Using error.Is and error.As

* This allow using error.Is and error.As within vsp.
* Add test cases for apiError type.

webapi/errors.go

@@ -6,6 +6,8 @@ package webapi
 
 import "net/http"
 
+// apiError is a kind of error.  It has full support for errors.Is and
+// errors.As.
 type apiError int
 
 const (
@@ -73,8 +75,8 @@ func (e apiError) httpStatus() int {
 	}
 }
 
-// defaultMessage returns a descriptive error string for a given error code.
-func (e apiError) defaultMessage() string {
+// String returns a descriptive error string for a given error code.
+func (e apiError) String() string {
 	switch e {
 	case errBadRequest:
 		return "bad request"
@@ -116,3 +118,8 @@ func (e apiError) defaultMessage() string {
 		return "unknown error"
 	}
 }
+
+// Error satisfies the error interface and returns a human-readable error string.
+func (e apiError) Error() string {
+	return e.String()
+}

webapi/errors_test.go

@@ -0,0 +1,90 @@
+// Copyright (c) 2022 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package webapi
+
+import (
+	"errors"
+	"testing"
+)
+
+// TestApiErrorString tests the stringized output for the apiError type.
+func TestApiErrorString(t *testing.T) {
+	tests := []struct {
+		in   apiError
+		want string
+	}{
+		{errBadRequest, "bad request"},
+		{errInternalError, "internal error"},
+		{errVspClosed, "vsp is closed"},
+		{errFeeAlreadyReceived, "fee tx already received for ticket"},
+		{errInvalidFeeTx, "invalid fee tx"},
+		{errFeeTooSmall, "fee too small"},
+		{errUnknownTicket, "unknown ticket"},
+		{errTicketCannotVote, "ticket not eligible to vote"},
+		{errFeeExpired, "fee has expired"},
+		{errInvalidVoteChoices, "invalid vote choices"},
+		{errBadSignature, "bad request signature"},
+		{errInvalidPrivKey, "invalid private key"},
+		{errFeeNotReceived, "no fee tx received for ticket"},
+		{errInvalidTicket, "not a valid ticket tx"},
+		{errCannotBroadcastTicket, "ticket transaction could not be broadcast"},
+		{errCannotBroadcastFee, "fee transaction could not be broadcast"},
+		{errCannotBroadcastFeeUnknownOutputs, "fee transaction could not be broadcast due to unknown outputs"},
+		{errInvalidTimestamp, "old or reused timestamp"},
+	}
+
+	for i, test := range tests {
+		result := test.in.Error()
+		if result != test.want {
+			t.Errorf("%d: got: %s want: %s", i, result, test.want)
+			continue
+		}
+	}
+}
+
+// TestApiErrorIsAs ensures apiError can be identified via errors.Is and unwrapped via errors.As.
+func TestApiErrorIsAs(t *testing.T) {
+	tests := []struct {
+		name      string
+		err       error
+		target    error
+		wantMatch bool
+		wantAs    apiError
+	}{{
+		name:      "errBadRequest == errBadRequest",
+		err:       errBadRequest,
+		target:    errBadRequest,
+		wantMatch: true,
+		wantAs:    errBadRequest,
+	}, {
+		name:      "errBadRequest != errInternalError",
+		err:       errBadRequest,
+		target:    errInternalError,
+		wantMatch: false,
+		wantAs:    errBadRequest,
+	}}
+	for _, test := range tests {
+		// Ensure the error matches or not depending on the expected result.
+		result := errors.Is(test.err, test.target)
+		if result != test.wantMatch {
+			t.Errorf("%s: incorrect error identification -- got %v, want %v",
+				test.name, result, test.wantMatch)
+			continue
+		}
+
+		// Ensure the underlying apiError can be unwrapped and is the
+		// expected type.
+		var err apiError
+		if !errors.As(test.err, &err) {
+			t.Errorf("%s: unable to unwrap error", test.name)
+			continue
+		}
+		if err != test.wantAs {
+			t.Errorf("%s: unexpected unwrapped error -- got %v, want %v",
+				test.name, err, test.wantAs)
+			continue
+		}
+	}
+}

webapi/webapi.go

@@ -285,7 +285,7 @@ func sendJSONResponse(resp interface{}, c *gin.Context) (string, string) {
 // sendError sends an error response to the client using the default error
 // message.
 func sendError(e apiError, c *gin.Context) {
-	msg := e.defaultMessage()
+	msg := e.Error()
 	sendErrorWithMsg(msg, e, c)
 }