// createAndExtractImage creates a docker container based on the option's image with containerName.
// It will then insepct the container and image and then attempt to extract the image to
// option's destination path. If the destination path is empty it will write to a temp directory
// and update the option's destination path with a /var/tmp directory. /var/tmp is used to
// try and ensure it is a non-in-memory tmpfs.
func (i *defaultImageInspector) createAndExtractImage(client *docker.Client, containerName string) (*docker.Image, error) {
container, err := client.CreateContainer(docker.CreateContainerOptions{
Name: containerName,
Config: &docker.Config{
Image: i.opts.Image,
// For security purpose we don't define any entrypoint and command
Entrypoint: []string{""},
Cmd: []string{""},
},
})
if err != nil {
return nil, fmt.Errorf("Unable to create docker container: %v\n", err)
}
// delete the container when we are done extracting it
defer func() {
client.RemoveContainer(docker.RemoveContainerOptions{
ID: container.ID,
})
}()
containerMetadata, err := client.InspectContainer(container.ID)
if err != nil {
return nil, fmt.Errorf("Unable to get docker container information: %v\n", err)
}
imageMetadata, err := client.InspectImage(containerMetadata.Image)
if err != nil {
return imageMetadata, fmt.Errorf("Unable to get docker image information: %v\n", err)
}
if i.opts.DstPath, err = createOutputDir(i.opts.DstPath, "image-inspector-"); err != nil {
return imageMetadata, err
}
reader, writer := io.Pipe()
// handle closing the reader/writer in the method that creates them
defer writer.Close()
defer reader.Close()
log.Printf("Extracting image %s to %s", i.opts.Image, i.opts.DstPath)
// start the copy function first which will block after the first write while waiting for
// the reader to read.
errorChannel := make(chan error)
go func() {
errorChannel <- client.CopyFromContainer(docker.CopyFromContainerOptions{
Container: container.ID,
OutputStream: writer,
Resource: "/",
})
}()
// block on handling the reads here so we ensure both the write and the reader are finished
// (read waits until an EOF or error occurs).
handleTarStream(reader, i.opts.DstPath)
// capture any error from the copy, ensures both the handleTarStream and CopyFromContainer
// are done.
err = <-errorChannel
if err != nil {
return imageMetadata, fmt.Errorf("Unable to extract container: %v\n", err)
}
return imageMetadata, nil
}