This directory contains source code and tools to rework the Mbedtls error strings for micropython to use less space. In short, instead of storing and printing something like "SSL - Our own certificate(s) is/are too large to send in an SSL message" it prints the name of the error #define, which would be "MBEDTLS_ERR_SSL_CERTIFICATE_TOO_LARGE" in this case, and only stores SSL_CERTIFICATE_TOO_LARGE in flash. The exact Mbedtls error defines are used because they're easy to search for to find more detailed information.

Mbedtls defines a specific format for error value #defines and includes a Perl script to gather all MBEDTLS_ERR defines from includes files together with english error text. From that the Perl script generates mbedtls_strerror(). The files in this directory modify this process to produce a more space efficient error lookup table with shorter error strings.

The files are as follows:

• generate_errors.diff - diff for original mbedtls perl script
• error.fmt - modified code template for MicroPython
• mp_mbedtls_errors.c - source file with mbedtls_strerror this is built using the include files in ../mbedtls
• do-mp.sh - shell script to produce mp_mbedtls_errors.c
• tester.c - simple C main to test mp_mbedtls_errors.c locally on a dev box
• do-test.sh - shell script to produce mp_mbedtls_errors.c and compile the tester app
• do-esp32.sh - shell script to produce esp32_mbedtls_errors.c -- see below

In order not to store multiple copies of mbedtls_errors.c (https://github.com/micropython/micropython/pull/5819#discussion_r445528006) it is assumed that all ports use the same version of mbedtls with the same error #defines. This is true as of MP v1.13, and ESP-IDF versions 3.3.2 and 4.0.1. If anything changes in the future the do-esp32.sh script can be used to generate an esp32-specific version.

• To build MicroPython all that is needed is to include the mp_mbedtls_errors.c into the build (the Makefiles do this automatically). Note that Perl is not needed for routine MicroPython builds.
• When a new version of Mbedtls is pulled-in the do-mp.sh script should be run to re-generate mp_mbedtls_errors.c.
• The tester app should be run if changes to the string handling in error.fmt are made: it tests that there is not an off-by-one error in the string copying/appending, etc.
• To include mbedtls_strerror error strings define MBEDTLS_ERROR_C in the build.