fix: ensure fallback url is reachable

package.json

@@ -91,6 +91,7 @@
     "@microlink/mql": "~0.12.2",
     "@microlink/ping-url": "~1.4.11",
     "@microlink/ua": "~1.2.0",
+    "async-memoize-one": "~1.1.6",
     "browserless": "~10.2.4",
     "cacheable-lookup": "~6.1.0",
     "cacheable-response": "~2.8.10",
@@ -110,7 +111,6 @@
     "is-email-like": "~1.0.0",
     "is-url-http": "~2.3.7",
     "lodash": "~4.17.21",
-    "memoize-one": "~6.0.0",
     "ms": "~2.1.3",
     "on-finished": "~2.4.1",
     "p-any": "~3.0.0",

src/avatar/resolve.js

@@ -1,9 +1,10 @@
 'use strict'
 
 const debug = require('debug-logfmt')('unavatar:resolve')
+const reachableUrl = require('../util/reachable-url')
 const isAbsoluteUrl = require('is-absolute-url')
+const memoizeOne = require('async-memoize-one')
 const { getTtl } = require('../send/cache')
-const memoizeOne = require('memoize-one')
 const isUrlHttp = require('is-url-http')
 const pTimeout = require('p-timeout')
 const pReflect = require('p-reflect')
@@ -44,16 +45,18 @@ const optimizeUrl = async (url, query) => {
   }).toString()}`
 }
 
-const getDefaultFallbackUrl = memoizeOne(
-  ({ protocol, host }) => `${protocol}://${host}/fallback.png`
-)
+const getDefaultFallbackUrl = ({ protocol, host }) =>
+  this.url || (this.url = `${protocol}://${host}/fallback.png`)
 
-const getFallbackUrl = memoizeOne(({ query, protocol, host }) => {
+const getFallbackUrl = memoizeOne(async ({ query, protocol, host }) => {
   const { fallback } = query
   if (fallback === false) return null
-
-  return isUrlHttp(fallback) && isAbsoluteUrl(fallback)
-    ? fallback
+  if (!isUrlHttp(fallback) || !isAbsoluteUrl(fallback)) {
+    return getDefaultFallbackUrl({ protocol, host })
+  }
+  const { statusCode, url } = await reachableUrl(fallback)
+  return reachableUrl.isReachable({ statusCode })
+    ? url
     : getDefaultFallbackUrl({ protocol, host })
 })
 
@@ -74,7 +77,7 @@ module.exports = fn => async (req, res) => {
   }
 
   if (value === undefined) {
-    const data = getFallbackUrl({ query, protocol, host })
+    const data = await getFallbackUrl({ query, protocol, host })
     value = data ? { type: 'url', data } : null
   }
 

src/server.js

@@ -21,3 +21,9 @@ server.listen(PORT, () => {
     address: API_URL
   })
 })
+
+process.on('uncaughtException', error => {
+  debug.error('uncaughtException', {
+    requestUrl: error.response?.requestUrl
+  })
+})

test/query-parameters.js

@@ -36,6 +36,21 @@ test('fallback', async t => {
   t.is(headers['content-type'], 'application/json; charset=utf-8')
 })
 
+test('fallback # use default value if fallback provided is not reachable', async t => {
+  const serverUrl = await runServer(t)
+
+  const { headers, body } = await got(
+    'github/__notexistprofile__?fallback=https://nexmoe.com/thisis404.png&json',
+    {
+      prefixUrl: serverUrl,
+      responseType: 'json'
+    }
+  )
+
+  t.is(body.url, `${serverUrl.toString()}fallback.png`)
+  t.is(headers['content-type'], 'application/json; charset=utf-8')
+})
+
 test('ttl', t => {
   t.is(getTtl(), CACHE_TTL)
   t.is(getTtl(null), CACHE_TTL)