Date: Thu, 13 Mar 2008 12:11:28 -0600 From: "Andrew Falanga" <af300wsm@gmail.com> To: "Patrick Mahan" <mahan@mahan.org> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: Network programming question Message-ID: <340a29540803131111g20315740n629ee146bc2f8602@mail.gmail.com> In-Reply-To: <47D9682B.5060402@mahan.org> References: <340a29540803130910l2a5badacxe50cd81ace87e1f7@mail.gmail.com> <47D9682B.5060402@mahan.org>
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On Thu, Mar 13, 2008 at 11:45 AM, Patrick Mahan <mahan@mahan.org> wrote:
>
>
> Andrew Falanga presented these words - circa 3/13/08 9:10 AM->
>
> > Hi,
>
> See man inet_pton . . . for details.
>
> Briefly, inet_pton() doesn't understand sockaddr structures. Instead,
> it only understands in_addr or in6_addr structures which are included
> inside the sockaddr structure. So your above example should be changed
> to
>
Ok, I should have thought of that when reading the manual.
>
> if ((res = inet_pton(AF_INET, "192.168.0.1", &sa.sin_addr)) < 0)
> perror("inet_pton");
>
>
> Because it is treating the sockaddr_in structure as an in_addr structure
> which is clobbering the sin_family field.
>
If this is true, then why are my packets sent at all? The definition
of sockaddr_in (from /usr/include/netinet/in.h):
struct sockaddr_in {
uint8_t sin_len;
sa_family_t sin_family;
in_port_t sin_port;
struct in_addr sin_addr;
char sin_zero[8];
};
The definition of in_addr (from /usr/include/netinet/in.h):
struct in_addr {
in_addr_t s_addr;
};
The definition of in_addr_t (from /usr/include/netinet/in.h):
typedef uint32_t in_addr_t;
Passing in what I have, the address should indeed (as you've pointed
out) clobber the sin_family member. However, since in_addr is
basically an unsigned integer, i.e. 4 bytes wide, shouldn't
inet_pton(3) clobber sin_len, sin_family & sin_port before ever
reaching sin_addr? The sin_len & sin_family are 8 bit quantities, the
sin_port is 16 bits, that's 32. If inet_pton(3) is expecting only an
in_addr I would think that a call to sendto(2) would fail because the
address in sin_addr is not filled, correct?
Andy
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
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