Fix GH-12899 (copy() target is blank)

NEWS

@@ -56,6 +56,7 @@ PHP                                                                        NEWS
     brigade. (ndossche, Matthias Goergens, Jakub Zelenka)
   . Fixed bug GH-24175 (Use-after-free when pclose() closes a stream from its
     user filter). (Edmond)
+  . Fixed bug GH-12899 (copy() target is blank). (Kamil Tekiela)
 
 19 Nov 2026, PHP 8.4.28
 

ext/standard/tests/file/gh12899.phpt

@@ -0,0 +1,35 @@
+--TEST--
+GH-12899 (copy() target is blank in PHP 8.3.0)
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY !== 'Linux') die('skip Linux only');
+if (!is_readable('/proc/version')) die('skip /proc/version is not readable');
+?>
+--FILE--
+<?php
+/* procfs files report a size of 0, so copy_file_range() can return 0 for them */
+$src = '/proc/version';
+$dest = __DIR__ . '/gh12899_dest.txt';
+$expected = file_get_contents($src);
+var_dump(strlen($expected) > 0);
+
+var_dump(copy($src, $dest));
+var_dump(file_get_contents($dest) === $expected);
+
+$in = fopen($src, 'r');
+$out = fopen($dest, 'w');
+var_dump(stream_copy_to_stream($in, $out) === strlen($expected));
+fclose($in);
+fclose($out);
+var_dump(file_get_contents($dest) === $expected);
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . '/gh12899_dest.txt');
+?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)

main/streams/streams.c

@@ -1763,9 +1763,9 @@ PHPAPI zend_result _php_stream_copy_to_stream_ex(php_stream *src, php_stream *de
 
 				/* there may be more data; continue copying using the fallback code below */
 			} else if (result == 0) {
-				/* end of file */
-				*len = haveread;
-				return SUCCESS;
+				/* Nothing was copied yet, but this does not prove end-of-file: some kernels return 0
+				 * for sources that are not empty, e.g. procfs files or VirtualBox shared folders.
+				 * Fall back to classic copying, which detects end-of-file reliably. */
 			} else if (result < 0) {
 				switch (errno) {
 					case EINVAL: