proof: add new MetaJson meta type

In this commit, we add a new meta json type. We update the validation
logic to ensure we obtain a valid JSON string, add additional tests, and
prep for an itest with a more descriptive error message.

Author: Roasbeef

proof/meta.go

@@ -3,6 +3,7 @@ package proof
 import (
 	"bytes"
 	"crypto/sha256"
+	"encoding/json"
 	"errors"
 	"io"
 
@@ -18,6 +19,11 @@ const (
 	// bytes without any specific interpretation.
 	MetaOpaque MetaType = 0
 
+	// MetaJson signals that the meta data is a JSON object.
+	MetaJson MetaType = 1
+)
+
+const (
 	// MetaDataMaxSizeBytes is the maximum length of the meta data. We limit
 	// this to 1MiB for now. This should be of sufficient size to commit to
 	// any JSON data or even medium resolution images. If there is need to
@@ -35,6 +41,9 @@ var (
 
 	// ErrMetaDataTooLarge signals that the meta data is too large.
 	ErrMetaDataTooLarge = errors.New("meta data too large")
+
+	// ErrInvalidJSON signals that the meta data is not a valid JSON.
+	ErrInvalidJSON = errors.New("invalid JSON")
 )
 
 // MetaReveal is an optional TLV type that can be added to the proof of a
@@ -66,6 +75,13 @@ func (m *MetaReveal) Validate() error {
 		return ErrMetaDataTooLarge
 	}
 
+	// If the type is JSON, then it should be parseable as a JSON string.
+	if m.Type == MetaJson {
+		if !json.Valid(m.Data) {
+			return ErrInvalidJSON
+		}
+	}
+
 	return nil
 }
 

proof/meta_test.go

@@ -13,32 +13,53 @@ func TestValidateMetaReveal(t *testing.T) {
 		name        string
 		reveal      *MetaReveal
 		expectedErr error
-	}{{
-		name:        "nil reveal",
-		reveal:      nil,
-		expectedErr: nil,
-	}, {
-		name: "valid reveal",
-		reveal: &MetaReveal{
-			Type: MetaOpaque,
-			Data: []byte("data"),
+	}{
+		{
+			name:        "nil reveal",
+			reveal:      nil,
+			expectedErr: nil,
 		},
-		expectedErr: nil,
-	}, {
-		name: "missing data",
-		reveal: &MetaReveal{
-			Type: MetaOpaque,
-			Data: nil,
+		{
+			name: "valid reveal",
+			reveal: &MetaReveal{
+				Type: MetaOpaque,
+				Data: []byte("data"),
+			},
+			expectedErr: nil,
 		},
-		expectedErr: ErrMetaDataMissing,
-	}, {
-		name: "too much data",
-		reveal: &MetaReveal{
-			Type: MetaOpaque,
-			Data: make([]byte, MetaDataMaxSizeBytes+1),
+		{
+			name: "missing data",
+			reveal: &MetaReveal{
+				Type: MetaOpaque,
+				Data: nil,
+			},
+			expectedErr: ErrMetaDataMissing,
 		},
-		expectedErr: ErrMetaDataTooLarge,
-	}}
+		{
+			name: "too much data",
+			reveal: &MetaReveal{
+				Type: MetaOpaque,
+				Data: make([]byte, MetaDataMaxSizeBytes+1),
+			},
+			expectedErr: ErrMetaDataTooLarge,
+		},
+		{
+			name: "invalid JSON",
+			reveal: &MetaReveal{
+				Type: MetaJson,
+				Data: []byte("invalid"),
+			},
+			expectedErr: ErrInvalidJSON,
+		},
+		{
+			name: "valid JSON",
+			reveal: &MetaReveal{
+				Type: MetaJson,
+				Data: []byte(`{"key": "value"}`),
+			},
+			expectedErr: nil,
+		},
+	}
 
 	for _, tc := range testCases {
 		tc := tc

rpcserver.go

@@ -455,7 +455,7 @@ func (r *rpcServer) MintAsset(ctx context.Context,
 		// If the asset meta field was specified, then the data inside
 		// must be valid. Let's check that now.
 		if err := seedling.Meta.Validate(); err != nil {
-			return nil, err
+			return nil, fmt.Errorf("invalid asset meta: %v", err)
 		}
 	}