qbig

There are three easy to make mistakes in go. I present them here in the way they are often found in the wild, not in the way that is easiest to understand.

All three of these mistakes have been made in Kubernetes code, getting past code review at least once each that I know of.

1. Loop variables are scoped outside the loop.

What do these lines do? Make predictions and then scroll down.

func print(pi *int) { fmt.Println(*pi) }

qbig

package main

import (
	"database/sql"
	"log"
)

func main() {
	db, err := sql.Open("VENDOR_HERE", "YOUR_DSN_HERE")
	handleError(err)

qbig

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"

	"github.com/gorilla/mux"
	"github.com/jinzhu/gorm"

qbig

package main

import (
	"fmt"
	"reflect"
)

type Foo struct {
	FirstName string `tag_name:"tag 1"`
	LastName  string `tag_name:"tag 2"`

qbig

//
// The new assembly support in Solidity makes writing helpers easy.
// Many have complained how complex it is to use `ecrecover`, especially in conjunction
// with the `eth_sign` RPC call. Here is a helper, which makes that a matter of a single call.
//
// Sample input parameters:
// (with v=0)
// "0x47173285a8d7341e5e972fc677286384f802f8ef42a5ec5f03bbfa254cb01fad",
// "0xaca7da997ad177f040240cdccf6905b71ab16b74434388c3a72f34fd25d6439346b2bac274ff29b48b3ea6e2d04c1336eaceafda3c53ab483fc3ff12fac3ebf200",
// "0x0e5cb767cce09a7f3ca594df118aa519be5e2b5a"

qbig

package main

import (
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"log"
)

qbig

const message = web3.sha3('Hello World');
const signature = await web3.eth.sign(account, message);
const { v, r, s } = ethUtil.fromRpcSig(signature);

qbig

function getOriginAddress(bytes32 signedMessage, uint8 v, bytes32 r, bytes32 s) constant returns(address) {
  bytes memory prefix = "\x19Ethereum Signed Message:\n32";
  bytes32 prefixedHash = keccak256(prefix, signedMessage);
  return ecrecover(prefixedHash, v, r, s);
}

qbig

// For eth_sign, we need to sign arbitrary data:
signMessage (withAccount, data) {
  const wallet = this._getWalletForAccount(withAccount)
  const message = ethUtil.stripHexPrefix(data)
  var privKey = wallet.getPrivateKey()
  var msgSig = ethUtil.ecsign(new Buffer(message, 'hex'), privKey)
  var rawMsgSig = ethUtil.bufferToHex(sigUtil.concatSig(msgSig.v, msgSig.r, msgSig.s))
  return Promise.resolve(rawMsgSig)
}

qbig

EC.prototype.sign = function sign(msg, key, enc, options) {
  if (typeof enc === 'object') {
    options = enc;
    enc = null;
  }
  if (!options)
    options = {};

  key = this.keyFromPrivate(key, enc);
  msg = this._truncateToN(new BN(msg, 16));