Read docker containers logs in JSON format - Golang - docker

Question

I have a requirement to fetch docker container's logs, I'm using below code to fetch docker logs,
ctx := context.Background()
cli, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())
if err != nil {
panic(err)
}
options := types.ContainerLogsOptions{
ShowStdout: true,
ShowStderr: true,
Since: "",
Until: "",
Timestamps: false,
Follow: true,
Tail: "",
Details: true,
}
out, err := cli.ContainerLogs(ctx, "bcd693465a62", options)
if err != nil {
panic(err)
}
buf := new(strings.Builder)
_, err = io.Copy(buf, out)
if err != nil {
fmt.Println(err)
}
fmt.Printf("%s", buf)
My problem is I'm getting docker logs in two different format, for some containers it's just plain text
exec /entrypoint.sh: no such file or directory
but in containerID-json.log file it's showing in below format
{"log":"exec /entrypoint.sh: no such file or directory\n","stream":"stderr","time":"2022-09-06T12:23:57.741316145Z"}
and for some containers it's showing in dynamic format/schema like
time="2022-09-05T02:13:44Z" level=debug msg="cleanup aborting ingest" ref="buildkit/1/layer-sha256:2774afd0c4d3ded992c58f3b5e5939d091bd26f40e507c6dc21dcbd8b7ff486f"
time="2022-09-05T02:13:44Z" level=debug msg="content garbage collected" d=2.971574ms
How I can collect all docker container's logs in same schema/format so it can be stored in below JSON format?
{
"containerID": "bcd693465a62",
"logs": [
{"log":"exec /entrypoint.sh: no such file or directory\n","stream":"stderr","time":"2022-09-06T12:23:57.741316145Z"},
{"log":"cleanup aborting ingest","stream":"stdout","time":"2022-09-05T02:13:44Z"}
]
}
Any help is appreciated

Answer 1

I wrote below code with the help of code reference by #BrianWagner to fulfill my requirements (It works as expected), please suggest if it can be done better way, or if any improvements.
package main
import (
"context"
"encoding/binary"
"fmt"
"io"
"log"
"strings"
"github.com/docker/docker/api/types"
"github.com/docker/docker/client"
)
type DockerContainerLog struct {
ContainerID string `json:"containerID"`
DockerLogs []DockerLog `json:"dockerLogs"`
}
type DockerLog struct {
Time string `json:"time"`
Stream string `json:"stream"`
Log string `json:"log"`
}
func main() {
logs := getContainerLogs("cd3d8362ba45")
fmt.Print(logs)
}
func getContainerLogs(cid string) DockerContainerLog {
cli, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())
if err != nil {
panic(err)
}
options := types.ContainerLogsOptions{
ShowStdout: true,
ShowStderr: true,
Since: "",
Until: "",
Timestamps: true,
Follow: true,
Tail: "",
Details: false,
}
reader, err := cli.ContainerLogs(context.Background(), cid, options)
if err != nil {
log.Fatal(err)
}
defer reader.Close()
dockerLogs := DockerContainerLog{ContainerID: cid}
hdr := make([]byte, 8)
for {
var docLog DockerLog
_, err := reader.Read(hdr)
if err != nil {
if err == io.EOF {
return dockerLogs
}
log.Fatal(err)
}
count := binary.BigEndian.Uint32(hdr[4:])
dat := make([]byte, count)
_, err = reader.Read(dat)
if err != nil && err != io.EOF {
log.Fatal(err)
}
time, log, found := strings.Cut(string(dat), " ")
if found {
docLog.Time = time
docLog.Log = log
switch hdr[0] {
case 1:
docLog.Stream = "Stdout"
default:
docLog.Stream = "Stderr"
}
dockerLogs.DockerLogs = append(dockerLogs.DockerLogs, docLog)
}
}
}