_internet_on: try IPv4, if not acceptable — try IPv6

[vazhnov]

Hello!

Thank you for this great project!

I use IPv6-only workstation with Gentoo GNU/Linux. To connect to IPv4-only resources, I use public services NAT64 + DNS64.

All the software works fine, except PlatformIO:

 % pio update --dry-run

Platform Manager
================
Platform gd32v
--------
Checking platformio/gd32v                     1.2.1                              [Off-line]
Checking platformio/framework-gd32vf103-sdk   1.0.0 @ ~1.0.0                     [Off-line]
Checking platformio/tool-openocd-gd32v        0.1.1 @ ~0.1.1                     [Off-line]
Checking platformio/tool-gd32vflash           0.1.0 @ ~0.1.0                     [Off-line]
Checking platformio/toolchain-gd32v           9.2.0 @ ~9.2.0                     [Off-line]
Checking platformio/tool-dfuutil              1.9.200310 @ ~1.9.200310           [Off-line]


Library Manager
===============
Library Storage: /home/user/.platformio/lib
Failed to check for PlatformIO upgrades. Please check your Internet connection.

I found function _internet_on() uses IPv4-only code s = socket.socket(socket.AF_INET, socket.SOCK_STREAM). The next command, s.connect((host, 80)), raises an error "[Errno 101] Network is unreachable" in my OS.

Then I found official documentation https://docs.python.org/3/library/socket.html, there are examples "… The next two examples are identical to the above two, but support both IPv4 and IPv6. …". I found these examples a bit complicated to integrate into PlatformIO (but you can create your own, better solution, based on official Python examples).

I created a patch, which works fine: if IPv4 is not available, try IPv6. Here is an example:

 % pio --version
PlatformIO Core, version 5.2.4

 % pio update

Platform Manager
================
Platform gd32v
--------
Updating platformio/gd32v                     1.2.1                              [Up-to-date]
Updating platformio/framework-gd32vf103-sdk   1.0.0 @ ~1.0.0                     [Up-to-date]
Updating platformio/tool-openocd-gd32v        0.1.1 @ ~0.1.1                     [Up-to-date]
Updating platformio/tool-gd32vflash           0.1.0 @ ~0.1.0                     [Up-to-date]
Updating platformio/toolchain-gd32v           9.2.0 @ ~9.2.0                     [Up-to-date]
Updating platformio/tool-dfuutil              1.9.200310 @ ~1.9.200310           [Up-to-date]


Library Manager
===============
Library Storage: /home/user/.platformio/lib

P.S.: maybe it is better to try first IPv6, and then IPv4, so IPv4 users will have good error message. But right now, as I understand, PlatformIO doesn't show error message, so this is doesn't matter.

[CLAassistant]

All committers have signed the CLA.

[vazhnov]

This looks even better: socket.create_connection(address[, timeout[, source_address]]):

Connect to a TCP service listening on the internet address (a 2-tuple (host, port)), and return the socket object. This is a higher-level function than socket.connect(): if host is a non-numeric hostname, it will try to resolve it for both AF_INET and AF_INET6, and then try to connect to all possible addresses in turn until a connection succeeds. This makes it easy to write clients that are compatible to both IPv4 and IPv6.

[vazhnov]

Code rewrited with socket.create_connection.
It works for me.

Thanks to Wrocław Hackerspace for this advice!

[ivankravets]

Thanks for the valuable PR! 🙏