ZLNetworkException {
 		LitResAuthenticationManager mgr = (LitResAuthenticationManager) Link.authenticationManager();
 		if (mgr.isAuthorised(true).Status == ZLBoolean3.B3_FALSE) {
-			return NetworkErrors.errorMessage(NetworkErrors.ERROR_AUTHENTICATION_FAILED);
+			throw new ZLNetworkException(NetworkErrors.ERROR_AUTHENTICATION_FAILED);
 		}
-		String error = null;
+		try {
-		if (myForceReload) {
+			if (myForceReload) {
-			error = mgr.reloadPurchasedBooks();
+				mgr.reloadPurchasedBooks();
+			}
+		} finally {
+			myForceReload = true;
+			// TODO: implement asynchronous loading
+			LinkedList<NetworkLibraryItem> children = new LinkedList<NetworkLibraryItem>();
+			mgr.collectPurchasedBooks(children);
+			Collections.sort(children, new NetworkBookItemComparator());
+			for (NetworkLibraryItem item: children) {
+				listener.onNewItem(Link, item);
+			}
+			listener.commitItems(Link);
 		}
-		myForceReload = true;
-		// TODO: implement asynchronous loading
-		LinkedList<NetworkLibraryItem> children = new LinkedList<NetworkLibraryItem>();
-		mgr.collectPurchasedBooks(children);
-		Collections.sort(children, new NetworkBookItemComparator());
-		for (NetworkLibraryItem item: children) {
-			listener.onNewItem(Link, item);
-		}
-		listener.commitItems(Link);
-		return error;
 	}
 }

src/org/geometerplus/fbreader/network/authentication/litres/LitResLoginXMLReader.java

@@ -20,12 +20,11 @@
 package org.geometerplus.fbreader.network.authentication.litres;
 
 import org.geometerplus.zlibrary.core.xml.ZLStringMap;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 import org.geometerplus.fbreader.network.NetworkErrors;
 
-
 class LitResLoginXMLReader extends LitResAuthenticationXMLReader {
-
 	private static final String TAG_AUTHORIZATION_OK = "catalit-authorization-ok";
 	private static final String TAG_AUTHORIZATION_FAILED = "catalit-authorization-failed";
 
@@ -41,13 +40,13 @@ class LitResLoginXMLReader extends LitResAuthenticationXMLReader {
 	public boolean startElementHandler(String tag, ZLStringMap attributes) {
 		tag = tag.toLowerCase().intern();
 		if (TAG_AUTHORIZATION_FAILED == tag) {
-			setErrorCode(NetworkErrors.ERROR_AUTHENTICATION_FAILED);
+			throw new ZLNetworkException(NetworkErrors.ERROR_AUTHENTICATION_FAILED);
 		} else if (TAG_AUTHORIZATION_OK == tag) {
 			FirstName = attributes.getValue("first-name");
 			LastName = attributes.getValue("first-name");
 			Sid = attributes.getValue("sid");
 		} else {
-			setErrorCode(NetworkErrors.ERROR_SOMETHING_WRONG, HostName);
+			throw new ZLNetworkException(NetworkErrors.ERROR_SOMETHING_WRONG, HostName);
 		}
 		return true;
 	}

src/org/geometerplus/fbreader/network/authentication/litres/LitResNetworkRequest.java

@@ -23,11 +23,10 @@ import java.io.InputStream;
 import java.io.IOException;
 import java.net.URLConnection;
 
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 import org.geometerplus.zlibrary.core.network.ZLNetworkRequest;
 
-
 class LitResNetworkRequest extends ZLNetworkRequest {
-
 	public final LitResAuthenticationXMLReader Reader;
 
 	public LitResNetworkRequest(String url, String sslCertificate, LitResAuthenticationXMLReader reader) {
@@ -36,8 +35,7 @@ class LitResNetworkRequest extends ZLNetworkRequest {
 	}
 
 	@Override
-	public String handleStream(URLConnection connection, InputStream inputStream) throws IOException {
+	public void handleStream(URLConnection connection, InputStream inputStream) throws IOException, ZLNetworkException {
 		Reader.read(inputStream);
-		return Reader.getErrorMessage();
 	}
 }

src/org/geometerplus/fbreader/network/authentication/litres/LitResPasswordRecoveryXMLReader.java

