Return Diffusion diffs through Files, not directly over Conduit

Summary:
Fixes T10423. Ref T11524. This changes `diffusion.rawdiffquery` to return a file PHID instead of a blob of data.

This is better in general, but particularly better for huge diffs (as in T10423) and diffs with non-utf8 data (as in T10423).

Test Plan:
  - Used `bin/differential extract` to extract a latin1 diff, got a clean diff.
  - Used `bin/repository reparse --herald` to rerun herald on a latin1 diff, got a clean result.
  - Pushed latin1 diffs to test commit hooks.
  - Triggered the the too large / too slow logic.
  - Viewed latin1 diffs in Diffusion.
  - Used "blame past this change" in Diffusion to hit the `before` logic.

Reviewers: chad

Reviewed By: chad

Subscribers: eadler

Maniphest Tasks: T10423, T11524

Differential Revision: https://secure.phabricator.com/D16460

src/applications/diffusion/controller/DiffusionCommitController.php

@@ -1027,24 +1027,26 @@ final class DiffusionCommitController extends DiffusionController {
   }
 
   private function buildRawDiffResponse(DiffusionRequest $drequest) {
-    $raw_diff = $this->callConduitWithDiffusionRequest(
+    $diff_info = $this->callConduitWithDiffusionRequest(
       'diffusion.rawdiffquery',
       array(
         'commit' => $drequest->getCommit(),
         'path' => $drequest->getPath(),
       ));
 
-    $file = PhabricatorFile::buildFromFileDataOrHash(
-      $raw_diff,
-      array(
-        'name' => $drequest->getCommit().'.diff',
-        'ttl' => (60 * 60 * 24),
-        'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
-      ));
+    $file_phid = $diff_info['filePHID'];
 
-    $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
-      $file->attachToObject($drequest->getRepository()->getPHID());
-    unset($unguarded);
+    $file = id(new PhabricatorFileQuery())
+      ->setViewer($this->getViewer())
+      ->withPHIDs(array($file_phid))
+      ->executeOne();
+    if (!$file) {
+      throw new Exception(
+        pht(
+          'Failed to load file ("%s") returned by "%s".',
+          $file_phid,
+          'diffusion.rawdiffquery'));
+    }
 
     return $file->getRedirectResponse();
   }