Historically we've used SOL_IP/SOL_IPV6/SOL_TCP everywhere as the socket
level value in getsockopt() and setsockopt() but as we've seen over time
it regularly broke the build and required to have them defined to their
IPPROTO_* equivalent. The Linux ip(7) man page says:
Using the SOL_IP socket options level isn't portable; BSD-based
stacks use the IPPROTO_IP level.
And it indeed looks like a pure linuxism inherited from old examples and
documentation. strace also reports SOL_* instead of IPPROTO_*, which does
not help... A check to linux/in.h shows they have the same values. Only
SOL_SOCKET and other non-IP values make sense since there is no IPPROTO
equivalent.
Let's get rid of this annoying confusion by removing all redefinitions of
SOL_IP/IPV6/TCP and using IPPROTO_* instead, just like any other operating
system. This also removes duplicated tests for the same value.
Note that this should not result in exposing syscalls to other OSes
as the only ones that were still conditionned to SOL_IPV6 were for
IPV6_UNICAST_HOPS which already had an IPPROTO_IPV6 equivalent, and
IPV6_TRANSPARENT which is Linux-specific.
This performs a connect(AF_UNSPEC) over an existing connection. This is
mainly for compatibility testing. At this step it only seems to work on
linux for TCP sockets (both listening and established), while SO_LINGER
successfully resets established connections on freebsd and aix.
Sometimes it's convenient to be able to execute a command directly on
the stream, whether we're connecting or accepting an incoming connection.
New command 'X' makes this possible. It simply calls execvp() on the
next arguments and branches stdin/stdout/stderr on the socket. Optionally
it's possible to limit the passed FDs to any combination of them by
appending 'i', 'o', 'e' after the X. In any case the program ends just
after executing this command.
Examples :
- chargen server
tcploop 8001 L A Xo cat /dev/zero
- telnet server
tcploop 8001 L W N A X /usr/sbin/in.telnetd
NULL is Linux-centric and we're not focused on performance here but
portability and reproducibility. Don't use NULL and use the trash
instead. It may lead to multiple recv() calls for large blocks but
as a benefit it will be possible to see the contents with strace.
Just got this while cross-compiling :
tcploop.c: In function 'tcp_recv':
tcploop.c:444:48: error: 'INT_MAX' undeclared (first use in this function)
tcploop.c:444:48: note: each undeclared identifier is reported only once for each function it appears in
This one jumps back to the oldest post-fork and post-accept action,
so it allows to recv(), pause() and send() in loops after a fork()
and an accept() for example. This is handy for bugs that reproduce
once in a while or to keep idle connections working.
By passing "S:<string>" instead of S<size> it's possible to send
a pre-defined string, which is convenient to write HTTP requests or
responses.
Example : produce two responses, one in keep-alive, one not for ab :
./tcploop 8001 L W N2 A R S:"HTTP/1.0 200 OK\r\nConnection: keep-alive\r\nContent-length: 50\r\n\r\n0123456789.123456789.123456789.123456789.123456789" R S:"HTTP/1.0 200 OK\r\nContent-length: 50\r\n\r\n0123456789.123456789.123456789.123456789.123456789"
With 20 such keep-alive responses and 10 parallel processes, ab achieves
350kreq/s, so it should be possible to get precise timings.
This is helpful to show what state we're dealing with. The pid is
written, optionally followed by the time in 3 different formats
(relative/absolute) depending on the command line option (-t, -tt, -ttt).
Fork is a very convenient way to deal with independant yet properly
timed connections. It's particularly useful here for accept(), and
ensures that any accepted FD will automatically be released. The
principle is that when we hit a fork command, the parent restarts
evaluating the actions from the beginning and the child continues
to evaluate the next actions. Listen and connect are skipped if the
connection is already established. Fork() is amazingly cheap on
Linux, 21k forked connections per second are handled on a single
core, and 38k on two cores.
For now it's not possible to have two different code paths so in order
to have both a listener and a connector, two distinct commands are
still needed.
netcat, nc6 and socat are only partially convenient as reproducers for
state machine bugs, but when it comes to adding delays, forcing resets,
waiting for data to be acked, they become useless.
The purpose of this utility is to be able to easily script some TCP
operations such as connect, accept, send, receive, shutdown and of
course pauses.