@@ -20,12 +20,11 @@
 package org.geometerplus.fbreader.network.authentication.litres;
 
 import org.geometerplus.zlibrary.core.xml.ZLStringMap;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 import org.geometerplus.fbreader.network.NetworkErrors;
 
-
 class LitResPasswordRecoveryXMLReader extends LitResAuthenticationXMLReader {
-
 	private static final String TAG_PASSWORD_RECOVERY_OK = "catalit-pass-recover-ok";
 	private static final String TAG_PASSWORD_RECOVERY_FAILED = "catalit-pass-recover-failed";
 
@@ -39,16 +38,16 @@ class LitResPasswordRecoveryXMLReader extends LitResAuthenticationXMLReader {
 		if (TAG_PASSWORD_RECOVERY_FAILED == tag) {
 			final String error = attributes.getValue("error");
 			if ("1".equals(error)) {
-				setErrorCode(NetworkErrors.ERROR_NO_USER_EMAIL);
+				throw new ZLNetworkException(NetworkErrors.ERROR_NO_USER_EMAIL);
 			} else if ("2".equals(error)) {
-				setErrorCode(NetworkErrors.ERROR_EMAIL_WAS_NOT_SPECIFIED);
+				throw new ZLNetworkException(NetworkErrors.ERROR_EMAIL_WAS_NOT_SPECIFIED);
 			} else {
-				setErrorCode(NetworkErrors.ERROR_INTERNAL);
+				throw new ZLNetworkException(NetworkErrors.ERROR_INTERNAL);
 			}
 		} else if (TAG_PASSWORD_RECOVERY_OK == tag) {
 			// NOP
 		} else {
-			setErrorCode(NetworkErrors.ERROR_SOMETHING_WRONG, HostName);
+			throw new ZLNetworkException(NetworkErrors.ERROR_SOMETHING_WRONG, HostName);
 		}
 		return true;
 	}

src/org/geometerplus/fbreader/network/authentication/litres/LitResPurchaseXMLReader.java

@@ -20,12 +20,11 @@
 package org.geometerplus.fbreader.network.authentication.litres;
 
 import org.geometerplus.zlibrary.core.xml.ZLStringMap;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 import org.geometerplus.fbreader.network.NetworkErrors;
 
-
 class LitResPurchaseXMLReader extends LitResAuthenticationXMLReader {
-
 	private static final String TAG_AUTHORIZATION_FAILED = "catalit-authorization-failed";
 	private static final String TAG_PURCHASE_OK = "catalit-purchase-ok";
 	private static final String TAG_PURCHASE_FAILED = "catalit-purchase-failed";
@@ -41,7 +40,7 @@ class LitResPurchaseXMLReader extends LitResAuthenticationXMLReader {
 	public boolean startElementHandler(String tag, ZLStringMap attributes) {
 		tag = tag.toLowerCase().intern();
 		if (TAG_AUTHORIZATION_FAILED == tag) {
-			setErrorCode(NetworkErrors.ERROR_AUTHENTICATION_FAILED);
+			throw new ZLNetworkException(NetworkErrors.ERROR_AUTHENTICATION_FAILED);
 		} else {
 			Account = attributes.getValue("account");
 			BookId = attributes.getValue("art");
@@ -50,16 +49,16 @@ class LitResPurchaseXMLReader extends LitResAuthenticationXMLReader {
 			} else if (TAG_PURCHASE_FAILED == tag) {
 				final String error = attributes.getValue("error");
 				if ("1".equals(error)) {
-					setErrorCode(NetworkErrors.ERROR_PURCHASE_NOT_ENOUGH_MONEY);
+					throw new ZLNetworkException(NetworkErrors.ERROR_PURCHASE_NOT_ENOUGH_MONEY);
 				} else if ("2".equals(error)) {
-					setErrorCode(NetworkErrors.ERROR_PURCHASE_MISSING_BOOK);
+					throw new ZLNetworkException(NetworkErrors.ERROR_PURCHASE_MISSING_BOOK);
 				} else if ("3".equals(error)) {
-					setErrorCode(NetworkErrors.ERROR_PURCHASE_ALREADY_PURCHASED);
+					throw new ZLNetworkException(NetworkErrors.ERROR_PURCHASE_ALREADY_PURCHASED);
 				} else {
-					setErrorCode(NetworkErrors.ERROR_INTERNAL);
+					throw new ZLNetworkException(NetworkErrors.ERROR_INTERNAL);
 				}
 			} else {
-				setErrorCode(NetworkErrors.ERROR_SOMETHING_WRONG, HostName);
+				throw new ZLNetworkException(NetworkErrors.ERROR_SOMETHING_WRONG, HostName);
 			}
 		}
 		return true;

src/org/geometerplus/fbreader/network/authentication/litres/LitResRegisterUserXMLReader.java

