Add a contactExists() method to the contactManager

This requires exposing the `containsContact()` method to the `DatabaseComponent`
and is needed for finding out efficiently whether a contact already exists.

briar-api/src/org/briarproject/api/contact/ContactManager.java

@@ -5,6 +5,7 @@ import org.briarproject.api.db.DbException;
 import org.briarproject.api.db.Transaction;
 import org.briarproject.api.identity.Author;
 import org.briarproject.api.identity.AuthorId;
+import org.briarproject.api.identity.LocalAuthor;
 
 import java.util.Collection;
 
@@ -44,6 +45,14 @@ public interface ContactManager {
 	/** Marks a contact as active or inactive. */
 	void setContactActive(ContactId c, boolean active) throws DbException;
 
+	/** Return true if a contact with this name and public key already exists */
+	boolean contactExists(Transaction txn, AuthorId remoteAuthorID,
+			AuthorId localAuthorId) throws DbException;
+
+	/** Return true if a contact with this name and public key already exists */
+	boolean contactExists(AuthorId remoteAuthorID, AuthorId localAuthorId)
+			throws DbException;
+
 	interface AddContactHook {
 		void addingContact(Transaction txn, Contact c) throws DbException;
 	}

briar-api/src/org/briarproject/api/db/DatabaseComponent.java

@@ -162,6 +162,13 @@ public interface DatabaseComponent {
 	Collection<ContactId> getContacts(Transaction txn, AuthorId a)
 			throws DbException;
 
+	/**
+	 * Returns true if the database contains the given contact for the given
+	 * local pseudonym.
+	 */
+	boolean containsContact(Transaction txn, AuthorId remote, AuthorId local)
+			throws DbException;
+
 	/**
 	 * Returns the unique ID for this device.
 	 * <p/>

briar-core/src/org/briarproject/contact/ContactManagerImpl.java

@@ -125,6 +125,26 @@ class ContactManagerImpl implements ContactManager, RemoveIdentityHook {
 		}
 	}
 
+	@Override
+	public boolean contactExists(Transaction txn, AuthorId remoteAuthorID,
+			AuthorId localAuthorId) throws DbException {
+		return db.containsContact(txn, remoteAuthorID, localAuthorId);
+	}
+
+	@Override
+	public boolean contactExists(AuthorId remoteAuthorID,
+			AuthorId localAuthorId) throws DbException {
+		boolean exists = false;
+		Transaction txn = db.startTransaction(true);
+		try {
+			exists = contactExists(txn, remoteAuthorID, localAuthorId);
+			txn.setComplete();
+		} finally {
+			db.endTransaction(txn);
+		}
+		return exists;
+	}
+
 	private void removeContact(Transaction txn, ContactId c)
 			throws DbException {
 		Contact contact = db.getContact(txn, c);

briar-core/src/org/briarproject/db/DatabaseComponentImpl.java

@@ -342,6 +342,14 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.getContacts(txn, a);
 	}
 
+	public boolean containsContact(Transaction transaction, AuthorId remote,
+			AuthorId local) throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsLocalAuthor(txn, local))
+			throw new NoSuchLocalAuthorException();
+		return db.containsContact(txn, remote, local);
+	}
+
 	public DeviceId getDeviceId(Transaction transaction) throws DbException {
 		T txn = unbox(transaction);
 		return db.getDeviceId(txn);