php://output和php://stdout的区别

2018-02-03 10:38:01来源:segmentfault作者:tlanyan人点击

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PHP包含了以php://开头的一系列输出输出流,如php://stdin, php://stdout等。今天查看代码时,忽然想到一个问题:php://output和php://stdout有什么区别?


从PHP的官方文献中找答案,对输入流php://stdin和php://input的解释分别如下(输出流的解释过于简略):



php://stdin
php://stdin, php://stdout and php://stderr allow direct access to the corresponding input or output stream of the PHPprocess. The stream references a duplicate file descriptor, so if you open php://stdin and later close it, you close only your copy of the descriptor-the actual stream referenced by STDIN is unaffected. Note that PHP exhibited buggy behavior in this regard until PHP 5.2.1. It is recommended that you simply use the constants STDIN, STDOUT and STDERR instead of manually opening streams using these wrappers.

php://stdin is read-only, whereas php://stdout and php://stderr are
write-only.


php://input
php://input is a read-only stream that allows you to read raw data from the request body. In the case of POST requests, it is preferable to use php://input instead of $HTTP_RAW_POST_DATA as it does not depend on special php.ini directives. Moreover, for those cases where $HTTP_RAW_POST_DATA is not populated by default, it is a potentially less memory intensive alternative to activating always_populate_raw_post_data. php://input is not available with enctype="multipart/form-data".



文档并未直接阐述两者的区别,仔细对比可得出以下信息:1. 均是只读流; 2. php://stdin是PHP进程的标准输入,php://input用来读取请求正文的原始数据。联想PHP进程的执行过程和SAPI,可以得到两者主要区别:php://stdin是PHP进程的输入流,执行生命周期内均可能有数据流入(例如CLI下的交互式输入);php://input是PHP执行时的外部输入流,一般数据只能读一次(具体看SAPI的实现)。同理可得到php://stdout和php://output的区别:php://stdout是PHP进程的标准输出流,php://output是返回上层的结果数据流。


下面用代码验证结论:


// file: test.php
file_put_contents("php://output", "message sent by output" . PHP_EOL);
file_put_contents("php://stdout", "message sent by stdout" . PHP_EOL);
print("message sent by print" . PHP_EOL);echo "SAPI:" , PHP_SAPI , PHP_EOL;

命令行执行文件,输出如下:


message sent by output
message sent by stdout
message sent by print
SAPI:cli

浏览器端请求,输出如下:


message sent by output
message sent by print
SAPI:fpm-fcgi

在命令行下,PHP进程的标准输出流和结果输出流均指向终端,所有消息都打印出来。在浏览器端,PHP进程的输出流被忽略,只有结果数据流被发送到web服务器。同时,print和echo调用的信息都作为执行结果发往结果输出流,所以都正常显示。


参考
http://php.net/manual/en/wrap...

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