@@ -20,12 +20,11 @@
 package org.geometerplus.fbreader.network.authentication.litres;
 
 import org.geometerplus.zlibrary.core.xml.ZLStringMap;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 import org.geometerplus.fbreader.network.NetworkErrors;
 
-
 class LitResRegisterUserXMLReader extends LitResAuthenticationXMLReader {
-
 	private static final String TAG_AUTHORIZATION_OK = "catalit-authorization-ok";
 	private static final String TAG_REGISTRATION_FAILED = "catalit-registration-failed";
 
@@ -41,22 +40,22 @@ class LitResRegisterUserXMLReader extends LitResAuthenticationXMLReader {
 		if (TAG_REGISTRATION_FAILED == tag) {
 			final String error = attributes.getValue("error");
 			if ("1".equals(error)) {
-				setErrorCode(NetworkErrors.ERROR_LOGIN_ALREADY_TAKEN);
+				throw new ZLNetworkException(NetworkErrors.ERROR_LOGIN_ALREADY_TAKEN);
 			} else if ("2".equals(error)) {
-				setErrorCode(NetworkErrors.ERROR_LOGIN_WAS_NOT_SPECIFIED);
+				throw new ZLNetworkException(NetworkErrors.ERROR_LOGIN_WAS_NOT_SPECIFIED);
 			} else if ("3".equals(error)) {
-				setErrorCode(NetworkErrors.ERROR_PASSWORD_WAS_NOT_SPECIFIED);
+				throw new ZLNetworkException(NetworkErrors.ERROR_PASSWORD_WAS_NOT_SPECIFIED);
 			} else if ("4".equals(error)) {
-				setErrorCode(NetworkErrors.ERROR_INVALID_EMAIL);
+				throw new ZLNetworkException(NetworkErrors.ERROR_INVALID_EMAIL);
 			} else if ("5".equals(error)) {
-				setErrorCode(NetworkErrors.ERROR_TOO_MANY_REGISTRATIONS);
+				throw new ZLNetworkException(NetworkErrors.ERROR_TOO_MANY_REGISTRATIONS);
 			} else {
-				setErrorCode(NetworkErrors.ERROR_INTERNAL);
+				throw new ZLNetworkException(NetworkErrors.ERROR_INTERNAL);
 			}
 		} else if (TAG_AUTHORIZATION_OK == tag) {
 			Sid = attributes.getValue("sid");
 		} else {
-			setErrorCode(NetworkErrors.ERROR_SOMETHING_WRONG, HostName);
+			throw new ZLNetworkException(NetworkErrors.ERROR_SOMETHING_WRONG, HostName);
 		}
 		return true;
 	}

src/org/geometerplus/fbreader/network/opds/OPDSCatalogItem.java

@@ -22,8 +22,9 @@ package org.geometerplus.fbreader.network.opds;
 import java.util.Map;
 import java.util.HashSet;
 
-import org.geometerplus.zlibrary.core.network.ZLNetworkRequest;
 import org.geometerplus.zlibrary.core.network.ZLNetworkManager;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
+import org.geometerplus.zlibrary.core.network.ZLNetworkRequest;
 
 import org.geometerplus.fbreader.network.*;
 
@@ -51,24 +52,24 @@ class OPDSCatalogItem extends NetworkCatalogItem {
 		super(link, title, summary, cover, urlByType, visibility, catalogType);
 	}
 
-	private String doLoadChildren(NetworkOperationData.OnNewItemListener listener,
+	private void doLoadChildren(NetworkOperationData.OnNewItemListener listener,
-			ZLNetworkRequest networkRequest) {
+			ZLNetworkRequest networkRequest) throws ZLNetworkException {
 		while (networkRequest != null) {
-			final String errorMessage = ZLNetworkManager.Instance().perform(networkRequest);
+			try {
-			if (errorMessage != null) {
+				ZLNetworkManager.Instance().perform(networkRequest);
+			} catch (ZLNetworkException e) {
 				myLoadingState = null;
-				return errorMessage;
+				throw e;
 			}
 			if (listener.confirmInterrupt()) {
-				return null;
+				return;
 			}
 			networkRequest = myLoadingState.resume();
 		}
-		return null;
 	}
 
