From: obz@sisd.kodak.com (Orest Zborowski COMP) Subject: Re: Problems with domain sockets in porting lpr Date: Fri, 28 Aug 1992 01:04:11 GMT
Corey Minyard (minyard@crchh453.bnr.ca) wrote:
>I have ported plp (a public lpr spooling package) to linux but I have
>experienced a problem with domain sockets. If I do the following:
>
...
>
> if (bind(s, &saddr, sizeof(saddr)) < 0)
> {
> error...
>
>The bind will fail. I turned on socket debugging and found it was getting
>an invalid length. It turns out if you pass "sizeof(saddr)" to bind
>(or connect) if fails. I looked in the kernel, and that is what it was
>coded to do.
>
>Is this behavior correct? I changed the size to be
>
> sizeof(saddr.sun_family) + strlen(filename)
>
>and it worked just fine. The documentation I have on domain sockets
>mentions nothing about this.
>
>----------------------------------------------------------------------
>
>Corey Minyard
>minyard@bnr.ca
i based the implementation on the book "unix network programming" by
w. richard stevens (1990), a fine text for this sort of thing. in it
it explicitly states that the filename in the unix socket struct is
not null terminated (i.e. not expected to be), so you have to explicitly
tell it how large the address is by adding the length of the name to
the size of the family member. most people never use names of length 108
(which is the maximum), and they use strcpy (which copies the null), so
its safe to use strlen(). in fact, its bad practice to pass more than
14 bytes (which is why most sockets are built in /tmp) due to some of
the other system calls. i found the strlen form in every piece of code
i found which used unix sockets (including x11), so i'm pretty confident
it's correct.
zorst
-- zorst (orest zborowski) [obz@raster.Kodak.COM]