Implement support for variadic functions.

Currently, the variadic part must all be the same type, because there's
no "generic" arg converter.

sqlite3.go

@@ -165,9 +165,10 @@ type SQLiteRows struct {
 }
 
 type functionInfo struct {
-	f             reflect.Value
-	argConverters []callbackArgConverter
-	retConverter  callbackRetConverter
+	f                 reflect.Value
+	argConverters     []callbackArgConverter
+	variadicConverter callbackArgConverter
+	retConverter      callbackRetConverter
 }
 
 func (fi *functionInfo) error(ctx *C.sqlite3_context, err error) {
@@ -178,7 +179,12 @@ func (fi *functionInfo) error(ctx *C.sqlite3_context, err error) {
 
 func (fi *functionInfo) Call(ctx *C.sqlite3_context, argv []*C.sqlite3_value) {
 	var args []reflect.Value
-	for i, arg := range argv {
+
+	if len(argv) < len(fi.argConverters) {
+		fi.error(ctx, fmt.Errorf("function requires at least %d arguments", len(fi.argConverters)))
+	}
+
+	for i, arg := range argv[:len(fi.argConverters)] {
 		v, err := fi.argConverters[i](arg)
 		if err != nil {
 			fi.error(ctx, err)
@@ -187,6 +193,17 @@ func (fi *functionInfo) Call(ctx *C.sqlite3_context, argv []*C.sqlite3_value) {
 		args = append(args, v)
 	}
 
+	if fi.variadicConverter != nil {
+		for _, arg := range argv[len(fi.argConverters):] {
+			v, err := fi.variadicConverter(arg)
+			if err != nil {
+				fi.error(ctx, err)
+				return
+			}
+			args = append(args, v)
+		}
+	}
+
 	ret := fi.f.Call(args)
 
 	if len(ret) == 2 && ret[1].Interface() != nil {
@@ -218,7 +235,8 @@ func (tx *SQLiteTx) Rollback() error {
 // The function can accept arguments of any real numeric type
 // (i.e. not complex), as well as []byte and string. It must return a
 // value of one of those types, and optionally an error as a second
-// value.
+// value. Variadic functions are allowed, if the variadic argument is
+// one of the allowed types.
 //
 // If pure is true. SQLite will assume that the function's return
 // value depends only on its inputs, and make more aggressive
@@ -230,9 +248,6 @@ func (c *SQLiteConn) RegisterFunc(name string, impl interface{}, pure bool) erro
 	if t.Kind() != reflect.Func {
 		return errors.New("Non-function passed to RegisterFunc")
 	}
-	if t.IsVariadic() {
-		return errors.New("Variadic SQLite functions are not supported")
-	}
 	if t.NumOut() != 1 && t.NumOut() != 2 {
 		return errors.New("SQLite functions must return 1 or 2 values")
 	}
@@ -240,7 +255,12 @@ func (c *SQLiteConn) RegisterFunc(name string, impl interface{}, pure bool) erro
 		return errors.New("Second return value of SQLite function must be error")
 	}
 
-	for i := 0; i < t.NumIn(); i++ {
+	numArgs := t.NumIn()
+	if t.IsVariadic() {
+		numArgs--
+	}
+
+	for i := 0; i < numArgs; i++ {
 		conv, err := callbackArg(t.In(i))
 		if err != nil {
 			return err
@@ -248,6 +268,18 @@ func (c *SQLiteConn) RegisterFunc(name string, impl interface{}, pure bool) erro
 		fi.argConverters = append(fi.argConverters, conv)
 	}
 
+	if t.IsVariadic() {
+		conv, err := callbackArg(t.In(numArgs).Elem())
+		if err != nil {
+			return err
+		}
+		fi.variadicConverter = conv
+		// Pass -1 to sqlite so that it allows any number of
+		// arguments. The call helper verifies that the minimum number
+		// of arguments is present for variadic functions.
+		numArgs = -1
+	}
+
 	conv, err := callbackRet(t.Out(0))
 	if err != nil {
 		return err
@@ -263,7 +295,7 @@ func (c *SQLiteConn) RegisterFunc(name string, impl interface{}, pure bool) erro
 	if pure {
 		opts |= C.SQLITE_DETERMINISTIC
 	}
-	rv := C.sqlite3_create_function_v2(c.db, cname, C.int(t.NumIn()), C.int(opts), unsafe.Pointer(&fi), (*[0]byte)(unsafe.Pointer(C.callbackTrampoline)), nil, nil, nil)
+	rv := C.sqlite3_create_function_v2(c.db, cname, C.int(numArgs), C.int(opts), unsafe.Pointer(&fi), (*[0]byte)(unsafe.Pointer(C.callbackTrampoline)), nil, nil, nil)
 	if rv != C.SQLITE_OK {
 		return c.lastError()
 	}

sqlite3_test.go

@@ -1071,6 +1071,13 @@ func TestFunctionRegistration(t *testing.T) {
 	regex := func(re, s string) (bool, error) {
 		return regexp.MatchString(re, s)
 	}
+	variadic := func(a, b int64, c ...int64) int64 {
+		ret := a + b
+		for _, d := range c {
+			ret += d
+		}
+		return ret
+	}
 
 	sql.Register("sqlite3_FunctionRegistration", &SQLiteDriver{
 		ConnectHook: func(conn *SQLiteConn) error {
@@ -1098,6 +1105,9 @@ func TestFunctionRegistration(t *testing.T) {
 			if err := conn.RegisterFunc("regex", regex, true); err != nil {
 				return err
 			}
+			if err := conn.RegisterFunc("variadic", variadic, true); err != nil {
+				return err
+			}
 			return nil
 		},
 	})
@@ -1121,6 +1131,9 @@ func TestFunctionRegistration(t *testing.T) {
 		{"SELECT not(0)", true},
 		{`SELECT regex("^foo.*", "foobar")`, true},
 		{`SELECT regex("^foo.*", "barfoobar")`, false},
+		{"SELECT variadic(1,2)", int64(3)},
+		{"SELECT variadic(1,2,3,4)", int64(10)},
+		{"SELECT variadic(1,1,1,1,1,1,1,1,1,1)", int64(10)},
 	}
 
 	for _, op := range ops {