 	@Override
-	public final String loadChildren(NetworkOperationData.OnNewItemListener listener) {
+	public final void loadChildren(NetworkOperationData.OnNewItemListener listener) throws ZLNetworkException {
 		OPDSNetworkLink opdsLink = (OPDSNetworkLink) Link;
 
 		myLoadingState = opdsLink.createOperationData(Link, listener);
@@ -76,7 +77,7 @@ class OPDSCatalogItem extends NetworkCatalogItem {
 		ZLNetworkRequest networkRequest =
 			opdsLink.createNetworkData(URLByType.get(URL_CATALOG), myLoadingState);
 
-		return doLoadChildren(listener, networkRequest);
+		doLoadChildren(listener, networkRequest);
 	}
 
 	@Override
@@ -85,12 +86,11 @@ class OPDSCatalogItem extends NetworkCatalogItem {
 	}
 
 	@Override
-	public final String resumeLoading(NetworkOperationData.OnNewItemListener listener) {
+	public final void resumeLoading(NetworkOperationData.OnNewItemListener listener) throws ZLNetworkException {
-		if (myLoadingState == null) {
+		if (myLoadingState != null) {
-			return null;
+			myLoadingState.Listener = listener;
+			ZLNetworkRequest networkRequest = myLoadingState.resume();
+			doLoadChildren(listener, networkRequest);
 		}
-		myLoadingState.Listener = listener;
-		ZLNetworkRequest networkRequest = myLoadingState.resume();
-		return doLoadChildren(listener, networkRequest);
 	}
 }

src/org/geometerplus/fbreader/network/opds/OPDSCustomLink.java

@@ -25,6 +25,7 @@ import java.net.URLConnection;
 import java.util.*;
 
 import org.geometerplus.zlibrary.core.network.ZLNetworkManager;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 import org.geometerplus.zlibrary.core.network.ZLNetworkRequest;
 import org.geometerplus.zlibrary.core.util.ZLMiscUtil;
 
@@ -109,35 +110,39 @@ class OPDSCustomLink extends OPDSNetworkLink implements ICustomNetworkLink {
 	}
 
 
-	public String reloadInfo() {
+	public void reloadInfo() throws ZLNetworkException {
 		final LinkedList<String> opensearchDescriptionURLs = new LinkedList<String>();
 		final List<OpenSearchDescription> descriptions = Collections.synchronizedList(new LinkedList<OpenSearchDescription>());
 
-		String err = ZLNetworkManager.Instance().perform(new ZLNetworkRequest(getLink(INetworkLink.URL_MAIN)) {
+		ZLNetworkException error = null;
-			@Override
+		try {
-			public String handleStream(URLConnection connection, InputStream inputStream) throws IOException {
+			ZLNetworkManager.Instance().perform(new ZLNetworkRequest(getLink(INetworkLink.URL_MAIN)) {
-				final CatalogInfoReader info = new CatalogInfoReader(URL, OPDSCustomLink.this, opensearchDescriptionURLs);
+				@Override
-				new OPDSXMLReader(info).read(inputStream);
+				public void handleStream(URLConnection connection, InputStream inputStream) throws IOException, ZLNetworkException {
-
+					final CatalogInfoReader info = new CatalogInfoReader(URL, OPDSCustomLink.this, opensearchDescriptionURLs);
-				if (!info.FeedStarted) {
+					new OPDSXMLReader(info).read(inputStream);
-					return NetworkErrors.errorMessage("notAnOPDS");
+        
+					if (!info.FeedStarted) {
+						throw new ZLNetworkException("notAnOPDS");
+					}
+					if (info.Title == null) {
+						throw new ZLNetworkException("noRequiredInformation");
+					}
+					myTitle = info.Title;
+					if (info.Icon != null) {
+						myIcon = info.Icon;
+					}
+					if (info.Summary != null) {
+						mySummary = info.Summary;
+					}
+					if (info.DirectOpenSearchDescription != null) {
+						descriptions.add(info.DirectOpenSearchDescription);
+					}
 				}
-				if (info.Title == null) {
+			});
-					return NetworkErrors.errorMessage("noRequiredInformation");
+		} catch (ZLNetworkException e) {
-				}
+			error = e;
-				myTitle = info.Title;
+		}
-				if (info.Icon != null) {
-					myIcon = info.Icon;
-				}
-				if (info.Summary != null) {
-					mySummary = info.Summary;
-				}
-				if (info.DirectOpenSearchDescription != null) {
-					descriptions.add(info.DirectOpenSearchDescription);
-				}
-				return null;
-			}
-		});
 
