New "browse" UI

Also, separated out browse, ?meta, and ?module request handlers.

Fixes #82

modules/actions/serveDirectoryBrowser.js

@@ -0,0 +1,81 @@
+import path from 'path';
+import gunzip from 'gunzip-maybe';
+import tar from 'tar-stream';
+
+import bufferStream from '../utils/bufferStream.js';
+import getContentType from '../utils/getContentType.js';
+import getIntegrity from '../utils/getIntegrity.js';
+import { getPackage } from '../utils/npm.js';
+import serveBrowsePage from './serveBrowsePage.js';
+
+async function findMatchingEntries(stream, filename) {
+  // filename = /some/dir/name
+  return new Promise((accept, reject) => {
+    const entries = {};
+
+    stream
+      .pipe(gunzip())
+      .pipe(tar.extract())
+      .on('error', reject)
+      .on('entry', async (header, stream, next) => {
+        const entry = {
+          // Most packages have header names that look like `package/index.js`
+          // so we shorten that to just `/index.js` here. A few packages use a
+          // prefix other than `package/`. e.g. the firebase package uses the
+          // `firebase_npm/` prefix. So we just strip the first dir name.
+          path: header.name.replace(/^[^/]+/, ''),
+          type: header.type
+        };
+
+        // Dynamically create "directory" entries for all subdirectories
+        // in this entry's path. Some tarballs omit directory entries for
+        // some reason, so this is the "brute force" method.
+        let dir = path.dirname(entry.path);
+        while (dir !== '/') {
+          if (!entries[dir] && path.dirname(dir) === filename) {
+            entries[dir] = { path: dir, type: 'directory' };
+          }
+          dir = path.dirname(dir);
+        }
+
+        // Ignore non-files and files that aren't in this directory.
+        if (entry.type !== 'file' || path.dirname(entry.path) !== filename) {
+          stream.resume();
+          stream.on('end', next);
+          return;
+        }
+
+        const content = await bufferStream(stream);
+
+        entry.contentType = getContentType(entry.path);
+        entry.integrity = getIntegrity(content);
+        entry.size = content.length;
+
+        entries[entry.path] = entry;
+
+        next();
+      })
+      .on('finish', () => {
+        accept(entries);
+      });
+  });
+}
+
+export default async function serveDirectoryBrowser(req, res) {
+  const stream = await getPackage(req.packageName, req.packageVersion);
+
+  const filename = req.filename.slice(0, -1) || '/';
+  const entries = await findMatchingEntries(stream, filename);
+
+  if (Object.keys(entries).length === 0) {
+    return res.status(404).send(`Not found: ${req.packageSpec}${req.filename}`);
+  }
+
+  req.browseTarget = {
+    path: filename,
+    type: 'directory',
+    details: entries
+  };
+
+  serveBrowsePage(req, res);
+}