Merge pull request #11 from basecamp/html-errors

HTML error responses

internal/cmd/stop.go

@@ -24,6 +24,7 @@ func newStopCommand() *stopCommand {
 	}
 
 	stopCommand.cmd.Flags().DurationVar(&stopCommand.args.DrainTimeout, "drain-timeout", server.DefaultDrainTimeout, "How long to allow in-flight requests to complete")
+	stopCommand.cmd.Flags().StringVar(&stopCommand.args.Message, "message", server.DefaultStopMessage, "Message to display to clients while stopped")
 
 	return stopCommand
 }

internal/server/commands.go

@@ -35,6 +35,7 @@ type PauseArgs struct {
 type StopArgs struct {
 	Service      string
 	DrainTimeout time.Duration
+	Message      string
 }
 
 type ResumeArgs struct {
@@ -121,7 +122,7 @@ func (h *CommandHandler) Pause(args PauseArgs, reply *bool) error {
 }
 
 func (h *CommandHandler) Stop(args StopArgs, reply *bool) error {
-	return h.router.StopService(args.Service, args.DrainTimeout)
+	return h.router.StopService(args.Service, args.DrainTimeout, args.Message)
 }
 
 func (h *CommandHandler) Resume(args ResumeArgs, reply *bool) error {

internal/server/error_page_middleware.go

@@ -0,0 +1,94 @@
+package server
+
+import (
+	"context"
+	"embed"
+	"fmt"
+	"html/template"
+	"log/slog"
+	"net/http"
+)
+
+var (
+	//go:embed pages
+	pages embed.FS
+
+	contextKeyErrorResponse = contextKey("error-response")
+)
+
+type errorResponseContent struct {
+	StatusCode        int
+	TemplateArguments any
+}
+
+type ErrorPageMiddleware struct {
+	template *template.Template
+	next     http.Handler
+}
+
+func WithErrorPageMiddleware(next http.Handler) http.Handler {
+	template, err := template.ParseFS(pages, "pages/*.html")
+	if err != nil {
+		slog.Error("Failed to parse error page templates", "error", err)
+		template = nil
+	}
+
+	return &ErrorPageMiddleware{
+		template: template,
+		next:     next,
+	}
+}
+
+func SetErrorResponse(w http.ResponseWriter, r *http.Request, statusCode int, templateArguments any) {
+	errorResponse, ok := r.Context().Value(contextKeyErrorResponse).(*errorResponseContent)
+	if ok {
+		errorResponse.StatusCode = statusCode
+		errorResponse.TemplateArguments = templateArguments
+	} else {
+		http.Error(w, http.StatusText(statusCode), statusCode)
+	}
+}
+
+func (h *ErrorPageMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	var errorResponseContext errorResponseContent
+	ctx := context.WithValue(r.Context(), contextKeyErrorResponse, &errorResponseContext)
+	r = r.WithContext(ctx)
+
+	h.next.ServeHTTP(w, r)
+
+	if errorResponseContext.StatusCode != 0 {
+		h.respondWithErrorPage(w, errorResponseContext.StatusCode, errorResponseContext.TemplateArguments)
+	}
+}
+
+// Private
+
+func (h *ErrorPageMiddleware) respondWithErrorPage(w http.ResponseWriter, statusCode int, templateArguments any) {
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	w.WriteHeader(statusCode)
+
+	template := h.getTemplate(statusCode)
+	if template == nil {
+		slog.Error("Failed to render error page due to missing template", "status", statusCode)
+		h.writeErrorWithoutTemplate(w, statusCode)
+		return
+	}
+
+	err := template.Execute(w, templateArguments)
+	if err != nil {
+		slog.Error("Failed to render error page template", "name", template.Name, "error", err)
+		h.writeErrorWithoutTemplate(w, statusCode)
+	}
+}
+
+func (h *ErrorPageMiddleware) getTemplate(statusCode int) *template.Template {
+	if h.template == nil {
+		return nil
+	}
+
+	return h.template.Lookup(fmt.Sprintf("%d.html", statusCode))
+}
+
+func (h *ErrorPageMiddleware) writeErrorWithoutTemplate(w http.ResponseWriter, statusCode int) {
+	fmt.Fprintf(w, "<h1>%d %s</h1>", statusCode, http.StatusText(statusCode))
+}

