add ability to indicate bad args

connector.go

@@ -28,6 +28,30 @@ import (
 	"github.com/pkg/errors"
 )
 
+// ErrBadArgs allows connectors to indicate to their upstreams
+// that something about the args they recieved for a particular operation
+// are not valid.
+type ErrBadArgs struct {
+	msg string
+}
+
+func NewErrBadArgs(msg string) error {
+	return &ErrBadArgs{
+		msg: msg,
+	}
+}
+
+// Error returns the error message for an ErrBadArgs error.
+func (e *ErrBadArgs) Error() string {
+	return e.msg
+}
+
+// ErrorIsBadArgs checks if the error is an "ErrBadArgs".
+func ErrorIsBadArgs(err error) bool {
+	_, ok := errors.Cause(err).(*ErrBadArgs)
+	return ok
+}
+
 //go:generate stringer -type=Operator
 
 // Operator defines an operator against some data for range scans

connector_test.go

@@ -0,0 +1,16 @@
+package dosa
+
+import (
+	"testing"
+
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestErrorIsBadArgs(t *testing.T) {
+	badArgsErr := NewErrBadArgs("you can't use that!")
+	assert.True(t, ErrorIsBadArgs(badArgsErr))
+
+	regErr := errors.New("hello")
+	assert.False(t, ErrorIsBadArgs(regErr))
+}