docker build in Go client fail on COPY - docker

Question

I'm trying to build an image using docker's Go client. Here is the Go program I'm running:
func main() {
ctx := context.Background()
cli, err := client.NewEnvClient()
if err != nil {
log.Fatal(err, " :unable to init client")
}
buf := new(bytes.Buffer)
tw := tar.NewWriter(buf)
defer tw.Close()
dockerFile := "Dockerfile"
dockerFileReader, err := os.Open("./Dockerfile")
if err != nil {
log.Fatal(err, " :unable to open Dockerfile")
}
readDockerFile, err := ioutil.ReadAll(dockerFileReader)
if err != nil {
log.Fatal(err, " :unable to read dockerfile")
}
tarHeader := &tar.Header{
Name: dockerFile,
Size: int64(len(readDockerFile)),
}
err = tw.WriteHeader(tarHeader)
if err != nil {
log.Fatal(err, " :unable to write tar header")
}
_, err = tw.Write(readDockerFile)
if err != nil {
log.Fatal(err, " :unable to write tar body")
}
dockerFileTarReader := bytes.NewReader(buf.Bytes())
imageBuildResponse, err := cli.ImageBuild(
ctx,
dockerFileTarReader,
types.ImageBuildOptions{
Dockerfile: dockerFile,
Tags: []string{"devbuild"},
Remove: true})
if err != nil {
log.Fatal(err, " :unable to build docker image")
}
defer imageBuildResponse.Body.Close()
_, err = io.Copy(os.Stdout, imageBuildResponse.Body)
if err != nil {
log.Fatal(err, " :unable to read image build response")
}
}
It puts the Dockerfile (located in the current directory) in a tar file and builds an image using cli.ImageBuild. This solution was taken from this post, and my Dockerfile looks like this:
FROM alpine:latest
WORKDIR /gopath/src/build
COPY ./binary_build/ /usr/local/bin/
I'm constantly getting the error on the last step:
{"stream":"Step 3/3 : COPY /binary_build/ /usr/local/bin/"}
{"stream":"\n"}
{"errorDetail":{"message":"COPY failed: stat /var/lib/docker/tmp/docker-builder389608393/binary_build: no such file or directory"},"error":"COPY failed: stat /var/lib/docker/tmp/docker-builder389608393/binary_build: no such file or directory"}
There seems to be similar issue in the past reported here, but it seems to have been patched. I ran go get github.com/docker/docker#latest and my docker version in go.mod is github.com/docker/docker v1.13.1. The issue still persists.

Answer 1

If you just build a docker image, that code means nothing, because the docker building process won't run the program.
You should put your Dockerfile and executable file "binary_build" in a sole folder，may be the Dockerfile should like:
FROM alpine:latest
WORKDIR /gopath/src/build
COPY binary_build /usr/local/bin/