offer a json response for grabbing short links (#4671)

bskylink/src/routes/redirect.ts

@@ -11,6 +11,7 @@ export default function (ctx: AppContext, app: Express) {
     '/:linkId',
     handler(async (req, res) => {
       const linkId = req.params.linkId
+      const contentType = req.accepts(['html', 'json'])
       assert(
         typeof linkId === 'string',
         'express guarantees id parameter is a string',
@@ -21,9 +22,19 @@ export default function (ctx: AppContext, app: Express) {
         .where('id', '=', linkId)
         .executeTakeFirst()
       if (!found) {
-        // potentially broken or mistyped link— send user to the app
-        res.setHeader('Location', `https://${ctx.cfg.service.appHostname}`)
+        // potentially broken or mistyped link
         res.setHeader('Cache-Control', 'no-store')
+        if (contentType === 'json') {
+          return res
+            .status(404)
+            .json({
+              error: 'NotFound',
+              message: 'Link not found',
+            })
+            .end()
+        }
+        // send the user to the app
+        res.setHeader('Location', `https://${ctx.cfg.service.appHostname}`)
         return res.status(302).end()
       }
       // build url from original url in order to preserve query params
@@ -32,8 +43,11 @@ export default function (ctx: AppContext, app: Express) {
         `https://${ctx.cfg.service.appHostname}`,
       )
       url.pathname = found.path
-      res.setHeader('Location', url.href)
       res.setHeader('Cache-Control', `max-age=${(7 * DAY) / SECOND}`)
+      if (contentType === 'json') {
+        return res.json({url: url.href}).end()
+      }
+      res.setHeader('Location', url.href)
       return res.status(301).end()
     }),
   )