Revert "Remove btcsuite/btcd dep (#272)"

[marten-seemann]

This reverts commit 8814b31. The underlying issue was not fixed in #272, and this continues to break downstream users. Most recently, go-libp2p-webtransport is not able to update to v0.19.1:

❯ go mod tidy
github.com/marten-seemann/go-libp2p-webtransport imports
        github.com/libp2p/go-libp2p-core/crypto imports
        github.com/btcsuite/btcd/btcec/v2/ecdsa tested by
        github.com/btcsuite/btcd/btcec/v2/ecdsa.test imports
        github.com/btcsuite/btcd/chaincfg/chainhash loaded from github.com/btcsuite/btcd/chaincfg/chainhash@v1.0.1,
        but go 1.16 would fail to locate it:
        ambiguous import: found package github.com/btcsuite/btcd/chaincfg/chainhash in multiple modules:
        github.com/btcsuite/btcd v0.21.0-beta (/Users/marten/src/go/pkg/mod/github.com/btcsuite/btcd@v0.21.0-beta/chaincfg/chainhash)
        github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1 (/Users/marten/src/go/pkg/mod/github.com/btcsuite/btcd/chaincfg/chainhash@v1.0.1)

To proceed despite packages unresolved in go 1.16:
        go mod tidy -e
If reproducibility with go 1.16 is not needed:
        go mod tidy -compat=1.17
For other options, see:
        https://golang.org/doc/modules/pruning

[MarcoPolo]

What does go mod graph say in webtransport? I can take a look later, but I’d like to avoid this if possible.

[marten-seemann]

The only repo pulling in github.com/btcsuite/btcd@v0.21.0-beta is this repo, but removing the indirect dependency leads to this error:

github.com/marten-seemann/go-libp2p-webtransport imports
        github.com/libp2p/go-libp2p-core/crypto imports
        github.com/btcsuite/btcd/btcec/v2/ecdsa tested by
        github.com/btcsuite/btcd/btcec/v2/ecdsa.test imports
        github.com/btcsuite/btcd/chaincfg/chainhash: ambiguous import: found package github.com/btcsuite/btcd/chaincfg/chainhash in multiple modules:
        github.com/btcsuite/btcd v0.21.0-beta (/Users/marten/src/go/pkg/mod/github.com/btcsuite/btcd@v0.21.0-beta/chaincfg/chainhash)
        github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1 (/Users/marten/src/go/pkg/mod/github.com/btcsuite/btcd/chaincfg/chainhash@v1.0.1)

[marten-seemann]

I think I (kind of) understand what's going on here. The problem only occurs if you're importing two packages (or two versions of a package, via a transitive dependency) that import different versions of btcd / btcec.

As annoying as this is, at least we can point users in the right direction when this problem occurs. Either

• update all your dependencies
• if that's not feasible, implement a workaround like force usage of github.com/btcsuite/btcd v0.22.1 or newer #254 to force selection of the selection of a certain version

With that solution figured out, I withdraw this PR.