Developer Guide

Developer Guide extends User Guide with some information, which is relevant for:

  • Sipplauncher developers and contributors
  • Users, who wish to understand how Sipplauncher works under the hood

1. Initialization

  1. Set up the signal handler

    We need to perform proper cleanup in case if:

    • a user interrupts with CTRL+C
    • Sipplaucnher is terminated with any other signal

    Otherwise, we'll leave stray "dummy" interfaces and partially-configured DUT.

    Thus, we set up our signal handler.

    There is a tricky place in signal handling - we can't do much inside the signal handler. We can't even log a message, because sometimes it causes a deadlock. The details of this issue are described in

    To work around this issue - we set a global variable inside the signal handler. And later we check this variable from the main code. Therefore, we have interruption points, which are deadlock-free.

  2. Parse command-line arguments

    To support Command-line arguments, we use the argparse library.

  3. Set up TLS session keys interception

    To support Decrypting Diffie-Hellman TLS traffic, we include a 3rd-party library sipplauncher/sslkeylog.c. In we set the environment variable LD_PRELOAD, which points to

    When we launch a child SIPp application, Linux checks this environment variable and preloads before running SIPp. This library overwrites some methods in the standard OpenSSL library. This makes possible to intercept and log TLS session keys.

Then Sipplauncher passes control to, which is defined at runs in a single thread and performs the following steps:

2. SIPpTest list collection

TestPool instance, defined at, collects names of subfolders inside a test suite folder. The names of subfolders are considered the Test names. Then TestPool:

  1. Sorts test names in alphabetical order
  2. Iterates over the test names.

During iterating, each test name is checked. The test is skipped, if:

  1. A test name matches the Template folder name.
  2. The --pattern-exclude command-line argument is specified and a test name matches it.
  3. The --pattern-only command-line argument is specified and a test name doesn't match it.

If the test isn't skipped, a SIPpTest is instantiated from a test name and the instance is added to the list. A SIPpTest instance, defined at, encapsulates everything, needed to execute the test.

A list of SIPpTest instances, sorted alphabetically by the test name, is returned to

3. SIPpTest list processing

Then the --group command-line argument is considered. takes a slice of SIPpTests, which consists of a --group of elements, from the beginning of a SIPpTest list. This slice is considered a SIPpTest run group. Then processes a SIPpTest run group.

Then takes the next slice from the SIPpTest list and processes it.

This repeats until all SIPpTests from the list are processed.

4. SIPpTest run group processing

SIPpTest run group processing could be divided into stages:

  • consecutive stages Pre-run and Post-run: they're run in the context of the thread.
  • concurrent stage Run: it's run in the context of multiple spawned threads and processes.

During the stages each SIPpTest transits through states:

State colors:

color description displayed to a user
#65c295 green state during normal operation yes
#7da7d8 blue state during normal operation no
#f04e4d red state during error yes

Here is the order of these stages:

1. Pre-run

All SIPpTests in a run group start in the CREATED state. consecutively iterates over SIPpTests in a run group. For each of them, SIPpTest.pre_run() method is executed, which:

  1. Transits the Test into PREPARING state
  2. Assigns dynamic IP addresses

    The high-level overview is given in Dynamically assigned IP address. For a developer it's worth to add a few notes:

    1. The check if the randomly obtained address is already occupied, is performed through the ARP ping. It's used instead of regular ICMP ping because some hosts in LAN might have ICMP replies disabled. And therefore, if we based on ICMP ping, we could cause Ethernet conflicts. The ARP ping is performed using the Scapy library.

    2. A new "dummy" interface is created for each Test. Dummy interface is named with pattern sipp-<test_run_id>. Then the randomly generated IP addresses are assigned to the "dummy" interface. This way we do IP aliasing. We do the "dummy" interface approach instead of creating IP aliases via the ip address add <addr> dev eth0 approach for the following reasons:

      1. to ease network cleanup: just destroy all interfaces which name matches the sipp-<> pattern
      2. to remove the need to specify or calculate network interface on which to create aliases: we rely on the Linux routing system
  3. Creates a test run folder

    Test run folder is created by copying Test folder to location /var/tmp/sipplaucnher/<test_name>/<test_run_id>.

    Copying is performed using shutil.copytree().

  4. Sets up logging into Test run folder

    Sipplauncher logging facilities and paths are configured in /usr/local/etc/sipplauncher/sipplauncher.configlog.conf. Static log location is by default defined there as /tmp/sipplauncher.log.

