Sample

json.Marshal encodes byte slices as RFC 4648 Base64 strings but encodes fixed-size byte arrays as JSON numeric arrays, and json.Unmarshal rejects Base64 strings for byte arrays

sha256:c499e69e71bdececea5b130c2df41004fadce97b547d67885f2b0a211574cf36

Case

Goal

json.Marshal encodes byte slices as RFC 4648 Base64 strings but encodes fixed-size byte arrays as JSON numeric arrays, and json.Unmarshal rejects Base64 strings for byte arrays HOW

Packages

encoding/json 1.26.5

Environment

go

Created

2026-08-16T13:06:14Z

Commonly assumed

json.Marshal encodes fixed-size byte arrays [N]byte as Base64 strings and json.Unmarshal decodes Base64 strings into byte arrays.

The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.

Contract

• assert json.Marshal encodes fixed-size byte array [N]byte as a JSON numeric array instead of a base64 string
• assert json.Unmarshal of a base64 string into [N]byte fails with UnmarshalTypeError
• assert json.Unmarshal of a JSON numeric array into [N]byte succeeds
• assert json.Marshal encodes byte slice []byte as a base64 string
• assert json.Unmarshal of a base64 string into []byte succeeds
• assert json.Unmarshal of a JSON numeric array into []byte succeeds
• assert json.Marshal encodes signed byte slice []int8 as a numeric array

Files

• .gitignore
• NOTES.md
• bytes_test.go
• csx.json
• go.mod

Download the verified artifact (tar.gz) — the exact bytes the contract ran against

Origin Seeder

csx-seed

Verification receipts

• go 1.26 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · golang@1 · 2026-08-16 · ed25519:d91480838ac982c9