 		// TODO: Use ALL available descriptions and not only Direct
 		if (descriptions.isEmpty() && !opensearchDescriptionURLs.isEmpty()) {
@@ -145,15 +150,17 @@ class OPDSCustomLink extends OPDSNetworkLink implements ICustomNetworkLink {
 			for (String url: opensearchDescriptionURLs) {
 				requests.add(new ZLNetworkRequest(url) {
 					@Override
-					public String handleStream(URLConnection connection, InputStream inputStream) throws IOException {
+					public void handleStream(URLConnection connection, InputStream inputStream) throws IOException, ZLNetworkException {
 						new OpenSearchXMLReader(URL, descriptions, 20).read(inputStream);
-						return null;
 					}
 				});
 			}
-			final String err2 = ZLNetworkManager.Instance().perform(requests);
+			try {
-			if (err == null) {
+				ZLNetworkManager.Instance().perform(requests);
-				err = err2;
+			} catch (ZLNetworkException e) {
+				if (error == null) {
+					error = e;
+				}
 			}
 		}
 
@@ -161,6 +168,8 @@ class OPDSCustomLink extends OPDSNetworkLink implements ICustomNetworkLink {
 			// TODO: May be do not use '%s'??? Use Description instead??? (this needs to rewrite SEARCH engine logic a little)
 			setLink(URL_SEARCH, descriptions.get(0).makeQuery("%s"));
 		}
-		return err;
+		if (error != null) {
+			throw error;
+		}
 	}
 }

src/org/geometerplus/fbreader/network/opds/OPDSLinkReader.java

@@ -27,6 +27,7 @@ import java.util.Map;
 import java.net.URL;
 
 import org.geometerplus.zlibrary.core.network.ZLNetworkManager;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 
 import org.geometerplus.fbreader.Paths;
 import org.geometerplus.fbreader.network.*;
@@ -54,23 +55,23 @@ public class OPDSLinkReader {
 	public static final int CACHE_UPDATE = 1;
 	public static final int CACHE_CLEAR = 2;
 
-	public static String loadOPDSLinks(int cacheMode, final NetworkLibrary.OnNewLinkListener listener) {
+	public static void loadOPDSLinks(int cacheMode, final NetworkLibrary.OnNewLinkListener listener) throws ZLNetworkException {
 		final File dirFile = new File(Paths.networkCacheDirectory());
 		if (!dirFile.exists() && !dirFile.mkdirs()) {
 			try {
 				// Hmm, I'm not sure this solution is good enough; it uses java.net.URL directly instead of ZLNetworkManager
 				//    -- NP
 				new OPDSLinkXMLReader(listener, null).read(new URL(CATALOGS_URL).openStream());
-				return null;
+				return;
 			} catch (Exception e) {
-				return NetworkErrors.errorMessage("cacheDirectoryError");
+				throw new ZLNetworkException("cacheDirectoryError");
 			}
 		}
 
 		final String fileName = "fbreader_catalogs-"
 			+ CATALOGS_URL.substring(CATALOGS_URL.lastIndexOf(File.separator) + 1);
 
-		boolean goodCache = false;
+		boolean cacheIsGood = false;
 		File oldCache = null;
 		ATOMUpdated cacheUpdatedTime = null;
 		final File catalogsFile = new File(dirFile, fileName);
@@ -80,7 +81,7 @@ public class OPDSLinkReader {
 				final long diff = System.currentTimeMillis() - catalogsFile.lastModified();
 				final long valid = 7 * 24 * 60 * 60 * 1000; // one week in milliseconds; FIXME: hardcoded const
 				if (diff >= 0 && diff <= valid) {
-					return null;
+					return;
 				}
 				/* FALLTHROUGH */
 			case CACHE_CLEAR:
@@ -100,7 +101,7 @@ public class OPDSLinkReader {
 				}
 				break;
 			case CACHE_LOAD:
-				goodCache = true;
+				cacheIsGood = true;
 				break;
 			default:
 				throw new IllegalArgumentException("Invalid cacheMode value (" + cacheMode
@@ -108,23 +109,25 @@ public class OPDSLinkReader {
 			}
 		}
 
