eth: check nil block for tracer api

eth/api_tracer.go

@@ -106,6 +106,32 @@ type txTraceTask struct {
 	index   int            // Transaction offset in the block
 }
 
+// blockByNumber is the wrapper of the chain access function offered by the backend.
+// It will return an error if the block is not found.
+func (api *PrivateDebugAPI) blockByNumber(ctx context.Context, number rpc.BlockNumber) (*types.Block, error) {
+	block, err := api.eth.ApiBackend.BlockByNumber(ctx, number)
+	if err != nil {
+		return nil, err
+	}
+	if block == nil {
+		return nil, fmt.Errorf("block #%d not found", number)
+	}
+	return block, nil
+}
+
+// blockByHash is the wrapper of the chain access function offered by the backend.
+// It will return an error if the block is not found.
+func (api *PrivateDebugAPI) blockByHash(ctx context.Context, hash common.Hash) (*types.Block, error) {
+	block, err := api.eth.ApiBackend.BlockByHash(ctx, hash)
+	if err != nil {
+		return nil, err
+	}
+	if block == nil {
+		return nil, fmt.Errorf("block %s not found", hash.Hex())
+	}
+	return block, nil
+}
+
 // TraceChain returns the structured logs created during the execution of EVM
 // between two blocks (excluding start) and returns them as a JSON object.
 func (api *PrivateDebugAPI) TraceChain(ctx context.Context, start, end rpc.BlockNumber, config *TraceConfig) (*rpc.Subscription, error) {
@@ -640,7 +666,7 @@ func (api *PrivateDebugAPI) TraceCall(ctx context.Context, args ethapi.CallArgs,
 		block *types.Block
 	)
 	if hash, ok := blockNrOrHash.Hash(); ok {
-		block, err = api.eth.ApiBackend.BlockByHash(ctx, hash)
+		block, err = api.blockByHash(ctx, hash)
 	} else if number, ok := blockNrOrHash.Number(); ok {
 		if number == rpc.PendingBlockNumber {
 			// We don't have access to the miner here. For tracing 'future' transactions,
@@ -650,7 +676,7 @@ func (api *PrivateDebugAPI) TraceCall(ctx context.Context, args ethapi.CallArgs,
 			// of what the next actual block is likely to contain.
 			return nil, errors.New("tracing on top of pending is not supported")
 		}
-		block, err = api.eth.ApiBackend.BlockByNumber(ctx, number)
+		block, err = api.blockByNumber(ctx, number)
 	} else {
 		return nil, errors.New("invalid arguments; neither block nor hash specified")
 	}