Golang Docker SDK image build failing with COPY - docker

Question

So I am trying to build a docker image with the Golang SDK, everything runs except the section in the Dockerfile where I use COPY to copy a file across into the image:
COPY testfile.txt /testfile.txt
My code is as follows:
func buildImage() {
// Run in directory where Dockerfile is found
os.Chdir("build-dir")
cli, err := client.NewEnvClient()
if err != nil {log.Fatal(err, " :unable to init client")}
// Image Build requiresa tar file
tar := new(archivex.TarFile)
tar.Create("dockerfile.tar")
tar.AddAll(".", true)
tar.Close()
// Use tar file as docker context
dockerBuildContext, err := os.Open("dockerfile.tar")
defer dockerBuildContext.Close()
options := types.ImageBuildOptions{
SuppressOutput: false,
Remove: true,
ForceRemove: true,
PullParent: true,
Tags: []string{"latest"},
Dockerfile: "Dockerfile",
}
buildResponse, err := cli.ImageBuild(context.Background(), dockerBuildContext, options)
defer buildResponse.Body.Close()
if err != nil {
log.Fatal(err, " :unable to build docker image")
}
// Copy out response of stream
_, err = io.Copy(os.Stdout, buildResponse.Body)
if err != nil {
log.Fatal(err, " :unable to read image build response")
}
}
The code fails with:
{
"errorDetail": {
"message":"COPY failed: stat /var/lib/docker/tmp/docker-builder264844317/testfile.txt: no such file or directory"
},
"error":"COPY failed: stat /var/lib/docker/tmp/docker-builder264844317/testfile.txt: no such file or directory"
}
So far I have tried copying the files into the tar before building and then I have also tried moving the textfile.txt into the directory I run the command from but I still can not seem to get past this point
Extra information:
The file is in the same directory as the Dockerfile:
-- build-dir
|-- Dockerfile
|-- testfile.txt

Answer 1

From Source
The docker build command builds Docker images from a Dockerfile and a “context”. A build’s context is the set of files located in the specified PATH or URL. The build process can refer to any of the files in the context. For example, your build can use a COPY instruction to reference a file in the context.
Docker build-context is the entire directory you send to the docker engine. While building your image, Docker engine will try to find the files from the root of your build-context.
In your case, the file was not added to the build-context.

Answer 2

So a colleague pointed out to me instead of just running just `tar.AddAll' i also need to specify the files I want to add, see updated code below:
func buildCIImage() {
os.Chdir("ci-cd")
cli, err := client.NewEnvClient()
if err != nil {log.Fatal(err, " :unable to init client")}
// open the file to pass into the tar
file, err := os.OpenFile("testfile.txt", os.O_RDWR, os.ModePerm)
// Used to get the files information
fileInfo, err := os.Stat("testfile.txt")
tar := new(archivex.TarFile)
tar.Create("dockerfile.tar")
tar.AddAll(".", true)
// Add file into tar
tar.Add("testfile.txt", file, fileInfo)
tar.Close()
dockerBuildContext, err := os.Open("dockerfile.tar")
defer dockerBuildContext.Close()
options := types.ImageBuildOptions{
SuppressOutput: false,
Remove: true,
ForceRemove: true,
PullParent: true,
Tags: []string{"bootstrap"},
Dockerfile: "Dockerfile",
}
buildResponse, err := cli.ImageBuild(context.Background(), dockerBuildContext, options)
defer buildResponse.Body.Close()
if err != nil {
log.Fatal(err, " :unable to build docker image")
}
_, err = io.Copy(os.Stdout, buildResponse.Body)
if err != nil {
log.Fatal(err, " :unable to read image build response")
}
}