Stop trying to assess the image dimensions of large files and file chunks

Summary:
Depends on D18828. Ref T7789. See <https://discourse.phabricator-community.org/t/git-lfs-fails-with-large-images/584>.

Currently, when you upload a large (>4MB) image, we may try to assess the dimensions for the image and for each individual chunk.

At best, this is slow and not useful. At worst, it fatals or consumes a ton of memory and I/O we don't need to be using.

Instead:

  - Don't try to assess dimensions for chunked files.
  - Don't try to assess dimensions for the chunks themselves.
  - Squelch errors for bad data, etc., that `gd` can't actually read, since we recover sensibly.

Test Plan:
  - Created a 2048x2048 PNG in Photoshop using the "Random Noise" filter which weighs 8.5MB.
  - Uploaded it.
  - Before patch: got complaints in log about `imagecreatefromstring()` failing, although the actual upload went OK in my environment.
  - After patch: clean log, no attempt to detect the size of a big image.
  - Also uploaded a small image, got dimensions detected properly still.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T7789

Differential Revision: https://secure.phabricator.com/D18830

src/applications/files/conduit/FileUploadChunkConduitAPIMethod.php

@@ -64,6 +64,7 @@ final class FileUploadChunkConduitAPIMethod
     $params = array(
       'name' => $file->getMonogram().'.chunk-'.$chunk->getID(),
       'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
+      'chunk' => true,
     );
 
     if ($mime_type !== null) {

src/applications/files/storage/PhabricatorFile.php

@@ -40,6 +40,7 @@ final class PhabricatorFile extends PhabricatorFileDAO
   const METADATA_PROFILE = 'profile';
   const METADATA_STORAGE = 'storage';
   const METADATA_INTEGRITY = 'integrity';
+  const METADATA_CHUNK = 'chunk';
 
   const STATUS_ACTIVE = 'active';
   const STATUS_DELETED = 'deleted';
@@ -410,7 +411,7 @@ final class PhabricatorFile extends PhabricatorFileDAO
     try {
       $file->updateDimensions(false);
     } catch (Exception $ex) {
-      // Do nothing
+      // Do nothing.
     }
 
     $file->saveAndIndex();
@@ -1057,9 +1058,20 @@ final class PhabricatorFile extends PhabricatorFileDAO
       throw new Exception(pht('Cannot retrieve image information.'));
     }
 
+    if ($this->getIsChunk()) {
+      throw new Exception(
+        pht('Refusing to assess image dimensions of file chunk.'));
+    }
+
+    $engine = $this->instantiateStorageEngine();
+    if ($engine->isChunkEngine()) {
+      throw new Exception(
+        pht('Refusing to assess image dimensions of chunked file.'));
+    }
+
     $data = $this->loadFileData();
 
-    $img = imagecreatefromstring($data);
+    $img = @imagecreatefromstring($data);
     if ($img === false) {
       throw new Exception(pht('Error when decoding image.'));
     }
@@ -1255,6 +1267,15 @@ final class PhabricatorFile extends PhabricatorFileDAO
     return $this;
   }
 
+  public function getIsChunk() {
+    return idx($this->metadata, self::METADATA_CHUNK);
+  }
+
+  public function setIsChunk($value) {
+    $this->metadata[self::METADATA_CHUNK] = $value;
+    return $this;
+  }
+
   public function setIntegrityHash($integrity_hash) {
     $this->metadata[self::METADATA_INTEGRITY] = $integrity_hash;
     return $this;
@@ -1339,6 +1360,7 @@ final class PhabricatorFile extends PhabricatorFileDAO
         'mime-type' => 'optional string',
         'builtin' => 'optional string',
         'storageEngines' => 'optional list<PhabricatorFileStorageEngine>',
+        'chunk' => 'optional bool',
       ));
 
     $file_name = idx($params, 'name');
@@ -1416,6 +1438,11 @@ final class PhabricatorFile extends PhabricatorFileDAO
       $this->setMimeType($mime_type);
     }
 
+    $is_chunk = idx($params, 'chunk');
+    if ($is_chunk) {
+      $this->setIsChunk(true);
+    }
+
     return $this;
   }
 

src/applications/files/uploadsource/PhabricatorFileUploadSource.php

@@ -189,6 +189,7 @@ abstract class PhabricatorFileUploadSource
     $params = array(
       'name' => $file->getMonogram().'.chunk-'.$offset,
       'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
+      'chunk' => true,
     );
 
     // If this isn't the initial chunk, provide a dummy MIME type so we do not