common/cbor: Add debug.strict_cbor

We might as well add round-trip sanity checking, at least when we are
testing things.  I'm not sure if this should be enabled all the time,
and it is written under the assumption that it is not, as round-trip
failures will crash the node if the flag is enabled.

go/common/cbor/cbor.go

@@ -5,7 +5,21 @@
 // to always have the same serialization.
 package cbor
 
-import "github.com/fxamacker/cbor"
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+
+	"github.com/fxamacker/cbor"
+	flag "github.com/spf13/pflag"
+	"github.com/spf13/viper"
+)
+
+// CfgDebugStrictCBOR enables CBOR round-trip enforcement.
+const CfgDebugStrictCBOR = "debug.strict_cbor"
+
+// Flags has the flags used by the CBOR wrapper.
+var Flags = flag.NewFlagSet("", flag.ContinueOnError)
 
 // FixSliceForSerde will convert `nil` to `[]byte` to work around serde
 // brain damage.
@@ -46,6 +60,25 @@ func Unmarshal(data []byte, dst interface{}) error {
 		return nil
 	}
 
+	err := cbor.Unmarshal(data, dst)
+	if err != nil {
+		return err
+	}
+
+	// If we are running with the strict CBOR debug option, ensure that
+	// the structure round-trips.
+	if viper.GetBool(CfgDebugStrictCBOR) {
+		reencoded := Marshal(dst)
+		if !bytes.Equal(data, reencoded) {
+			msg := fmt.Sprintf(
+				"common/cbor: encoded %T does not round-trip (expected: %s, actual: %s)",
+				hex.EncodeToString(data),
+				hex.EncodeToString(reencoded),
+			)
+			panic(msg)
+		}
+	}
+
 	return cbor.Unmarshal(data, dst)
 }
 
@@ -56,3 +89,9 @@ func MustUnmarshal(data []byte, dst interface{}) {
 		panic(err)
 	}
 }
+
+func init() {
+	Flags.Bool(CfgDebugStrictCBOR, false, "(DEBUG) Enforce that CBOR blobs roundtrip")
+
+	_ = viper.BindPFlags(Flags)
+}

go/oasis-node/cmd/common/common.go

@@ -12,6 +12,7 @@ import (
 	"github.com/spf13/viper"
 
 	"github.com/oasislabs/oasis-core/go/common"
+	"github.com/oasislabs/oasis-core/go/common/cbor"
 	"github.com/oasislabs/oasis-core/go/common/crypto/signature"
 	fileSigner "github.com/oasislabs/oasis-core/go/common/crypto/signature/signers/file"
 	"github.com/oasislabs/oasis-core/go/common/entity"
@@ -95,6 +96,9 @@ func init() {
 	RootFlags.Bool(CfgDebugAllowTestKeys, false, "Allow test keys (UNSAFE)")
 	_ = viper.BindPFlags(RootFlags)
 	RootFlags.AddFlagSet(loggingFlags)
+
+	// Common debugging flags.
+	RootFlags.AddFlagSet(cbor.Flags)
 }
 
 // InitConfig initializes the command configuration.

go/oasis-test-runner/oasis/args.go

@@ -36,6 +36,11 @@ type argBuilder struct {
 	vec []string
 }
 
+func (args *argBuilder) debugStrictCBOR() *argBuilder {
+	args.vec = append(args.vec, "--"+cbor.CfgDebugStrictCBOR)
+	return args
+}
+
 func (args *argBuilder) debugAllowTestKeys() *argBuilder {
 	args.vec = append(args.vec, "--"+cmdCommon.CfgDebugAllowTestKeys)
 	return args

go/oasis-test-runner/oasis/oasis.go

@@ -380,6 +380,7 @@ func (net *Network) startOasisNode(
 			registryDebugAllowUnroutableAddresses().
 			tendermintDebugAddrBookLenient()
 	}
+	extraArgs = extraArgs.debugStrictCBOR()
 	args := append([]string{}, subCmd...)
 	args = append(args, baseArgs...)
 	args = append(args, extraArgs.vec...)