Experimental code to better handle interpreter errors.

Currently, a lot of interpreter runtime errors, such as an access to
an unset optional record field, cause Bro to abort with an internal
error. This is an experimental branch that turns such errors into
non-fatal runtime errors by internally raising exceptions. These are
caught upstream and processing continues afterwards.

For now, not many errors actually raise exceptions (the example above
does though). We'll need to go through them eventually and adapt the
current Internal() calls (and potentially others). More generally, at
some point we should cleanup the interpreter error handling (unifying
errors reported at parse- and runtime; and switching to exceptions for
all Expr/Stmt/Vals). But that's a larger change and left for later.

The main question for now is if this code is already helpful enough to
go into 2.0. It will quite likely prevent a number of crashes due to
script errors.

src/Reporter.h

@@ -14,6 +14,22 @@
 
 class Connection;
 class Location;
+class Reporter;
+
+// One cannot raise this exception directly, go through the
+// Reporter's methods instead.
+
+class ReporterException {
+protected:
+	friend class Reporter;
+	ReporterException()	{}
+};
+
+class InterpreterException : public ReporterException {
+protected:
+	friend class Reporter;
+	InterpreterException()	{}
+};
 
 class Reporter {
 public:
@@ -42,6 +58,10 @@ public:
 	// reported and always generate a core dump.
 	void FatalErrorWithCore(const char* fmt, ...);
 
+	// Report a runtime error in evaluating a Bro script expression. This
+	// function will not return but raise an InterpreterException.
+	void ExprRuntimeError(const Expr* expr, const char* fmt, ...);
+
 	// Report a traffic weirdness, i.e., an unexpected protocol situation
 	// that may lead to incorrectly processing a connnection.
 	void Weird(const char* name);	// Raises net_weird().
@@ -87,7 +107,9 @@ public:
 	void EndErrorHandler()	{ --in_error_handler; }
 
 private:
-	void DoLog(const char* prefix, EventHandlerPtr event, FILE* out, Connection* conn, val_list* addl, bool location, bool time, const char* fmt, va_list ap);
+	void DoLog(const char* prefix, EventHandlerPtr event, FILE* out,
+		   Connection* conn, val_list* addl, bool location, bool time,
+		   const char* postfix, const char* fmt, va_list ap);
 
 	// The order if addl, name needs to be like that since fmt_name can
 	// contain format specifiers