Allow default function/hook/event parameters. Addresses #972.

And changed the endianness parameter of bytestring_to_count() BIF to
default to false (big endian), mostly just to prove that the BIF parser
doesn't choke on default parameters.

doc/scripts/builtins.rst

@@ -459,6 +459,31 @@ The Bro scripting language supports the following built-in types.
 
         print greeting("Dave");
 
+    Function parameters may specify default values as long as they appear
+    last in the parameter list:
+
+    .. code:: bro
+
+        global foo: function(s: string, t: string &default="abc", u: count &default=0);
+
+    If a function was previously declared with default parameters, the
+    default expressions can be omitted when implementing the function
+    body and they will still be used for function calls that lack those
+    arguments.
+
+    .. code:: bro
+
+        function foo(s: string, t: string, u: count)
+            {
+            print s, t, u;
+            }
+
+    And calls to the function may omit the defaults from the argument list:
+
+    .. code:: bro
+
+        foo("test");
+
 .. bro:type:: event
 
     Event handlers are nearly identical in both syntax and semantics to
@@ -597,10 +622,10 @@ scripting language supports the following built-in attributes.
 
 .. bro:attr:: &default
 
-    Uses a default value for a record field or container elements. For
-    example, ``table[int] of string &default="foo" }`` would create a
-    table that returns the :bro:type:`string` ``"foo"`` for any
-    non-existing index.
+    Uses a default value for a record field, a function/hook/event
+    parameter, or container elements.  For example, ``table[int] of
+    string &default="foo" }`` would create a table that returns the
+    :bro:type:`string` ``"foo"`` for any non-existing index.
 
 .. bro:attr:: &redef
 

src/Expr.cc

@@ -5478,6 +5478,50 @@ int check_and_promote_exprs(ListExpr*& elements, TypeList* types)
 	return 1;
 	}
 
+int check_and_promote_args(ListExpr*& args, RecordType* types)
+	{
+	expr_list& el = args->Exprs();
+	int ntypes = types->NumFields();
+
+	// give variadic BIFs automatic pass
+	if ( ntypes == 1 && types->FieldDecl(0)->type->Tag() == TYPE_ANY )
+		return 1;
+
+	if ( el.length() < ntypes )
+		{
+		expr_list def_elements;
+
+		// Start from rightmost parameter, work backward to fill in missing
+		// arguments using &default expressions.
+		for ( int i = ntypes - 1; i >= el.length(); --i )
+			{
+			TypeDecl* td = types->FieldDecl(i);
+			Attr* def_attr = td->attrs ? td->attrs->FindAttr(ATTR_DEFAULT) : 0;
+
+			if ( ! def_attr )
+				{
+				types->Error("parameter mismatch", args);
+				return 0;
+				}
+
+			def_elements.insert(def_attr->AttrExpr());
+			}
+
+		loop_over_list(def_elements, i)
+			el.append(def_elements[i]->Ref());
+		}
+
+	TypeList* tl = new TypeList();
+
+	for ( int i = 0; i < types->NumFields(); ++i )
+		tl->Append(types->FieldType(i)->Ref());
+
+	int rval = check_and_promote_exprs(args, tl);
+	Unref(tl);
+
+	return rval;
+	}
+
 int check_and_promote_exprs_to_type(ListExpr*& elements, BroType* type)
 	{
 	expr_list& el = elements->Exprs();

src/Expr.h

@@ -1082,13 +1082,14 @@ Expr* get_assign_expr(Expr* op1, Expr* op2, int is_init);
 // match, promote it as necessary (modifying the ref parameter accordingly)
 // and return 1.
 //
-// The second and third forms are for promoting a list of
+// The second, third, and fourth forms are for promoting a list of
 // expressions (which is updated in place) to either match a list of
 // types or a single type.
 //
 // Note, the type is not "const" because it can be ref'd.
 extern int check_and_promote_expr(Expr*& e, BroType* t);
 extern int check_and_promote_exprs(ListExpr*& elements, TypeList* types);
+extern int check_and_promote_args(ListExpr*& args, RecordType* types);
 extern int check_and_promote_exprs_to_type(ListExpr*& elements, BroType* type);
 
