From 3b1cb8cdebd93b893bce612136180c3185fa35bc Mon Sep 17 00:00:00 2001
From: "Christoph M. Becker" <cmbecker69@gmx.de>
Date: Fri, 26 Nov 2021 13:44:36 +0100
Subject: [PATCH] Fix #81659: stream_get_contents() may unnecessarily
 overallocate

Since we're going to read from the current stream position anyway, the
`max_len` should be the size of the file minus the current position
(still catering to potentially filtered streams).  We must, however,
make sure to cater to the file position being beyond the actual file
size.

While we're at, we also fix the step size in the comment, which is 8K.

A further optimization could be done for unfiltered streams, thus
saving that step size, but 8K might not be worth it.
---
 ext/standard/tests/streams/bug81659.phpt | 24 ++++++++++++++++++++++++
 main/streams/streams.c                   |  4 ++--
 2 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 ext/standard/tests/streams/bug81659.phpt

diff --git a/ext/standard/tests/streams/bug81659.phpt b/ext/standard/tests/streams/bug81659.phpt
new file mode 100644
index 0000000000000..62e0cbad181ee
--- /dev/null
+++ b/ext/standard/tests/streams/bug81659.phpt
@@ -0,0 +1,24 @@
+--TEST--
+Bug #81659 (stream_get_contents() may unnecessarily overallocate)
+--FILE--
+<?php
+$stream = fopen(__DIR__ . "/81659.txt", "w+");
+
+for ($i = 0; $i < 1024; $i++) {
+    fwrite($stream, str_repeat("*", 1024));
+}
+
+fseek($stream, 1023 * 1024);
+
+$m0 = memory_get_peak_usage();
+var_dump(strlen(stream_get_contents($stream)));
+$m1 = memory_get_peak_usage();
+var_dump($m1 < $m0 + 512 * 1024);
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . "/81659.txt");
+?>
+--EXPECT--
+int(1024)
+bool(true)
diff --git a/main/streams/streams.c b/main/streams/streams.c
index d2ee3371c9eb6..a320a90b5252e 100644
--- a/main/streams/streams.c
+++ b/main/streams/streams.c
@@ -1502,9 +1502,9 @@ PHPAPI zend_string *_php_stream_copy_to_mem(php_stream *src, size_t maxlen, int
 	 * result may be inaccurate, as the filter may inflate or deflate the
 	 * number of bytes that we can read.  In order to avoid an upsize followed
 	 * by a downsize of the buffer, overestimate by the step size (which is
-	 * 2K).  */
+	 * 8K).  */
 	if (php_stream_stat(src, &ssbuf) == 0 && ssbuf.sb.st_size > 0) {
-		max_len = ssbuf.sb.st_size + step;
+		max_len = MAX(ssbuf.sb.st_size - src->position, 0) + step;
 	} else {
 		max_len = step;
 	}