fix: Use unique build name for build and tag

[rutvijmehta-harness]

Bug:

Created 2 dockerfiles where we set the below environment variables and built them in parallel:
testimg:1.0 : ENV GOPATH=$HOME/go
testimg2:2.0 : ENV GOPATH=$HOME/go2

Parallel Step 1:

Parallel Step 2:

Reproduced the bug where both testimg and testimg2 were the same (since the environment variable set was the same) after they were built. Ideally the should be different:
Commands used:
testimg:1.0:
docker run --name=testcontainer1 rutvijspit/testimg:1.0
docker exec testcontainer1 sh -c /usr/bin/env | grep GOPATH

testimg2:2.0:
docker run --name=testcontainer2 rutvijspit/testimg2:2.0
docker exec testcontainer2 sh -c /usr/bin/env | grep GOPATH

After the fix:

Parallel Step 1:

Parallel Step 2:

Verification that different environement variable is set:

[shubham149]

What if build is triggered for a run without git clone?

[rutvijmehta-harness]

Moved away from this approach. We now generate a temporary tag using a random string.

[bradrydzewski]

Looks good. I would recommend one minor change.

I would recommend using crypto/rand to ensure you have a truly random string. The challenge with math/rand is that it is deterministic, and if you seed with time, there is still the possibility of conflicts.

import "crypto/rand"

// random generates a random string
func random() string {
	result := make([]rune, 32)
	runes := []rune("0123456789abcdef")
	x := int64(len(runes))
	for i := range result {
		num, err := rand.Int(rand.Reader, big.NewInt(x))
		if err != nil {
			panic("error creating random number") // should never happen
		}
		result[i] = runes[num.Int64()]
	}
	return string(result)
}

alternatively you can use a library that handles this. In other Drone projects we use the below library since it is lightweight and feature complete, with zero external dependencies:

import "github.com/dchest/uniuri"

s := uniuri.New()

[rutvijmehta-harness]

Thanks @bradrydzewski for the review. I've used github.com/dchest/uniuri to generate the temporary tag.