New "browse" UI

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

Fixes #82

modules/actions/serveFileBrowser.js

@@ -0,0 +1,84 @@
+import gunzip from 'gunzip-maybe';
+import tar from 'tar-stream';
+
+import bufferStream from '../utils/bufferStream.js';
+import createDataURI from '../utils/createDataURI.js';
+import getContentType from '../utils/getContentType.js';
+import getIntegrity from '../utils/getIntegrity.js';
+import { getPackage } from '../utils/npm.js';
+import getHighlights from '../utils/getHighlights.js';
+import getLanguageName from '../utils/getLanguageName.js';
+
+import serveBrowsePage from './serveBrowsePage.js';
+
+async function findEntry(stream, filename) {
+  // filename = /some/file/name.js
+  return new Promise((accept, reject) => {
+    let foundEntry = null;
+
+    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
+        };
+
+        // Ignore non-files and files that don't match the name.
+        if (entry.type !== 'file' || entry.path !== filename) {
+          stream.resume();
+          stream.on('end', next);
+          return;
+        }
+
+        entry.content = await bufferStream(stream);
+        foundEntry = entry;
+
+        next();
+      })
+      .on('finish', () => {
+        accept(foundEntry);
+      });
+  });
+}
+
+export default async function serveFileBrowser(req, res) {
+  const stream = await getPackage(req.packageName, req.packageVersion);
+  const entry = await findEntry(stream, req.filename);
+
+  if (!entry) {
+    return res.status(404).send(`Not found: ${req.packageSpec}${req.filename}`);
+  }
+
+  const details = {
+    contentType: getContentType(entry.path),
+    integrity: getIntegrity(entry.content),
+    language: getLanguageName(entry.path),
+    size: entry.content.length
+  };
+
+  if (/^image\//.test(details.contentType)) {
+    details.uri = createDataURI(details.contentType, entry.content);
+    details.highlights = null;
+  } else {
+    details.uri = null;
+    details.highlights = getHighlights(
+      entry.content.toString('utf8'),
+      entry.path
+    );
+  }
+
+  req.browseTarget = {
+    path: req.filename,
+    type: 'file',
+    details
+  };
+
+  serveBrowsePage(req, res);
+}