-		String error = null;
+		if (!cacheIsGood) {
-		if (!goodCache) {
+			try {
-			error = ZLNetworkManager.Instance().downloadToFile(CATALOGS_URL, catalogsFile);
+				ZLNetworkManager.Instance().downloadToFile(CATALOGS_URL, catalogsFile);
-		}
+			} catch (ZLNetworkException e) {
-
+				if (oldCache == null) {
-		if (error != null) {
+					throw e;
-			if (oldCache == null) {
+				}
-				return error;
+				catalogsFile.delete();
+				if (!oldCache.renameTo(catalogsFile)) {
+					oldCache.delete();
+					oldCache = null;
+					throw e;
+				}
+			} finally {
+				if (oldCache != null) {
+					oldCache.delete();
+					oldCache = null;
+				}
 			}
-			catalogsFile.delete();
-			if (!oldCache.renameTo(catalogsFile)) {
-				oldCache.delete();
-				return error;
-			}
-		} else if (oldCache != null) {
-			oldCache.delete();
-			oldCache = null;
 		}
 
 		try {
@@ -132,6 +135,5 @@ public class OPDSLinkReader {
 		} catch (FileNotFoundException e) {
 			throw new RuntimeException("That's impossible!!!", e); 
 		}
-		return null;
 	}
 }

src/org/geometerplus/fbreader/network/opds/OPDSNetworkLink.java

@@ -26,6 +26,7 @@ import java.io.IOException;
 
 import org.geometerplus.zlibrary.core.util.ZLMiscUtil;
 import org.geometerplus.zlibrary.core.util.ZLNetworkUtil;
+import org.geometerplus.zlibrary.core.network.ZLNetworkException;
 import org.geometerplus.zlibrary.core.network.ZLNetworkRequest;
 
 import org.geometerplus.fbreader.network.*;
@@ -89,9 +90,9 @@ class OPDSNetworkLink extends AbstractNetworkLink {
 		url = rewriteUrl(url, false);
 		return new ZLNetworkRequest(url) {
 			@Override
-			public String handleStream(URLConnection connection, InputStream inputStream) throws IOException {
+			public void handleStream(URLConnection connection, InputStream inputStream) throws IOException, ZLNetworkException {
 				if (result.Listener.confirmInterrupt()) {
-					return null;
+					return;
 				}
 
 				new OPDSXMLReader(
@@ -110,7 +111,6 @@ class OPDSNetworkLink extends AbstractNetworkLink {
 				} else {
 					result.Listener.commitItems(OPDSNetworkLink.this);
 				}
-				return null;
 			}
 		};
 	}

src/org/geometerplus/zlibrary/core/network/ZLNetworkManager.java

@@ -41,20 +41,7 @@ public class ZLNetworkManager {
 		return ourManager;
 	}
 
-
+	private void setCommonHTTPOptions(ZLNetworkRequest request, HttpURLConnection httpConnection) throws ZLNetworkException {
-	private String doBeforeRequest(ZLNetworkRequest request) {
-		final String err = request.doBefore();
-		if (err != null) {
-			return err;
-		}
-
-		/*if (request.isInstanceOf(ZLNetworkPostRequest::TYPE_ID)) {
-			return doBeforePostRequest((ZLNetworkPostRequest &) request);
-		}*/
-		return null;
-	}
-
-	private String setCommonHTTPOptions(ZLNetworkRequest request, HttpURLConnection httpConnection) {
 		httpConnection.setInstanceFollowRedirects(request.FollowRedirects);
 		httpConnection.setConnectTimeout(15000); // FIXME: hardcoded timeout value!!!
 		httpConnection.setReadTimeout(30000); // FIXME: hardcoded timeout value!!!
@@ -69,7 +56,7 @@ public class ZLNetworkManager {
 					ZLResourceFile file = ZLResourceFile.createResourceFile(request.SSLCertificate);
 					stream = file.getInputStream();
 				} catch (IOException ex) {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_BAD_FILE, request.SSLCertificate);
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_BAD_FILE, request.SSLCertificate);
 				}
 				try {
 					TrustManager[] managers = new TrustManager[] { new ZLX509TrustManager(stream) };
@@ -77,13 +64,13 @@ public class ZLNetworkManager {
 					context.init(null, managers, null);
 					httpsConnection.setSSLSocketFactory(context.getSocketFactory());
 				} catch (CertificateExpiredException ex) {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_EXPIRED, request.SSLCertificate);
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_EXPIRED, request.SSLCertificate);
 				} catch (CertificateNotYetValidException ex) {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_NOT_YET_VALID, request.SSLCertificate);
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_NOT_YET_VALID, request.SSLCertificate);
 				} catch (CertificateException ex) {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_BAD_FILE, request.SSLCertificate);
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_BAD_FILE, request.SSLCertificate);
 				} catch (GeneralSecurityException ex) {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_SUBSYSTEM);
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_SUBSYSTEM);
 				} finally {
 					try {
 						stream.close();
@@ -93,118 +80,104 @@ public class ZLNetworkManager {
 			}
 		}
 		// TODO: handle Authentication
-		return null;
 	}
 
