Follow up work on docker_log input (#6008)

internal/docker/docker.go

@@ -0,0 +1,36 @@
+package docker
+
+import "strings"
+
+// Adapts some of the logic from the actual Docker library's image parsing
+// routines:
+// https://github.com/docker/distribution/blob/release/2.7/reference/normalize.go
+func ParseImage(image string) (string, string) {
+	domain := ""
+	remainder := ""
+
+	i := strings.IndexRune(image, '/')
+
+	if i == -1 || (!strings.ContainsAny(image[:i], ".:") && image[:i] != "localhost") {
+		remainder = image
+	} else {
+		domain, remainder = image[:i], image[i+1:]
+	}
+
+	imageName := ""
+	imageVersion := "unknown"
+
+	i = strings.LastIndex(remainder, ":")
+	if i > -1 {
+		imageVersion = remainder[i+1:]
+		imageName = remainder[:i]
+	} else {
+		imageName = remainder
+	}
+
+	if domain != "" {
+		imageName = domain + "/" + imageName
+	}
+
+	return imageName, imageVersion
+}

internal/docker/docker_test.go

@@ -0,0 +1,59 @@
+package docker_test
+
+import (
+	"testing"
+
+	"github.com/influxdata/telegraf/internal/docker"
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseImage(t *testing.T) {
+	tests := []struct {
+		image         string
+		parsedName    string
+		parsedVersion string
+	}{
+		{
+			image:         "postgres",
+			parsedName:    "postgres",
+			parsedVersion: "unknown",
+		},
+		{
+			image:         "postgres:latest",
+			parsedName:    "postgres",
+			parsedVersion: "latest",
+		},
+		{
+			image:         "coreos/etcd",
+			parsedName:    "coreos/etcd",
+			parsedVersion: "unknown",
+		},
+		{
+			image:         "coreos/etcd:latest",
+			parsedName:    "coreos/etcd",
+			parsedVersion: "latest",
+		},
+		{
+			image:         "quay.io/postgres",
+			parsedName:    "quay.io/postgres",
+			parsedVersion: "unknown",
+		},
+		{
+			image:         "quay.io:4443/coreos/etcd",
+			parsedName:    "quay.io:4443/coreos/etcd",
+			parsedVersion: "unknown",
+		},
+		{
+			image:         "quay.io:4443/coreos/etcd:latest",
+			parsedName:    "quay.io:4443/coreos/etcd",
+			parsedVersion: "latest",
+		},
+	}
+	for _, tt := range tests {
+		t.Run("parse name "+tt.image, func(t *testing.T) {
+			imageName, imageVersion := docker.ParseImage(tt.image)
+			require.Equal(t, tt.parsedName, imageName)
+			require.Equal(t, tt.parsedVersion, imageVersion)
+		})
+	}
+}