internal/server/error_page_middleware_test.go

@@ -0,0 +1,63 @@
+package server
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestErrorPageMiddleware(t *testing.T) {
+	check := func(handler http.HandlerFunc) (int, string, string) {
+		middleware := WithErrorPageMiddleware(handler)
+
+		req := httptest.NewRequest("GET", "http://example.com", nil)
+		resp := httptest.NewRecorder()
+
+		middleware.ServeHTTP(resp, req)
+
+		return resp.Result().StatusCode, resp.Header().Get("Content-Type"), resp.Body.String()
+	}
+
+	t.Run("When setting a custom error response", func(t *testing.T) {
+		status, contentType, body := check(func(w http.ResponseWriter, r *http.Request) {
+			SetErrorResponse(w, r, http.StatusNotFound, nil)
+		})
+
+		assert.Equal(t, http.StatusNotFound, status)
+		assert.Equal(t, "text/html; charset=utf-8", contentType)
+		assert.Regexp(t, "Not Found", body)
+	})
+
+	t.Run("When including template arguments in a custom error response", func(t *testing.T) {
+		status, contentType, body := check(func(w http.ResponseWriter, r *http.Request) {
+			SetErrorResponse(w, r, http.StatusServiceUnavailable, struct{ Message string }{"Gone to lunch"})
+		})
+
+		assert.Equal(t, http.StatusServiceUnavailable, status)
+		assert.Equal(t, "text/html; charset=utf-8", contentType)
+		assert.Regexp(t, "Service Temporarily Unavailable", body)
+		assert.Regexp(t, "Gone to lunch", body)
+	})
+
+	t.Run("When trying to set an error that we don't have a template for", func(t *testing.T) {
+		status, contentType, body := check(func(w http.ResponseWriter, r *http.Request) {
+			SetErrorResponse(w, r, http.StatusTeapot, nil)
+		})
+
+		assert.Equal(t, http.StatusTeapot, status)
+		assert.Equal(t, "text/html; charset=utf-8", contentType)
+		assert.Regexp(t, "I'm a teapot", body)
+	})
+
+	t.Run("When the backend returns an error normally", func(t *testing.T) {
+		status, contentType, body := check(func(w http.ResponseWriter, r *http.Request) {
+			http.Error(w, http.StatusText(http.StatusTeapot), http.StatusTeapot)
+		})
+
+		assert.Equal(t, http.StatusTeapot, status)
+		assert.Equal(t, "text/plain; charset=utf-8", contentType)
+		assert.Regexp(t, "I'm a teapot", body)
+	})
+}

internal/server/pages/404.html

@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+
+    <title>Not Found</title>
+
+    <style>
+    body {
+      font-family: system-ui, sans-serif;
+      font-size: 16px;
+      display: grid;
+      height: 80vh;
+      place-items: center;
+
+      background-color: #fff;
+      color: #333;
+    }
+
+    @media (prefers-color-scheme: dark) {
+      body {
+        background-color: #333;
+        color: #fff;
+      }
+    }
+    </style>
+  </head>
+
+  <body>
+    <h1>Not Found</h1>
+  </body>
+</html>

internal/server/pages/413.html

@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+
+    <title>Request Too Large</title>
+
+    <style>
+    body {
+      font-family: system-ui, sans-serif;
+      font-size: 16px;
+      display: grid;
+      height: 80vh;
+      place-items: center;
+
+      background-color: #fff;
+      color: #333;
+    }
+
+    @media (prefers-color-scheme: dark) {
+      body {
+        background-color: #333;
+        color: #fff;
+      }
+    }
+    </style>
+  </head>
+
+  <body>
+    <h1>Request Too Large</h1>
+  </body>
+</html>

internal/server/pages/502.html

@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+
+    <title>Bad Gateway</title>
+
+    <style>
+    body {
+      font-family: system-ui, sans-serif;
+      font-size: 16px;
+      display: grid;
+      height: 80vh;
+      place-items: center;
+
+      background-color: #fff;
+      color: #333;
+    }
+
+    @media (prefers-color-scheme: dark) {
+      body {
+        background-color: #333;
+        color: #fff;
+      }
+    }
+    </style>
+  </head>
+
+  <body>
+    <h1>Bad Gateway</h1>
+  </body>
+</html>

internal/server/pages/503.html

@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+
+    <title>Service Temporarily Unavailable</title>
+
+    <style>
+    body {
+      font-family: system-ui, sans-serif;
+      font-size: 16px;
+      display: grid;
+      height: 80vh;
+      place-items: center;
+
+      background-color: #fff;
+      color: #333;
+    }
+
+    @media (prefers-color-scheme: dark) {
+      body {
+        background-color: #333;
+        color: #fff;
+      }
+    }
+    </style>
+  </head>
+
+  <body>
+    <div>
+      <h1>Service Temporarily Unavailable</h1>
+      <p>{{ .Message }}</p>
+    </div>
+  </body>
+</html>

internal/server/pages/504.html

@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+
+    <title>Gateway Timeout</title>
+
+    <style>
+    body {
+      font-family: system-ui, sans-serif;
+      font-size: 16px;
+      display: grid;
+      height: 80vh;
+      place-items: center;
+
+      background-color: #fff;
+      color: #333;
+    }
+
+    @media (prefers-color-scheme: dark) {
+      body {
+        background-color: #333;
+        color: #fff;
+      }
+    }
+    </style>
+  </head>
+
+  <body>
+    <h1>Gateway Timeout</h1>
+  </body>
+</html>