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cel: Some ideas for ergonomics improvements #145

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Dec 3, 2021
Merged

cel: Some ideas for ergonomics improvements #145

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8e9e153
cel: Make Record struct contain decoded values
josephlr Dec 3, 2021
55c8904
cel: make unmarshal TLV methods private
josephlr Dec 3, 2021
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76 changes: 31 additions & 45 deletions cel/canonical_eventlog.go
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,7 @@ type TLV struct {
}

// MarshalBinary marshals a TLV to a byte slice.
func (tlv *TLV) MarshalBinary() (data []byte, err error) {
func (tlv TLV) MarshalBinary() (data []byte, err error) {
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typically they are pointer receivers: https://cs.opensource.google/search?q=MarshalBinary()&ss=go%2Fgo:src%2F&start=1

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So it seems like:

So I think it's fine to use a value receiver here. The type is small, marshaling doesn't change the value, and if I change it to a pointer receiver the code doesn't compile.

This is because you then can't do something like:

createRecNumField(r.RecNum).MarshalBinary()

as temporary values do not have an address.

buf := make([]byte, len(tlv.Value)+tlvTypeFieldLength+tlvLengthFieldLength)

buf[0] = tlv.Type
Expand Down Expand Up @@ -98,9 +98,9 @@ func UnmarshalFirstTLV(buf *bytes.Buffer) (tlv TLV, err error) {

// Record represents a Canonical Eventlog Record.
type Record struct {
RECNUM TLV
PCR TLV
Digests TLV
RecNum uint64
PCR uint8
Digests map[crypto.Hash][]byte
Content TLV
}

Expand Down Expand Up @@ -132,9 +132,11 @@ func (c *CEL) AppendEvent(tpm io.ReadWriteCloser, pcr int, hashAlgos []crypto.Ha
// TODO: extend the digest to TPM PCR
}

celr, err := createCELR(uint64(len(c.Records)), uint8(pcr), digestsMap, event)
if err != nil {
return err
celr := Record{
RecNum: uint64(len(c.Records)),
PCR: uint8(pcr),
Digests: digestsMap,
Content: event.GetTLV(),
}

c.Records = append(c.Records, celr)
Expand All @@ -149,7 +151,7 @@ func createRecNumField(recNum uint64) TLV {

// UnmarshalRecNum takes in a TLV with its type equals to the recnum type value (0), and
// return its record number.
func UnmarshalRecNum(tlv TLV) (uint64, error) {
func unmarshalRecNum(tlv TLV) (uint64, error) {
if tlv.Type != recnumTypeValue {
return 0, fmt.Errorf("type of the TLV [%d] indicates it is not a recnum field [%d]",
tlv.Type, recnumTypeValue)
Expand All @@ -168,7 +170,7 @@ func createPCRField(pcrNum uint8) TLV {

// UnmarshalPCR takes in a TLV with its type equals to the PCR type value (1), and
// return its PCR number.
func UnmarshalPCR(tlv TLV) (pcrNum uint8, err error) {
func unmarshalPCR(tlv TLV) (pcrNum uint8, err error) {
if tlv.Type != pcrTypeValue {
return 0, fmt.Errorf("type of the TLV [%d] indicates it is not a PCR field [%d]",
tlv.Type, pcrTypeValue)
Expand Down Expand Up @@ -208,7 +210,7 @@ func createDigestField(digestMap map[crypto.Hash][]byte) (TLV, error) {

// UnmarshalDigests takes in a TLV with its type equals to the digests type value (3), and
// return its digests content in a map, the key is its TPM hash algorithm.
func UnmarshalDigests(tlv TLV) (digestsMap map[crypto.Hash][]byte, err error) {
func unmarshalDigests(tlv TLV) (digestsMap map[crypto.Hash][]byte, err error) {
if tlv.Type != digestsTypeValue {
return nil, fmt.Errorf("type of the TLV indicates it doesn't contain digests")
}
Expand All @@ -232,31 +234,22 @@ func UnmarshalDigests(tlv TLV) (digestsMap map[crypto.Hash][]byte, err error) {
return digestsMap, nil
}

func createCELR(recNum uint64, pcr uint8, digestsmap map[crypto.Hash][]byte, event Content) (celr Record, err error) {
recnumField := createRecNumField(recNum)
pcrField := createPCRField(pcr)

