description: Tutorial on how to subscribe to latest blocks in Ethereum with Go.

Subscribing to New Blocks

In this section we’ll go over how to set up a subscription to get events when their is a new block mined. First thing is we need an Ethereum provider that supports RPC over websockets. In this example we’ll use the infura websocket endpoint.

  1. client, err := ethclient.Dial("wss://ropsten.infura.io/ws")
  2. if err != nil {
  3.   log.Fatal(err)
  4. }

Next we’ll create a new channel that will be receiving the latest block headers.

  1. headers := make(chan *types.Header)

Now we call the client’s SubscribeNewHead method which takes in the headers channel we just created, which will return a subscription object.

  1. sub, err := client.SubscribeNewHead(context.Background(), headers)
  2. if err != nil {
  3.   log.Fatal(err)
  4. }

The subscription will push new block headers to our channel so we’ll use a select statement to listen for new messages. The subscription object also contains an error channel that will send a message in case of a failure with the subscription.

  1. for {
  2.   select {
  3.   case err := <-sub.Err():
  4.     log.Fatal(err)
  5.   case header := <-headers:
  6.     fmt.Println(header.Hash().Hex()) // 0xbc10defa8dda384c96a17640d84de5578804945d347072e091b4e5f390ddea7f
  7.   }
  8. }

To get the full contents of the block, we can pass the block header hash to the client’s BlockByHash function.

  1. block, err := client.BlockByHash(context.Background(), header.Hash())
  2. if err != nil {
  3.   log.Fatal(err)
  4. }
  6. fmt.Println(block.Hash().Hex())        // 0xbc10defa8dda384c96a17640d84de5578804945d347072e091b4e5f390ddea7f
  7. fmt.Println(block.Number().Uint64())   // 3477413
  8. fmt.Println(block.Time())              // 1529525947
  9. fmt.Println(block.Nonce())             // 130524141876765836
  10. fmt.Println(len(block.Transactions())) // 7

As you can see, you can read the entire block’s metadata fields, list of transactions, and much more.

Full code

block_subscribe.go

  1. package main
  3. import (
  4.     "context"
  5.     "fmt"
  6.     "log"
  8.     "github.com/ethereum/go-ethereum/core/types"
  9.     "github.com/ethereum/go-ethereum/ethclient"
  10. )
  12. func main() {
  13.     client, err := ethclient.Dial("wss://ropsten.infura.io/ws")
  14.     if err != nil {
  15.         log.Fatal(err)
  16.     }
  18.     headers := make(chan *types.Header)
  19.     sub, err := client.SubscribeNewHead(context.Background(), headers)
  20.     if err != nil {
  21.         log.Fatal(err)
  22.     }
  24.     for {
  25.         select {
  26.         case err := <-sub.Err():
  27.             log.Fatal(err)
  28.         case header := <-headers:
  29.             fmt.Println(header.Hash().Hex()) // 0xbc10defa8dda384c96a17640d84de5578804945d347072e091b4e5f390ddea7f
  31.             block, err := client.BlockByHash(context.Background(), header.Hash())
  32.             if err != nil {
  33.                 log.Fatal(err)
  34.             }
  36.             fmt.Println(block.Hash().Hex())        // 0xbc10defa8dda384c96a17640d84de5578804945d347072e091b4e5f390ddea7f
  37.             fmt.Println(block.Number().Uint64())   // 3477413
  38.             fmt.Println(block.Time())              // 1529525947
  39.             fmt.Println(block.Nonce())             // 130524141876765836
  40.             fmt.Println(len(block.Transactions())) // 7
  41.         }
  42.     }
  43. }