PkgPath contains vendor path prefix

[rsteube]

PkgPath can contain the vendor path prefix when using vendored dependencies in a traefik plugin.

equals then tries to compare an id with the prefix with one without it:

"*github.com/rsteube/traefik-plugin-brotli/vendor/github.com/andybalholm/brotli.encoderDictionary" == "`*github.com/andybalholm/brotli.encoderDictionary"

The following triggers an unexpected error:

# hash.go
type hasherCommon struct {
	params           hasherParams
	is_prepared_     bool
	dict_num_lookups uint
	dict_num_matches uint
}

type hasherHandle interface {
	Common() *hasherCommon
	Initialize(params *encoderParams)
	Prepare(one_shot bool, input_size uint, data []byte)
	StitchToPreviousBlock(num_bytes uint, position uint, ringbuffer []byte, ringbuffer_mask uint)
	HashTypeLength() uint
	StoreLookahead() uint
	PrepareDistanceCache(distance_cache []int)
	FindLongestMatch(dictionary *encoderDictionary, data []byte, ring_buffer_mask uint, distance_cache []int, cur_ix uint, max_length uint, max_backward uint, gap uint, max_distance uint, out *hasherSearchResult)
	StoreRange(data []byte, mask uint, ix_start uint, ix_end uint)
	Store(data []byte, mask uint, ix uint)
}

# h10.go
type h10 struct {
	hasherCommon
	window_mask_ uint
	buckets_     [1 << 17]uint32
	invalid_pos_ uint32
	forest       []uint32
}

func (*h10) FindLongestMatch(dictionary *encoderDictionary, data []byte, ring_buffer_mask uint, distance_cache []int, cur_ix uint, max_length uint, max_backward uint, gap uint, max_distance uint, out *hasherSearchResult) {
	panic("unimplemented")
}


# encode.go -  where the error occurs
createZopfliBackwardReferences(uint(bytes), uint(wrapped_last_processed_pos), data, uint(mask), &s.params, s.hasher_.(*h10), s.dist_cache_[:], &s.last_insert_len_, &s.commands, &s.num_literals_)

Expected result:

executes without error

Got:

/plugins/go/src/github.com/rsteube/traefik-plugin-brotli/vendor/github.com/andybalholm/brotli/encode.go:812:110:
impossible type assertion: *github.com/andybalholm/brotli.h10
does not implement github.com/rsteube/traefik-plugin-brotli/vendor/github.com/andybalholm/brotli.hasherHandle

To fix this the prefix might be removed from PkgPath as others have done.

see also golang/go#12739

[mvertes]

Why is this causing problem ? Do you have a specific example, failing without, and succeeding with the behavior you propose ?

[rsteube]

Strill trying to recreate it. It fails with brotli at:

/plugins/go/src/github.com/rsteube/traefik-plugin-brotli/vendor/github.com/andybalholm/brotli/encode.go:812:110:
impossible type assertion: *github.com/andybalholm/brotli.h10
does not implement github.com/rsteube/traefik-plugin-brotli/vendor/github.com/andybalholm/brotli.hasherHandle

When removing the prefix i get to to a different error: hash_forgetful_chain.go:77:39: CFG post-order panic: reflect: call of reflect.Value.Interface on zero Value, so i currently assume that it fixes the error (which might be wrong of course as the brotli code is not yet completely working).

[rsteube]

Updated the example with snippets from brotli related to the error, this is incomplete though and no executable sample.go yet.

[rsteube]

would need to be applied to t.path and t.rtype.PkgPath()

// id returns a unique type identificator string.
func (t *itype) id() (res string) {
    if t.name != "" {
        if t.path != "" {
            return t.path + "." + t.name
            return fixPkgPathVendoring(t.path) + "." + t.name
        }
        return t.name
    }
@ interp/type.go:1121 @ func (t *itype) id() (res string) {
    case valueT:
        res = ""
        if t.rtype.PkgPath() != "" {
            res += t.rtype.PkgPath() + "."
            res += fixPkgPathVendoring(t.rtype.PkgPath()) + "."
        }
        res += t.rtype.Name()
    }

[rsteube]

keeping a branch open where the error occurs:
https://github.com/rsteube/traefik-plugin-brotli/tree/vendor-prefix-bug

docker-compose up

[mvertes]

Hello @rsteube, could you check if #944 improves this particular issue as well ?
Thanks!

[rsteube]

will do

[rsteube]

@mvertes yes, boots up fine and plugin is visible in dashboard.
Invocation of brotli itself fails the same way as with my "workaround" due to a different error so i would say it fixes the issue.

[mvertes]

ok thanks. Other changes are coming to fix the remaining issues in brotli.