dex: general purpose go 1.13 error type

client/asset/interface.go

@@ -11,11 +11,11 @@ import (
 	"decred.org/dcrdex/dex/config"
 )
 
-// CoinNotFoundError is returned when a coin cannot be found, either because
-// it has been spent or it never existed. This error may be returned from
-// AuditContract, Refund or Redeem as those methods expect the provided coin
-// to exist and be unspent.
-const CoinNotFoundError = dex.Error("coin not found")
+// CoinNotFoundError is returned when a coin cannot be found, either because it
+// has been spent or it never existed. This error may be returned from
+// AuditContract, Refund or Redeem as those methods expect the provided coin to
+// exist and be unspent.
+const CoinNotFoundError = dex.ErrorKind("coin not found")
 
 // WalletInfo is auxiliary information about an ExchangeWallet.
 type WalletInfo struct {

dex/asset.go

@@ -9,14 +9,11 @@ import (
 	"time"
 )
 
-type Error string
-
-func (err Error) Error() string { return string(err) }
-
 const (
-	UnsupportedScriptError = Error("unsupported script type")
-	defaultLockTimeTaker   = 24 * time.Hour
-	defaultlockTimeMaker   = 48 * time.Hour
+	UnsupportedScriptError = ErrorKind("unsupported script type")
+
+	defaultLockTimeTaker = 24 * time.Hour
+	defaultlockTimeMaker = 48 * time.Hour
 )
 
 var (

dex/errors.go

@@ -0,0 +1,39 @@
+// This code is available on the terms of the project LICENSE.md file,
+// also available online at https://blueoakcouncil.org/license/1.0.0.
+
+package dex
+
+// ErrorKind identifies a kind of error that can be used to define new errors
+// via const SomeError = dex.ErrorKind("something").
+type ErrorKind string
+
+// Error satisfies the error interface and prints human-readable errors.
+func (e ErrorKind) Error() string {
+	return string(e)
+}
+
+// Error pairs an error with details.
+type Error struct {
+	wrapped error
+	detail  string
+}
+
+// Error satisfies the error interface, combining the wrapped error message with
+// the details.
+func (e Error) Error() string {
+	return e.wrapped.Error() + ": " + e.detail
+}
+
+// Unwrap returns the wrapped error, allowing errors.Is and errors.As to work.
+func (e Error) Unwrap() error {
+	return e.wrapped
+}
+
+// NewError wraps the provided Error with details in a Error, facilitating the
+// use of errors.Is and errors.As via errors.Unwrap.
+func NewError(err error, detail string) Error {
+	return Error{
+		wrapped: err,
+		detail:  detail,
+	}
+}

dex/errors_test.go

@@ -0,0 +1,45 @@
+package dex
+
+import (
+	"errors"
+	"testing"
+)
+
+type testErr string
+
+func (te testErr) Error() string {
+	return string(te)
+}
+
+const (
+	err0 = testErr("other error")
+	err1 = ErrorKind("error 1")
+	err2 = ErrorKind("error 2")
+)
+
+func TestDexError(t *testing.T) {
+
+	dexErr := NewError(err1, "stuff")
+
+	var err1Back ErrorKind
+	if !errors.As(dexErr, &err1Back) {
+		t.Errorf("it wasn't an ErrorKind")
+	}
+	wantErrStr := err1.Error() + ": " + "stuff"
+	if dexErr.Error() != wantErrStr {
+		t.Errorf("incorrect error string %v, want %v", dexErr.Error(), wantErrStr)
+	}
+
+	if !errors.Is(dexErr, err1) {
+		t.Errorf("it wasn't err1")
+	}
+	if errors.Is(dexErr, err2) {
+		t.Errorf("it was err2")
+	}
+
+	otherErr := NewError(err0, "other stuff")
+	var err0Back testErr
+	if !errors.As(otherErr, &err0Back) {
+		t.Errorf("it wasn't an testErr")
+	}
+}

server/asset/btc/btc.go

@@ -56,7 +56,7 @@ var (
 const (
 	assetName                = "btc"
 	btcToSatoshi             = 1e8
-	immatureTransactionError = dex.Error("immature output")
+	immatureTransactionError = dex.ErrorKind("immature output")
 )
 
 // btcNode represents a blockchain information fetcher. In practice, it is

server/asset/btc/utxo.go

@@ -16,7 +16,7 @@ import (
 	"github.com/btcsuite/btcutil"
 )
 
-const ErrReorgDetected = dex.Error("reorg detected")
+const ErrReorgDetected = dex.ErrorKind("reorg detected")
 
 // TXIO is common information stored with an Input or Output.
 type TXIO struct {

server/asset/common.go

@@ -13,7 +13,7 @@ import (
 // CoinNotFoundError is to be returned from Contract, Redemption, and
 // FundingCoin when the specified transaction cannot be found. Used by the
 // server to handle network latency.
-const CoinNotFoundError = dex.Error("coin not found")
+const CoinNotFoundError = dex.ErrorKind("coin not found")
 
 // The Backend interface is an interface for a blockchain backend.
 type Backend interface {

server/asset/dcr/dcr.go

@@ -57,11 +57,9 @@ var (
 	blockPollInterval = time.Second
 )
 
-type Error = dex.Error
-
 const (
 	assetName                = "dcr"
-	immatureTransactionError = Error("immature output")
+	immatureTransactionError = dex.ErrorKind("immature output")
 )
 
 // dcrNode represents a blockchain information fetcher. In practice, it is

server/asset/dcr/utxo.go

@@ -16,7 +16,7 @@ import (
 	"github.com/decred/dcrd/dcrutil/v2"
 )
 
-const ErrReorgDetected = dex.Error("reorg detected")
+const ErrReorgDetected = dex.ErrorKind("reorg detected")
 
 // TXIO is common information stored with an Input or Output.
 type TXIO struct {