Add ErrFault error marker.

v2alpha/soap/envelope/envelope.go

@@ -3,10 +3,14 @@ package envelope
 
 import (
 	"encoding/xml"
+	"errors"
 	"fmt"
 	"io"
 )
 
+// ErrFault can be used as a target with errors.Is.
+var ErrFault error = errors.New("xml fault")
+
 // FaultDetail carries XML-encoded application-specific Fault details.
 type FaultDetail struct {
 	Raw []byte `xml:",innerxml"`
@@ -24,6 +28,10 @@ func (fe *Fault) Error() string {
 	return fmt.Sprintf("SOAP fault code=%s: %s", fe.Code, fe.String)
 }
 
+func (fe *Fault) Is(target error) bool {
+	return target == ErrFault
+}
+
 // Various "constant" bytes used in the written envelope.
 var (
 	envOpen  = []byte(xml.Header + `<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><s:Body>`)

v2alpha/soap/envelope/envelope_test.go

@@ -3,6 +3,9 @@ package envelope
 import (
 	"bytes"
 	"encoding/xml"
+	"errors"
+	"fmt"
+	"io"
 	"reflect"
 	"testing"
 )
@@ -76,3 +79,36 @@ s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
 		t.Errorf("want %+v, got %+v", wantFault, gotFault)
 	}
 }
+
+func TestFault(t *testing.T) {
+	tests := []struct {
+		name   string
+		err    error
+		wantIs bool
+	}{
+		{"plain fault", &Fault{Code: "code"}, true},
+		{"wrapped fault", fmt.Errorf("wrapper: %w", &Fault{Code: "code"}), true},
+		{"other error", io.EOF, false},
+	}
+
+	for _, test := range tests {
+		test := test // copy for closure
+		t.Run(test.name, func(t *testing.T) {
+			if got, want := errors.Is(test.err, ErrFault), test.wantIs; got != want {
+				t.Errorf("got errors.Is(%v, ErrFault)=>%t, want %t", test.err, got, want)
+			}
+			if !test.wantIs {
+				return
+			}
+
+			var fault *Fault
+			if got, want := errors.As(test.err, &fault), true; got != want {
+				t.Fatalf("got errors.As(%v, ...)=>%t, want %t", test.err, got, want)
+			}
+
+			if got, want := fault.Code, "code"; got != want {
+				t.Errorf("got fault.Code=%q, want %q", got, want)
+			}
+		})
+	}
+}