eth/filters, eth/tracers: add request cancellation checks (#26320)

This ensures that RPC method handlers will react to a timeout or
cancelled request soon after the event occurs.


Co-authored-by: Sina Mahmoodi <itz.s1na@gmail.com>

eth/tracers/api.go

@@ -549,6 +549,9 @@ func (api *API) IntermediateRoots(ctx context.Context, hash common.Hash, config
 		deleteEmptyObjects = chainConfig.IsEIP158(block.Number())
 	)
 	for i, tx := range block.Transactions() {
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
 		var (
 			msg, _    = tx.AsMessage(signer, block.BaseFee())
 			txContext = core.NewEVMTxContext(msg)
@@ -609,14 +612,13 @@ func (api *API) traceBlock(ctx context.Context, block *types.Block, config *Trac
 		signer  = types.MakeSigner(api.backend.ChainConfig(), block.Number())
 		txs     = block.Transactions()
 		results = make([]*txTraceResult, len(txs))
-
-		pend = new(sync.WaitGroup)
-		jobs = make(chan *txTraceTask, len(txs))
+		pend    sync.WaitGroup
 	)
 	threads := runtime.NumCPU()
 	if threads > len(txs) {
 		threads = len(txs)
 	}
+	jobs := make(chan *txTraceTask, threads)
 	blockHash := block.Hash()
 	for th := 0; th < threads; th++ {
 		pend.Add(1)
@@ -640,12 +642,20 @@ func (api *API) traceBlock(ctx context.Context, block *types.Block, config *Trac
 			}
 		}()
 	}
+
 	// Feed the transactions into the tracers and return
 	var failed error
 	blockCtx := core.NewEVMBlockContext(block.Header(), api.chainContext(ctx), nil)
+txloop:
 	for i, tx := range txs {
 		// Send the trace task over for execution
-		jobs <- &txTraceTask{statedb: statedb.Copy(), index: i}
+		task := &txTraceTask{statedb: statedb.Copy(), index: i}
+		select {
+		case <-ctx.Done():
+			failed = ctx.Err()
+			break txloop
+		case jobs <- task:
+		}
 
 		// Generate the next state snapshot fast without tracing
 		msg, _ := tx.AsMessage(signer, block.BaseFee())
@@ -653,12 +663,13 @@ func (api *API) traceBlock(ctx context.Context, block *types.Block, config *Trac
 		vmenv := vm.NewEVM(blockCtx, core.NewEVMTxContext(msg), statedb, api.backend.ChainConfig(), vm.Config{})
 		if _, err := core.ApplyMessage(vmenv, msg, new(core.GasPool).AddGas(msg.Gas())); err != nil {
 			failed = err
-			break
+			break txloop
 		}
 		// Finalize the state so any modifications are written to the trie
 		// Only delete empty objects if EIP158/161 (a.k.a Spurious Dragon) is in effect
 		statedb.Finalise(vmenv.ChainConfig().IsEIP158(block.Number()))
 	}
+
 	close(jobs)
 	pend.Wait()