Fix empty objects in credential throws error

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@docknetwork/crypto-wasm-ts",
-  "version": "0.31.2",
+  "version": "0.31.3",
   "description": "Typescript abstractions over Dock's Rust crypto library's WASM wrapper",
   "homepage": "https://github.com/docknetwork/crypto-wasm-ts",
   "main": "lib/index.js",

src/anonymous-credentials/schema.ts

@@ -544,6 +544,7 @@ export class CredentialSchema extends Versioned {
 
   static validateGeneric(schema: object, ignoreKeys: Set<string> = new Set()) {
     const [names, values] = this.flattenSchemaObj(schema);
+
     for (let i = 0; i < names.length; i++) {
       if (ignoreKeys.has(names[i])) {
         continue;
@@ -644,16 +645,16 @@ export class CredentialSchema extends Versioned {
           properties: {
             id: {
               type: 'string'
-            },
-          },
+            }
+          }
         },
         proof: {
           type: 'object',
           properties: {
             type: {
               type: 'string'
-            },
-          },
+            }
+          }
         }
       }
     };
@@ -1101,13 +1102,19 @@ export class CredentialSchema extends Versioned {
         } else if (schemaProps[key]['type'] == 'object' && typ == 'object') {
           const schemaKeys = new Set([...Object.keys(schemaProps[key]['properties'])]);
           const valKeys = new Set([...Object.keys(value)]);
-          for (const vk of valKeys) {
-            CredentialSchema.generateFromCredential(value, schemaProps[key]['properties']);
-          }
-          // Delete extra keys not in cred
-          for (const sk of schemaKeys) {
-            if (value[sk] === undefined) {
-              delete schemaKeys[sk];
+
+          // If empty object, skip it here otherwise causes problems downstream
+          if (schemaKeys.size === 0) {
+            delete schemaProps[key];
+          } else {
+            for (const vk of valKeys) {
+              CredentialSchema.generateFromCredential(value, schemaProps[key]['properties']);
+            }
+            // Delete extra keys not in cred
+            for (const sk of schemaKeys) {
+              if (value[sk] === undefined) {
+                delete schemaKeys[sk];
+              }
             }
           }
         } else {

src/anonymous-credentials/util.ts

@@ -32,6 +32,7 @@ import { ValueType, ValueTypes } from './schema';
 import { Encoder } from '../bbs-plus';
 import { SetupParam, Statement, WitnessEqualityMetaStatement } from '../composite-proof';
 import { SetupParamsTracker } from './setup-params-tracker';
+import { isEmptyObject } from '../util';
 
 export function dockAccumulatorParams(): AccumulatorParams {
   return Accumulator.generateParams(ACCUMULATOR_PARAMS_LABEL_BYTES);
@@ -56,7 +57,8 @@ export function dockSaverEncryptionGensUncompressed(): SaverEncryptionGensUncomp
 export function flattenTill2ndLastKey(obj: object): [string[], object[]] {
   const flattened = {};
   const temp = flatten(obj) as object;
-  for (const k of Object.keys(temp)) {
+  const tempKeys = Object.keys(temp).filter((key) => typeof temp[key] !== 'object' || !isEmptyObject(temp[key]));
+  for (const k of tempKeys) {
     // taken from https://stackoverflow.com/a/5555607
     const pos = k.lastIndexOf('.');
     const name = k.substring(0, pos);

src/bbs-plus/encoder.ts

@@ -1,5 +1,5 @@
 import { SignatureG1 } from './signature';
-import { flattenObjectToKeyValuesList, isPositiveInteger } from '../util';
+import { flattenObjectToKeyValuesList, isEmptyObject, isPositiveInteger } from '../util';
 
 /**
  * A function that encodes the input to field element bytes
@@ -65,10 +65,15 @@ export class Encoder {
   encodeMessageObject(messages: object, strict = false): [string[], Uint8Array[]] {
     const [names, values] = flattenObjectToKeyValuesList(messages);
     const encoded: Uint8Array[] = [];
-    for (let i = 0; i < names.length; i++) {
-      encoded.push(this.encodeMessage(names[i], values[i], strict));
+    for (let i = names.length - 1; i >= 0; i--) {
+      // Filter  to remove empty objects, this is done because schema generation removes empty objects + nothing to encode
+      if (typeof values[i] !== 'object' || !isEmptyObject(values[i])) {
+        encoded.push(this.encodeMessage(names[i], values[i], strict));
+      } else {
+        names.splice(i, 1);
+      }
     }
-    return [names, encoded];
+    return [names, encoded.reverse()];
   }
 
   encodeDefault(value: unknown, strict = false): Uint8Array {

tests/anonymous-credentials/credential.spec.ts

@@ -871,4 +871,17 @@ describe('Credential signing and verification', () => {
       checkResult(recreatedCred.verify(pk));
     }
   });
+
+  it('for credential with auto-generated schema and empty objects', () => {
+    const builder = new CredentialBuilder();
+    builder.schema = new CredentialSchema(CredentialSchema.essential());
+    builder.subject = {
+      fname: 'John',
+      emptyObject: {},
+      lname: 'Smith',
+    };
+
+    const cred = builder.sign(sk, undefined, {requireSameFieldsAsSchema: false});
+    checkResult(cred.verify(pk));
+  });
 });