 // Returns a fully simplified form of the expression.  Note that passed

src/Type.cc

@@ -671,9 +671,25 @@ FuncType::FuncType(RecordType* arg_args, BroType* arg_yield, function_flavor arg
 
 	arg_types = new TypeList();
 
+	bool has_default_arg = false;
+
 	for ( int i = 0; i < args->NumFields(); ++i )
+		{
+		const TypeDecl* td = args->FieldDecl(i);
+
+		if ( td->attrs && td->attrs->FindAttr(ATTR_DEFAULT) )
+			has_default_arg = true;
+
+		else if ( has_default_arg )
+			{
+			const char* err_str = fmt("required parameter '%s' must precede "
+			                          "default parameters", td->id);
+			args->Error(err_str);
+			}
+
 		arg_types->Append(args->FieldType(i)->Ref());
 		}
+	}
 
 string FuncType::FlavorString() const
 	{
@@ -708,7 +724,7 @@ BroType* FuncType::YieldType()
 
 int FuncType::MatchesIndex(ListExpr*& index) const
 	{
-	return check_and_promote_exprs(index, arg_types) ?
+	return check_and_promote_args(index, args) ?
 			MATCHES_INDEX_SCALAR : DOES_NOT_MATCH_INDEX;
 	}
 

src/Var.cc

@@ -318,6 +318,29 @@ void add_type(ID* id, BroType* t, attr_list* attr, int /* is_event */)
 		id->SetAttrs(new Attributes(attr, tnew, false));
 	}
 
+static void transfer_arg_defaults(RecordType* args, RecordType* recv)
+	{
+	for ( int i = 0; i < args->NumFields(); ++i )
+		{
+		TypeDecl* args_i = args->FieldDecl(i);
+		TypeDecl* recv_i = recv->FieldDecl(i);
+
+		Attr* def = args_i->attrs ? args_i->attrs->FindAttr(ATTR_DEFAULT) : 0;
+
+		if ( ! def ) continue;
+
+		if ( ! recv_i->attrs )
+			{
+			attr_list* a = new attr_list();
+			a->append(def);
+			recv_i->attrs = new Attributes(a, recv_i->type, true);
+			}
+
+		else if ( ! recv_i->attrs->FindAttr(ATTR_DEFAULT) )
+			recv_i->attrs->AddAttr(def);
+		}
+	}
+
 void begin_func(ID* id, const char* module_name, function_flavor flavor,
 		int is_redef, FuncType* t)
 	{
@@ -335,6 +358,11 @@ void begin_func(ID* id, const char* module_name, function_flavor flavor,
 		{
 		if ( ! same_type(id->Type(), t) )
 			id->Type()->Error("incompatible types", t);
+
+		// If a previous declaration of the function had &default params,
+		// automatically transfer any that are missing (convenience so that
+		// implementations don't need to specify the &default expression again).
+		transfer_arg_defaults(id->Type()->AsFuncType()->Args(), t->Args());
 		}
 
 	else if ( is_redef )

src/bif_arg.cc

@@ -30,11 +30,13 @@ BuiltinFuncArg::BuiltinFuncArg(const char* arg_name, int arg_type)
 	type_str = "";
 	}
 
-BuiltinFuncArg::BuiltinFuncArg(const char* arg_name, const char* arg_type_str)
+BuiltinFuncArg::BuiltinFuncArg(const char* arg_name, const char* arg_type_str,
+                               const char* arg_attr_str)
 	{
 	name = arg_name;
 	type = TYPE_OTHER;
 	type_str = arg_type_str;
+	attr_str = arg_attr_str;
 
 	for ( int i = 0; builtin_func_arg_type[i].bif_type[0] != '\0'; ++i )
 		if ( ! strcmp(builtin_func_arg_type[i].bif_type, arg_type_str) )
@@ -46,7 +48,8 @@ BuiltinFuncArg::BuiltinFuncArg(const char* arg_name, const char* arg_type_str)
 
