add error handler to intercept status code >= 400 <= 509

hawry · Jan 11, 2018 · 67a1680 · 67a1680
1 parent ec9ed4f
commit 67a1680
Showing 1 changed file with 88 additions and 0 deletions.
diff --git a/error_handler.go b/error_handler.go
@@ -0,0 +1,88 @@
+package middlewares
+
+import (
+	"html/template"
+	"log"
+	"net/http"
+)
+
+type errorHandler struct {
+	http.ResponseWriter
+	statusCode int
+	body       []byte
+}
+
+const errBody = `<!doctype HTML>
+<html>
+<head>
+	<meta charset="utf-8"/>
+	<meta name="viewport" content="width=device-width, initial-scale=1.0">
+	<title>{{.StatusCode}} - {{.StatusText}}</title>
+	<style type="text/css">
+	h1 {
+		color:#666;
+	}
+	.content {
+		text-align:center;
+		margin-left: auto;
+		margin-right: auto;
+		max-width: 75%;
+		font-size: 1.5rem;
+	}
+	.error-text {
+		color:#666;
+	}
+	</style>
+</head>
+<body>
+
+	<div class="content">
+		<h1>{{.StatusCode}}</h1>
+		<p class="error-text">
+			{{.StatusMessage}}
+		</p>
+	</div>
+
+</body>
+</html>
+`
+
+var errTemplate *template.Template
+
+func init() {
+	errTemplate = template.Must(template.New("err").Parse(errBody))
+}
+
+//ErrorHandler will inject a html response to any error status code
+func ErrorHandler(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		eh := &errorHandler{ResponseWriter: w, statusCode: http.StatusOK}
+		next.ServeHTTP(eh, r)
+		if eh.statusCode >= 400 && eh.statusCode <= 509 {
+			// do something
+			dval := map[string]interface{}{
+				"StatusCode":    eh.statusCode,
+				"StatusText":    http.StatusText(eh.statusCode),
+				"StatusMessage": string(eh.body),
+			}
+			errTemplate.Execute(w, dval)
+		}
+	})
+}
+
+// WriteHeader shadows ResponseWriter.Write
+func (e *errorHandler) WriteHeader(code int) {
+	e.statusCode = code
+	e.ResponseWriter.WriteHeader(code)
+}
+
+//Write shadows http.ResponseWriter.Write
+func (e *errorHandler) Write(b []byte) (n int, err error) {
+	if e.statusCode >= 400 && e.statusCode <= 509 {
+		log.Printf("err handler write called")
+		e.body = append(e.body, b...) // use any written text as the error message
+	} else {
+		e.ResponseWriter.Write(b)
+	}
+	return
+}