GODRIVER-3056 fix panic on type conversion of nil val in bson codec_cache

[adhocore]

GODRIVER-3056
(i created an issue in the jira but it vanished never to be found again - also for a opensource project hosted in github it is a bit of a stretch to login to yet another server just to file an issue)

Summary

[ERROR] interface conversion: interface is nil, not bsoncodec.Value

v1.13.0 (in fact v1.12.2 also) introduces panics and hence a breaking change with the bson codec_cache
below is stack trace from the system that encountered issue - and it is confirmed that v1.12.1 does not have this issue which i re tested by reverting the version back.

Stack trace:

goroutine 292 [running]:
runtime/debug.Stack()
	/usr/local/go/src/runtime/debug/stack.go:24 +0x5e
github.com/adhocore/module/web.errlogc(0xc00090a480, {0xc0004bdb58?, 0x1, 0xc000000b40?})
	~/projects/my/module/web/helper.go:297 +0xcc
github.com/adhocore/module/web.errlog(0xc18500?, {0xc0004bdb58, 0x1, 0x1})
	~/projects/my/module/web/helper.go:282 +0x39
github.com/adhocore/module/web.errorx(0xc000209800, {0x7f77785800b8?, 0xc000300390})
	~/projects/my/module/web/helper.go:175 +0x66e
github.com/adhocore/module/web.bootstrap.func2(0x10?, {0xc17300?, 0xc000300390?})
	~/projects/my/module/web/app.go:150 +0x3e
github.com/adhocore/module/web.bootstrap.New.func3.1()
	~/go/pkg/mod/github.com/gofiber/fiber/[email protected]/middleware/recover/recover.go:31 +0x72
panic({0xc17300?, 0xc000300390?})
	/usr/local/go/src/runtime/panic.go:914 +0x21f
go.mongodb.org/mongo-driver/bson/bsoncodec.(*typeEncoderCache).LoadOrStore(...)
	~/go/pkg/mod/go.mongodb.org/[email protected]/bson/bsoncodec/codec_cache.go:45
go.mongodb.org/mongo-driver/bson/bsoncodec.(*Registry).storeTypeEncoder(0xc00032e2a0?, {0xf48e88?, 0xc17100?}, {0x0, 0x0})
	~/go/pkg/mod/go.mongodb.org/[email protected]/bson/bsoncodec/registry.go:416 +0x77
go.mongodb.org/mongo-driver/bson/bsoncodec.(*Registry).LookupEncoder(0xc00032e2a0, {0xf48e88, 0xc17100})
	~/go/pkg/mod/go.mongodb.org/[email protected]/bson/bsoncodec/registry.go:411 +0x1fa
go.mongodb.org/mongo-driver/bson/bsoncodec.(*StructCodec).describeStructSlow(0xc0001db4c0, 0xcc0380?, {0xf48e88, 0xcce820}, 0x0, 0x0)
	~/go/pkg/mod/go.mongodb.org/[email protected]/bson/bsoncodec/struct_codec.go:515 +0x225
go.mongodb.org/mongo-driver/bson/bsoncodec.(*StructCodec).describeStruct(0xc0001db4c0, 0x1c?, {0xf48e88?, 0xcce820}, 0x53?, 0x5c?)
	~/go/pkg/mod/go.mongodb.org/[email protected]/bson/bsoncodec/struct_codec.go:483 +0x9a
go.mongodb.org/mongo-driver/bson/bsoncodec.(*StructCodec).DecodeValue(0xc0001db4c0, {0xc00032e2a0, 0x0, {0x0, 0x0}, {0x0, 0x0}, 0x0, 0x0, 0x0, ...}, ...)
	~/go/pkg/mod/go.mongodb.org/[email protected]/bson/bsoncodec/struct_codec.go:282 +0x111
go.mongodb.org/mongo-driver/bson/bsoncodec.(*PointerCodec).DecodeValue(0xc0001db500, {0xc00032e2a0, 0x0, {0x0, 0x0}, {0x0, 0x0}, 0x0, 0x0, 0x0, ...}, ...)
	~/go/pkg/mod/go.mongodb.org/[email protected]/bson/bsoncodec/pointer_codec.go:91 +0x2ab
go.mongodb.org/mongo-driver/bson.(*Decoder).Decode(0xc0006a00f0, {0xbc92a0, 0xc0003e8108})
	~/go/pkg/mod/go.mongodb.org/[email protected]/bson/decoder.go:134 +0x3e3
go.mongodb.org/mongo-driver/mongo.(*Cursor).Decode(0x7f777857e6b0?, {0xbc92a0, 0xc0003e8108})
	~/go/pkg/mod/go.mongodb.org/[email protected]/mongo/cursor.go:275 +0x8e
github.com/adhocore/module/model.(*Scrip).fromCursor(0xc00035e1c0, 0xf40328?)
	~/projects/my/module/model/scrip.go:150 +0x6b
github.com/adhocore/module/model.(*Stocks).loadScrips(0xc000aaac60, 0x0, {0x0, 0x0, 0x0})
	~/projects/my/module/model/stocks.go:234 +0x2a9

for some reason the cache returned nil as value with true as loaded flag but this is buggy.

Background & Motivation

the issue is noticed in LoadOrStore() but not in Load() and i am sure they both need to work similarly. Load() already checks if the value itself is nil or not but LoadOrStore doesn't, this PR fixes that

[adhocore]

any updates on it please? if there is another PR with more proper fix then we can link up and close it i guess. what is important is we have a release fixing the issue with breaking change. thanks

[qingyang-hu]

Hello @adhocore, we appreciate your contribution to the MongoDB Go Driver. Currently, the team is reviewing PR #1477, which fixes the root cause of the nil interface panic. The cache mechanism introduced in v1.12.2 and v1.13.0 stores nil encoders/decoders, so the panic happens when they are retrieved at mongo-driver/bson/bsoncodec.(*StructCodec).describeStructSlow. We will close this one if PR #1477 is accepted. You are welcome to comment on the PR #1477, too.

[adhocore]

thank you very much. i am all in for fixing the root cause, more so than fixing symptoms. so yea let me close it ;)