PLT-7407: Back-end plugin mechanism (#7177)

* begin backend plugin wip

* flesh out rpcplugin. everything done except for minor supervisor stubs

* done with basic plugin infrastructure

* simplify tests

* remove unused test lines

plugin/manifest_test.go

@@ -0,0 +1,97 @@
+package plugin
+
+import (
+	"encoding/json"
+	"gopkg.in/yaml.v2"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFindManifest(t *testing.T) {
+	for _, tc := range []struct {
+		Filename       string
+		Contents       string
+		ExpectError    bool
+		ExpectNotExist bool
+	}{
+		{"foo", "bar", true, true},
+		{"plugin.json", "bar", true, false},
+		{"plugin.json", `{"id": "foo"}`, false, false},
+		{"plugin.yaml", `id: foo`, false, false},
+		{"plugin.yaml", "bar", true, false},
+		{"plugin.yml", `id: foo`, false, false},
+		{"plugin.yml", "bar", true, false},
+	} {
+		dir, err := ioutil.TempDir("", "mm-plugin-test")
+		require.NoError(t, err)
+		defer os.RemoveAll(dir)
+
+		path := filepath.Join(dir, tc.Filename)
+		f, err := os.Create(path)
+		require.NoError(t, err)
+		_, err = f.WriteString(tc.Contents)
+		f.Close()
+		require.NoError(t, err)
+
+		m, mpath, err := FindManifest(dir)
+		assert.True(t, (err != nil) == tc.ExpectError, tc.Filename)
+		assert.True(t, (err != nil && os.IsNotExist(err)) == tc.ExpectNotExist, tc.Filename)
+		if !tc.ExpectNotExist {
+			assert.Equal(t, path, mpath, tc.Filename)
+		} else {
+			assert.Empty(t, mpath, tc.Filename)
+		}
+		if !tc.ExpectError {
+			require.NotNil(t, m, tc.Filename)
+			assert.NotEmpty(t, m.Id, tc.Filename)
+		}
+	}
+}
+
+func TestManifestUnmarshal(t *testing.T) {
+	expected := Manifest{
+		Id: "theid",
+		Backend: &ManifestBackend{
+			Executable: "theexecutable",
+		},
+	}
+
+	var yamlResult Manifest
+	require.NoError(t, yaml.Unmarshal([]byte(`
+id: theid
+backend:
+    executable: theexecutable
+`), &yamlResult))
+	assert.Equal(t, expected, yamlResult)
+
+	var jsonResult Manifest
+	require.NoError(t, json.Unmarshal([]byte(`{
+	"id": "theid",
+	"backend": {
+		"executable": "theexecutable"
+	}
+	}`), &jsonResult))
+	assert.Equal(t, expected, jsonResult)
+}
+
+func TestFindManifest_FileErrors(t *testing.T) {
+	for _, tc := range []string{"plugin.yaml", "plugin.json"} {
+		dir, err := ioutil.TempDir("", "mm-plugin-test")
+		require.NoError(t, err)
+		defer os.RemoveAll(dir)
+
+		path := filepath.Join(dir, tc)
+		require.NoError(t, os.Mkdir(path, 0700))
+
+		m, mpath, err := FindManifest(dir)
+		assert.Nil(t, m)
+		assert.Equal(t, path, mpath)
+		assert.Error(t, err, tc)
+		assert.False(t, os.IsNotExist(err), tc)
+	}
+}