Fixed bug in keepalive code. Cleaned up some exceptions.

Keepalive could cause a segfault if the server closed the connection.  This fixes that as well as updates some of the exception-throwing code to use more appropriate ImapErrors.

src/engine/imap/ClientConnection.vala

@@ -56,7 +56,9 @@ public class Geary.Imap.ClientConnection {
         // TODO: Close connection as gracefully as possible
     }
     
-    // Generates a unique tag for the IMAP connection in the form of "<a-z><000-999>".
+    /**
+     * Generates a unique tag for the IMAP connection in the form of "<a-z><000-999>".
+     */
     public Tag generate_tag() {
         // watch for odometer rollover
         if (++tag_counter >= 1000) {
@@ -71,9 +73,15 @@ public class Geary.Imap.ClientConnection {
         return new Tag("%c%03d".printf(tag_prefix, tag_counter));
     }
     
+    /**
+     * Returns silently if a connection is already established.
+     */
     public async void connect_async(Cancellable? cancellable = null) throws Error {
-        if (cx != null)
-            throw new IOError.EXISTS("Already connected to %s", to_string());
+        if (cx != null) {
+            debug("Already connected to %s", to_string());
+            
+            return;
+        }
         
         cx = yield socket_client.connect_to_host_async(host_specifier, default_port, cancellable);
         ser = new Serializer(new BufferedOutputStream(cx.output_stream));
@@ -159,7 +167,7 @@ public class Geary.Imap.ClientConnection {
     
     private void check_for_connection() throws Error {
         if (cx == null)
-            throw new IOError.CLOSED("Not connected to %s", to_string());
+            throw new ImapError.NOT_CONNECTED("Not connected to %s", to_string());
     }
     
     public string to_string() {

src/engine/imap/ClientSession.vala

@@ -337,8 +337,11 @@ public class Geary.Imap.ClientSession {
         fsm.set_logging(false);
     }
     
-    public Tag? generate_tag() {
-        return (cx != null) ? cx.generate_tag() : null;
+    public Tag generate_tag() throws ImapError {
+        if (cx == null)
+            throw new ImapError.NOT_CONNECTED("Not connected to %s", to_string());
+        
+        return cx.generate_tag();
     }
     
     public string? get_current_mailbox() {
@@ -559,7 +562,15 @@ public class Geary.Imap.ClientSession {
     }
     
     private bool on_keepalive() {
-        send_command_async.begin(new NoopCommand(generate_tag()), null, on_keepalive_completed);
+        try {
+            send_command_async.begin(new NoopCommand(generate_tag()), null, on_keepalive_completed);
+        } catch (ImapError ierr) {
+            message("Unable to keepalive %s, halting attempts: %s", to_string(), ierr.message);
+            
+            keepalive_id = 0;
+            
+            return false;
+        }
         
         return true;
     }
@@ -610,7 +621,7 @@ public class Geary.Imap.ClientSession {
         if (cmd.has_name(LoginCommand.NAME) || cmd.has_name(LogoutCommand.NAME)
             || cmd.has_name(SelectCommand.NAME) || cmd.has_name(ExamineCommand.NAME)
             || cmd.has_name(CloseCommand.NAME)) {
-            throw new IOError.NOT_SUPPORTED("Use direct calls rather than commands");
+            throw new ImapError.NOT_SUPPORTED("Use direct calls rather than commands");
         }
         
         SendCommandParams params = new SendCommandParams(cmd, cancellable, send_command_async.callback);
@@ -937,7 +948,7 @@ public class Geary.Imap.ClientSession {
         assert(object != null);
         
         AsyncParams params = (AsyncParams) object;
-        params.err = new IOError.CLOSED("Connection to %s closing or closed", to_string());
+        params.err = new ImapError.NOT_CONNECTED("Connection to %s closing or closed", to_string());
         
         return state;
     }
@@ -973,7 +984,7 @@ public class Geary.Imap.ClientSession {
         Cancellable? cancellable = null) {
         if (cx == null) {
             return new AsyncCommandResponse(null, user,
-                new IOError.CLOSED("Not connected to %s", server));
+                new ImapError.NOT_CONNECTED("Not connected to %s", server));
         }
         
         try {

src/engine/imap/Error.vala

@@ -10,6 +10,8 @@ public errordomain Geary.ImapError {
     SERVER_ERROR,
     NOT_CONNECTED,
     COMMAND_FAILED,
-    UNAUTHENTICATED
+    UNAUTHENTICATED,
+    NOT_SUPPORTED,
+    NOT_SELECTED
 }
 

src/engine/imap/Mailbox.vala

@@ -27,7 +27,7 @@ public class Geary.Imap.Mailbox : Geary.SmartReference, Geary.Folder {
     public async Gee.List<EmailHeader>? read(int low, int count, Cancellable? cancellable = null)
         throws Error {
         if (mailbox.is_closed())
-            throw new IOError.NOT_FOUND("Mailbox %s closed", mailbox.to_string());
+            throw new ImapError.NOT_SELECTED("Mailbox %s closed", mailbox.to_string());
         
         CommandResponse resp = yield mailbox.session.send_command_async(
             new FetchCommand(mailbox.session.generate_tag(), new MessageSet.range(low, count),
@@ -53,7 +53,7 @@ public class Geary.Imap.Mailbox : Geary.SmartReference, Geary.Folder {
         assert(header != null);
         
         if (mailbox.is_closed())
-            throw new IOError.NOT_FOUND("Folder closed");
+            throw new ImapError.NOT_SELECTED("Folder closed");
         
         CommandResponse resp = yield mailbox.session.send_command_async(
             new FetchCommand(mailbox.session.generate_tag(), new MessageSet(hdr.msg_num),