Add ErrKeyExists that is compatible with errors.Is on kv.Create

jserrors.go

@@ -123,6 +123,8 @@ const (
 	JSErrCodeMessageNotFound ErrorCode = 10037
 
 	JSErrCodeBadRequest ErrorCode = 10003
+
+	JSErrCodeStreamWrongLastSequence ErrorCode = 10071
 )
 
 // APIError is included in all API responses if there was an error.

kv.go

@@ -297,7 +297,10 @@ var (
 	ErrKeyDeleted             = errors.New("nats: key was deleted")
 	ErrHistoryToLarge         = errors.New("nats: history limited to a max of 64")
 	ErrNoKeysFound            = errors.New("nats: no keys found")
-	ErrKeyExists              = errors.New("nats: key exists")
+)
+
+var (
+	ErrKeyExists JetStreamError = &jsError{apiErr: &APIError{ErrorCode: JSErrCodeStreamWrongLastSequence, Code: 400}, message: "key exists"}
 )
 
 const (
@@ -632,10 +635,9 @@ func (kv *kvs) Create(key string, value []byte) (revision uint64, err error) {
 
 	// Check if the expected last subject sequence is not zero which implies
 	// the key already exists.
-	if aerr, ok := err.(*APIError); ok {
-		if aerr.ErrorCode == 10071 {
-			return 0, ErrKeyExists
-		}
+	if errors.Is(err, ErrKeyExists) {
+		jserr := ErrKeyExists.(*jsError)
+		return 0, fmt.Errorf("%w: %s", err, jserr.message)
 	}
 
 	return 0, err

kv_test.go

@@ -14,6 +14,7 @@
 package nats
 
 import (
+	"errors"
 	"fmt"
 	"testing"
 	"time"
@@ -222,7 +223,31 @@ func TestKeyValueCreate(t *testing.T) {
 	}
 
 	_, err = kv.Create("key", []byte("1"))
-	if err != ErrKeyExists {
+	expected := "nats: wrong last sequence: 1: key exists"
+	if err.Error() != expected {
+		t.Fatalf("Expected %q, got: %v", expected, err)
+	}
+	if !errors.Is(err, ErrKeyExists) {
 		t.Fatalf("Expected ErrKeyExists, got: %v", err)
 	}
+	aerr := &APIError{}
+	if !errors.As(err, &aerr) {
+		t.Fatalf("Expected APIError, got: %v", err)
+	}
+	if aerr.Description != "wrong last sequence: 1" {
+		t.Fatalf("Unexpected APIError message, got: %v", aerr.Description)
+	}
+	if aerr.ErrorCode != 10071 {
+		t.Fatalf("Unexpected error code, got: %v", aerr.ErrorCode)
+	}
+	if aerr.Code != ErrKeyExists.APIError().Code {
+		t.Fatalf("Unexpected error code, got: %v", aerr.Code)
+	}
+	var kerr JetStreamError
+	if !errors.As(err, &kerr) {
+		t.Fatalf("Expected KeyValueError, got: %v", err)
+	}
+	if kerr.APIError().ErrorCode != 10071 {
+		t.Fatalf("Unexpected error code, got: %v", kerr.APIError().ErrorCode)
+	}
 }