[#3] signature: Refactor sign and verify

Split methods to separate files, drop redundant intefaces

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

signature/verify.go

@@ -0,0 +1,111 @@
+package signature
+
+import (
+	"errors"
+	"fmt"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/refs"
+	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/session"
+	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/util/collection"
+	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/util/signature"
+)
+
+type signatureProvider interface {
+	GetBodySignature() *refs.Signature
+	GetMetaSignature() *refs.Signature
+	GetOriginSignature() *refs.Signature
+}
+
+// VerifyServiceMessage verifies service message.
+func VerifyServiceMessage(msg interface{}) error {
+	switch v := msg.(type) {
+	case nil:
+		return nil
+	case serviceRequest:
+		return verifyServiceRequest(v)
+	case serviceResponse:
+		return verifyServiceResponse(v)
+	default:
+		panic(fmt.Sprintf("unsupported session message %T", v))
+	}
+}
+
+func verifyServiceRequest(v serviceRequest) error {
+	meta := v.GetMetaHeader()
+	verificationHeader := v.GetVerificationHeader()
+	body := serviceMessageBody(v)
+	size := collection.Max(body.StableSize(), meta.StableSize(), verificationHeader.StableSize())
+	buf := make([]byte, 0, size)
+	return verifyServiceRequestRecursive(body, meta, verificationHeader, buf)
+}
+
+func verifyServiceRequestRecursive(body stableMarshaler, meta *session.RequestMetaHeader, verify *session.RequestVerificationHeader, buf []byte) error {
+	verificationHeaderOrigin := verify.GetOrigin()
+	metaOrigin := meta.GetOrigin()
+
+	stop, err := verifyMessageParts(body, meta, verificationHeaderOrigin, verificationHeaderOrigin != nil, verify, buf)
+	if err != nil {
+		return err
+	}
+	if stop {
+		return nil
+	}
+
+	return verifyServiceRequestRecursive(body, metaOrigin, verificationHeaderOrigin, buf)
+}
+
+func verifyMessageParts(body, meta, originHeader stableMarshaler, hasOriginHeader bool, sigProvider signatureProvider, buf []byte) (stop bool, err error) {
+	if err := verifyServiceMessagePart(meta, sigProvider.GetMetaSignature, buf); err != nil {
+		return false, fmt.Errorf("could not verify meta header: %w", err)
+	}
+
+	if err := verifyServiceMessagePart(originHeader, sigProvider.GetOriginSignature, buf); err != nil {
+		return false, fmt.Errorf("could not verify origin of verification header: %w", err)
+	}
+
+	if !hasOriginHeader {
+		if err := verifyServiceMessagePart(body, sigProvider.GetBodySignature, buf); err != nil {
+			return false, fmt.Errorf("could not verify body: %w", err)
+		}
+
+		return true, nil
+	}
+
+	if sigProvider.GetBodySignature() != nil {
+		return false, errors.New("body signature misses at the matryoshka upper level")
+	}
+
+	return false, nil
+}
+
+func verifyServiceResponse(v serviceResponse) error {
+	meta := v.GetMetaHeader()
+	verificationHeader := v.GetVerificationHeader()
+	body := serviceMessageBody(v)
+	size := collection.Max(body.StableSize(), meta.StableSize(), verificationHeader.StableSize())
+	buf := make([]byte, 0, size)
+	return verifyServiceResponseRecursive(body, meta, verificationHeader, buf)
+}
+
+func verifyServiceResponseRecursive(body stableMarshaler, meta *session.ResponseMetaHeader, verify *session.ResponseVerificationHeader, buf []byte) error {
+	verificationHeaderOrigin := verify.GetOrigin()
+	metaOrigin := meta.GetOrigin()
+
+	stop, err := verifyMessageParts(body, meta, verificationHeaderOrigin, verificationHeaderOrigin != nil, verify, buf)
+	if err != nil {
+		return err
+	}
+	if stop {
+		return nil
+	}
+
+	return verifyServiceResponseRecursive(body, metaOrigin, verificationHeaderOrigin, buf)
+}
+
+func verifyServiceMessagePart(part stableMarshaler, sigRdr func() *refs.Signature, buf []byte) error {
+	return signature.VerifyDataWithSource(
+		&StableMarshalerWrapper{part},
+		sigRdr,
+		signature.WithBuffer(buf),
+	)
+}