try to make ascii reader a little bit more robust to failure - mainly ignore messages after a reader has disabled itself

src/input/ReaderBackend.cc

@@ -203,6 +203,9 @@ bool ReaderBackend::Init(string arg_source, int mode, bool arg_autostart)
 }
 
 bool ReaderBackend::StartReading() {
+	if ( disabled ) 
+		return false;
+
 	int success = DoStartReading();
 	
 	if ( success == false ) {
@@ -215,6 +218,9 @@ bool ReaderBackend::StartReading() {
 bool ReaderBackend::AddFilter(int id, int arg_num_fields,
 					   const Field* const * arg_fields) 
 {
+	if ( disabled ) 
+		return false;
+
 	bool success = DoAddFilter(id, arg_num_fields, arg_fields);
 	if ( success && autostart) {
 		autostart = false;
@@ -225,6 +231,9 @@ bool ReaderBackend::AddFilter(int id, int arg_num_fields,
 
 bool ReaderBackend::RemoveFilter(int id) 
 {
+	if ( disabled ) 
+		return false;
+
 	bool success = DoRemoveFilter(id);
 	SendOut(new FilterRemovedMessage(frontend, id));
 	return success; // yes, I know, noone reads this.
@@ -240,11 +249,20 @@ void ReaderBackend::Finish()
 
 bool ReaderBackend::Update() 
 {
-	return DoUpdate();
+	if ( disabled ) 
+		return false;
+
+	bool success = DoUpdate();
+	if ( !success ) {
+		DisableFrontend();
+	}
+
+	return success;
 }
 
 void ReaderBackend::DisableFrontend()
 {
+	disabled = true; // we also set disabled here, because there still may be other messages queued and we will dutifully ignore these from now
 	SendOut(new DisableMessage(frontend));
 }
 

src/input/ReaderBackend.h

@@ -177,7 +177,12 @@ protected:
 	 *
 	 * A reader implementation must override this method but it can just ignore
 	 * calls, if a forced update does not fit the input source or the current input
-	 * reading mode
+	 * reading mode.
+	 *
+	 * If it returns false, it will be assumed that a fatal error has occured
+	 * that prevents the reader from further operation; it will then be
+	 * disabled and eventually deleted. When returning false, an implementation
+	 * should also call Error to indicate what happened.
 	 */
 	virtual bool DoUpdate() = 0;
 	

src/input/readers/Ascii.cc

@@ -458,7 +458,10 @@ bool Ascii::DoUpdate() {
 			if ( file && file->is_open() ) {
 				if ( mode == STREAM ) {
 					file->clear(); // remove end of file evil bits
-					ReadHeader(true); // in case filters changed
+					if ( !ReadHeader(true) )  // in case filters changed
+					{
+						return false; // header reading failed
+					}
 					break;
 				}
 				file->close();
@@ -522,6 +525,7 @@ bool Ascii::DoUpdate() {
 
 				Value* val = EntryToVal(stringfields[(*fit).position], *fit);
 				if ( val == 0 ) {
+					Error("Could not convert String value to Val");
 					return false;
 				}
 				
@@ -580,7 +584,7 @@ bool Ascii::DoHeartbeat(double network_time, double current_time)
 			break;
 		case REREAD:
 		case STREAM:
-			DoUpdate();
+			Update(); // call update and not DoUpdate, because update actually checks disabled.
 			break;
 		default:
 			assert(false);