Finding how much data is available for read from a SOCK_SEQPACKET

Finding how much data is available for read from a SOCK_SEQPACKET

[Francois Grieu]

Hello,

I have a working program that receives blocks of data from a
SOCK_SEQPACKET using a blocking read(). So far I use a
fixed-size buffer of the maximum size.

I would like to query for the size available, malloc a block
of the appropriate size, then read. Is that feasible?

Note: I think that I can not put the size at the head of the
packet since 
" SOCK_SEQPACKET
   Provides a sequenced, reliable, two-way connection-based
   data transmission path for datagrams of fixed maximum length;
   a consumer is required to read an entire packet with each
   read system call."

TIA,
  Francois Grieu

Re: Finding how much data is available for read from a SOCK_SEQPACKET

[Glynn Clements]

Francois Grieu wrote:

> I have a working program that receives blocks of data from a
> SOCK_SEQPACKET using a blocking read(). So far I use a
> fixed-size buffer of the maximum size.
> 
> I would like to query for the size available, malloc a block
> of the appropriate size, then read. Is that feasible?

It doesn't look like it. Unfortunately, ioctl(SIOCINQ) returns the
total number of bytes in all queued incoming packets, not the next
packet.

You could malloc() a maximum size packet then realloc() it once you've
received the data.

-- 
Glynn Clements <glynn@gclements.plus.com>