Added Http cache awareness

to skip updating the database when the remote file has not changed.

app/src/main/java/be/digitalia/fosdem/activities/MainActivity.java

@@ -150,6 +150,9 @@ public class MainActivity extends ActionBarActivity implements ListView.OnItemCl
 				case FosdemApi.RESULT_ERROR:
 					message = getString(R.string.schedule_loading_error);
 					break;
+				case FosdemApi.RESULT_UP_TO_DATE:
+					message = getString(R.string.events_download_up_to_date);
+					break;
 				case 0:
 					message = getString(R.string.events_download_empty);
 					break;

app/src/main/java/be/digitalia/fosdem/api/FosdemApi.java

@@ -1,12 +1,12 @@
 package be.digitalia.fosdem.api;
 
-import java.io.InputStream;
-import java.util.concurrent.locks.Lock;
-import java.util.concurrent.locks.ReentrantLock;
-
 import android.content.Context;
 import android.content.Intent;
 import android.support.v4.content.LocalBroadcastManager;
+
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
 import be.digitalia.fosdem.db.DatabaseManager;
 import be.digitalia.fosdem.model.Event;
 import be.digitalia.fosdem.parsers.EventsParser;
@@ -27,6 +27,7 @@ public class FosdemApi {
 	public static final String EXTRA_RESULT = "RESULT";
 
 	public static final int RESULT_ERROR = -1;
+	public static final int RESULT_UP_TO_DATE = -2;
 
 	private static final Lock scheduleLock = new ReentrantLock();
 
@@ -43,16 +44,29 @@ public class FosdemApi {
 
 		int result = RESULT_ERROR;
 		try {
-			InputStream is = HttpUtils.get(context, FosdemUrls.getSchedule(), ACTION_DOWNLOAD_SCHEDULE_PROGRESS, EXTRA_PROGRESS);
+			DatabaseManager dbManager = DatabaseManager.getInstance();
+			HttpUtils.HttpResult httpResult = HttpUtils.get(
+					context,
+					FosdemUrls.getSchedule(),
+					dbManager.getLastModifiedTag(),
+					ACTION_DOWNLOAD_SCHEDULE_PROGRESS,
+					EXTRA_PROGRESS);
+			if (httpResult.inputStream == null) {
+				// Nothing to parse, the result is up-to-date.
+				result = RESULT_UP_TO_DATE;
+				return;
+			}
+
 			try {
-				Iterable<Event> events = new EventsParser().parse(is);
-				result = DatabaseManager.getInstance().storeSchedule(events);
+				Iterable<Event> events = new EventsParser().parse(httpResult.inputStream);
+				result = dbManager.storeSchedule(events, httpResult.lastModified);
 			} finally {
 				try {
-					is.close();
+					httpResult.inputStream.close();
 				} catch (Exception ignored) {
 				}
 			}
+
 		} catch (Exception e) {
 			e.printStackTrace();
 		} finally {

app/src/main/java/be/digitalia/fosdem/db/DatabaseManager.java

@@ -50,6 +50,7 @@ public class DatabaseManager {
 
 	private static final String DB_PREFS_FILE = "database";
 	private static final String LAST_UPDATE_TIME_PREF = "last_update_time";
+	private static final String LAST_MODIFIED_TAG_PREF = "last_modified_tag";
 
 	private static DatabaseManager instance;
 
@@ -117,13 +118,21 @@ public class DatabaseManager {
 		return getSharedPreferences().getLong(LAST_UPDATE_TIME_PREF, -1L);
 	}
 
+	/**
+	 *
+	 * @return The time identifier of the current version of the database.
+	 */
+	public String getLastModifiedTag() {
+		return getSharedPreferences().getString(LAST_MODIFIED_TAG_PREF, null);
+	}
+
 	/**
 	 * Stores the schedule to the database.
 	 * 
 	 * @param events
 	 * @return The number of events processed.
 	 */
-	public int storeSchedule(Iterable<Event> events) {
+	public int storeSchedule(Iterable<Event> events, String lastModifiedTag) {
 		boolean isComplete = false;
 
 		SQLiteDatabase db = helper.getWritableDatabase();
@@ -260,8 +269,11 @@ public class DatabaseManager {
 				// Clear cache
 				cachedDays = null;
 				year = -1;
-				// Set last update time
-				getSharedPreferences().edit().putLong(LAST_UPDATE_TIME_PREF, System.currentTimeMillis()).commit();
+				// Set last update time and server's last modified tag
+				getSharedPreferences().edit()
+						.putLong(LAST_UPDATE_TIME_PREF, System.currentTimeMillis())
+						.putString(LAST_MODIFIED_TAG_PREF, lastModifiedTag)
+						.commit();
 
 				context.getContentResolver().notifyChange(URI_TRACKS, null);
 				context.getContentResolver().notifyChange(URI_EVENTS, null);

app/src/main/java/be/digitalia/fosdem/utils/HttpUtils.java

@@ -43,9 +43,9 @@ public class HttpUtils {
 		});
 