-	public String perform(ZLNetworkRequest request) {
+	public void perform(ZLNetworkRequest request) throws ZLNetworkException {
 		boolean success = false;
 		try {
-			final String error = doBeforeRequest(request);
+			request.doBefore();
-			if (error != null) {
-				return error;
-			}
 			HttpURLConnection httpConnection = null;
 			int response = -1;
 			for (int retryCounter = 0; retryCounter < 3 && response == -1; ++retryCounter) {
 				final URL url = new URL(request.URL);
 				final URLConnection connection = url.openConnection();
 				if (!(connection instanceof HttpURLConnection)) {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_UNSUPPORTED_PROTOCOL);
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_UNSUPPORTED_PROTOCOL);
 				}
 				httpConnection = (HttpURLConnection) connection;
-				String err = setCommonHTTPOptions(request, httpConnection);
+				setCommonHTTPOptions(request, httpConnection);
-				if (err != null) {
-					return err;
-				}
 				httpConnection.connect();
 				response = httpConnection.getResponseCode();
 			}
 			if (response == HttpURLConnection.HTTP_OK) {
 				InputStream stream = httpConnection.getInputStream();
 				try {
-					final String err = request.doHandleStream(httpConnection, stream);
+					request.doHandleStream(httpConnection, stream);
-					if (err != null) {
-						return err;
-					}
 				} finally {
 					stream.close();
 				}
 				success = true;
 			} else {
 				if (response == HttpURLConnection.HTTP_UNAUTHORIZED) {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_AUTHENTICATION_FAILED);
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_AUTHENTICATION_FAILED);
 				} else {
-					return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SOMETHING_WRONG, ZLNetworkUtil.hostFromUrl(request.URL));
+					throw new ZLNetworkException(ZLNetworkErrors.ERROR_SOMETHING_WRONG, ZLNetworkUtil.hostFromUrl(request.URL));
 				}
 			}
 		} catch (SSLHandshakeException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_CONNECT, ZLNetworkUtil.hostFromUrl(request.URL));
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_CONNECT, ZLNetworkUtil.hostFromUrl(request.URL));
 		} catch (SSLKeyException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_BAD_KEY, ZLNetworkUtil.hostFromUrl(request.URL));
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_BAD_KEY, ZLNetworkUtil.hostFromUrl(request.URL));
 		} catch (SSLPeerUnverifiedException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_PEER_UNVERIFIED, ZLNetworkUtil.hostFromUrl(request.URL));
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_PEER_UNVERIFIED, ZLNetworkUtil.hostFromUrl(request.URL));
 		} catch (SSLProtocolException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_PROTOCOL_ERROR);
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_PROTOCOL_ERROR);
 		} catch (SSLException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SSL_SUBSYSTEM);
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_SSL_SUBSYSTEM);
 		} catch (ConnectException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_CONNECTION_REFUSED, ZLNetworkUtil.hostFromUrl(request.URL));
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_CONNECTION_REFUSED, ZLNetworkUtil.hostFromUrl(request.URL));
 		} catch (NoRouteToHostException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_HOST_CANNOT_BE_REACHED, ZLNetworkUtil.hostFromUrl(request.URL));
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_HOST_CANNOT_BE_REACHED, ZLNetworkUtil.hostFromUrl(request.URL));
 		} catch (UnknownHostException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_RESOLVE_HOST, ZLNetworkUtil.hostFromUrl(request.URL));
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_RESOLVE_HOST, ZLNetworkUtil.hostFromUrl(request.URL));
 		} catch (MalformedURLException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_INVALID_URL);
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_INVALID_URL);
 		} catch (SocketTimeoutException ex) {
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_TIMEOUT);
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_TIMEOUT);
 		} catch (IOException ex) {
 			ex.printStackTrace();
-			return ZLNetworkErrors.errorMessage(ZLNetworkErrors.ERROR_SOMETHING_WRONG, ZLNetworkUtil.hostFromUrl(request.URL));
+			throw new ZLNetworkException(ZLNetworkErrors.ERROR_SOMETHING_WRONG, ZLNetworkUtil.hostFromUrl(request.URL));
 		} finally {
-			final String err = request.doAfter(success);
+			request.doAfter(success);
-			if (success && err != null) {
-				return err;
-			}
 		}
-		return null;
 	}
 
