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Wsock-trace v. 0.3.5:

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A drop-in tracing library / DLL for most normal Winsock calls. It sits between your program and the Winsock library (ws2_32.dll). It works best for MSVC since the stack-walking code requires the program's PDB symbol-file to be present. And unfortunately MinGW/CygWin doesn't produce PDB-symbols (GNU-debugger instead relies on the archaic BFD library). So currently, the MinGW, CygWin and OpenWatcom targets will only show raw addresses for the traced functions.

A MSVC example output from c:\> ahost showing all the addresses of
(ahost is part of the DNS library C-ares):



  • Colourised trace of the Winsock calls with function parameters and return values. The colours are configurable.

  • Runtime caller information: Using Microsoft's dbghelp (or psapi) APIs together with the programs PDB-file, the filename, line-number of the calling function-name is shown. In the above example, WSAStartup() is called from ahost.c, line 67. Which should be 59 bytes into the main() function. This should be here.

  • Precise Timestamps: All trace-lines starts with a precise timestamp obtained from QueryPerformanceCounter().
    The timestamp is controlled by trace_time in the wsock_trace config-file.

  • Extension functions: Winsock has several Microsoft-specific extension functions (like AcceptEx() and ConnectEx()). Wsock-trace is able to trace these too.

  • IP-Country information thanks to the MaxMind Lite databases. Thanks to the Tor-project for a simplified CSV version of these MaxMind GeoIP-databases. (using the CSV files geoip and geoip6 are always enabled).

  • IP-Location information (City and Region) from IP2Location. The above Mountain View/California is Google's well-known location. Many thanks to IP2Location [3] for their data-bases.

  • Domain Name System-based Blackhole List (DNSBL) support: with the help of DROP-files from the Spamhaus project, it can detect IPv4 / IPv6-addresses uses by spammers and cyber-criminals. The more potent Spamhaus BGPf / BCL is on the to-do list.

  • Slowdown; For testing too fast programs, all receive, transmit, select() and WSAPoll() calls can be delayed a number of milli-seconds. E.g. slowing down a recv() call is controlled by recv_delay = 0 in wsock_trace config-file.

  • Firewall activity; report activity causing events from the Window Filtering Platform (the Internet Connection Firewall; ICF). See below.

  • LuaJIT script support is very preliminary at the moment. The idea is that .lua scripts could change the behaviour of Wsock-trace at runtime without rebuilding it.
    Only the absolute minimum of the needed files are in ./LuaJIT.
    Goto here for the complete LuaJIT.


The following assumes you will install this package in c:\prog\wsock_trace. To clone this repository, do this in an empty c:\prog\wsock_trace directory:

  • c:\prog\wsock_trace> git clone .

To be able to get more precise Geo-IP information for addresses (city and region), Wsock-trace will use a IP2Location LITE database. To make best use of it, do this:

  • Sign-up for an account and download a free IP2Location LITE database. Or in case you have an account, go here.
  • Download and use a file named like IP2LOCATION-LITE-DBx.IPV6.BIN.
    Such a file contains both IPv4 and IPv6 records.
  • Copy IP2LOCATION-LITE-DBx.IPV6.BIN into your %APPDATA% directory and edit the keyword in the [geoip] section to read:
    ip2location_bin_file = %APPDATA%\IP2LOCATION-LITE-DBx.IPV6.BIN

Note: IP2Location-C-Library is no longer used as a submodule (since I've made several local changes to it). It has been merged into src/ip2loc.c and simplified.


Enter the src sub-directory and do the respective make allcommand.
If the all command succeeded, you can do the respective make install command:

Builder make allcommand make install result
CygWin make -f Makefile.CygWin cp wsock_trace_cyg.dll to /usr/bin and
cp libwsock_trace_cyg.a to /usr/lib
MinGW32 make -f Makefile.MinGW cp wsock_trace_mw.dll to $(MINGW32)/bin and
cp libwsock_trace_mw.a to $(MINGW32)/lib
MSVC nmake -f makefile.vc6 copy wsock_trace.dll to %VCINSTALLDIR%\bin and
copy wsock_trace.lib to %VCINSTALLDIR%\lib
OpenWatcom wmake -f Makefile.Watcom copy wsock_trace_ow.dll to %WATCOM\binnt and
copy wsock_trace_ow.lib to %WATCOM\lib386\nt


Link with one of these libraries (instead of the default libws32_2.a or ws2_32.lib):

Builder Library
CygWin libwsock_trace.a
MinGW libwsock_trace.a
MSVC wsock_trace.lib
OpenWatcom wsock_trace_ow.lib

Thus most normal Winsock calls are traced on entry and exit.

