feat(rpc/ndr): add NDR encoder mirroring the decoder - #42
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Add Encoder/NewEncoder/Encode (and Marshal helper) producing DCE/RPC NDR Type-Serialization-v1 output, the inverse of the existing Decoder: same ndr struct tags, alignment, conformant-array hoisting, deferred pointers, and common/private headers. Verified by round-tripping the decoder's own test vectors (decode -> encode -> identical bytes). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Signed-off-by: Henry Stern <henry@stern.ca>
A pointer-tagged field equal to its type's zero value is a NULL NDR pointer and must emit a zero referent id, round-tripping back to the zero value. The encoder previously emitted a present referent for any non-Go-pointer kind, so a nil pointer slice became a present empty array and a zero-value value type (e.g. an absent RPC_SID embedded by pointer) became a present, populated struct. Both broke decode -> encode -> decode and would corrupt a marshalled MS-PAC's absent fields such as ExtraSIDs or ResourceGroupDomainSID. Use reflect.Value.IsZero, which mirrors the decoder's representation of a NULL pointer (the field is left at its zero value), so encoding the zero value as NULL round-trips. A present, fully-zero value type is invalid in practice (an RPC_SID has Revision 1) and is indistinguishable from NULL to the decoder. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Signed-off-by: Henry Stern <henry@stern.ca>
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Adds an NDR encoder (Encoder/NewEncoder/Encode + Marshal) — the inverse of the existing decoder, honoring the same ndr struct tags, alignment, conformant-array hoisting, deferred pointers, and Type-Serialization-v1 headers. Verified by round-tripping every decoder test vector (decode -> encode -> identical bytes) plus encode->decode->DeepEqual. Needed to marshal an MS-PAC (KERB_VALIDATION_INFO) downstream in go-krb5/krb5.