allow requireCloudflare setting to work when hosted on fly.io (#7781)

core/server/server.js

@@ -201,6 +201,14 @@ function addHandlerAtIndex(camp, index, handlerFn) {
   camp.stack.splice(index, 0, handlerFn)
 }
 
+function isOnHeroku() {
+  return !!process.env.DYNO
+}
+
+function isOnFly() {
+  return !!process.env.FLY_APP_NAME
+}
+
 /**
  * The Server is based on the web framework Scoutcamp. It creates
  * an http server, sets up helpers for token persistence and monitoring.
@@ -301,13 +309,19 @@ class Server {
     // Set `req.ip`, which is expected by `cloudflareMiddleware()`. This is set
     // by Express but not Scoutcamp.
     addHandlerAtIndex(this.camp, 0, function (req, res, next) {
-      // On Heroku, `req.socket.remoteAddress` is the Heroku router. However,
-      // the router ensures that the last item in the `X-Forwarded-For` header
-      // is the real origin.
-      // https://stackoverflow.com/a/18517550/893113
-      req.ip = process.env.DYNO
-        ? req.headers['x-forwarded-for'].split(', ').pop()
-        : req.socket.remoteAddress
+      if (isOnHeroku()) {
+        // On Heroku, `req.socket.remoteAddress` is the Heroku router. However,
+        // the router ensures that the last item in the `X-Forwarded-For` header
+        // is the real origin.
+        // https://stackoverflow.com/a/18517550/893113
+        req.ip = req.headers['x-forwarded-for'].split(', ').pop()
+      } else if (isOnFly()) {
+        // On Fly we can use the Fly-Client-IP header
+        // https://fly.io/docs/reference/runtime-environment/#request-headers
+        req.ip = req.headers['fly-client-ip']
+      } else {
+        req.ip = req.socket.remoteAddress
+      }
       next()
     })
     addHandlerAtIndex(this.camp, 1, cloudflareMiddleware())