 void BuiltinFuncArg::PrintBro(FILE* fp)
 	{
-	fprintf(fp, "%s: %s%s", name, builtin_func_arg_type[type].bro_type, type_str);
+	fprintf(fp, "%s: %s%s %s", name, builtin_func_arg_type[type].bro_type,
+	        type_str, attr_str);
 	}
 
 void BuiltinFuncArg::PrintCDef(FILE* fp, int n)

src/bif_arg.h

@@ -25,7 +25,10 @@ extern const char* builtin_func_arg_type_bro_name[];
 class BuiltinFuncArg {
 public:
 	BuiltinFuncArg(const char* arg_name, int arg_type);
-	BuiltinFuncArg(const char* arg_name, const char* arg_type_str);
+	BuiltinFuncArg(const char* arg_name, const char* arg_type_str,
+	               const char* arg_attr_str = "");
+
+	void SetAttrStr(const char* arg_attr_str) { attr_str = arg_attr_str; };
 
 	const char* Name() const	{ return name; }
 	int Type() const		{ return type; }
@@ -39,6 +42,7 @@ protected:
 	const char* name;
 	int type;
 	const char* type_str;
+	const char* attr_str;
 };
 
 #endif

src/bro.bif

@@ -2472,7 +2472,7 @@ function bytestring_to_double%(s: string%): double
 ##
 ## Returns: The value contained in *s*, or 0 if the conversion failed.
 ##
-function bytestring_to_count%(s: string, is_le: bool%): count
+function bytestring_to_count%(s: string, is_le: bool &default=F%): count
 	%{
 #ifdef HOST_BIGENDIAN
 	static const bool host_bigendian = true;

src/builtin-func.l

@@ -26,6 +26,7 @@ int check_c_mode(int t)
 %}
 
 WS	[ \t]+
+OWS	[ \t]*
  /* Note, bifcl only accepts a single "::" in IDs while the policy
     layer acceptes multiple. (But the policy layer doesn't have 
 	a hierachy. */
@@ -101,7 +102,13 @@ HEX	[0-9a-fA-F]+
 	return TOK_ID;
 	}
 
-&{ID}	{
+  /*
+  Hacky way to pass along arbitrary attribute expressions since the BIF parser
+  has little understanding of valid Bro expressions.  With this pattern, the
+  attribute expression should stop when it reaches another attribute, another
+  function argument, or the end of the function declaration.
+  */
+&{ID}({OWS}={OWS}[^&%;,]+)?	{
 	int t = check_c_mode(TOK_ATTR);
 
 	if ( t == TOK_ATTR )

src/builtin-func.y

@@ -277,7 +277,7 @@ void print_event_c_body(FILE *fp)
 
 %left ',' ':'
 
-%type <str> TOK_C_TOKEN TOK_ID TOK_CSTR TOK_WS TOK_COMMENT TOK_ATTR TOK_INT opt_ws type
+%type <str> TOK_C_TOKEN TOK_ID TOK_CSTR TOK_WS TOK_COMMENT TOK_ATTR TOK_INT opt_ws type attr_list opt_attr_list
 %type <val> TOK_ATOM TOK_BOOL
 
 %union	{
@@ -375,7 +375,8 @@ type_def_types: TOK_RECORD
 			{ set_definition_type(TYPE_DEF, "Table"); }
 	;
 
-event_def:	event_prefix opt_ws plain_head opt_attr end_of_head ';'
+event_def:	event_prefix opt_ws plain_head opt_attr_list
+			{ fprintf(fp_bro_init, "%s", $4); } end_of_head ';'
 			{
 			print_event_c_prototype(fp_func_h, true);
 			print_event_c_prototype(fp_func_def, false);
@@ -458,20 +459,17 @@ const_def:	TOK_CONST opt_ws TOK_ID opt_ws ':' opt_ws TOK_ID opt_ws ';'
 				accessor);
 			}
 
-
-/* Currently support only boolean and string values */
-opt_attr_init:	/* nothing */
-	|	'=' opt_ws TOK_BOOL opt_ws
-			{
-			fprintf(fp_bro_init, "=%s%c%s", $2, ($3) ? 'T' : 'F', $4);
-			}
-	|	'=' opt_ws TOK_CSTR opt_ws
-			{ fprintf(fp_bro_init, "=%s%s%s", $2, $3, $4); }
+attr_list:
+		attr_list TOK_ATTR
+			{ $$ = concat($1, $2); }
+	|
+		TOK_ATTR
 	;
 
