From e9d4e4acbc037dc580eec06fb4c2670d0b74a172 Mon Sep 17 00:00:00 2001
From: Paul Yang <TeBoring@users.noreply.github.com>
Date: Fri, 30 Aug 2019 10:47:25 -0700
Subject: [PATCH] Fix the issue for parsing zero length message (#6592)

* When length is zero, substr returns null instead of emptry string, which breaks the invariable for message.
* Tested in https://github.com/protocolbuffers/protobuf/pull/6560
---
 php/src/Google/Protobuf/Internal/CodedInputStream.php | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/php/src/Google/Protobuf/Internal/CodedInputStream.php b/php/src/Google/Protobuf/Internal/CodedInputStream.php
index 33f4a456af..33b1f5a9ba 100644
--- a/php/src/Google/Protobuf/Internal/CodedInputStream.php
+++ b/php/src/Google/Protobuf/Internal/CodedInputStream.php
@@ -299,8 +299,12 @@ class CodedInputStream
             return false;
         }
 
-        $buffer = substr($this->buffer, $this->current, $size);
-        $this->advance($size);
+        if ($size === 0) {
+          $buffer = "";
+        } else {
+          $buffer = substr($this->buffer, $this->current, $size);
+          $this->advance($size);
+        }
 
         return true;
     }