add circular checks in resolver

src/utils/DIDResolved.ts

@@ -43,6 +43,11 @@ export default class DIDResolved {
         return item && item.valueType === "DDO"
     }
 
+    public isDID(): boolean {
+        const item = this.getLastItem()
+        return item && (item.valueType === "DID"  || item.valueType === "DIDRef")
+    }
+
     public getValue(): string {
         const item = this.getLastItem()
         let result: string = null
@@ -55,4 +60,13 @@ export default class DIDResolved {
         }
         return result
     }
+    
+    public isDIDIdVisited(didId: string): boolean {
+        for ( let item of this.items) {
+            if ( item.didId === didId ) {
+                return true
+            }
+        }
+        return false
+    }
 }

src/utils/DIDResolver.ts

@@ -30,14 +30,22 @@ export default class DIDResolver {
     }
 
     public async resolve(did: string, maxHopCount?: number): Promise<DIDResolved> {
-
+        
         maxHopCount = maxHopCount ? maxHopCount : 0
 
         let didId = DIDTools.didToId(did)
         const resolved = new DIDResolved()
+
         let data: DIDRecord = await this.getDID(didId)
         while ( data && (maxHopCount === 0 || resolved.hopCount() < maxHopCount) ) {
+            // need to search after the result
+            if ( resolved.isDIDIdVisited(data.didId) ) {
+                // error circular ref
+                // TODO: raise an error
+                break
+            }
             resolved.addData(data)
+            
             didId = null
             if (data.valueType === "URL" || data.valueType === "DDO" ) {
                 data = null
@@ -57,6 +65,9 @@ export default class DIDResolver {
                 if ( didId ) {
                     data = await this.getDID(didId)
                 }
+                else {
+                    data = null
+                }
             }
         }
         return resolved

test/keeper/DIDResolver.test.ts

@@ -82,9 +82,22 @@ describe("DIDResolver", () => {
             assert(didResolved)
             assert(didResolved.isURL())
             assert(didResolved.getValue() === testURL)
+            
+            // test circular link
+            const didIdFirst = DIDTools.didToId(didList[0])
+
+            const receiptLastCircular = await didRegistry.registerAttribute(didIdLast, ValueType.DID, providerKey,
+                didIdFirst, ownerAccount.getId())
+            assert(receiptLastCircular)
+            
+            // resolve from the first DID in the chain
+            const didResolvedCircular = await didResolver.resolve(didList[0])
+            assert(didResolvedCircular)
+            assert(didResolvedCircular.isDID())
 
         })
 
+        
     })
 
 })