Tips

Go

Useful GoLang tips.

References

• Useful examples = https://gobyexample.com/
• Static analysis = https://github.com/analysis-tools-dev/static-analysis#go

Point to Local

While refactoring and troubleshooting code it is sometimes necessary to point to the local version of a package.

You can do this by modifying the go.mod file as follows:

require (
    github.com/queone/utl v1.0.0
)

replace github.com/queone/utl => /Users/myuser/mycode/utl

Build Issues

1. If you get:

   $ go build
   go: go.mod file not found in current directory or any parent directory; see 'go help modules'
   

   Try this

   go mod init <package_name>   # For example, this would be 'zls' for github.com/git719/zls
   go mod tidy
   

2. If you get incompatible modules, try go clean -modcache
3. You may also want to install staticcheck and run:

   go vet ./...
   staticcheck ./...
   

   This will check for common code issues.

Install Go

Use the install-golang.sh BASH script

1. curl -LO https://raw.githubusercontent.com/git719/tools/main/bash/install-golang.sh to download the script
2. ./install-golang.sh 1.22.0 to install GoLang version 1.22.0
3. Above tries to install at $HOME/go, so if you have a previous version there you will first need to back that up
4. Finally, set GOPATH variable to ~/go; add it in your PATH; and also add $GOPATH/bin to it

This script can be used to install Go on:

• Within a Windows GitBASH shell
• On macOS, or
• On Linux Redhat (Note that RHEL shasum command is in package perl-Digest-SHA)

Reduce Binary Executable Size

To reduce binary executable sizes:

1. Always compile with -ldflags "-s -w"
2. And use UPX:

   brew install upx
   upx -9 <binary>
   

Useful Code Snippets

• Check if field exists in given struct

  func FieldInStruct(Field string, Struct interface{}) bool {
    val := reflect.ValueOf(Struct)
    for i := 1; i < val.Type().NumField(); i++ {
        if val.Type().Field(i).Name == Field {
            return true
        }
    }
    return false
  }
  

• Return list of JSON objects in local data file

  func GetListFromLocalFile(storeFile string) interface{} {
    localFile := filepath.Join(progConfDir, storeFile)  // Note progConfDir is global
    JSONData, err := ioutil.ReadFile(localFile)
    if err != nil {
        panic(err)
    }
  
    switch storeFile {
    case InstanceDataFile:                     // Return list of instance records
        var list []InstanceType
        err = json.Unmarshal(JSONData, &list)
        if err != nil { panic(err) }
        return list
    case DNSDataFile:                          // Return list of DNS records
        var list []ResourceRecordSetType
        err = json.Unmarshal(JSONData, &list)
        if err != nil { panic(err) }
        return list
    case ELBDatafile:                          // Return list of ELB records
        var list []LoadBalancerDescriptionType
        err = json.Unmarshal(JSONData, &list)
        if err != nil { panic(err) }
        return list
    case ZoneDataFile:                         // Return list of zone records
        var list []HostedZoneType
        err = json.Unmarshal(JSONData, &list)
        if err != nil { panic(err) }
        return list
    case StackDataFile:                        // Return list of stack records
        var list []StackType
        err = json.Unmarshal(JSONData, &list)
        if err != nil { panic(err) }
        return list
    default:                                   // Return list of generic JSON records
        var list interface{}
        err = json.Unmarshal(JSONData, &list)
        if err != nil { panic(err) }
        return list
    }
  }
  

Common Makefile

Makefiles are usually not needed with Go, but if you must, this one for macOS and Linux will build target binaries for multiple OSes.

# Makefile
# Assumes GOPATH is already set up properly, e.g., $HOME/go

default:
  GOOS=darwin GOARCH=amd64 go build -ldflags "-s -w" -o build/macos/awsinfo
all:
  rm -rf build
  mkdir -p build/{macos,centos,windows}
  go get -u github.com/aws/aws-sdk-go/...
  go get -u github.com/vaughan0/go-ini
  GOOS=darwin GOARCH=amd64 go build -ldflags "-s -w" -o build/macos/awsinfo
  GOOS=linux GOARCH=amd64 go build -ldflags "-s -w" -o build/centos/awsinfo
  GOOS=windows GOARCH=amd64 go build -ldflags "-s -w" -o build/windows/awsinfo.exe

# Modify below target to where you keep your binaries
install:
  cp build/macos/awsinfo $(HOME)/data/bin
clean:
  rm -rf build