extmod/modussl_mbedtls: Wire in support for DTLS

[damz]

What is this PR trying to solve?

This PR enables support for DTLS (i.e. TLS over datagram transport protocols like UDP). While support for DTLS is absent in cpython, it is worth supporting it in micropython because it is the basis of the ubiquitous CoAP protocol, used in many IOT projects. See #5270

How does this PR solve the problem?

A new set of "protocols" are added to SSLContext:

• ssl.PROTOCOL_DTLS_CLIENT
• ssl.PROTOCOL_DTLS_SERVER

They act as you expect. If one of these is set, the library assumes that the underlying socket is a datagram-like socket (i.e. UDP or similar).

Implement our own timer callbacks as the out of the box implementation relies on gettimeofday().

TODO: To fully support asyncio for DTLS socket, we will need to return a readable or writable event in poll(MP_STREAM_POLL, ...) if _mbedtls_timing_get_delay(self) >= 1. This is left for future work so as not to interfere with #9871.

[damz]

Note that I only enabled it on the esp32 port so far. The size increase of the micropython.elf file on that port is 8.68 kB. Do we think it is reasonable to enable on all mbedtls-based ports?

[stigbjorlykke]

Is it possible to check the underlying socket type (SOCK_DGRAM) instead of adding a new variable for dtls?

[keenanjohnson]

Hey @stigbjorlykke after looking into this a bit, I don't believe that it is possible. DTLS lives on top of UDP, so the SOCK_DGRAM type doesn't have that context needed.

[keenanjohnson]

Hey all! I would really like to see this change go through and I'm happy to help jump in and push this through. @stigbjorlykke is your comment a requirement before we merge this or is it a suggestion we are ok with accepting for now?

Are there any other changes needed by the reviewers?

[stigbjorlykke]

@stigbjorlykke is your comment a requirement before we merge this or is it a suggestion we are ok with accepting for now?

This is not a requirement, it's a suggestion for a better API. The socket already know it's type, and adding an extra (superfluous) variable makes it easier to write faulty code. I have no idea how easy it is to check this, which is why I ask.

[keenanjohnson]

I've looked into the comment and I don't believe that the socket does know it's DTLS type, so I believe the extra variable is required.

Are you looking at an additional set of the defined SOCK_DGRAM types @stigbjorlykke?

Any help to get this merged as soon as possible would really help out our project :)

Thanks!

[mynameisvasco]

Any update on this?

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (42eab32) 98.36% compared to head (ddb064f) 98.33%.

Files	Patch %	Lines
extmod/modssl_mbedtls.c	63.15%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10062      +/-   ##
==========================================
- Coverage   98.36%   98.33%   -0.04%     
==========================================
  Files         159      159              
  Lines       21088    21106      +18     
==========================================
+ Hits        20743    20754      +11     
- Misses        345      352       +7     

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[github-actions]

Code size report:

   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64: +8720 +1.079% standard[incl +192(data)]
      stm32:    +0 +0.000% PYBV10
     mimxrt:    +0 +0.000% TEENSY40
        rp2:    +0 +0.000% RPI_PICO
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS

[projectgus]

This is an automated heads-up that we've just merged a Pull Request
that removes the STATIC macro from MicroPython's C API.

See #13763

A search suggests this PR might apply the STATIC macro to some C code. If it
does, then next time you rebase the PR (or merge from master) then you should
please replace all the STATIC keywords with static.

Although this is an automated message, feel free to @-reply to me directly if
you have any questions about this.