From 67f4d5cb7925313e9216ddffaf1def84e0858d77 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20L=C3=BCck?= <christian@clue.engineering>
Date: Wed, 1 Apr 2020 21:39:36 +0200
Subject: [PATCH] Work around compressing empty stream on PHP 7+

---
 README.md                                 |  1 -
 src/Compressor.php                        |  2 ++
 src/ZlibFilterStream.php                  | 15 +++++++++++++++
 tests/ZlibFilterDeflateCompressorTest.php |  2 --
 tests/ZlibFilterGzipCompressorTest.php    |  2 --
 tests/ZlibFilterZlibCompressorTest.php    |  2 --
 6 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index 7d2536b..939dafa 100644
--- a/README.md
+++ b/README.md
@@ -232,7 +232,6 @@ As such, we've spotted several inconsistencies (or *bugs*) between different PHP
 These inconsistencies exist in the underlying PHP engines and there's little we can do about this in this library.
 
 * All Zend PHP versions: Decompressing invalid data does not emit any data (and does not raise an error)
-* PHP 7 only: Compressing an empty string does not emit any data (not a valid compression stream)
 * HHVM only: does not currently support the GZIP and ZLIB format at all (and does not raise an error)
 * HHVM only: The [`zlib.deflate` filter function](https://github.com/facebook/hhvm/blob/fee8ae39ce395c7b9b8910dfde6f22a7745aea83/hphp/system/php/stream/default-filters.php#L77) buffers the whole string. This means that compressing a stream of 100 MB actually stores the whole string in memory before invoking the underlying compression algorithm.
 * PHP 5.3 only: Tends to SEGFAULT occasionally on shutdown?
diff --git a/src/Compressor.php b/src/Compressor.php
index 8ed49c9..22b518f 100644
--- a/src/Compressor.php
+++ b/src/Compressor.php
@@ -46,5 +46,7 @@ public function __construct($encoding, $level = -1)
         parent::__construct(
             Filter\fun('zlib.deflate', array('window' => $encoding, 'level' => $level))
         );
+
+        $this->emptyWrite = $encoding;
     }
 }
diff --git a/src/ZlibFilterStream.php b/src/ZlibFilterStream.php
index 95cd4bd..45dae7b 100644
--- a/src/ZlibFilterStream.php
+++ b/src/ZlibFilterStream.php
@@ -74,6 +74,13 @@ public static function createZlibDecompressor()
 
     private $filter;
 
+    /**
+     * @var int|null
+     * @see Compressor
+     * @internal
+     */
+    protected $emptyWrite;
+
     public function __construct($filter)
     {
         $this->filter = $filter;
@@ -85,6 +92,7 @@ protected function transformData($chunk)
         $ret = $filter($chunk);
 
         if ($ret !== '') {
+            $this->emptyWrite = null;
             $this->forwardData($ret);
         }
     }
@@ -94,6 +102,13 @@ protected function transformEnd($chunk)
         $filter = $this->filter;
         $ret = $filter($chunk) . $filter();
 
+        // Stream ends successfully and did not emit any data whatsoever?
+        // This happens when compressing an empty stream with PHP 7 only.
+        // Bypass filter and manually compress/encode empty string.
+        if ($this->emptyWrite !== null && $ret === '') {
+            $ret = \zlib_encode('', $this->emptyWrite);
+        }
+
         if ($ret !== '') {
             $this->forwardData($ret);
         }
diff --git a/tests/ZlibFilterDeflateCompressorTest.php b/tests/ZlibFilterDeflateCompressorTest.php
index 2aed4ba..2d4aa26 100644
--- a/tests/ZlibFilterDeflateCompressorTest.php
+++ b/tests/ZlibFilterDeflateCompressorTest.php
@@ -13,8 +13,6 @@ public function setUp()
 
     public function testDeflateEmpty()
     {
-        if (PHP_VERSION >= 7) $this->markTestSkipped('Not supported on PHP 7 (empty chunk will not be emitted)');
-
         $this->compressor->on('data', $this->expectCallableOnceWith("\x03\x00"));
         $this->compressor->on('end', $this->expectCallableOnce());
 
diff --git a/tests/ZlibFilterGzipCompressorTest.php b/tests/ZlibFilterGzipCompressorTest.php
index ac54887..8a86a27 100644
--- a/tests/ZlibFilterGzipCompressorTest.php
+++ b/tests/ZlibFilterGzipCompressorTest.php
@@ -15,8 +15,6 @@ public function setUp()
 
     public function testCompressEmpty()
     {
-        if (PHP_VERSION >= 7) $this->markTestSkipped('Not supported on PHP 7 (empty chunk will not be emitted)');
-
         $os = "\x03"; // UNIX (0x03) or UNKNOWN (0xFF)
         $this->compressor->on('data', $this->expectCallableOnceWith("\x1f\x8b\x08\x00\x00\x00\x00\x00\x00" . $os . "\x03\x00" . "\x00\x00\x00\x00\x00\x00\x00\x00"));
         $this->compressor->on('end', $this->expectCallableOnce());
diff --git a/tests/ZlibFilterZlibCompressorTest.php b/tests/ZlibFilterZlibCompressorTest.php
index aa047d6..b927f8b 100644
--- a/tests/ZlibFilterZlibCompressorTest.php
+++ b/tests/ZlibFilterZlibCompressorTest.php
@@ -15,8 +15,6 @@ public function setUp()
 
     public function testCompressEmpty()
     {
-        if (PHP_VERSION >= 7) $this->markTestSkipped('Not supported on PHP 7 (empty chunk will not be emitted)');
-
         $this->compressor->on('data', $this->expectCallableOnceWith("\x78\x9c" . "\x03\x00" . "\x00\x00\x00\x01"));
         $this->compressor->on('end', $this->expectCallableOnce());