Programming

Hello mates:

I met problem with using read() & write(). I m trying to use read twice on client first time is the size of buffer, 2nd time is the buffer. I think I have to, coz I dnot know file size. So, I write twice on server as well -- 1st, filesize; 2nd, buffer.

The problem is, sometimes, I cannot get anything at 2nd time. The file I got is empty, nothing. However, if I put a sleep(1) before the 2nd write() on server, I can read( but this sometimes may cause a segmentation fault)...

i.e.:
Client Server

read() 1st write() 1st <-----both OK

(if I put a sleep(1)here, it's OK)

read() 2d write() 2nd <-----problem


Does anybody know the reason?

BEST REGARDS,

Elton

If you are using sockets send() and recv() offer much greater control over your data transmission

But ordinary read and write should still work, yes? No reason for them to segfault without an error in the program. If my hunch is correct send() and recv() could suffer the same issues...

Check to make sure you're recieving the number of bytes you intended. I think you might be getting crazy numbers for filesize, which could cause the crash.

Try them and if the error disappears then the reason exists

How so? Even if the error goes away, the program still lacks the error-checking to handle them. It should fail, not crash.

It's really a frustrating problem


I m trying to use 2 write() in a row, first write() is used to send file size, 2nd send the file. On client side, I use malloc() for the buf size and free later.

Current situation is if I put sth (like sleep(1) or a read()) btw 2 write() , they both work fine. Othrewise, I lose some bytes on client side which is from the 2nd write(). That makes the browser cannnot recognize the HTTP header....

REGARDS,

ELton

OK, I suggest that you set up a proper handshake. Currently your scenario is like this:
server -- write size
client -- read size
server -- write data_buffer
client -- read data_buffer

Change that to:
server -- write size
client -- read size
client -- write ACK
server -- read ACK
server -- write data_buffer
client -- read data_buffer
client -- write ACK

and so on....
So it will never be that your server is continuously writing to a socket that the client is not able to read cause it crashed...