    We have the following requirements:

    1. We need to easily separate the logs of different Test runs. Thus, we want to log the execution of each Test into a Test run folder. The log path should look like /var/tmp/sipplauncher/<test_name>/<test_run_id>/sipplauncher.log, where <test_run_id> is random and isn't known beforehand. Therefore, the Test run log file location can't be static. It should be dynamic.

    2. We want to preserve the possibility to configure log message format in /usr/local/etc/sipplauncher/sipplauncher.configlog.conf.

    To fulfill the above requirements, we implement the logging class sipplauncher.utils.Log.DynamicFileHandler. It should be specified as a logging class for those logs, which need to be stored into a Test run folder.

    At runtime, we check if the logging class is set to sipplauncher.utils.Log.DynamicFileHandler. And if yes, we supply an actual Test run folder path to sipplauncher.utils.Log.DynamicFileHandler instance.

  5. Replaces keywords using the Template Engine

    A list of files, which need to be processed using the Template engine, is collected:

    All these files are rendered by the Jinja2 API Template.render().

    If the rendering result differs from the original file content - the file is overwritten with the newly rendered content.

  6. Generates SSL certificates and keys

    The process is described here. Python OpenSSL library is used.

  7. Adds DNS zone description to the embedded DNS server

    If the Embedded DNS server hasn't been launched yet, it's launched now.

    Then a DNS zone description file is added to the embedded DNS server.

    Python dnslib library is used.

  8. Activates pcap sniffing

    We use scapy.sendrecv.AsyncSniffer to start a new background thread. This thread installs the BPF on all system network interfaces. The BPF matches all traffic regarding Dynamically assigned IP addresses for this particular Test run. The captured traffic is stored in the memory buffer.

  9. Runs

    If is present in a Test run folder, we execute it with subprocess.Popen() API.

    Then we wait for it to finish and check its exit code.

  10. Transits the Test into the READY state

    If we got an error at any of the steps above - the TEST gets transited into the NOT READY state. Sipplauncher doesn't move to the next stages in this case.

2. Run iterates over SIPpTests in a run group and for each of them launches the method in a dedicated Python Thread.

Then waits for threads to finish. method performs following steps:

  1. Transits the Test into STARTING state

  2. Forks a new PysippProcess

    PysippProcess is a subclass of the multiprocessing.Process.

    We need to fork the Process, because we have the requirement to store all the logs, which relate to Test run, in the Test run folder.

    From this requirement we get the following outcome:

    1. Some of the SIPp log locations are not configurable and are logged to a current working directory. Therefore we need to os.chdir() into a Test run folder before running SIPp.
    2. os.chdir() changes the current working directory for a whole current process. However, we are going to use it inside the concurrently running Threads. Therefore, this introduces the race condition.
    3. Therefore, we need to launch a child Process from a Thread. And then, inside the child Process, call os.chdir() and then run SIPp. This way, we change the working directory inside the child process and avoid the race condition in the parent process.

    PysippProcess determines the SIPp launch order from SIPp scenario file names. This process is described here. Then PysippProcess launches SIPp instances using the API of the Pysipp library.

  3. Reports test result waits for PysippProcess to finish.

    The test is reported as FAIL if exitcode is non-zero, SUCCESS otherwise.

    A Thread measures time from its begging and reports the amount of time elapsed.

3. Post-run

Post-run performs a rollback of actions, which were done in the Pre-run. The rollback is performed in the opposite order of the Pre-run. consecutively iterates over SIPpTests in a run group. For each of them, SIPpTest.post_run() method is executed, which:

  1. Transits the Test into the CLEANING state

  2. Runs

    If is present in a Test run folder, we execute it with subprocess.Popen() API.

    Then we wait for it to finish and check its exit code.

  3. Deactivates pcap sniffing

    We invoke scapy.sendrecv.AsyncSniffer.stop() and wait until the background Thread terminates.

    Then we sort the memory buffer with pcap frames by the frame timestamp. This is needed, because in case if traffic goes through different network interfaces, it could appear in a slightly wrong order inside the memory buffer.

    Then we store the sorted memory buffer in file sipp-<test_run_id>.pcap in a Test run folder.

  4. Removes DNS zone description from the embedded DNS server

  5. Removes a test run folder

    We remove it with shutil.rmtree(), unless the --leave-temp command-line argument was provided.

  6. Removes dynamic IP addresses

    We remove a "dummy" pseudo-interface with name sipp-<test_run_id>.

  7. Transits the Test into the CLEAN state

    If we got an error at any of the steps above - the TEST gets transited into the DIRTY state.

Last update: 2022-08-30