「docker pull」 をGo言語で
以下のコードを実行するとdocker pull httpdと同様の動作を行えます
package main
import (
"context"
"io"
"os"
"github.com/docker/docker/api/types"
"github.com/docker/docker/client"
)
const (
dockerClientVersion = "1.42"
)
func main() {
ctx := context.Background()
cli, err := client.NewClientWithOpts(client.FromEnv, client.WithVersion(dockerClientVersion))
if err != nil {
panic(err)
}
defer cli.Close()
reader, err := cli.ImagePull(ctx, "docker.io/library/httpd", types.ImagePullOptions{})
if err != nil {
panic(err)
}
io.Copy(os.Stdout, reader)
}
コードの解説
以下のコードでは、ImagePull関数を使用して、httpdのイメージをDockerの公式リポジトリからプルしています。この関数は2つの戻り値を返します。
1つ目はreaderで、これはプルしたイメージのデータを読み取るためのオブジェクトです。二つ目はerrで、これはイメージのプル操作中にエラーが発生した場合にその情報を保持します。
reader, err := cli.ImagePull(ctx, "docker.io/library/httpd", types.ImagePullOptions{})
if err != nil {
panic(err)
}
readerには逐次文字列が投げ込まれていくのでio.Copyを使って標準出力を行います。
io.Copy(os.Stdout, reader)
実際に実行すると以下のようにdocker pullを行ったときと同じような出力が行われます。
$ go run main.go
{"status":"Pulling from library/httpd","id":"latest"}
{"status":"Already exists","progressDetail":{},"id":"2c6d21737d83"}
{"status":"Pulling fs layer","progressDetail":{},"id":"d1bd5114fbcb"}
{"status":"Pulling fs layer","progressDetail":{},"id":"4f4fb700ef54"}
{"status":"Pulling fs layer","progressDetail":{},"id":"076d30352063"}
{"status":"Pulling fs layer","progressDetail":{},"id":"1efe13fa30a0"}
{"status":"Pulling fs layer","progressDetail":{},"id":"01bce57a32a8"}
{"status":"Waiting","progressDetail":{},"id":"1efe13fa30a0"}
{"status":"Waiting","progressDetail":{},"id":"01bce57a32a8"}
{"status":"Downloading","progressDetail":{"current":146,"total":146},"progress":"[==================================================\u003e] 146B/146B","id":"d1bd5114fbcb"}
{"status":"Download complete","progressDetail":{},"id":"4f4fb700ef54"}
{"status":"Verifying Checksum","progressDetail":{},"id":"d1bd5114fbcb"}
{"status":"Download complete","progressDetail":{},"id":"d1bd5114fbcb"}
{"status":"Extracting","progressDetail":{"current":146,"total":146},"progress":"[==================================================\u003e] 146B/146B","id":"d1bd5114fbcb"}
{"status":"Extracting","progressDetail":{"current":146,"total":146},"progress":"[==================================================\u003e] 146B/146B","id":"d1bd5114fbcb"}
{"status":"Downloading","progressDetail":{"current":38872,"total":3823952},"progress":"[\u003e ] 38.87kB/3.824MB","id":"076d30352063"}
{"status":"Downloading","progressDetail":{"current":3201351,"total":3823952},"progress":"[=========================================\u003e ] 3.201MB/3.824MB","id":"076d30352063"}
{"status":"Verifying Checksum","progressDetail":{},"id":"076d30352063"}
{"status":"Download complete","progressDetail":{},"id":"076d30352063"}
{"status":"Pull complete","progressDetail":{},"id":"d1bd5114fbcb"}
{"status":"Extracting","progressDetail":{"current":32,"total":32},"progress":"[==================================================\u003e] 32B/32B","id":"4f4fb700ef54"}
{"status":"Extracting","progressDetail":{"current":32,"total":32},"progress":"[==================================================\u003e] 32B/32B","id":"4f4fb700ef54"}
{"status":"Pull complete","progressDetail":{},"id":"4f4fb700ef54"}
{"status":"Extracting","progressDetail":{"current":65536,"total":3823952},"progress":"[\u003e ] 65.54kB/3.824MB","id":"076d30352063"}
{"status":"Extracting","progressDetail":{"current":3080192,"total":3823952},"progress":"[========================================\u003e ] 3.08MB/3.824MB","id":"076d30352063"}
{"status":"Extracting","progressDetail":{"current":3823952,"total":3823952},"progress":"[==================================================\u003e] 3.824MB/3.824MB","id":"076d30352063"}
{"status":"Pull complete","progressDetail":{},"id":"076d30352063"}
{"status":"Downloading","progressDetail":{"current":293,"total":293},"progress":"[==================================================\u003e] 293B/293B","id":"01bce57a32a8"}
{"status":"Download complete","progressDetail":{},"id":"01bce57a32a8"}
{"status":"Downloading","progressDetail":{"current":334150,"total":32418239},"progress":"[\u003e ] 334.1kB/32.42MB","id":"1efe13fa30a0"}
{"status":"Downloading","progressDetail":{"current":4315462,"total":32418239},"progress":"[======\u003e ] 4.315MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Downloading","progressDetail":{"current":8943942,"total":32418239},"progress":"[=============\u003e ] 8.944MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Downloading","progressDetail":{"current":15522118,"total":32418239},"progress":"[=======================\u003e ] 15.52MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Downloading","progressDetail":{"current":20470086,"total":32418239},"progress":"[===============================\u003e ] 20.47MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Downloading","progressDetail":{"current":25413958,"total":32418239},"progress":"[=======================================\u003e ] 25.41MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Downloading","progressDetail":{"current":30341446,"total":32418239},"progress":"[==============================================\u003e ] 30.34MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Verifying Checksum","progressDetail":{},"id":"1efe13fa30a0"}
{"status":"Download complete","progressDetail":{},"id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":327680,"total":32418239},"progress":"[\u003e ] 327.7kB/32.42MB","id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":2621440,"total":32418239},"progress":"[====\u003e ] 2.621MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":8847360,"total":32418239},"progress":"[=============\u003e ] 8.847MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":19005440,"total":32418239},"progress":"[=============================\u003e ] 19.01MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":23592960,"total":32418239},"progress":"[====================================\u003e ] 23.59MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":24903680,"total":32418239},"progress":"[======================================\u003e ] 24.9MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":28835840,"total":32418239},"progress":"[============================================\u003e ] 28.84MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":32418239,"total":32418239},"progress":"[==================================================\u003e] 32.42MB/32.42MB","id":"1efe13fa30a0"}
{"status":"Pull complete","progressDetail":{},"id":"1efe13fa30a0"}
{"status":"Extracting","progressDetail":{"current":293,"total":293},"progress":"[==================================================\u003e] 293B/293B","id":"01bce57a32a8"}
{"status":"Extracting","progressDetail":{"current":293,"total":293},"progress":"[==================================================\u003e] 293B/293B","id":"01bce57a32a8"}
{"status":"Pull complete","progressDetail":{},"id":"01bce57a32a8"}
{"status":"Digest: sha256:bb56126969beb90ea4912aa6353be3b419b05ca89e1c12621d4457cd5c02ed16"}
{"status":"Status: Downloaded newer image for httpd:latest"}
終了後、イメージの一覧を確認すると最新版のhttpdイメージが無事取り込まれていました。