PHP 5.6环境下PHPMailer报stream_select()错误的原因排查求助

问题状态 #

• 2022年11月24日更新：问题已解决，未定位到根本原因，推测是PHP源码损坏导致。从PHP官网重新下载对应版本源码覆盖原文件后，错误消失。

环境说明 #

• 本地系统：Windows 10
• 仅PHP 5.6版本触发错误，PHP 7.0及以上版本使用PHPMailer完全正常
• 无socket相关知识，无法自行排查底层问题

触发的两类错误 #

TLS协议+25端口场景 #

Connection failed. Error #2: stream_select(): unable to select [11]: No such file or directory

SSL协议+465端口场景 #

Connection failed. error #2: stream_select(): unable to select [11]: Resource temporarily unavailable.

两类错误均由PHPMailer/src/SMTP.php文件第1228行的stream_select()函数调用引发。

调试日志（SSL协议+465端口场景） #

Connection: opening to ssl://smtp.qq.com:465, timeout=300, options=array()
Connection: opened
Connection failed. Error #2: stream_select(): unable to select [11]: Resource temporarily unavailable (max_fd=772) [\vendor\phpmailer\phpmailer\src\SMTP.php line 1228]
SMTP -> get_lines(): select failed (stream_select(): unable to select [11]: Resource temporarily unavailable (max_fd=772))
SERVER -> CLIENT:
Connection: closing due to error
Connection: closed
SMTP Error: Could not connect to SMTP host.

内容的提问来源于stack exchange，提问作者lee