Provided by: libsocket-wrapper_1.3.4-1_amd64 
NAME
socket_wrapper - A library passing all socket communications through unix sockets.
SYNOPSIS
LD_PRELOAD=libsocket_wrapper.so SOCKET_WRAPPER_DIR=/tmp/tmp.bQRELqDrhM
SOCKET_WRAPPER_DEFAULT_IFACE=10 ./myapplication
DESCRIPTION
socket_wrapper aims to help client/server software development teams willing to gain full
functional test coverage. It makes possible to run several instances of the full software
stack on the same machine and perform locally functional testing of complex network
configurations.
• Redirects all network communication to happen over Unix sockets.
• Support for IPv4 and IPv6 socket and addressing emulation.
• Ability to capture network traffic in pcap format.
• Passing IP sockets (up to 6) via SCM_RIGHTS is supported, but pcap support only works
reliable if the socket is used by a single process at a time.
ENVIRONMENT VARIABLES
SOCKET_WRAPPER_DIR
The user defines a directory where to put all the unix sockets using the environment
variable "SOCKET_WRAPPER_DIR=/path/to/socket_dir". When a server opens a port or a
client wants to connect, socket_wrapper will translate IP addresses to a special
socket_wrapper name and look for the relevant Unix socket in the SOCKET_WRAPPER_DIR.
SOCKET_WRAPPER_IPV4_NETWORK
By default the loopback IPv4 network "127.0.0.0/8" and the "127.0.0.x" can be used. In
order to make more realistic testing possible it is possible to use the "10.0.0.0/8"
IPv4 network instead. But note within "10.0.0.0/8" only "10.53.57.<ID>" can be used,
but the broadcast address is "10.255.255.255". The following two value are allowed:
SOCKET_WRAPPER_IPV4_NETWORK="127.0.0.0" (the default) and
SOCKET_WRAPPER_IPV4_NETWORK="10.53.57.0".
SOCKET_WRAPPER_DEFAULT_IFACE
Additionally, the default interface to be used by an application is defined with
"SOCKET_WRAPPER_DEFAULT_IFACE=<ID>" where the valid range for <ID> starts with 1 (the
default) and ends with 64. This is analogous to use the IPv4 addresses
"127.0.0.<ID>"/"10.53.57.<ID>" or IPv6 addresses "fd00::5357:5f<IDx>" (where <IDx> is
a hexadecimal presentation of <ID>). You should always set the default interface. If
you listen on INADDR_ANY then it will use the default interface to listen on.
SOCKET_WRAPPER_PCAP_FILE
When debugging, it is often interesting to investigate the network traffic between the
client and server within your application. If you define
SOCKET_WRAPPER_PCAP_FILE=/path/to/file.pcap, socket_wrapper will dump all your network
traffic to the specified file. After the test has been finished you’re able to open
the file for example with Wireshark.
SOCKET_WRAPPER_MTU
With this variable you can change the MTU size. However we do not recomment to do that
as the default size of 1500 byte is best for formatting PCAP files.
The minimum value you can set is 512 and the maximum 32768.
SOCKET_WRAPPER_MAX_SOCKETS
This variable can be used to set the maximum number of sockets to be used by an
application.
The default value is set to 65535 and the maximum 256000.
SOCKET_WRAPPER_DEBUGLEVEL
If you need to see what is going on in socket_wrapper itself or try to find a bug, you
can enable logging support in socket_wrapper if you built it with debug symbols.
• 0 = ERROR
• 1 = WARNING
• 2 = DEBUG
• 3 = TRACE
SOCKET_WRAPPER_DISABLE_DEEPBIND
This allows you to disable deep binding in socket_wrapper. This is useful for running
valgrind tools or sanitizers like (address, undefined, thread).
SOCKET_WRAPPER_DIR_ALLOW_ORIG
SOCKET_WRAPPER_DIR is resolved by socket_wrapper using realpath(3). Given that Unix
sockets are constructed relative to this directory, the resulting path can sometimes
be too long to allow valid socket paths to be constructed due to length restrictions.
Setting this variable (to any value) allows socket_wrapper to fall back to the
original value of SOCKET_WRAPPER_DIR if realpath(3) makes it too long to be usable.
EXAMPLE
# Open a console and create a directory for the unix sockets.
$ mktemp -d
/tmp/tmp.bQRELqDrhM
# Then start nc to listen for network traffic using the temporary directory.
$ LD_PRELOAD=libsocket_wrapper.so \
SOCKET_WRAPPER_DIR=/tmp/tmp.bQRELqDrhM \
SOCKET_WRAPPER_DEFAULT_IFACE=10 nc -v -l 127.0.0.10 7
# (If nc, listens on 0.0.0.0 then listener will be open on 127.0.0.10 because
# it is the default interface)
# Now open another console and start 'nc' as a client to connect to the server:
$ LD_PRELOAD=libsocket_wrapper.so \
SOCKET_WRAPPER_DIR=/tmp/tmp.bQRELqDrhM \
SOCKET_WRAPPER_DEFAULT_IFACE=100 nc -v 127.0.0.10 7
# (The client will use the address 127.0.0.100 when connecting to the server)
# Now you can type 'Hello!' which will be sent to the server and should appear
# in the console output of the server.
PUBLIC FUNCTIONS
Socket wrapper advanced helpers.
Applications with the need to alter their behaviour when socket wrapper is active, can
link use these functions.
By default it’s required for applications to use any of these functions as
libsocket_wrapper.so is injected at runtime via LD_PRELOAD.
Applications using these functions should link against libsocket_wrapper_noop.so by using
-lsocket_wrapper_noop, or implement their own noop stubs.
#include <socket_wrapper.h>
bool socket_wrapper_enabled(void);
• This returns true when socket wrapper is actively in use.
void socket_wrapper_indicate_no_inet_fd(int fd);
• This allows socket_wrapper aware applications to indicate that the given fd does not
belong to an inet socket.
• socket_wrapper may not be able to intercept the __close_nocancel() syscall made from
within libc.so. As result it’s possible that the in memory meta date of socket_wrapper
references stale file descriptors, which are already reused for unrelated kernel
objects, e.g. files, directories, ...
• Socket wrapper already intercepts a lot of unrelated functions like eventfd(),
timerfd_create(), ... in order to remove stale meta data for the returned fd, but it
will never be able to handle all possible syscalls.
• socket_wrapper_indicate_no_inet_fd() gives applications a way to do the same,
explicitly without waiting for new syscalls to be added to libsocket_wrapper.so.
• This is a no-op if socket_wrapper is not in use or if the there is no in memory meta
data for the given fd.
RESOURCES
Project web site: https://cwrap.org
AUTHOR
Samba Team
2021-02-24 SOCKET_WRAPPER(1)