Unable to use ESP_AT, TCP connection get closed during connect

[joelguittet]

Hello community !

I'm trying to develop an HTTPS client application using an STM32 + ESP_AT hardware connected using Tx/Rx UART interface to have the Wifi support.

• The server is available online and I'm able to resolve it's IP address (using getaddrinfo- I see some traffic over the UART interface with socket 0 used to ask the DNS address resolution of the server name) ✔️
• Then I'm trying to connect using connect, nothing specific there, I see some traffic over the UART interface with socket 1 used to establish the TCP connection with the server ✔️
• While connecting, ESP_AT responds with 1,CONNECT so it looks good until now and some binary data are exchanged over the UART interface, I presume to finalize establishing the connection ✔️
• However, before connection is finalized, ESP_AT send 1,CLOSED prematurely 🙅 and as a result connect fails, it returns -1 and errno is set to 113 ⛔

Anyone with the same issue ? Any feedback appreciated, I d'ont know where to go. Do I need to analyze the details of the binary data exchanged during connect ?

The wanted connection is HTTPS over port 443. Is "TCP" the right protocol to use when opening socket over ESP_AT interface ? Isn't supposed to be "SSL" ? (maybe SSL is managed on top of the connection by Zephyr in this use case ?)

Thanks!
Joel

[joelguittet]

Responding my own issue, the problem comes from the cipher suite I'm using, not compatible with the server. Discovered using a dump of network data. Reworking the mbedtls configuration permitted to solve the issue.