feature #11857 [Filesystem] Check number of bytes copied. (skigun)

This PR was merged into the 2.6-dev branch.

Discussion
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[Filesystem] Check number of bytes copied.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10838
| License       | MIT
| Doc PR        | n/a

This only test local files (because of `filesize`), wonder if we should include the remote files using `get_headers` in order to get the Content-length for example. However, it will perform an additional request...

Here's a little benchmark for 500 copy from a remote origin file :
- Standard without check -> Time: 47.34 seconds, Memory: 3.75Mb
- Check with `get_headers` ->Time: 1.32 minutes, Memory: 3.75Mb

Commits
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81eca38 [Filesystem] Check number of bytes copied.

src/Symfony/Component/Filesystem/Filesystem.php

@@ -60,14 +60,18 @@ public function copy($originFile, $targetFile, $override = false)
                 throw new IOException(sprintf('Failed to copy "%s" to "%s" because target file could not be opened for writing.', $originFile, $targetFile), 0, null, $originFile);
             }
 
-            stream_copy_to_stream($source, $target);
+            $bytesCopied = stream_copy_to_stream($source, $target);
             fclose($source);
             fclose($target);
             unset($source, $target);
 
             if (!is_file($targetFile)) {
                 throw new IOException(sprintf('Failed to copy "%s" to "%s".', $originFile, $targetFile), 0, null, $originFile);
             }
+
+            if (stream_is_local($originFile) && $bytesCopied !== filesize($originFile)) {
+                throw new IOException(sprintf('Failed to copy the whole content of "%s" to "%s %g bytes copied".', $originFile, $targetFile, $bytesCopied), 0, null, $originFile);
+            }
         }
     }