http: allow Endpoint to register custom error handler

The new field ErrorHandler on Endpoint allow the implementor to define
their own function to handler error from Endpoint.Call.

If the ErrorHandler is nil it will default to DefaultErrorHandler.

1 files changed, 64 insertions, 0 deletions

diff --git a/lib/http/callback_error_handler.go b/lib/http/callback_error_handler.go
new file mode 100644
index 00000000..199e1a12
--- /dev/null
+++ b/lib/http/callback_error_handler.go
@@ -0,0 +1,64 @@
+// Copyright 2020, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package http
+
+import (
+	"encoding/json"
+	"errors"
+	"log"
+	"net/http"
+
+	liberrors "github.com/shuLhan/share/lib/errors"
+)
+
+//
+// CallbackErrorHandler define the function that can be used to handle an
+// error returned from Endpoint.Call.
+// By default, if Endpoint.Call is nil, it will use DefaultErrorHandler.
+//
+type CallbackErrorHandler func(http.ResponseWriter, *http.Request, error)
+
+//
+// DefaultErrorHandler define the default function that will called to handle
+// the error returned from Callback function, if the Endpoint.ErrorHandler is
+// not defined.
+//
+// First, it will check if error instance of errors.E. If its true, it will
+// use the Code value for HTTP status code, otherwise if its zero or invalid,
+// it will set to http.StatusInternalServerError.
+//
+// Second, it will set the HTTP content-type to "application/json" and write
+// the response body as JSON format,
+//
+//	{"code":<HTTP_STATUS_CODE>, "message":<err.Error()>}
+//
+func DefaultErrorHandler(res http.ResponseWriter, req *http.Request, err error) {
+	errInternal := &liberrors.E{}
+	if errors.As(err, &errInternal) {
+		if errInternal.Code <= 0 || errInternal.Code >= 512 {
+			errInternal.Code = http.StatusInternalServerError
+		}
+	} else {
+		log.Printf("DefaultErrorHandler: %d %s %s %s\n",
+			http.StatusInternalServerError,
+			req.Method, req.URL.Path, err)
+
+		errInternal = liberrors.Internal(err)
+	}
+
+	res.Header().Set(HeaderContentType, ContentTypeJSON)
+	res.WriteHeader(errInternal.Code)
+
+	rsp, err := json.Marshal(errInternal)
+	if err != nil {
+		log.Println("DefaultErrorHandler: " + err.Error())
+		return
+	}
+
+	_, err = res.Write(rsp)
+	if err != nil {
+		log.Println("DefaultErrorHandler: " + err.Error())
+	}
+}