Incorrect error message being logged

[guanzo]

This code assumes the err is ErrExtraneousBlock if it's not EOF, but other errors like context canceled will lead to this confusing log message: error closing car writer: extraneous block in CAR. It makes me think the upstream provider is returning invalid CARs which isn't the case.

lassie/pkg/verifiedcar/verifiedcar.go

Lines 140 to 143 in 1d22d1f

	_, err = cbr.Next()
	if !errors.Is(err, io.EOF) {
	return 0, 0, ErrExtraneousBlock
	}

I'm able to repro with

lassie daemon -p 8989 --vv

and

curl "localhost:8989/ipfs/bafkreifyxdnkixhcqz4agfx6jekd27ib7kwxvhaddbvh4ycj4n22jj5d7y?dag-scope=entity&format=car" -v

The context canceled error inconsistently occurs if curl has no output option, if you provide an output (-o /dev/null) then it works consistently. I guess curl cancels the request if it can't write the output to somewhere?

[rvagg]

Nicely diagnosed. It probably should be err != nil && !errors.Is(err, io.EOF). I'll get that sorted.

[rvagg]

This is wilder than I imagined .. I think ipld/go-ipld-prime#524 is involved in this, an error not propagating from the traversal system. Multiple ways to address this but certainly not as simple as I thought when I first started tackling this.

[rvagg]

This should address the problem: #338, the main fix here is to check for context cancellation errors in that position. Unfortunately testing this specific error path is very hard so it's not included there but I've verified that the correct error comes up for the case you've outlined—that the writer is borked.

While in there I've fixed a few other tangentially related things.

[rvagg]

#343 is something not resolved by #338 but arises from this issue and should be looked at. It's not urgent, but a goroutine leak could lead to resource exhaustion over time.