Can you tell me something about the HTTP response message header when the file was downloaded?

Please consult the HTTP response message header when downloading the file.
This post was last edited by love_u_qt on 2012-08-05 15:08:30

When I was learning to use PHP for file downloads, the textbook said it needed to provide three HTTP message headers:

Header ("Content-type:application/octet-stream");          A high-speed browser passes a file stream
Header ("accept-length:2048");                             File size
Header ("content-disposition:attachment; Filename=abc.txt "); Specify file name

Of these, "Content-type" and "content-disposition" two message headers, I still a little bit not understand, so I did two separate examples:

a.php:

 
  
Header ("Content-type:application/octet-stream");
Header ("accept-length:2048");

Echo 123;

b.php:

 
  
Header ("accept-length:2048");
Header ("content-disposition:attachment; Filename=abc.txt ");

Echo 123;

My question is:
1, these two pages are less a message header, why can still successfully download files?
2, although I specify the size of the file is 2048 bytes, but the real output only "123" three bytes, why can i download the file as normal?
"Accept-length" message header is can be set can not set it?

I just learned http, trouble people to answer the questions I asked, do not draw a deeper concept, because I can not understand.
Thank you very much! ：）
------to solve the idea----------------------
1, these two pages are less a message header, why can still successfully download files?

Because you do not set content-length, the output at the end of the default connection is the download content.

2, although I specify the size of the file is 2048 bytes, but the real output only "123" three bytes, why can i download the file as normal? "Accept-length" message header is can be set can not set it?

Accept-length means the length of the maximum acceptable string. So it can be set to No.

