pkg/snet: ignore decoding/parsing reading errors on SCIONPacketConn

[JordiSubira]

So far, the snet/SCIONPacketConn was bubbling up decoding/parsing errors to the calling applications. In principle, these errors are not recoverable by the application. The current solution simulates that the network stack simply discards incorrect/malformated packets. Otherwise,some libraries/applications would misbehave (similar to what would happen if were to receive SCMP errors). If we believe that SCION-aware applications using the low-level SCIONPacketConn should receive the error, we can move this up to Conn.

[jiceatscion]

This change is 

[jiceatscion]

I think this isn't too high. Someone has even argued that broken packets should die earlier than that: #4264

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @JordiSubira)

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pkg/snet/packet_conn.go line 218 at r1 (raw file):

	if err := pkt.Decode(); err != nil {
		metrics.CounterInc(c.Metrics.ParseErrors)
		// XXX(JordiSubira): We avoid bubbling up parsing errors to the

I don't think you need so much in-line explanations as a future reader can git blame, if curious.

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pkg/snet/packet_conn.go line 240 at r1 (raw file):

		lastHop, err = c.lastHop(pkt)
		if err != nil {
			// XXX(JordiSubira): We avoid bubbling up parsing errors to the

Ditto

[oncilla]

Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @JordiSubira)

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pkg/snet/packet_conn.go line 227 at r1 (raw file):

		// SCIONPacketConn should receive the error, we can move this up to
		// Conn.
		log.Error("decoding packet", "error", err)

I would log at most at debug level here.

Otherwise, there is a lot of garbage logs someone can induce.

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pkg/snet/packet_conn.go line 249 at r1 (raw file):

			// SCIONPacketConn should receive the error, we can move this up to
			// Conn.
			log.Error("extracting last hop based on packet path", "error", err)

ditto

[JordiSubira]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @jiceatscion and @oncilla)

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pkg/snet/packet_conn.go line 218 at r1 (raw file):

Previously, jiceatscion wrote…

I don't think you need so much in-line explanations as a future reader can git blame, if curious.

Done.

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pkg/snet/packet_conn.go line 227 at r1 (raw file):

Previously, oncilla (Dominik Roos) wrote…

I would log at most at debug level here.

Otherwise, there is a lot of garbage logs someone can induce.

Done.

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pkg/snet/packet_conn.go line 240 at r1 (raw file):

Previously, jiceatscion wrote…

Ditto

Done.

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pkg/snet/packet_conn.go line 249 at r1 (raw file):

Previously, oncilla (Dominik Roos) wrote…

ditto

Done.

[jiceatscion]

Reviewed all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @oncilla)

[oncilla]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @JordiSubira)