Handle missing links gracefully. (#112)

Herein, we do two things:

1- implement a custom handler for the virtual filesystem that,
   rather than returning a simple (and ugly) 404 page, redirects
   the client back to the root URL with the `customUrl` query
   parameter filled out with the value of the request path.

2- In home.js, if the `customUrl` param is filled out, automatically
   select the `custom` state setting, and pre-fill out the CustomID
   input field with the value of that param.

In short, the server will never again return a 404 error, but instead
will gracefully prompt the user to fill in the missing link.

internal/handlers/handlers.go

@@ -166,14 +166,65 @@ func (h *Handler) setHandlers() error {
 
 	// Handling the shorted URLs, if no one exists, it checks
 	// in the filesystem and sets headers for caching
-	h.engine.NoRoute(h.handleAccess, func(c *gin.Context) {
-		c.Header("Vary", "Accept-Encoding")
-		c.Header("Cache-Control", "public, max-age=2592000")
-		c.Header("ETag", util.VersionInfo.Commit)
-	}, gin.WrapH(http.FileServer(FS(false))))
+	h.engine.NoRoute(
+		h.handleAccess, // look up shortcuts
+		func(c *gin.Context) { // no shortcut found, prep response for FS
+			c.Header("Vary", "Accept-Encoding")
+			c.Header("Cache-Control", "public, max-age=2592000")
+			c.Header("ETag", util.VersionInfo.Commit)
+		},
+		// Pass down to the embedded FS, but let 404s escape via
+		// the interceptHandler.
+		gin.WrapH(interceptHandler(http.FileServer(FS(false)), customErrorHandler)),
+		// not in FS; redirect to root with customURL target filled out
+		func(c *gin.Context) {
+			// if we get to this point we should not let the client cache
+			c.Header("Cache-Control", "no-cache, no-store")
+			c.Redirect(http.StatusTemporaryRedirect, "/?customUrl="+c.Request.URL.Path[1:])
+		})
 	return nil
 }
 
+type interceptResponseWriter struct {
+	http.ResponseWriter
+	errH func(http.ResponseWriter, int)
+}
+
+func (w *interceptResponseWriter) WriteHeader(status int) {
+	if status >= http.StatusBadRequest {
+		w.errH(w.ResponseWriter, status)
+		w.errH = nil
+	} else {
+		w.ResponseWriter.WriteHeader(status)
+	}
+}
+
+type errorHandler func(http.ResponseWriter, int)
+
+func (w *interceptResponseWriter) Write(p []byte) (n int, err error) {
+	if w.errH == nil {
+		return len(p), nil
+	}
+	return w.ResponseWriter.Write(p)
+}
+
+func interceptHandler(next http.Handler, errH errorHandler) http.Handler {
+	if errH == nil {
+		errH = customErrorHandler
+	}
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		next.ServeHTTP(&interceptResponseWriter{w, errH}, r)
+	})
+}
+
+func customErrorHandler(w http.ResponseWriter, status int) {
+	// let 404s fall through: the next NoRoute handler will redirect
+	// them back to the main page with the customURL box filled out.
+	if status != 404 {
+		http.Error(w, "error", status)
+	}
+}
+
 // Listen starts the http server
 func (h *Handler) Listen() error {
 	return h.engine.Run(util.GetConfig().ListenAddr)

internal/handlers/public_test.go

@@ -275,8 +275,8 @@ func TestHandleDeletion(t *testing.T) {
 		t.Fatalf("could not send visit request: %v", err)
 	}
 	fmt.Println(body.URL)
-	if resp.StatusCode != http.StatusNotFound {
-		t.Fatalf("expected status: %d; got: %d", http.StatusNotFound, resp.StatusCode)
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("expected status: %d; got: %d", http.StatusOK, resp.StatusCode)
 	}
 }
 

web/src/Home/Home.js

@@ -10,21 +10,31 @@ import CustomCard from '../Card/Card'
 import './Home.css'
 
 export default class HomeComponent extends Component {
+  constructor(props) {
+      super(props);
+      this.urlParams = new URLSearchParams(window.location.search);
+      this.state = {
+        links: [],
+        usedSettings: this.urlParams.get('customUrl') ? ['custom'] : [],
+        customID: this.urlParams.get('customUrl') ? this.urlParams.get('customUrl') : '',
+        showCustomIDError: false,
+        expiration: null
+      }
+  }
   handleURLChange = (e, { value }) => this.url = value
   handlePasswordChange = (e, { value }) => this.password = value
   handleCustomExpirationChange = expire => this.setState({ expiration: expire })
   handleCustomIDChange = (e, { value }) => {
-    this.customID = value
+    this.setState({customID: value})
     util.lookupEntry(value, () => this.setState({ showCustomIDError: true }), () => this.setState({ showCustomIDError: false }))
   }
-  onSettingsChange = (e, { value }) => this.setState({ usedSettings: value })
-
-  state = {
-    links: [],
-    usedSettings: [],
-    showCustomIDError: false,
-    expiration: null
+  onSettingsChange = (e, { value }) => {
+    this.setState({ usedSettings: value })
   }
+    
+  
+
+  
   componentDidMount() {
     this.urlInput.focus()
   }
@@ -32,7 +42,7 @@ export default class HomeComponent extends Component {
     if (!this.state.showCustomIDError) {
       util.createEntry({
         URL: this.url,
-        ID: this.customID,
+        ID: this.state.customID,
         Expiration: this.state.usedSettings.includes("expire") && this.state.expiration ? this.state.expiration.toISOString() : undefined,
         Password: this.state.usedSettings.includes("protected") && this.password ? this.password : undefined
       }, r => this.setState({
@@ -56,13 +66,18 @@ export default class HomeComponent extends Component {
     return (
       <div>
         <Segment raised>
-          <Header size='huge'>Simplify your links</Header>
+          {this.urlParams.get("customUrl") && (
+            <Header size='medium'>I don't have a link named <em>"{this.urlParams.get("customUrl")}"</em> in my database, would
+            you like to create one?</Header>
+          ) || 
+            <Header size='huge'>Simplify your links</Header>
+          }
           <Form onSubmit={this.handleURLSubmit} autoComplete="off">
             <Form.Field>
               <Input required size='large' type='url' ref={input => this.urlInput = input} onChange={this.handleURLChange} placeholder='Paste a link to shorten it' action>
                 <input />
                 <MediaQuery query="(min-width: 768px)">
-                  <Select options={options} placeholder='Settings' onChange={this.onSettingsChange} multiple />
+                  <Select options={options} placeholder='Settings' value={this.state.usedSettings} onChange={this.onSettingsChange} multiple />
                 </MediaQuery>
                 <Button type='submit'>Shorten<Icon name="arrow right" /></Button>
               </Input>
@@ -74,7 +89,7 @@ export default class HomeComponent extends Component {
             </MediaQuery>
             <Form.Group style={{ marginBottom: "1rem" }}>
               {usedSettings.includes("custom") && <Form.Field error={showCustomIDError} width={16}>
-                <Input label={window.location.origin + "/"} onChange={this.handleCustomIDChange} placeholder='my-shortened-url' />
+                <Input label={window.location.origin + "/"} onChange={this.handleCustomIDChange} placeholder='my-shortened-url' value={this.state.customID}/>
               </Form.Field>}
             </Form.Group>
             <Form.Group widths="equal">