investigate non blocking connect

[proppy]

apparently lwip support it: https://github.com/goertzenator/lwip/blob/master/contrib-1.4.0/apps/socket_examples/socket_examples.c#L25

[proppy]

esp8266 core uses lwip raw API which is supposed to be already non blocking.
https://github.com/esp8266/Arduino/blob/342c4ae6fb847bfc787f80b89a2bb888d942dc32/libraries/ESP8266WiFi/src/WiFiClient.cpp#L126

esp_yield yields control back to the OS until the connected callback is called:
https://github.com/esp8266/Arduino/blob/342c4ae6fb847bfc787f80b89a2bb888d942dc32/libraries/ESP8266WiFi/src/WiFiClient.cpp#L137

The callback will resume the sketch by calling esp_schedule:
https://github.com/esp8266/Arduino/blob/2b941f5e2c70267b65ed6cb8fc40c73e65ef26d5/cores/esp8266/core_esp8266_main.cpp#L76

esp_schedule will invoke the loop task:
https://github.com/esp8266/Arduino/blob/2b941f5e2c70267b65ed6cb8fc40c73e65ef26d5/cores/esp8266/core_esp8266_main.cpp#L75

Which will resume the loop_wrapper continuation in the connect() function:
https://github.com/esp8266/Arduino/blob/2b941f5e2c70267b65ed6cb8fc40c73e65ef26d5/cores/esp8266/core_esp8266_main.cpp#L110

@Links2004 explained it better here :)
https://gitter.im/esp8266/Arduino?at=568310093acb611716002cfd

[proppy]

A non blocking implementation would add a new connect_async function or a flag with a different callback and no yield/schedule call.

And the http connect version could return early rather than erroring:
https://github.com/esp8266/Arduino/blob/master/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp#L670-L673

[Links2004]

the HTTP client changes are more complex then just return.
connect is never called form outside the class:
https://github.com/esp8266/Arduino/blob/master/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.h#L192

its only called in sendRequest
https://github.com/esp8266/Arduino/blob/master/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp#L298

the connect shut be fast if the server is there,
only when there is no server it can block for a longer time until:
https://github.com/esp8266/Arduino/blob/342c4ae6fb847bfc787f80b89a2bb888d942dc32/libraries/ESP8266WiFi/src/WiFiClient.cpp#L149
is called.

[proppy]

@Links2004 yes, I was planning to investigate exposing connect with #28

[proppy]

also see https://github.com/me-no-dev/ESPAsyncTCP/blob/master/src/ESPAsyncTCP.cpp

[proppy]

Note that this would be affected by #353.

[yhua537]

Like the idea using ESPAsyncTCP(as I am using it for other connections), can I suggest use injection to allow us choosing which type of connection to use?

Also, should the scope of this library to a easier use of firebase API?

[kiralikbeyin]

#420 (comment)