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Map errors from FreeRTOS+TCP to mbedTLS and make read non-blocking when requesting start of frame (#452)

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From the FreeRTOS documentation, pdFREERTOS_ERRNO_ENOSPC means that timeout occurred before any data could be sent or received.
- In the plaintext transport-interface implementation, we would directly return `-pdFREERTOS_ERRNO_ENOSPC`. However, an error like this can occur when the TCP buffer is full, so this ought to be retriable. Libraries that consume the transport interface interpret a return value of 0 to mean that send/recv can be invoked again to get the data. As such, we should appropriately set the return value as 0 when the status is `-pdFREERTOS_ERRNO_ENOSPC`.
- In the mbedTLS port, we would directly return whatever `FreeRTOS_send` or `FreeRTOS_recv` returns. However, sometimes, the return value can be an error. In such cases, we ought to map an error from FreeRTOS+TCP to an equivalent error in mbedTLS. In the case of `-pdFREERTOS_ERRNO_ENOSPC`, we map that to `MBEDTLS_ERR_SSL_TIMEOUT`. When the mbedTLS transport-interface send/recv wrapper sees that value, it appropriately returns 0, so that the library can retry the send/recv. I've verified that when the mbedTLS port returns an error, that same error is returned by `mbedtls_ssl_write` & `mbedtls_ssl_read`.
- The TCP socket may have a receive block time.  If bytesToRecv is greater than 1 then a frame is likely already part way through reception and blocking to wait for the desired number of bytes to be available is the
most efficient thing to do.  If bytesToRecv is 1 then this may be a speculative call to read to find the start of a new frame, in which case blocking is not desirable as it could block an entire protocol agent task for the duration of the read block time and therefore negatively impact performance.  So if bytesToRecv is 1 then don't call recv unless it is known that bytes are already available.

Co-authored-by: abhidixi11 <44424462+abhidixi11@users.noreply.github.com>
Co-authored-by: RichardBarry <3073890+RichardBarry@users.noreply.github.com>
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Oscar Michael Abrina 2020-12-11 12:51:45 -08:00 • committed by GitHub
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FreeRTOS-Plus/Source/Utilities/mbedtls_freertos/mbedtls_error.c
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@ -1,5 +1,5 @@
/*
* FreeRTOS Error Code Stringification utilies for mbed TLS v2.16.0
* FreeRTOS V202011.00
* Copyright (C) 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
@ -18,6 +18,10 @@
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
* https://www.FreeRTOS.org
* https://github.com/FreeRTOS
*
*/
/**