Add a chunking storage engine for files

Summary:
Ref T7149. This isn't complete and isn't active yet, but does basically work. I'll shore it up in the next few diffs.

The new workflow goes like this:

> Client, file.allocate(): I'd like to upload a file with length L, metadata M, and hash H.

Then the server returns `upload` (a boolean) and `filePHID` (a PHID). These mean:

| upload | filePHID | means |
|---|---|---|
| false | false | Server can't accept file.
| false | true | File data already known, file created from hash.
| true | false | Just upload normally.
| true | true | Query chunks to start or resume a chunked upload.

All but the last case are uninteresting and work like exising uploads with `file.uploadhash` (which we can eventually deprecate).

In the last case:

> Client, file.querychunks(): Give me a list of chunks that I should upload.

This returns all the chunks for the file. Chunks have a start byte, an end byte, and a "complete" flag to indicate that the server already has the data.

Then, the client fills in chunks by sending them:

> Client, file.uploadchunk(): Here is the data for one chunk.

This stuff doesn't work yet or has some caveats:

  - I haven't tested resume much.
  - Files need an "isPartial()" flag for partial uploads, and the UI needs to respect it.
  - The JS client needs to become chunk-aware.
  - Chunk size is set crazy low to make testing easier.
  - Some debugging flags that I'll remove soon-ish.
  - Downloading works, but still streams the whole file into memory.
  - This storage engine is disabled by default (hardcoded as a unit test engine) because it's still sketchy.
  - Need some code to remove the "isParital" flag when the last chunk is uploaded.
  - Maybe do checksumming on chunks.

Test Plan:
  - Hacked up `arc upload` (see next diff) to be chunk-aware and uploaded a readme in 18 32-byte chunks. Then downloaded it. Got the same file back that I uploaded.
  - File UI now shows some basic chunk info for chunked files:

{F336434}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: joshuaspence, epriestley

Maniphest Tasks: T7149

Differential Revision: https://secure.phabricator.com/D12060

src/applications/files/controller/PhabricatorFileInfoController.php

@@ -295,6 +295,67 @@ final class PhabricatorFileInfoController extends PhabricatorFileController {
 
       $box->addPropertyList($media);
     }
+
+    $engine = null;
+    try {
+      $engine = $file->instantiateStorageEngine();
+    } catch (Exception $ex) {
+      // Don't bother raising this anywhere for now.
+    }
+
+    if ($engine) {
+      if ($engine->isChunkEngine()) {
+        $chunkinfo = new PHUIPropertyListView();
+        $box->addPropertyList($chunkinfo, pht('Chunks'));
+
+        $chunks = id(new PhabricatorFileChunkQuery())
+          ->setViewer($user)
+          ->withChunkHandles(array($file->getStorageHandle()))
+          ->execute();
+        $chunks = msort($chunks, 'getByteStart');
+
+        $rows = array();
+        $completed = array();
+        foreach ($chunks as $chunk) {
+          $is_complete = $chunk->getDataFilePHID();
+
+          $rows[] = array(
+            $chunk->getByteStart(),
+            $chunk->getByteEnd(),
+            ($is_complete ? pht('Yes') : pht('No')),
+          );
+
+          if ($is_complete) {
+            $completed[] = $chunk;
+          }
+        }
+
+        $table = id(new AphrontTableView($rows))
+          ->setHeaders(
+            array(
+              pht('Offset'),
+              pht('End'),
+              pht('Complete'),
+            ))
+          ->setColumnClasses(
+            array(
+              '',
+              '',
+              'wide',
+            ));
+
+        $chunkinfo->addProperty(
+          pht('Total Chunks'),
+          count($chunks));
+
+        $chunkinfo->addProperty(
+          pht('Completed Chunks'),
+          count($completed));
+
+        $chunkinfo->addRawContent($table);
+      }
+    }
+
   }
 
 }