wswrapper:
Getting the wswrapper.c LD_PRELOAD model working has turned out to
involve too many dark corners of the glibc/POSIX file descriptor
space. I realized that 95% of what I want can be accomplished by
adding a "wrap command" mode to wsproxy.
The code is still there for now, but consider it experimental at
best. Minor fix to dup2 and add dup and dup3 logging.
wsproxy Wrap Command:
In wsproxy wrap command mode, a command line is specified instead
of a target address and port. wsproxy then uses a much simpler
LD_PRELOAD library, rebind.so, to move intercept any bind() system
calls made by the program. If the bind() call is for the wsproxy
listen port number then the real bind() system call is issued for
an alternate (free high) port on loopback/localhost. wsproxy then
forwards from the listen address/port to the moved port.
The --wrap-mode argument takes three options that determine the
behavior of wsproxy when the wrapped command returns an exit code
(exit or daemonizing): ignore, exit, respawn.
For example, this runs vncserver on turns port 5901 into
a WebSockets port (rebind.so must be built first):
./utils/wsproxy.py --wrap-mode=ignore 5901 -- vncserver :1
The vncserver command backgrounds itself so the wrap mode is set
to "ignore" so that wsproxy keeps running even after it receives
an exit code from vncserver.
wstelnet:
To demonstrate the wrap command mode, I added WebSockets telnet
client.
For example, this runs telnetd (krb5-telnetd) on turns port 2023
into a WebSockets port (using "respawn" mode since telnetd exits
after each connection closes):
sudo ./utils/wsproxy.py --wrap-mode=respawn 2023 -- telnetd -debug 2023
Then the utils/wstelnet.html page can be used to connect to the
telnetd server on port 2023. The telnet client includes VT100.js
(from http://code.google.com/p/sshconsole) which handles the
terminal emulation and rendering.
rebind:
The rebind LD_PRELOAD library is used by wsproxy in wrap command
mode to intercept bind() system calls and move the port to
a different port on loopback/localhost. The rebind.so library can
be built by running make in the utils directory.
The rebind library can be used separately from wsproxy by setting
the REBIND_OLD_PORT and REBIND_NEW_PORT environment variables
prior to executing a command. For example:
export export REBIND_PORT_OLD="23"
export export REBIND_PORT_NEW="65023"
LD_PRELOAD=./rebind.so telnetd -debug 23
Alternately, the rebind script does the same thing:
rebind 23 65023 telnetd -debug 23
Other changes/notes:
- wsproxy no longer daemonizes by default. Remove -f/--foreground
option and add -D/--deamon option.
- When wsproxy is used to wrap a command in "respawn" mode, the
command will not be respawn more often than 3 times within 10
seconds.
- Move getKeysym routine out of Canvas object so that it can be called
directly.
- add dup2 functionality. This requires adding a ref cnt to the
_WS_connections structure so that we only free the structure once
all dup'd referenced are closed. Also, refactor malloc and free of
connection structure into _WS_alloc and _WS_free.
- allow select to accept a NULL timeout value which means sleep
forever instead of segfaulting.
- fix some compile warnings related to ppoll definition.
- move some WebSockets related html test pages into utils and symlink
them from tests.
The select call needs to timeout if a WebSocket socket keeps reporting
ready but actually isn't ready. To prevent it hanging forever in that
condition, the timeout value is now adjusted now for each call.
Move the DO_DEBUG and DO_TRACE settings to wswrapper.c.
Interpose on select/pselect so that WebSockets sockets are only
reported as ready if they have enough to actually decode at least
1 byte of real data. This prevents hanging in read/recv after
WebSocket is reported as ready but is not actually ready because empty
frames or less than four base64 bytes have been received.
Split defines and constant defintions into wswrapper.h.
Cleanup debug output and add TRACE for more detailed tracing debug
output.
Major TODO is that select needs to timeout if WebSocket socket keeps
reporting ready but actually isn't ready. That condition will
currently hang forever because the select timeout value is not
adjusted when looping.
Make path to ld preload library absolute so wswrapper works even if
path is changed before main program is executed (i.e. by the vncserver
wrapper script).
bind() was using the return value for the port number, but it's
actually the original port number that we should interpose on in the
bind() routine.
Allocate buffer and state memory for each accepted connection. This
allows all WebSockets connections to a given listen port to be wrapped
with WebSockets support.
wswrapper.so will only interpose on the listen port specified in
WSWRAP_PORT.
Add simple wswrap script that sets the WSWRAP_PORT, LD_PRELOAD and
invokes the command line to wrap.
wswrapper.so is LD_PRELOAD shared library that interposes and turns
a generic TCP socket into a WebSockets service.
This current version works but will only allow work for a single
connection, subsequent connections will not be wrapped. In addition
the wrapper interposes on the first incoming network connection. It
should read an environment variable to determine the port to interpose
on. Also, should limit origin based on another environment variable.
Then there should be a wswrap setup script that allows easier
invocation.
Joel Martin