Application auto build versioning

Question

The Go linker (go tool link) has an option to set the value of an uninitialised string variable:

-X importpath.name=value
  Set the value of the string variable in importpath named name to

value. Note that before Go 1.5 this option took two separate arguments. Now it takes one argument split on the first = sign.

As part of your build process, you could set a version string variable using this. You can pass this through the go tool using -ldflags. For example, given the following source file:

package main

import "fmt"

var xyz string

func main() {
    fmt.Println(xyz)
}

Then:

$ go run -ldflags "-X main.xyz=abc" main.go
abc

In order to set main.minversion to the build date and time when building:

go build -ldflags "-X main.minversion=`date -u +.%Y%m%d.%H%M%S`" service.go

If you compile without initializing main.minversion in this way, it will contain the empty string.

Additionally I would like to post a small example how to use git and a makefile:

--- Makefile ----

# This how we want to name the binary output
BINARY=gomake

# These are the values we want to pass for VERSION and BUILD
# git tag 1.0.1
# git commit -am "One more change after the tags"
VERSION=`git describe --tags`
BUILD=`date +%FT%T%z`

# Setup the -ldflags option for go build here, interpolate the variable values
LDFLAGS_f1=-ldflags "-w -s -X main.Version=${VERSION} -X main.Build=${BUILD} -X main.Entry=f1"
LDFLAGS_f2=-ldflags "-w -s -X main.Version=${VERSION} -X main.Build=${BUILD} -X main.Entry=f2"

# Builds the project
build:
    go build ${LDFLAGS_f1} -o ${BINARY}_f1
    go build ${LDFLAGS_f2} -o ${BINARY}_f2

# Installs our project: copies binaries
install:
    go install ${LDFLAGS_f1}

# Cleans our project: deletes binaries
clean:
    if [ -f ${BINARY} ] ; then rm ${BINARY} ; fi

.PHONY: clean install

The make file will create two executables. One is executing function one, the other will take function two as main entry:

package main

import (
        "fmt"
)

var (

        Version string
        Build   string
        Entry   string

        funcs = map[string]func() {
                "f1":functionOne,"f2":functionTwo,
        }

)

func functionOne() {
    fmt.Println("This is function one")
}

func functionTwo() {
    fmt.Println("This is function two")
}

func main() {

        fmt.Println("Version: ", Version)
        fmt.Println("Build Time: ", Build)

    funcs[Entry]()

}

Then just run:

make

You will get:

mab@h2470988:~/projects/go/gomake/3/gomake$ ls -al
total 2020
drwxrwxr-x 3 mab mab    4096 Sep  7 22:41 .
drwxrwxr-x 3 mab mab    4096 Aug 16 10:00 ..
drwxrwxr-x 8 mab mab    4096 Aug 17 16:40 .git
-rwxrwxr-x 1 mab mab 1023488 Sep  7 22:41 gomake_f1
-rwxrwxr-x 1 mab mab 1023488 Sep  7 22:41 gomake_f2
-rw-rw-r-- 1 mab mab     399 Aug 16 10:21 main.go
-rw-rw-r-- 1 mab mab     810 Sep  7 22:41 Makefile
mab@h2470988:~/projects/go/gomake/3/gomake$ ./gomake_f1
Version:  1.0.1-1-gfb51187
Build Time:  2016-09-07T22:41:38+0200
This is function one
mab@h2470988:~/projects/go/gomake/3/gomake$ ./gomake_f2
Version:  1.0.1-1-gfb51187
Build Time:  2016-09-07T22:41:39+0200
This is function two

Use ldflags to set variables in main package:

With file main.go:

package main

import "fmt"

var (
    version string
    build   string
)

func main() {
    fmt.Println("version=", version)
    fmt.Println("build=", build)
}

Then run:

go run \
  -ldflags "-X main.version=1.0.0 -X main.build=12082019" \ 
  main.go

Build:

go build -o mybinary \
  -ldflags "-X main.version=1.0.0 -X 'main.build=$(date)'" \ 
  main.go

---

Use ldflags to set variable in a non-main package:

With file config.go:

package config

import "fmt"

var (
    Version string
)

func LogVersion() {
    fmt.Println("version=", Version)
}

You will also need file main.go:

package main

import (
    "fmt"
    "github.com/user/repo/config"
}

func main() {
    config.LogVersion()
}

Build your binary first:

go build -o mybinary main.go 

Find the full path of variable name you want to set:

go tool nm <path_to_binary> | grep Version

Run and build the binary again but with the ldflags:

go run \
  -ldflags "-X github.com/user/repo/config.Version=1.0.0" \
  main.go --version       


go build -o mybinary \
  -ldflags "-X github.com/user/repo/config.Version=1.0.0" \
  main.go     

---

Inspired by https://github.com/golang/go/wiki/GcToolchainTricks#including-build-information-in-the-executable

---

Also if you are using goreleaser then read this https://goreleaser.com/environment/#using-the-mainversion :

Default wise GoReleaser sets three ldflags:

main.version: Current Git tag
main.commit: Current git commit SHA
main.date: Date according RFC3339

---

If you want to see this in action: https://github.com/hoto/fuzzy-repo-finder/blob/master/pkg/config/config.go

I had trouble using the -ldflags parameter when building my mixed command-line app and library project, so I ended up using a Makefile target to generate a Go source file containing my app's version and the build date:

BUILD_DATE := `date +%Y-%m-%d\ %H:%M`
VERSIONFILE := cmd/myapp/version.go

gensrc:
    rm -f $(VERSIONFILE)
    @echo "package main" > $(VERSIONFILE)
    @echo "const (" >> $(VERSIONFILE)
    @echo "  VERSION = \"1.0\"" >> $(VERSIONFILE)
    @echo "  BUILD_DATE = \"$(BUILD_DATE)\"" >> $(VERSIONFILE)
    @echo ")" >> $(VERSIONFILE)

In my init() method, I do this:

flag.Usage = func() {
    fmt.Fprintf(os.Stderr, "%s version %s\n", os.Args[0], VERSION)
    fmt.Fprintf(os.Stderr, "built %s\n", BUILD_DATE)
    fmt.Fprintln(os.Stderr, "usage:")
    flag.PrintDefaults()
}

If you wanted an atomically-increasing build number instead of a build date, however, you would probably need to create a local file that contained the last build number. Your Makefile would read the file contents into a variable, increment it, insert it in the version.go file instead of the date, and write the new build number back to the file.