Add a field to the config file for plugin use.

This is a bit manual (as the unit test attests) so we may find we want to add
some helpers/accessors, but this is enough to let plugins use it and to
preserve the information through round-trips.

Signed-off-by: Ian Campbell <ijc@docker.com>

cli/config/configfile/file.go

@@ -49,6 +49,7 @@ type ConfigFile struct {
 	Kubernetes           *KubernetesConfig           `json:"kubernetes,omitempty"`
 	CurrentContext       string                      `json:"currentContext,omitempty"`
 	CLIPluginsExtraDirs  []string                    `json:"cliPluginsExtraDirs,omitempty"`
+	Plugins              map[string]json.RawMessage  `json:"plugins,omitempty"`
 }
 
 // ProxyConfig contains proxy configuration settings
@@ -70,6 +71,7 @@ func New(fn string) *ConfigFile {
 		AuthConfigs: make(map[string]types.AuthConfig),
 		HTTPHeaders: make(map[string]string),
 		Filename:    fn,
+		Plugins:     make(map[string]json.RawMessage),
 	}
 }
 

cli/config/configfile/file_test.go

@@ -1,6 +1,8 @@
 package configfile
 
 import (
+	"bytes"
+	"encoding/json"
 	"io/ioutil"
 	"os"
 	"testing"
@@ -9,6 +11,7 @@ import (
 	"github.com/docker/cli/cli/config/types"
 	"gotest.tools/assert"
 	is "gotest.tools/assert/cmp"
+	"gotest.tools/golden"
 )
 
 func TestEncodeAuth(t *testing.T) {
@@ -429,3 +432,64 @@ func TestSave(t *testing.T) {
 	assert.NilError(t, err)
 	assert.Check(t, is.Equal(string(cfg), "{\n	\"auths\": {}\n}"))
 }
+
+func TestPluginConfig(t *testing.T) {
+	configFile := New("test-plugin")
+	defer os.Remove("test-plugin")
+
+	type PluginConfig1 struct {
+		Data1 string `json:"data1"`
+		Data2 int    `json:"data2"`
+	}
+	type PluginConfig2 struct {
+		Data3 string `json:"data3"`
+	}
+	p1 := PluginConfig1{
+		Data1: "some string",
+		Data2: 42,
+	}
+	p2 := PluginConfig2{
+		Data3: "some other string",
+	}
+
+	plugin1, err := json.MarshalIndent(p1, "", "\t")
+	assert.NilError(t, err)
+	configFile.Plugins["plugin1"] = plugin1
+
+	plugin2, err := json.MarshalIndent(p2, "", "\t")
+	assert.NilError(t, err)
+	configFile.Plugins["plugin2"] = plugin2
+
+	// Save a config file with some plugin config
+	err = configFile.Save()
+	assert.NilError(t, err)
+
+	// Read it back and check it has the expected content
+	cfg, err := ioutil.ReadFile("test-plugin")
+	assert.NilError(t, err)
+	golden.Assert(t, string(cfg), "plugin-config.golden")
+
+	// Load it, resave and check again that the content is
+	// preserved through a load/save cycle.
+	configFile2 := New("test-plugin2")
+	defer os.Remove("test-plugin2")
+	assert.NilError(t, configFile2.LoadFromReader(bytes.NewReader(cfg)))
+	err = configFile2.Save()
+	assert.NilError(t, err)
+	cfg, err = ioutil.ReadFile("test-plugin2")
+	assert.NilError(t, err)
+	golden.Assert(t, string(cfg), "plugin-config.golden")
+
+	// Check that the contents was retained properly
+	var p1bis PluginConfig1
+	assert.Assert(t, is.Contains(configFile2.Plugins, "plugin1"))
+	err = json.Unmarshal(configFile2.Plugins["plugin1"], &p1bis)
+	assert.NilError(t, err)
+	assert.DeepEqual(t, p1, p1bis)
+
+	var p2bis PluginConfig2
+	assert.Assert(t, is.Contains(configFile2.Plugins, "plugin2"))
+	err = json.Unmarshal(configFile2.Plugins["plugin2"], &p2bis)
+	assert.NilError(t, err)
+	assert.DeepEqual(t, p2, p2bis)
+}

cli/config/configfile/testdata/plugin-config.golden

@@ -0,0 +1,12 @@
+{
+	"auths": {},
+	"plugins": {
+		"plugin1": {
+			"data1": "some string",
+			"data2": 42
+		},
+		"plugin2": {
+			"data3": "some other string"
+		}
+	}
+}

docs/extend/cli_plugins.md

@@ -75,6 +75,18 @@ A plugin is required to support all of the global options of the
 top-level CLI, i.e. those listed by `man docker 1` with the exception
 of `-v`.
 
+## Configuration
+
+Plugins are expected to make use of existing global configuration
+where it makes sense and likewise to consider extending the global
+configuration (by patching `docker/cli` to add new fields) where that
+is sensible.
+
+Where plugins unavoidably require specific configuration the
+`.plugins.«name»` key in the global `config.json` is reserved for
+their use. However the preference should be for shared/global
+configuration whenever that makes sense.
+
 ## Connecting to the docker engine
 
 For consistency plugins should prefer to dial the engine by using the