Example screen-shot above or details in Running samples below.

MSVC: Remember to compile using -Zi to produce debug-symbols. For MSVC-2015 (or newer) it is recomended to use option -Zo too (which will eases the debug of optimised code. And remember to use -debug when linking your program. See src/Makefile.vc6 for an example. It is not adviced to use option -Oy (enable frame pointer omission) since that will make it difficult for StackWalk64() to figure out the filename and line of the calling function.


The trace-level and other settings are controlled by a config-file wsock_trace. This file is searched along these places until found:

  • The file pointed to by %WSOCK_TRACE.
  • The current directory.
  • The %HOME directory.
  • Then finally the %APPDATA directory.

wsock_trace is read in init.c at startup. Read it's contents; the comments therein should be self-explanatory.
If wsock_trace is not found in one of the above directories, the default trace_level is set to 1.

There is currently no install.bat file for Wsock-trace. So you should copy the following files (here at GitHub) to your
%HOME or %APPDATA directory:


These environment variables are on the form:

  • <drive>:\Documents and Settings\<User Name>\ProgramData. (Win-XP)
  • <drive>:\Users\<User Name>\AppData\Roaming. (Win-Vista+)

Since it's a confusing subject what a program's configuration directory should be, it's best to define a %HOME% to point to the excact place for such config-files.

Running samples

Example output from src/test.exe (built with MSVC):

  * ws_trace/test.c(45) (main+50):              WSAStartup (2.2) --> No error.
  * ws_trace/test.c(24) (do_wsock_tests+125):   gethostbyaddr (, 4, AF_INET) --> 0x003C8780.
  * ws_trace/test.c(27) (do_wsock_tests+150):   gethostbyaddr (, 4, AF_INET) --> 0x003C8780.
  * ws_trace/test.c(29) (do_wsock_tests+164):   gethostbyaddr (::1, 16, AF_INET6) --> 0x003C8780.
  * ws_trace/test.c(31) (do_wsock_tests+175):   gethostbyname (localhost) --> 0x003C8780.
  * ws_trace/test.c(31) (do_wsock_tests+187):   socket (AF_INET, SOCK_STREAM, 0) --> 1724.
  * ws_trace/test.c(33) (do_wsock_tests+196):   WSAGetLastError() --> No error.
  * ws_trace/test.c(36) (do_wsock_tests+343):   select (n=0-1724, rd, NULL, NULL, {tv=1.000001s}) --> No error.
  * ws_trace/test.c(37) (do_wsock_tests+358):   FD_ISSET (1724, fd) --> 0.
  * ws_trace/test.c(47) (main+61):              WSACleanup() --> No error.
    ^                ^   ^                      ^
    |                |   |                      |___ The traced Winsock function and the result.
    |                |   |
    |                |   |____ The calling function with displacement (i.e. offset from
    |                |                                          (nearest public symbol).
    |                |_____ Line number in src-file.
    |____ Source-file relative of the application.

Here is a more realistic and useful example with wsock_trace.lib linked to Nmap [1]:

  c:\> nmap -sT -P0 -p23,80
     * mswin32/ (win_pre_init+68):   WSAStartup (2.2) --> No error.

