fix(esp-tls): clean up is_tls flag (IDFGH-16662)

[erkia]

Description

Commit 2dd280f added a neat feature to support STARTTLS by doing something like this:

esp_tls_t *ftp;
esp_tls_cfg_t cfg;

memset(&cfg, 0, sizeof(cfg));

ftp = esp_tls_init();

cfg.is_plain_tcp = true;
esp_tls_conn_new_sync("example.com", strlen("example.com"), 21, &cfg, ftp);

// ... AUTH TLS or STARTTLS or what not ...

cfg.is_plain_tcp = false;
esp_tls_set_conn_state(ftp, ESP_TLS_CONNECTING);
esp_tls_conn_new_sync("example.com", strlen("example.com"), 21, &cfg, ftp);

However, when doing this, tls->is_tls flag is never set to true internally (as it is only set in ESP_TLS_INIT state), which prevents calling mbedtls_net_free() here.

Luckily, despite its name, mbedtls_net_free() does not free anything and only does a graceful shutdown of the socket, so it is not a big issue (socket is closed by esp-tls anyway). But as this is the only usecase for tls->is_tls flag, then it makes sense to clean it up, fixing the small inconsistency in the process.

[github-actions]

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[erkia]

_esp_tls_net_init() is called by esp_tls_init() anyway, no matter if plain or TLS.

It's only job is to set tls->server_fd.fd = -1; for mbedtls. For wolfssl, it is no-op. So it is safe to call it here always, especially, as tls->sockfd = -1; is forced also.

[Ashish285]

Hi @erkia , thanks for reporting and creating this issue.

Will setting the tls->is_tls flag inside ESP_TLS_CONNECTING state a better fix for this issue? The mbedtls_net_free() might not be doing much right now but it may in the future so we would probably want to keep that API for tls connections.

[erkia]

Hi @erkia , thanks for reporting and creating this issue.

Will setting the tls->is_tls flag inside ESP_TLS_CONNECTING state a better fix for this issue? The mbedtls_net_free() might not be doing much right now but it may in the future so we would probably want to keep that API for tls connections.

mbedtls_net_init() is called unconditionally by esp_tls_init() anyway, so it makes no sense to call mbedtls_net_free() conditionally.

[Ashish285]

mbedtls_net_init() is called unconditionally by esp_tls_init() anyway

Sure, I believe that's also not the correct way as it should be initialised only when tls will be used.