Custom ReasonML Server (#6970)

- A typesafe custom server built in reasonml.

examples/custom-server-reasonml/.gitignore

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+*.exe
+*.obj
+*.out
+*.compile
+*.native
+*.byte
+*.cmo
+*.annot
+*.cmi
+*.cmx
+*.cmt
+*.cmti
+*.cma
+*.a
+*.cmxa
+*.obj
+*~
+*.annot
+*.cmj
+*.bak
+lib/bs
+*.mlast
+*.mliast
+.vscode
+.merlin
+.bsb.lock

examples/custom-server-reasonml/README.md

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+# Custom server REASONML
+
+# Install it and run:
+```bash
+npm install
+npm run dev
+# or
+yarn
+yarn dev
+```
+
+# Build the app
+```bash
+yarn next:build
+npm run next:build
+```
+
+# Run the production app
+Run this command after yarn build.
+```bash
+yarn start
+```
+
+# The idea behind this example
+ReasonML is an exciting new language and since it can compile directly to JS via bucklescript
+that means that we can power our backend server with REASONML and also have the frontend built with 
+reasonreact, which is covered in another [example](https://github.com/zeit/next.js/tree/canary/examples/with-reasonml).
+This example shows how powerful & helpful it can be to build a next js custom server with a typesafe language.
+
+The example has been built off the `custom-server` example that uses pure `nodejs` to build the custom server.

examples/custom-server-reasonml/bsconfig.json

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+{
+  "name": "custom-server-reason",
+  "version": "0.1.0",
+  "sources": {
+    "dir": "server",
+    "subdirs": true
+  },
+  "package-specs": {
+    "module": "commonjs",
+    "in-source": true
+  },
+  "suffix": ".bs.js",
+  "bs-dependencies": []
+}

examples/custom-server-reasonml/package.json

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+{
+  "name": "custom-server-reason",
+  "version": "0.1.0",
+  "scripts": {
+    "clean": "bsb -clean-world",
+    "build": "bsb -make-world",
+    "watch": "bsb -make-world -w",
+    "next-build": "next build",
+    "dev": "bsb -make-world && node server/server.bs.js",
+    "next:build": "bsb -make-world && next build",
+    "start": "NODE_ENV=production node server/server.bs.js"
+  },
+  "keywords": [
+    "BuckleScript"
+  ],
+  "author": "",
+  "license": "MIT",
+  "devDependencies": {
+    "bs-platform": "^4.0.18"
+  },
+  "dependencies": {
+    "next": "^8.0.4",
+    "react": "^16.8.6",
+    "react-dom": "^16.8.6"
+  }
+}

examples/custom-server-reasonml/pages/a.js

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+import React from 'react'
+
+export default () => <div>a</div>

examples/custom-server-reasonml/pages/b.js

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+import React from 'react'
+
+export default () => <div>b</div>

examples/custom-server-reasonml/pages/index.js

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+import React from 'react'
+import Link from 'next/link'
+
+export default () => (
+  <ul>
+    <li>
+      <Link href='/b' as='/a'>
+        <a>a</a>
+      </Link>
+    </li>
+    <li>
+      <Link href='/a' as='/b'>
+        <a>b</a>
+      </Link>
+    </li>
+  </ul>
+)

examples/custom-server-reasonml/server/http.re

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+type http;
+
+[@bs.deriving abstract]
+type parsedObjectUrl = {
+  pathname: string,
+  query: string,
+};
+
+module Request = {
+  type t;
+  [@bs.get] external url: t => string = "";
+  [@bs.get] external method_: t => string = "method";
+};
+
+module Response = {
+  type t;
+  [@bs.send.pipe: t] external end_: 'a => unit = "end";
+  [@bs.send] external setHeader: (t, string, string) => unit = "";
+  [@bs.send] external writeHead: (t, int) => unit = "";
+  let setHeader = (header: string, value: string, response: t) => {
+    setHeader(response, header, value);
+    response;
+  };
+  let writeHead = (status: int, response: t) => {
+    writeHead(response, status);
+    response;
+  };
+};
+
+[@bs.module "http"]
+external createServer: ((Request.t, Response.t) => unit) => http = "";
+
+[@bs.send.pipe: http] external listen: (int, string => unit) => unit = "";
+
+[@bs.module "url"] external parse: (string, bool) => parsedObjectUrl = "";

examples/custom-server-reasonml/server/server.re

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+open Http;
+
+[@bs.deriving abstract]
+type nextparams = {dev: bool};
+
+type nextoutput;
+[@bs.send] external prepare: nextoutput => Js.Promise.t(unit) = "";
+
+[@bs.send]
+external getRequestHandler:
+  (nextoutput, unit) => (. Request.t, Response.t, parsedObjectUrl) => unit =
+  "";
+
+[@bs.send]
+external render: (nextoutput, Request.t, Response.t, string, string) => unit =
+  "";
+
+[@bs.module] external next: nextparams => nextoutput = "next";
+
+[@bs.val] [@bs.scope ("process", "env")]
+external port: Js.Nullable.t(int) = "PORT";
+
+[@bs.val] [@bs.scope ("process", "env")]
+external node_env: string = "NODE_ENV";
+
+[@bs.val] external parseInt: (int, int) => int = "parseInt";
+let port =
+  switch (Js.Nullable.toOption(port)) {
+  | Some(port) => port
+  | None => 3000
+  };
+let is_dev = node_env != "production";
+
+let nxt = nextparams(~dev=is_dev);
+let app = next(nxt);
+
+let handle = getRequestHandler(app, ());
+
+Js.Promise.(
+  prepare(app)
+  |> then_(() => {
+       createServer((req, res) => {
+         let parsedUrl = parse(Request.url(req), true);
+         let pathname = pathnameGet(parsedUrl);
+         let query = queryGet(parsedUrl);
+
+         switch (pathname) {
+         | "/a" => app->render(req, res, "/a", query)
+         | "/b" => app->render(req, res, "/b", query)
+         | _ => handle(. req, res, parsedUrl)
+         };
+       })
+       |> listen(port, _err =>
+            print_string(
+              "> Listening on port http://localhost:" ++ string_of_int(port),
+            )
+          );
+
+       resolve(print_string(""));
+     })
+);