442294 - NSPR doesn't provide any mechanism for disconnecting UDP sockets

Status: REOPENED

(NSPR :: NSPR, defect)

Description

[Alex Fritze]

For UDP sockets, POSIX connect() can be called to (re-)connect or disconnect the socket. The latter is done by calling connect() with a "null address". According to Stevens' Unix Network Programming (Vol 1, 3rd ed., sec. 8.11, p. 254): "The most portable solution is to zero out an address structure, set the family to AF_UNSPEC and pass it to connect."

Unfortunately NSPR's PR_Connect() doesn't accept PRNetAddr structures with family PR_AF_UNSPEC - at least not the implementation in ptio.c (pt_Connect).
One easy way of getting it to work for pt_Connect is to remove the assertion
    PR_ASSERT(IsValidNetAddr(addr) == PR_TRUE);
and change _PR_NetAddrSize() to return something like sizeof(addr->raw) instead of 0 for PR_AF_UNSPEC addresses. I'm a little unsure about the wider implications though.

Comment 1

[Wan-Teh Chang]

We should be able to change PR_Connect() to allow this.
Could you test your proposed changes?  They seem good to
me.

Comment 2

[Alex Fritze]

I've discovered that calling PR_Connect with PR_AF_INET "0.0.0.0" (or PR_AF_INET6 "::", as appropriate for a given socket) works just as well as PR_AF_UNSPEC. I've tested this on Linux, OS X and Windows. 
So it looks like the changes I was proposing above aren't needed... they only worked for platforms using ptio.c anyway.
Shall I close the bug as INVALID?

Comment 3

[Wan-Teh Chang]

OK.  It would still be nice if you could attach your
patch to this bug report for future reference.
Someone who reads Stevens' is likely to try PR_AF_UNSPEC
first, so supporting that could still be useful.  We
could easily adapt your changes to ptio.c for
platforms using prsocket.c.

Comment 4

[Alex Fritze]

It turns out that PR_AF_INET/PR_AF_INET6 don't work on Linux after all; the linux networking code explicitly checks for AF_UNSPEC for disconnecting sockets. My unit test didn't pick this up as I only tested the loopback interface.

So it would be great if we could legalize PR_AD_UNSPEC after all. Patch coming up.

Comment 5

[Alex Fritze]

Attachment: patch v1

Proposed patch allowing a PR_AF_UNSPEC address to be passed to pt_Connect.

Comment 6

[BugBot [:suhaib / :marco/ :calixte]]

The bug assignee is inactive on Bugzilla, so the assignee is being reset.