Rework offline detection on Linux

[pinkisemils]

To improve offline detection on Linux and desktop in general, I've done two things:

• Add an environment variable to allow disabling the offline check entirely, leaving it in an open state. This could later be reworked to being a proper option.
• Change offline detection on Linux to query the routing table for a path to a public IPv4 address to infer connectivity.

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This change is 

[dlon]

Reviewed 4 of 4 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @pinkisemils)

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talpid-core/src/offline/linux.rs, line 118 at r1 (raw file):

async fn public_ip_not_reachable(handle: &Handle) -> Result<bool> {

I think this should be public_ip_reachable (i.e., not negated).

[pinkisemils]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dlon)

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talpid-core/src/offline/linux.rs, line 118 at r1 (raw file):

Previously, dlon (David Lönnhager) wrote…

I think this should be public_ip_reachable (i.e., not negated).

public_ip_unreachable() would be better still IMO, since every time this function is called, it's return value is assigned to is_offline in one way or another. Or do you think that !pubilc_ip_reachable() is better?

[dlon]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @pinkisemils)

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talpid-core/src/offline/linux.rs, line 118 at r1 (raw file):

Previously, pinkisemils (Emīls Piņķis) wrote…

public_ip_unreachable() would be better still IMO, since every time this function is called, it's return value is assigned to is_offline in one way or another. Or do you think that !pubilc_ip_reachable() is better?

You're right.

[faern]

Reviewed 2 of 4 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @pinkisemils)

[faern]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @pinkisemils)

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talpid-core/src/offline/linux.rs, line 52 at r1 (raw file):

}

const PUBLIC_INTERNET_ADDRESS: Ipv4Addr = Ipv4Addr::new(193, 138, 218, 78);

Can we please leave a comment on such a magical constant? One that explains that any public IP should do, but we stick to one owned my Mullvad.

[faern]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @dlon and @pinkisemils)

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talpid-core/src/offline/linux.rs, line 118 at r1 (raw file):

Previously, dlon (David Lönnhager) wrote…

You're right.

I vote for anything that does not have a negation in the name. Evaluating "is not reachable: true" in my head always leads to smoke coming out of my ears. "Is unreachable: true" or "is reachable: false" is way easier to process.

[faern]

Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @dlon and @pinkisemils)

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talpid-core/src/offline/mod.rs, line 42 at r1 (raw file):

    #[cfg(target_os = "android")] android_context: AndroidContext,
) -> Result<MonitorHandle, Error> {
    let monitor = match std::env::var(TALPID_DISABLE_OFFLINE_MONITOR)

Maybe can be made simpler and more consistent if implemented with a lazy_static like the other env variable checks? Then the constant can contain the actual value and not just the name of the env var to check

mullvadvpn-app/talpid-core/src/tunnel/wireguard/mod.rs

Lines 65 to 67 in 6b91207

	static ref FORCE_USERSPACE_WIREGUARD: bool = env::var("TALPID_FORCE_USERSPACE_WIREGUARD")
	.map(|v| v != "0")
	.unwrap_or(false);

Also easier to verify that the logic is the same as the others

[pinkisemils]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @faern)

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talpid-core/src/offline/linux.rs, line 52 at r1 (raw file):

Previously, faern (Linus Färnstrand) wrote…

Can we please leave a comment on such a magical constant? One that explains that any public IP should do, but we stick to one owned my Mullvad.

Done.

[faern]

Reviewable status: 2 of 4 files reviewed, 1 unresolved discussion (waiting on @dlon and @pinkisemils)

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talpid-core/src/offline/mod.rs, line 25 at r2 (raw file):

lazy_static::lazy_static! {
    /// Disables offline monitor
    static ref FORCE_DISABLE_OFFLINE_MONITOR: bool = std::env::var("TALPID_FORCE_USERSPACE_WIREGUARD")

USERSPACE_WIREGUARD?

[pinkisemils]

Reviewable status: 2 of 4 files reviewed, 1 unresolved discussion (waiting on @dlon and @faern)

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talpid-core/src/offline/mod.rs, line 25 at r2 (raw file):

Previously, faern (Linus Färnstrand) wrote…

USERSPACE_WIREGUARD?

Done.

[dlon]

Reviewed 1 of 2 files at r2, 1 of 1 files at r3.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @faern)

[faern]

Reviewed 1 of 2 files at r2, 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved

[dlon]

Reviewed 2 of 2 files at r4.
Reviewable status: complete! all files reviewed, all discussions resolved