How does PHP accurately determine the extension of a remote file

How does PHP accurately determine the extension of a remote file?

The HTTP response header is as follows:
Array
(
[0] = = http/1.1-OK

[1] = content-length:345942

[2] = Content-type:application/octet-stream

[3] = server:microsoft-iis/6.0

[4] = X-powered-by:asp.net

[5] = Date:sun, Dec 05:44:39 GMT

[6] = Connection:close

)

There is no extension in the file name, disorganized.

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------Solution--------------------
The file name is only used to identify the block of data stored in the media
In network communication, the file name is meaningless.

Since Content-type:application/octet-stream has declared that it is a flow
And the length of the content-length:345942 is not too big, you can first as a picture to analyze
All traffic is marked with a specific identifier, and the previous stage has been where someone sent code, and you can find

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