Fix HTTP body decompression in PHP 5.6

Summary:
Ref T10264. Under PHP 5.6, you are no longer allowed to use `compress.zlib://php://input` as an argument to either `fopen()` or `file_get_contents()`.

Instead, open `php://input` as a file handle, then add `zlib.inflate` as a stream wrapper. This requires some level of magic to work properly.

Test Plan:
First, I constructed a synthetic gzipped payload by typing some words into a file and using `gzcompress()` to compress it.

Then I used a `curl` command like this to make requests with it:

```
$ curl -X POST -H "Content-Length: 66" -H "Content-Type: text/plain" -H "Content-Encoding: gzip" --data-binary @payload.deflate -v http://127.0.0.1/
```

I modified Phabricator to just dump the raw request body and exit, and reproduced the issue under PHP 5.6 (no body, error in log) by brining up a micro instance in EC2 and installing php56 on it.

After this patch, it dumped the body properly instead, and PHP 5.5 also continued worked properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10264

Differential Revision: https://secure.phabricator.com/D15314

support/PhabricatorStartup.php

@@ -135,13 +135,40 @@ final class PhabricatorStartup {
       $encoding = null;
     }
 
-    if ($encoding === 'gzip') {
+    $input_stream = fopen('php://input', 'rb');
-      $source_stream = 'compress.zlib://php://input';
+    if (!$input_stream) {
-    } else {
+      self::didFatal(
-      $source_stream = 'php://input';
+        'Unable to open "php://input" to read HTTP request body.');
     }
 
-    self::$rawInput = (string)file_get_contents($source_stream);
+    if ($encoding === 'gzip') {
+      $ok = stream_filter_append(
+        $input_stream,
+        'zlib.inflate',
+        STREAM_FILTER_READ,
+        array(
+          'window' => 30,
+        ));
+
+      if (!$ok) {
+        self::didFatal(
+          'Failed to append gzip inflate filter to HTTP request body input '.
+          'stream.');
+      }
+    }
+
+    $input_data = '';
+    while (!feof($input_stream)) {
+      $read_bytes = fread($input_stream, 16 * 1024);
+      if ($read_bytes === false) {
+        self::didFatal(
+          'Failed to read input bytes from HTTP request body.');
+      }
+      $input_data .= $read_bytes;
+    }
+    fclose($input_stream);
+
+    self::$rawInput = $input_data;
   }