When a message is shared, share its transitive dependencies

Like other recursive operations on the dependency graph, this is
not done in a single transaction to prevent an attacker from creating
arbitrary large transactions.

So at startup, the `ValidationManager` finds and resumes any
unfinished operations, by looking for shared messages with unshared
dependencies.

briar-api/src/org/briarproject/api/clients/ClientHelper.java

@@ -68,12 +68,6 @@ public interface ClientHelper {
 	void mergeMessageMetadata(Transaction txn, MessageId m,
 			BdfDictionary metadata) throws DbException, FormatException;
 
-	/**
-	 * Marks the given message as shared or unshared with other contacts.
-	 */
-	void setMessageShared(Transaction txn, MessageId m, boolean shared)
-			throws DbException;
-
 	byte[] toByteArray(BdfDictionary dictionary) throws FormatException;
 
 	byte[] toByteArray(BdfList list) throws FormatException;

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

@@ -258,6 +258,15 @@ public interface DatabaseComponent {
 	Collection<MessageId> getPendingMessages(Transaction txn, ClientId c)
 			throws DbException;
 
+	/**
+	 * Returns the IDs of any messages from the given client
+	 * that have a shared dependent, but are still not shared themselves.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<MessageId> getMessagesToShare(Transaction txn,
+			ClientId c) throws DbException;
+
 	/**
 	 * Returns the message with the given ID, in serialised form, or null if
 	 * the message has been deleted.
@@ -456,10 +465,9 @@ public interface DatabaseComponent {
 			throws DbException;
 
 	/**
-	 * Marks the given message as shared or unshared.
+	 * Marks the given message as shared.
 	 */
-	void setMessageShared(Transaction txn, MessageId m, boolean shared)
-			throws DbException;
+	void setMessageShared(Transaction txn, MessageId m) throws DbException;
 
 	/**
 	 * Sets the validation and delivery state of the given message.

briar-api/src/org/briarproject/api/sync/ValidationManager.java

@@ -55,8 +55,9 @@ public interface ValidationManager {
 
 		/**
 		 * Called once for each incoming message that passes validation.
+		 * @return whether or not this message should be shared
 		 */
-		void incomingMessage(Transaction txn, Message m, Metadata meta)
+		boolean incomingMessage(Transaction txn, Message m, Metadata meta)
 				throws DbException;
 	}
 }