Golang : Get final balance from bit coin address example

Here is an example of how to query blockchain.info to get the final balance(amount) with a given bitcoin transaction address. Some e-commerce merchants start to accept bitcoin instead of fiat money and this application can be useful in verifying the amount received before issuing a receipt and sending out the goods.

Basically what this program below does is to get the final balance of a transaction with the given bitcoin address. You can incorporate this code below into your e-commerce application to check for the bitcoin payment.

NOTE: The only known weakness in this program is that it relies on the HTML id final_balance when parsing the HTML nodes to retrieve the BTC amount. IF the id final_balance is removed from blockchain.info website, this program will break.

Here you go!

 package main

 import (
 "fmt"
 "golang.org/x/net/html"
 "io/ioutil"
 "net/http"
 "os"
 "strings"
 )

 func Get(httpClient *http.Client, url string) (resp *http.Response, err error) {
 req, err := http.NewRequest("GET", url, nil)
 resp, err = httpClient.Do(req)
 return
 }

 func GetHtmlBody(httpClient *http.Client, url string) (string, error) {
 response, err := Get(httpClient, url)
 defer response.Body.Close()
 htmlBody, err := ioutil.ReadAll(response.Body)
 body := string(htmlBody)
 return body, err
 }

 func main() {
 if len(os.Args) != 2 {
 fmt.Printf("Usage : %s <bitcoin transaction address>\n", os.Args[0])
 os.Exit(0)
 }

 // randomly pick one or two addresses from https://blockchain.info/blocks
 //bitcoinAddress := "152f1muMCNa7goXYhYAQC61hxEgGacmncB"
 bitcoinAddress := os.Args[1]

 fmt.Println("Querying Bitcoin address : ", bitcoinAddress)

 if bitcoinAddress == "" {
 fmt.Println("Bitcoin address cannot be empty!")
 os.Exit(0)
 }

 client := &http.Client{}
 body, err := GetHtmlBody(client, "https://blockchain.info/address/"+bitcoinAddress)
 if err != nil {
 fmt.Println(err)
 }
 htmlBody := string(body)

 // adapted from https://godoc.org/golang.org/x/net/html#Parse
 doc, err := html.Parse(strings.NewReader(htmlBody))
 if err != nil {
 fmt.Println(err)
 }

 var f func(*html.Node)
 f = func(n *html.Node) {
 if n.Type == html.ElementNode && n.Data == "td" {
 for _, attr := range n.Attr {
 if attr.Key == "id" && attr.Val == "final_balance" {
 if n.FirstChild != nil && n.FirstChild.FirstChild != nil {

 spanNode := n.FirstChild.FirstChild
 if spanNode.Data == "span" {
 if spanNode.FirstChild == nil {
 // do nothing
 }
 balance := spanNode.FirstChild.Data
 fmt.Println("Final balance: ", balance)
 break
 }

 }

 }
 }
 }
 for c := n.FirstChild; c != nil; c = c.NextSibling {
 f(c)
 }
 }
 f(doc)
 }

Sample output with bit coin transaction addresses randomly picked up from https://blockchain.info/blocks

$ ./queryblockchain 1KFHE7w8BhaENAswwryaoccDb6qcT6DbYY

Querying Bitcoin address : 1KFHE7w8BhaENAswwryaoccDb6qcT6DbYY

Final balance: 1,342.4838477 BTC

$ ./queryblockchain 1JyiMwNfLcXHztZVMQJ5UWH6cJEyL24jKR

Querying Bitcoin address : 1JyiMwNfLcXHztZVMQJ5UWH6cJEyL24jKR

Final balance: 0 BTC

$ ./queryblockchain 152f1muMCNa7goXYhYAQC61hxEgGacmncB

Querying Bitcoin address : 152f1muMCNa7goXYhYAQC61hxEgGacmncB

Final balance: 4,356.19141589 BTC

References:

https://godoc.org/golang.org/x/net/html#Parse