-	public String perform(List<ZLNetworkRequest> requests) {
+	public void perform(List<ZLNetworkRequest> requests) throws ZLNetworkException {
 		if (requests.size() == 0) {
-			return "";
+			throw new ZLNetworkException("");
 		}
 		if (requests.size() == 1) {
-			return perform(requests.get(0));
+			perform(requests.get(0));
 		}
 		HashSet<String> errors = new HashSet<String>();
 		// TODO: implement concurrent execution !!!
 		for (ZLNetworkRequest r: requests) {
-			final String e = perform(r);
+			try {
-			if (e != null && !errors.contains(e)) {
+				perform(r);
-				errors.add(e);
+			} catch (ZLNetworkException e) {
+				errors.add(e.getMessage());
 			}
 		}
-		if (errors.size() == 0) {
+		if (errors.size() > 0) {
-			return null;
+			StringBuilder message = new StringBuilder();
-		}
+			for (String e : errors) {
-		StringBuilder message = new StringBuilder();
+				if (message.length() != 0) {
-		for (String e: errors) {
+					message.append(", ");
-			if (message.length() != 0) {
+				}
-				message.append(", ");
+				message.append(e);
 			}
-			message.append(e);
+			throw new ZLNetworkException(true, message.toString());
 		}
-		return message.toString();
 	}
 
 
-	public final String downloadToFile(String url, final File outFile) {
+	public final void downloadToFile(String url, final File outFile) throws ZLNetworkException {
-		return downloadToFile(url, outFile, 8192);
+		downloadToFile(url, outFile, 8192);
 	}
 
-	public final String downloadToFile(String url, final File outFile, final int bufferSize) {
+	public final void downloadToFile(String url, final File outFile, final int bufferSize) throws ZLNetworkException {
-		return perform(new ZLNetworkRequest(url) {
+		perform(new ZLNetworkRequest(url) {
-			public String handleStream(URLConnection connection, InputStream inputStream) throws IOException {
+			public void handleStream(URLConnection connection, InputStream inputStream) throws IOException, ZLNetworkException {
 				OutputStream outStream = new FileOutputStream(outFile);
 				try {
 					final byte[] buffer = new byte[bufferSize];
@@ -218,7 +191,6 @@ public class ZLNetworkManager {
 				} finally {
 					outStream.close();
 				}
-				return null;
 			}
 		});
 	}

src/org/geometerplus/zlibrary/core/network/ZLNetworkRequest.java

@@ -50,12 +50,10 @@ public abstract class ZLNetworkRequest {
 		SSLCertificate = sslCertificate;
 	}
 
-	// callbacks return error messages
+	public void doBefore() throws ZLNetworkException {
-	public String doBefore() {
-		return null;
 	}
 	
-	String doHandleStream(URLConnection connection, InputStream inputStream) throws IOException {
+	void doHandleStream(URLConnection connection, InputStream inputStream) throws IOException, ZLNetworkException {
 		String encoding = connection.getContentEncoding();
 		if (encoding != null) {
 			encoding = encoding.toLowerCase();
@@ -63,12 +61,11 @@ public abstract class ZLNetworkRequest {
 				inputStream = new GZIPInputStream(inputStream);
 			}
 		}
-		return handleStream(connection, inputStream);
+		handleStream(connection, inputStream);
 	}
 
-	public abstract String handleStream(URLConnection connection, InputStream inputStream) throws IOException;
+	public abstract void handleStream(URLConnection connection, InputStream inputStream) throws IOException, ZLNetworkException;
 
-	public String doAfter(boolean success) { // returned error message is ignored when `success == false`
+	public void doAfter(boolean success) throws ZLNetworkException {
-		return null;
 	}
 }