Move static handlers for Auspice and Gatsby into endpoints/static

Better separation of concerns here.  Note that instead of using the
"fallthrough" option to expressStaticGzip (which passes it thru to
express.static, which passes it thru to serve-static), I stack an
"always 404" handler after the static handler.  Otherwise, the
fallthrough behaviour would be non-obvious and baffling to anyone
reading app.js.  Falling through is part of the routing, which belongs
solely in app.js, while how to serve the assets is part of the endpoint.

src/app.js

@@ -2,7 +2,6 @@
 const sslRedirect = require('heroku-ssl-redirect');
 const nakedRedirect = require('express-naked-redirect');
 const express = require("express");
-const expressStaticGzip = require("express-static-gzip");
 const favicon = require('serve-favicon');
 const compression = require('compression');
 const utils = require("./utils");
@@ -14,7 +13,7 @@ const production = process.env.NODE_ENV === "production";
 
 const charon = require("./endpoints/charon");
 const users = require("./endpoints/users");
-const {assetPath, auspiceAssetPath, gatsbyAssetPath, sendAuspiceEntrypoint, sendGatsbyEntrypoint, sendGatsbyPage, sendGatsby404} = require("./endpoints/static");
+const {assetPath, auspiceAssets, gatsbyAssets, sendAuspiceEntrypoint, sendGatsbyEntrypoint, sendGatsbyPage, sendGatsby404} = require("./endpoints/static");
 const {setSource, setGroupSource, setDataset, setNarrative, canonicalizeDataset, ifDatasetExists, ifNarrativeExists} = require("./endpoints/sources");
 const authn = require("./authn");
 const redirects = require("./redirects");
@@ -257,7 +256,7 @@ app.route(["/users", "/users/:name"])
  * so we must use that prefix here too.
  */
 app.route("/dist/*")
-  .all(expressStaticGzip(auspiceAssetPath(), {fallthrough: false, maxAge: '30d'}));
+  .all(auspiceAssets, (req, res, next) => next(new NotFound()));
 
 
 /* Gatsby static HTML pages and other assets.
@@ -281,7 +280,7 @@ if (app.locals.gatsbyDevUrl) {
    */
   app.use(createProxyMiddleware(app.locals.gatsbyDevUrl));
 } else {
-  app.use(express.static(gatsbyAssetPath()));
+  app.use(gatsbyAssets);
 }
 
 

src/endpoints/static.js

@@ -1,3 +1,5 @@
+const express = require("express");
+const expressStaticGzip = require("express-static-gzip");
 const {InternalServerError} = require("http-errors");
 const path = require("path");
 
@@ -16,6 +18,13 @@ const gatsbyAssetPath = (...subpath) =>
   assetPath("static-site", "public", ...subpath);
 
 
+/* Handlers for static assets.
+ */
+const auspiceAssets = expressStaticGzip(auspiceAssetPath(), {maxAge: '30d'});
+
+const gatsbyAssets = express.static(gatsbyAssetPath());
+
+
 /**
  * Send the file at the given `filePath` as the response.
  *
@@ -149,8 +158,8 @@ const sendGatsby404 = async (req, res) => {
 
 module.exports = {
   assetPath,
-  auspiceAssetPath,
-  gatsbyAssetPath,
+  auspiceAssets,
+  gatsbyAssets,
 
   sendFile,
   sendAuspiceEntrypoint,