feat(credentials): add CCache.Marshal and v4 builders - #94
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Add CCache.Marshal (the inverse of Unmarshal) plus NewV4CCache, AddCredential, SetDefaultPrincipal and NewPrincipal helpers, with a byte-exact round-trip test against the existing ccache test vector. Revives jcmturner/gokrb5#423 by @kula, ported to the go-krb5/krb5 tree as new files so no existing code changes. Signed-off-by: Henry Stern <henry@stern.ca>
The version-3 keyblock encodes the key type as two 16-bit integers (matching parseCredential), not a 16-bit value followed by a 32-bit one. Without this, Marshal was not a true inverse of Unmarshal for v3 caches. Add TestMarshalRoundTripV3, which builds a v3 cache and asserts its bytes survive an Unmarshal/Marshal round trip with the key type intact. Signed-off-by: Henry Stern <henry@stern.ca>
writeCredential wrote TicketFlags.Bytes verbatim, but parseCredential reads a fixed 4 bytes. A caller-built Credential with unset flags (nil Bytes) emitted zero bytes, shifting every following field by four so the parser read a garbage authorization-data count and panicked in readAuthDataEntry on Unmarshal. Always emit 4 bytes. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
Adds
CCache.Marshal()— the inverse ofUnmarshal()— plus v4 constructionhelpers (
NewV4CCache,AddCredential,SetDefaultPrincipal,NewPrincipal).Lands as two new files (
credentials/ccache_marshal.go,ccache_marshal_test.go);no existing files are changed.
Why
The library can read credential caches but not write them; marshalling is needed
to issue/persist ccaches programmatically.
Relationship to jcmturner/gokrb5#423
This revives @kula's stalled #423 (original maintainer inactive ~3 years), ported
to the current go-krb5/krb5 tree. It is not a verbatim port — it includes two
changes from the original:
a 16-bit value followed by a 32-bit value, but
parseCredentialreads it astwo 16-bit integers. As written,
Marshalwas therefore not a true inverseof
Unmarshalfor v3 caches. This PR writes two 16-bit integers to match theparser.
formatting, and splitting
writeCredentialinto smaller helpers).Test
TestMarshalRoundTripdecodes the existingtestdata.CCACHE_TEST(v4) vector,Unmarshals it,Marshals it back, and asserts the bytes are identical — abyte-exact round trip.
TestMarshalRoundTripV3builds a v3 cache and asserts its bytes survive anUnmarshal/Marshalround trip with the key type intact (there is no v3 testvector upstream, so this is built in memory). This guards the v3 keyblock fix
above.