Issue: Segmentation Fault in multipath_basic_test()

[arpan21020]

Description

I am testing the multipath_test code and attempting to run the multipath_basic_test() function. However, it results in a segmentation fault. Upon debugging, I identified that within multipath_basic_test(), the function multipath_test_one() is called. This function invokes tls_api_init_ctx_ex2(), which is defined in tls_api_test.c.

To investigate further, I added print statements inside the definition of tls_api_init_ctx_ex2(). These revealed that while the client is successfully created, the picoquic_create() function returns NULL when attempting to create the server.

Could someone help identify why picoquic_create() is failing for the server context?

[huitema]

The creation of a server side context will fail if the key and certificate are not properly created. The test keys are located in the source code. By default, the test assumes that it is running in the same directory as the source code. If it is not, you can use the "-S" option to picoquic_ct to document the location of the source code. If you fail to do that, the code will not find the test file, and will refuse to create the context.

That said, the code should not crash. Looks like a test bug.

[arpan21020]

I checked the code and in tls_api_test.c
there are two variables
char test_server_cert_file[512]="../ca-cert.pem";
char test_server_key_file[512]="../server-key.pem";

I am using the key that I generated while running the sample code of picoquic, do I have to generate the keys again? Because it is still not working,
also there is one more variable that I have no idea
char test_server_cert_store_file[512];

Can you provide me with the command for generating the keys and certificates??

[huitema]

Most people use openssl to generate keys and certs.

The tests are programmed to operate in a variety of environments. They use commands like:

ret = picoquic_get_input_path(test_server_cert_file, sizeof(test_server_cert_file), picoquic_solution_dir, PICOQUIC_TEST_FILE_SERVER_CERT);

to concatenate the path to the source files (picoquic_solution_dir) and the path to the file inside the solution (PICOQUIC_TEST_FILE_SERVER_CERT in that example). I suspect that when you are running your tests, the variable picoquic_solution_dir is not set correctly. What is the location (pwd) at which you are running picoquic_ct, and what is the path to the picoquic sources?

[arpan21020]

Thanks for your response. But I don't understand the use of picoquic_solution_dir, I set it to some random directory for instance to check.

I want to test the multipath functionality of the picoquic.
Can you guide me from scratch , how should I start, what all inputs I need to provide?
One thing I noticed that there is no main() function in the multipath_test.c, so I created one and called a function multipath_basic_test() which resulted in segmentation fault.
Am I doing something wrong here?

My aim is to stream video files using picoquic protocol. Please advise me how to proceed?

[huitema]

You don't need to build a main program. All the test functions can be called from picoquic_ct (picoquic_t.exe on Windows). Do something like:

picoquic_ct -S source_dir <name-of-test>

For example, if you built the code in a build folder of depot, and you want to run the basic multipath test you can do:

picoquic_ct -S .. multipath_basic

[huitema]

On the specific question of "stream video files using picoquic protocol", I suppose that you mean "stream video files using QUIC". There are 2 IETF working groups studying that, and proposing two different approaches. One is to use the real time transfer protcol, but instead of sending RTP packets over UDP, send them over a QUIC connection using QUIC datagrams -- see https://www.ietf.org/archive/id/draft-ietf-avtcore-rtp-over-quic-04.html. The other approach, "Media over QUIC" (MoQ), proposes sending media streams as series of QUIC streams and possibly datagrams, see https://datatracker.ietf.org/doc/draft-ietf-moq-transport/.

Either approach could be implemented using picoquic, using picoquic functions to send and receive datagrams or streams. Neither of these approaches requires the use of multipath. Use of multipath to transfer multiple media streams is indeed still a research project.

[arpan21020]

Thank you so much for your detailed response and the clarification about running test functions through picoquic_ct. That cleared up a lot of my confusion.

I am also currently working on this research project focused on streaming media using multipath QUIC, and I aim to leverage picoquic for this. However, I am facing some challenges in understanding the multipath functionality in picoquic and how to make custom modifications to multipath_test.c for my specific use case.

Could you guide me on how to approach modifying and testing the multipath_test.c file? Specifically:

1. How can I build and run a modified version of multipath_test.c for testing purposes?
2. Are there any additional inputs or configurations I need to consider when using multipath for media streaming?

Currently, when I runned the rest I am getting this error

Your insights would be incredibly helpful for me to proceed. Thanks again for your time!

[huitema]

As the name indicates, multipath_test.c is test code, meant to run in the test environment. You can use it to get some idea on how to use the various APIs, but it is not designed to run outside the test environment.

Do you have a version of your scenario running in a single path environment, i.e., without trying to create new paths? That might be a nice first step.

[arpan21020]

Could you please guide me on how to properly build multipath_test.c after making modifications? I’ve added some print statements in the file, but the changes don’t seem to reflect even after running the make command again.

Additionally, I encountered an error earlier (shared in the previous image). Could you help me understand and resolve it?

[huitema]

There is no way to build multipath_test.c in isolation. This is not a supported scenario. It can only be built as part of picoquic_t.

[arpan21020]

Can you help me out with this error

This is my solution dir, it has the certificate and the key

[huitema]

That's an errant message. The internal API picoquic_find_path_by_address is used to match incoming packets to the appropriate "path" context within a connection. In that case, if there is no path, we have an error. The same API is also used to check inside the picoquic_probe_new_path_ex API to check that the proposed path does not already exist. This is what we are seeing here, and "Could notfind path by addr" is the expected result, not an error.

But yes, that's confusing. There should not be a debug message in the "normal" case. It should be fixed.

The test actually succeeds. Two paths are created, and the load is shared between the two paths.