digestField, err := createDigestField(digestsmap)
if err != nil {
return Record{}, err
}
celr = Record{recnumField, pcrField, digestField, event.GetTLV()}

return celr, nil
}

// EncodeCELR encodes the CELR to bytes according to the CEL spec and write them
// to the bytes byffer.
func (r *Record) EncodeCELR(buf *bytes.Buffer) error {
recnumField, err := r.RECNUM.MarshalBinary()
recnumField, err := createRecNumField(r.RecNum).MarshalBinary()
if err != nil {
return err
}
pcrField, err := createPCRField(r.PCR).MarshalBinary()
if err != nil {
return err
}
pcrField, err := r.PCR.MarshalBinary()
digests, err := createDigestField(r.Digests)
if err != nil {
return err
}
digestsField, err := r.Digests.MarshalBinary()
digestsField, err := digests.MarshalBinary()
if err != nil {
return err
}
Expand Down Expand Up @@ -313,44 +306,37 @@ func DecodeToCEL(buf *bytes.Buffer) (CEL, error) {

// DecodeToCELR will read the buf for the next CELR, will return err if
// failed to unmarshal a correct CELR TLV from the buffer.
func DecodeToCELR(buf *bytes.Buffer) (Record, error) {
func DecodeToCELR(buf *bytes.Buffer) (r Record, err error) {
recnum, err := UnmarshalFirstTLV(buf)
if err != nil {
return Record{}, err
}
if recnum.Type != recnumTypeValue {
return Record{}, fmt.Errorf("recnum TLV doesn't have the correct type [%d], got [%d]",
recnumTypeValue, recnum.Type)
r.RecNum, err = unmarshalRecNum(recnum)
if err != nil {
return Record{}, err
}

pcr, err := UnmarshalFirstTLV(buf)
if err != nil {
return Record{}, err
}
if pcr.Type != pcrTypeValue {
return Record{}, fmt.Errorf("pcr TLV doesn't have the correct type [%d], got [%d]",
pcrTypeValue, pcr.Type)
r.PCR, err = unmarshalPCR(pcr)
if err != nil {
return Record{}, err
}

digests, err := UnmarshalFirstTLV(buf)
if err != nil {
return Record{}, err
}
if digests.Type != digestsTypeValue {
return Record{}, fmt.Errorf("digests TLV doesn't have the correct type [%d], got [%d]",
digestsTypeValue, digests.Type)
r.Digests, err = unmarshalDigests(digests)
if err != nil {
return Record{}, err
}

content, err := UnmarshalFirstTLV(buf)
r.Content, err = UnmarshalFirstTLV(buf)
if err != nil {
return Record{}, err
}
celr := Record{
recnum,
pcr,
digests,
content,
}

return celr, nil
return r, nil
}
13 changes: 5 additions & 8 deletions cel/canonical_eventlog_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -36,23 +36,20 @@ func TestCELEncodingDecoding(t *testing.T) {
if len(decodedcel.Records) != 2 {
t.Errorf("should have two records")
}
if recnum, err := UnmarshalRecNum(decodedcel.Records[0].RECNUM); err != nil || recnum != uint64(0) {
if decodedcel.Records[0].RecNum != 0 {
t.Errorf("recnum mismatch")
}
if recnum, err := UnmarshalRecNum(decodedcel.Records[1].RECNUM); err != nil || recnum != uint64(1) {
if decodedcel.Records[1].RecNum != 1 {
t.Errorf("recnum mismatch")
}
if pcr, err := UnmarshalPCR(decodedcel.Records[0].PCR); err != nil || pcr != uint8(13) {
if decodedcel.Records[0].PCR != 13 {
t.Errorf("pcr value mismatch")
}
if pcr, err := UnmarshalPCR(decodedcel.Records[1].PCR); err != nil || pcr != uint8(14) {
if decodedcel.Records[1].PCR != 14 {
t.Errorf("pcr value mismatch")
}

digestsMap, err := UnmarshalDigests(decodedcel.Records[0].Digests)
if err != nil {
t.Error(err)
}
digestsMap := decodedcel.Records[0].Digests
if len(digestsMap[crypto.SHA256]) != 32 {
t.Errorf("SHA256 digest length doesn't match")
}
Expand Down