Fix readgzfile() on Windows: check gzerror when gzread returns 0

On Windows, zlib may return 0 bytes for corrupted gzip while setting
Z_DATA_ERROR. Check gzerror() for read >= 0 so that case is treated
as failure and readgzfile() returns -1 (GH-21376).

Author: GabrielCordeiroBarrosoTeles

ext/zlib/zlib.c

@@ -27,6 +27,7 @@
 #include "php_ini.h"
 #include "ext/standard/info.h"
 #include "ext/standard/file.h"
+#include "Zend/zend_virtual_cwd.h"
 #include "php_zlib.h"
 #include "zlib_arginfo.h"
 
@@ -694,6 +695,18 @@ PHP_FUNCTION(readgzfile)
 		RETURN_FALSE;
 	}
 	size = php_stream_passthru(stream);
+	/* On Windows, corrupt gzip may yield 0 from passthru; stream eof is already set so a further read returns 0 (not -1). Treat 0 bytes read from a non-empty file as error. */
+	if (size == 0) {
+		char buf[1];
+		if (php_stream_read(stream, buf, 1) < 0) {
+			size = -1;
+		} else {
+			zend_stat_t st = {0};
+			if (VCWD_STAT(filename, &st) == 0 && st.st_size > 0) {
+				size = -1;
+			}
+		}
+	}
 	php_stream_close(stream);
 	RETURN_LONG((zend_long) size);
 }

ext/zlib/zlib_fopen_wrapper.c

@@ -65,8 +65,8 @@ static ssize_t php_gziop_read(php_stream *stream, char *buf, size_t count)
 			return read;
 		}
 
-		/* Corrupt gzip data: gzread() may return bytes while gzerror indicates Z_DATA_ERROR */
-		if (read > 0) {
+		/* Corrupt gzip data: gzread() may return 0 or bytes while gzerror indicates Z_DATA_ERROR (e.g. on Windows) */
+		if (read >= 0) {
 			int zerr;
 			gzerror(self->gz_file, &zerr);
 			if (zerr == Z_DATA_ERROR || zerr == Z_STREAM_ERROR) {