    Starting Nmap 6.02 ( ) at 2012-07-24 12:48 CET
      * g:/vc_2010/sdk/include/wspiapi.h(1011) (WspiapiGetAddrInfo+79):   WSASetLastError (0).
      * g:/vc_2010/sdk/include/wspiapi.h(1011) (WspiapiGetAddrInfo+79):   WSASetLastError (0).
      * g:/vc_2010/sdk/include/wspiapi.h(1011) (WspiapiGetAddrInfo+79):   WSASetLastError (0).
      * g:/vc_2010/sdk/include/wspiapi.h(1011) (WspiapiGetAddrInfo+79):   WSASetLastError (0).
      * g:/vc_2010/sdk/include/wspiapi.h(1011) (WspiapiGetAddrInfo+79):   WSASetLastError (0).
      * g:/vc_2010/sdk/include/wspiapi.h(1011) (WspiapiGetAddrInfo+79):   WSASetLastError (0).
      * (sendConnectScanProbe+266):   socket (AF_INET, SOCK_STREAM, 6) --> 1780.
      * nbase/nbase_misc.c(261) (unblock_socket+65):   ioctlsocket (1780, FIONBIO, 1) --> No error.
      * (init_socket+82):   setsockopt (1780, SOL_SOCKET, SO_LINGER, 1, 4) --> No error.
      * libnetutil/ (set_ttl+34):   setsockopt (1780, IPPROTO_IP, IP_TTL, ULONG_MAX, 4) --> WSAEINVAL: Invalid arguments (10022).
      * (sendConnectScanProbe+599):   connect (1780, --> WSAEWOULDBLOCK: Call would block (10035).
      * nbase/nbase_misc.c(133) (socket_errno+12):   WSAGetLastError() --> WSAEWOULDBLOCK: Call would block (10035).
      * (ConnectScanInfo::watchSD+82):   FD_ISSET (1780, fd) --> 0.
      * (sendConnectScanProbe+266):   socket (AF_INET, SOCK_STREAM, 6) --> 1720.
      * nbase/nbase_misc.c(261) (unblock_socket+65):   ioctlsocket (1720, FIONBIO, 1) --> No error.
      * (init_socket+82):   setsockopt (1720, SOL_SOCKET, SO_LINGER, 1, 4) --> No error.
      * libnetutil/ (set_ttl+34):   setsockopt (1720, IPPROTO_IP, IP_TTL, ULONG_MAX, 4) --> WSAEINVAL: Invalid arguments (10022).
      * (sendConnectScanProbe+599):   connect (1720, --> WSAEWOULDBLOCK: Call would block (10035).
      * nbase/nbase_misc.c(133) (socket_errno+12):   WSAGetLastError() --> WSAEWOULDBLOCK: Call would block (10035).
      * (ConnectScanInfo::watchSD+82):   FD_ISSET (1720, fd) --> 0.
      * (do_one_select_round+473):   select (n=0-1780, rd, wr, ex, {tv=0.985000s}) --> 3.
      * nbase/nbase_misc.c(133) (socket_errno+12):   WSAGetLastError() --> WSAEWOULDBLOCK: Call would block (10035).
      * (do_one_select_round+1894):   FD_ISSET (1720, fd) --> 0.
      * (do_one_select_round+1917):   FD_ISSET (1720, fd) --> 1.
      * (do_one_select_round+2012):   getsockopt (1720, SOL_SOCKET, SO_ERROR, 0, 4) --> No error.
      * (ConnectScanInfo::clearSD+82):   FD_ISSET (1720, fd) --> 1.
      * (ConnectProbe::~ConnectProbe+37):   closesocket (1720) --> No error.
      * (do_one_select_round+1894):   FD_ISSET (1780, fd) --> 1.
      * (do_one_select_round+2012):   getsockopt (1780, SOL_SOCKET, SO_ERROR, 0, 4) --> No error.
      * (ConnectScanInfo::clearSD+82):   FD_ISSET (1780, fd) --> 1.
      * (ConnectProbe::~ConnectProbe+37):   closesocket (1780) --> No error.
    Nmap scan report for router (
    Host is up (0.0019s latency).
    23/tcp open  telnet
    80/tcp open  http

    Nmap done: 1 IP address (1 host up) scanned in 7.61 seconds
      * mswin32/ (win_cleanup+12):   WSACleanup() --> No error.


  • Nmap uses wrong arguments to setsockopt(); a TTL of ULONG_MAX.
  • Nmap also calls WSAStartup() before the startup message.
  • Last but not least, notice how Wsock-trace handles (demangles) C++ symbols just fine thanks to dbghelp.dll and UnDecorateSymbolName(). I.e. the destructor ConnectProbe::~ConnectProbe above is calling closesocket() at offset 37. (you can turn off C++ demangling by cpp_demangle = 0 in the wsock_trace config-file).

And another example from C-ares's adig.c:

    c:\> adig -t PTR
      * adig.c(216) (main+105):   WSAStartup (2.2) --> No error.
      * ares_process.c(1065) (open_udp_socket+248):   socket (AF_INET, SOCK_DGRAM, 0) --> 1604.
      * ares_process.c(857) (setsocknonblock+61):   ioctlsocket (1604, FIONBIO, 1) --> No error.
      * ares_process.c(1077) (open_udp_socket+345):   connect (1604, --> No error.
      * ares_process.c(791) (ares__send_query+484):   send (1604, 0x00034BDA, 31, 0) --> 31 bytes tx.
      * adig.c(397) (main+1780):   select (n=0-1604, rd, wr, NULL, {tv=3.109000s}) --> 1.
      * ares_process.c(456) (read_udp_packets+146):   FD_ISSET (1604, fd) --> 1.
      * ares_process.c(485) (read_udp_packets+413):   recvfrom (1604, 0x0013F894, 513, 0, --> 106 bytes rx.
    Domain name not found
    id: 58187
    flags: qr rd ra
    opcode: QUERY
    rcode: NXDOMAIN
    .                PTR
    NS records:
                           .        1413    SOA
                                                    ( 2012072400 1800 900 604800 86400 )
    Additional records:
      * ares__close_sockets.c(63) (ares__close_sockets+408):   closesocket (1604) --> No error.
      * adig.c(411) (main+1894):   WSACleanup() --> No error.