-opt_attr:	/* nothing */
-	|	opt_attr TOK_ATTR { fprintf(fp_bro_init, "%s", $2); }
-		opt_ws opt_attr_init
+opt_attr_list:
+		attr_list
+	|	/* nothing */
+		{ $$ = ""; }
 	;
 
 func_prefix:	TOK_FUNCTION
@@ -579,9 +577,10 @@ args:		args_1
 			{ /* empty, to avoid yacc complaint about type clash */ }
 	;
 
-args_1:		args_1 ',' opt_ws arg opt_ws
-	|	opt_ws arg opt_ws
-			{ /* empty */ }
+args_1:		args_1 ',' opt_ws arg opt_ws opt_attr_list
+			{ if ( ! args.empty() ) args[args.size()-1]->SetAttrStr($6); }
+	|	opt_ws arg opt_ws opt_attr_list
+			{ if ( ! args.empty() ) args[args.size()-1]->SetAttrStr($4); }
 	;
 
 // TODO: Migrate all other compound types to this rule. Once the BiF language

testing/btest/Baseline/bifs.bytestring_to_count/out

@@ -34,3 +34,4 @@
 65535
 0
 0
+65535

testing/btest/Baseline/language.default-params/out

@@ -0,0 +1,15 @@
+foo_func, test
+foo_func, hello
+bar_func, hmm, hi, 5
+bar_func, cool, beans, 5
+bar_func, cool, beans, 13
+foo_hook, test
+foo_hook, hello
+bar_hook, hmm, hi, 5
+bar_hook, cool, beans, 5
+bar_hook, cool, beans, 13
+foo_event, test
+foo_event, hello
+bar_event, hmm, hi, 5
+bar_event, cool, beans, 5
+bar_event, cool, beans, 13

testing/btest/bifs/bytestring_to_count.bro

@@ -52,4 +52,7 @@ event bro_init()
 	print bytestring_to_count("\x00\x00\x00\x00\x00\x00\x00\x00", T); # 0
 	print bytestring_to_count("\x00\x00\x00\x00\x00\x00\x00\x00", F); # 0
 
+	# test the default endianness parameter
+	print bytestring_to_count("\x00\x00\x00\x00\x00\x00\xff\xff"); # 65535
+
 	}

testing/btest/language/default-params.bro

@@ -0,0 +1,65 @@
+# @TEST-EXEC: bro -b %INPUT >out
+# @TEST-EXEC: btest-diff out
+
+### functions
+
+global foo_func: function(a: string &default="hello");
+
+# &defaults transfer from the declaration automatically
+function foo_func(a: string)
+    {
+    print "foo_func", a;
+    }
+
+function bar_func(a: string, b: string &default="hi", c: count &default=5)
+    {
+    print "bar_func", a, b, c;
+    }
+
+### events
+
+global foo_event: event(a: string &default="hello");
+
+event foo_event(a: string)
+    {
+    print "foo_event", a;
+    }
+
+event bar_event(a: string, b: string &default="hi", c: count &default=5)
+    {
+    print "bar_event", a, b, c;
+    }
+
+### hooks
+
+global foo_hook: hook(a: string &default="hello");
+
+hook foo_hook(a: string)
+    {
+    print "foo_hook", a;
+    }
+
+hook bar_hook(a: string, b: string &default="hi", c: count &default=5)
+    {
+    print "bar_hook", a, b, c;
+    }
+
+{}
+
+foo_func("test");
+foo_func();
+bar_func("hmm");
+bar_func("cool", "beans");
+bar_func("cool", "beans", 13);
+
+event foo_event("test");
+event foo_event();
+event bar_event("hmm");
+event bar_event("cool", "beans");
+event bar_event("cool", "beans", 13);
+
+hook foo_hook("test");
+hook foo_hook();
+hook bar_hook("hmm");
+hook bar_hook("cool", "beans");
+hook bar_hook("cool", "beans", 13);