 		// Trust all HTTPS certificates
-		TrustManager[] trustAllCerts = new TrustManager[] { new X509TrustManager() {
+		TrustManager[] trustAllCerts = new TrustManager[]{new X509TrustManager() {
 			public java.security.cert.X509Certificate[] getAcceptedIssuers() {
-				return new java.security.cert.X509Certificate[] {};
+				return new java.security.cert.X509Certificate[]{};
 			}
 
 			public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {
@@ -53,7 +53,7 @@ public class HttpUtils {
 
 			public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {
 			}
-		} };
+		}};
 		try {
 			SSLContext sc = SSLContext.getInstance("TLS");
 			sc.init(null, trustAllCerts, new java.security.SecureRandom());
@@ -63,44 +63,67 @@ public class HttpUtils {
 		}
 	}
 
+	public static class HttpResult {
+		// Will be null when the local content is up-to-date
+		public InputStream inputStream;
+		public String lastModified;
+	}
+
 	public static InputStream get(Context context, String path) throws IOException {
-		return get(context, new URL(path), null, null);
+		return get(context, new URL(path), null, null, null).inputStream;
 	}
 
-	public static InputStream get(Context context, String path, String progressAction, String progressExtra) throws IOException {
-		return get(context, new URL(path), progressAction, progressExtra);
+	public static HttpResult get(Context context, String path, String lastModified,
+								 String progressAction, String progressExtra) throws IOException {
+		return get(context, new URL(path), lastModified, progressAction, progressExtra);
 	}
 
-	public static InputStream get(final Context context, URL url, final String progressAction, final String progressExtra) throws IOException {
+	public static HttpResult get(final Context context, URL url, String lastModified,
+								 final String progressAction, final String progressExtra) throws IOException {
+		HttpResult result = new HttpResult();
+
 		HttpURLConnection connection = (HttpURLConnection) url.openConnection();
 		connection.setReadTimeout(DEFAULT_TIMEOUT);
 		connection.setConnectTimeout(DEFAULT_TIMEOUT);
+		if (lastModified != null) {
+			connection.addRequestProperty("If-Modified-Since", lastModified);
+		}
 		connection.connect();
 
-		if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
+		result.lastModified = connection.getHeaderField("Last-Modified");
+
+		int responseCode = connection.getResponseCode();
+		if (responseCode != HttpURLConnection.HTTP_OK) {
 			connection.disconnect();
 
-			throw new IOException("Server returned response code: " + connection.getResponseCode());
+			if ((responseCode == HttpURLConnection.HTTP_NOT_MODIFIED) && (lastModified != null)) {
+				// Cached result is still valid; return an empty response
+				return result;
+			}
+
+			throw new IOException("Server returned response code: " + responseCode);
 		}
 
 		final int length = connection.getContentLength();
-		InputStream is = new BufferedInputStream(connection.getInputStream());
+		result.inputStream = new BufferedInputStream(connection.getInputStream());
 		if ((progressAction == null) || (length == -1)) {
 			// No progress support
-			return is;
+			return result;
 		}
 
 		// Broadcast the progression in percents, with a precision of 1/10 of the total file size
-		return new ByteCountInputStream(is, new ByteCountInputStream.ByteCountListener() {
+		result.inputStream = new ByteCountInputStream(result.inputStream,
+				new ByteCountInputStream.ByteCountListener() {
 
-			private LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(context);
+					private LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(context);
 
-			@Override
-			public void onNewCount(int byteCount) {
-				// Cap percent to 100
-				int percent = (byteCount >= length) ? 100 : byteCount * 100 / length;
-				lbm.sendBroadcast(new Intent(progressAction).putExtra(progressExtra, percent));
-			}
-		}, length / 10);
+					@Override
+					public void onNewCount(int byteCount) {
+						// Cap percent to 100
+						int percent = (byteCount >= length) ? 100 : byteCount * 100 / length;
+						lbm.sendBroadcast(new Intent(progressAction).putExtra(progressExtra, percent));
+					}
+				}, length / 10);
+		return result;
 	}
 }

app/src/main/res/values/strings.xml

@@ -10,6 +10,7 @@
     <string name="download_reminder_message">This will update the schedule database to the latest version. Make sure you are connected to the internet.</string>
     <string name="never">Never</string>
     <string name="update_events_db">Update events database</string>
+    <string name="events_download_up_to_date">Database is already up-to-date</string>
     <string name="events_download_empty">No new events found</string>
 
     <plurals name="events_download_completed">