By default, the tracing of htons(),htonl(), ntohs() and ntohl() are excluded from the trace.
You can edit the %HOME/wsock_trace config-file and exclude whatever calls you like. And the 2 traces above is showing the effect of the config-value compact = 1.

A more eleborated example from 2 OpenVPN programs; a client and a server running a simple test (in OpenVPN's root-dir). Started with the vpn.bat snippet:

cd sample
start /pos=200,50,1000,800   ..\openvpn.exe --config sample-config-files/loopback-server
start /pos=800,150,1000,1000 ..\openvpn.exe --config sample-config-files/loopback-client


A Larger version.

Firewall Monitor

The firewall_test.exe program show a screen like: screenshot

Together with [DNSBL], enable = 1 it shows remote addresses in SpamHaus DROP-lists. In this case the address in Ukraine / Donetsk is very active giving a Firewall event approximately every 5 minutes.

A good test of the firewall.c features is to open your WiFi FireWall and start a remote port-scan while firewall_test.exe is running. You'll see a lot of DROP-events like:

  layer:   (13) Inbound Transport v4 Discard-layer
  filter:  (277599) Filter to prevent port-scanning
  addr: ->, ports: 21 (ftp) / 52115
  country: United States, Troy/Michigan

Implementation notes

The names of the import libraries and the names of the 32-bit .DLLs are:

  • For MSVC: wsock_trace.lib and wsock_trace.dll .
  • For MinGW: libwsock_trace.a and wsock_trace_mw.dll .
  • For CygWin32: libwsock_trace.a and wsock_trace_cyg.dll.
  • For OpenWatcom: wsock_trace_ow.lib and wsock_trace_ow.dll.

And the 64-bit equivalents:

  • For MSVC: wsock_trace_x64.lib and wsock_trace_x64.dll .
  • For MinGW: libwsock_trace_x64.a and wsock_trace_mw_x64.dll .
  • For CygWin64: libwsock_trace_x64.a and wsock_trace_cyg_x64.dll.
  • For OpenWatcom: not possible (AFAIK there is no way to create x64 programs on OpenWatcom).

These DLLs off-course needs to be in current directory or on %PATH. The reason I've chosen to make it a DLL and not a static-lib is that applications using wsock_trace.lib needs not to be re-linked when I do change the inner workings of the Wsock-trace source code. As long as the ABI is stable (e.g. not adding new functions to the wsock_trace.def file), the application using wsock_trace.dll should work the same.

Note that some virus scanners may find the behaviour of programs linked to wsock_trace.lib suspicious.

Future plans:

  1. Get the decoding of calling function, file-name and lines in the MinGW/CygWin ports working.

  2. Lua-script integration; use a *.lua file to exclude/include processes and/or functions to trace.

  3. Injecting wsock_trace.dll into a remote process. Ref:

  4. Optionally load Wireshark's libwireshark.dll to dissect transport and application protocols.
    Do it for selected processes only.

  5. Deny certain applications to use AF_INET6 protocols (return -1 on socket(AF_INET6,...)).

  6. Make it possible to switch network stacks at run-time: select amongst Winsock2, lwIP, SwsSock and/or Cyclone TCP.

  7. Make a GUI trace viewer for it. Ref:

  8. Add a Json type config feature to support the above features. E.g.:

    wireshark_dissect {
      wget.exe : 1    # Wireshark dissection in wget and curl only.
      curl.exe : 1
    exclude_trace {
      select:    [curl.exe, wget.exe]  # Exclude trace of `select()` and `inet_ntoa()` in curl/wget.
      inet_ntoa: [curl.exe, wget.exe]
      htons:     [ * ]    # Exclude trace of `htons` globally.
    deny_ipv6 {
      pycurl.pyd : 1     # Deny AF_INET6 sockets in scripts using the PyCurl module.
      python27.dll : 1   # And in other Python scripts too.
    stack_mux {
      use_lwip: [wget.2exe, curl.exe]  # Force wget2.exe and curl.exe to use lwIP.dll

G. Vanem <> 2013 - 2020.


PS. This file is written with the aid of the Atom editor and it's Markdown-Preview. A real time-saver.


Tracing library for Winsock calls.




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