custom error page support

errorCatcher.go

@@ -0,0 +1,74 @@
+package main
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/aymerick/raymond"
+)
+
+// errorCatcher is a wrapper for http.ResponseWriter that
+// captures 4xx and 5xx status codes and handles them in
+// a custom manner
+type errorCatcher struct {
+	req          *http.Request
+	res          http.ResponseWriter
+	errorTpl     *raymond.Template
+	notFoundTpl  *raymond.Template
+	handledError bool
+}
+
+func (ec *errorCatcher) Header() http.Header {
+	return ec.res.Header()
+}
+
+func (ec *errorCatcher) Write(buf []byte) (int, error) {
+	// if we have already sent a response, pretend that this was successful
+	if ec.handledError {
+		return len(buf), nil
+	}
+	return ec.res.Write(buf)
+}
+
+func (ec *errorCatcher) WriteHeader(statusCode int) {
+	if ec.handledError {
+		return
+	}
+	if statusCode == 404 {
+		ctx := map[string]string{
+			"path": ec.req.URL.Path,
+		}
+		page, err := ec.notFoundTpl.Exec(ctx)
+		// if we don't have a page to write, return before
+		// we toggle the flag so we fall back to the original
+		// error page
+		if err != nil {
+			return
+		}
+		ec.res.Header().Add("content-type", "text/html")
+		ec.res.WriteHeader(statusCode)
+		ec.res.Write([]byte(page))
+		ec.handledError = true
+		return
+	}
+
+	if statusCode >= 400 && statusCode < 600 {
+		ctx := map[string]string{
+			"code": strconv.Itoa(statusCode),
+		}
+		page, err := ec.errorTpl.Exec(ctx)
+		// if we don't have a page to write, return before
+		// we toggle the flag so we fall back to the original
+		// error page
+		if err != nil {
+			return
+		}
+		ec.res.Header().Add("content-type", "text/html")
+		ec.res.WriteHeader(statusCode)
+		ec.res.Write([]byte(page))
+		ec.handledError = true
+		return
+	}
+
+	ec.res.WriteHeader(statusCode)
+}