1 files changed, 115 insertions, 0 deletions
diff --git a/workhorse/internal/badgateway/roundtripper.go b/workhorse/internal/badgateway/roundtripper.go
new file mode 100644
index 00000000000..a36cc9f4a9a
--- /dev/null
+++ b/workhorse/internal/badgateway/roundtripper.go
@@ -0,0 +1,115 @@
+package badgateway
+
+import (
+	"bytes"
+	"fmt"
+	"html/template"
+	"io/ioutil"
+	"net/http"
+	"strings"
+	"time"
+
+	"gitlab.com/gitlab-org/labkit/log"
+
+	"gitlab.com/gitlab-org/gitlab-workhorse/internal/helper"
+)
+
+// Error is a custom error for pretty Sentry 'issues'
+type sentryError struct{ error }
+
+type roundTripper struct {
+	next            http.RoundTripper
+	developmentMode bool
+}
+
+// NewRoundTripper creates a RoundTripper with a provided underlying next transport
+func NewRoundTripper(developmentMode bool, next http.RoundTripper) http.RoundTripper {
+	return &roundTripper{next: next, developmentMode: developmentMode}
+}
+
+func (t *roundTripper) RoundTrip(r *http.Request) (*http.Response, error) {
+	start := time.Now()
+
+	res, err := t.next.RoundTrip(r)
+	if err == nil {
+		return res, err
+	}
+
+	// httputil.ReverseProxy translates all errors from this
+	// RoundTrip function into 500 errors. But the most likely error
+	// is that the Rails app is not responding, in which case users
+	// and administrators expect to see a 502 error. To show 502s
+	// instead of 500s we catch the RoundTrip error here and inject a
+	// 502 response.
+	fields := log.Fields{"duration_ms": int64(time.Since(start).Seconds() * 1000)}
+	helper.LogErrorWithFields(
+		r,
+		&sentryError{fmt.Errorf("badgateway: failed to receive response: %v", err)},
+		fields,
+	)
+
+	injectedResponse := &http.Response{
+		StatusCode: http.StatusBadGateway,
+		Status:     http.StatusText(http.StatusBadGateway),
+
+		Request:    r,
+		ProtoMajor: r.ProtoMajor,
+		ProtoMinor: r.ProtoMinor,
+		Proto:      r.Proto,
+		Header:     make(http.Header),
+		Trailer:    make(http.Header),
+	}
+
+	message := "GitLab is not responding"
+	contentType := "text/plain"
+	if t.developmentMode {
+		message, contentType = developmentModeResponse(err)
+	}
+
+	injectedResponse.Body = ioutil.NopCloser(strings.NewReader(message))
+	injectedResponse.Header.Set("Content-Type", contentType)
+
+	return injectedResponse, nil
+}
+
+func developmentModeResponse(err error) (body string, contentType string) {
+	data := TemplateData{
+		Time:          time.Now().Format("15:04:05"),
+		Error:         err.Error(),
+		ReloadSeconds: 5,
+	}
+
+	buf := &bytes.Buffer{}
+	if err := developmentErrorTemplate.Execute(buf, data); err != nil {
+		return data.Error, "text/plain"
+	}
+
+	return buf.String(), "text/html"
+}
+
+type TemplateData struct {
+	Time          string
+	Error         string
+	ReloadSeconds int
+}
+
+var developmentErrorTemplate = template.Must(template.New("error502").Parse(`
+<html>
+<head>
+<title>502: GitLab is not responding</title>
+<script>
+window.setTimeout(function() { location.reload() }, {{.ReloadSeconds}} * 1000)
+</script>
+</head>
+
+<body>
+<h1>502</h1>
+<p>GitLab is not responding. The error was:</p>
+
+<pre>{{.Error}}</pre>
+
+<p>If you just started GDK it can take 60-300 seconds before GitLab has finished booting. This page will automatically reload every {{.ReloadSeconds}} seconds.</p>
+<footer>Generated by gitlab-workhorse running in development mode at {{.Time}}.</footer>
+</body>
+</html>
+`))