Add GetFile API in app and plugin (#9820)

app/file.go

@@ -640,6 +640,20 @@ func (a *App) GetFileInfo(fileId string) (*model.FileInfo, *model.AppError) {
 	return result.Data.(*model.FileInfo), nil
 }
 
+func (a *App) GetFile(fileId string) ([]byte, *model.AppError) {
+	info, err := a.GetFileInfo(fileId)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := a.ReadFile(info.Path)
+	if err != nil {
+		return nil, err
+	}
+
+	return data, nil
+}
+
 func (a *App) CopyFileInfos(userId string, fileIds []string) ([]string, *model.AppError) {
 	var newFileIds []string
 

app/plugin_api.go

@@ -484,6 +484,10 @@ func (api *PluginAPI) ReadFile(path string) ([]byte, *model.AppError) {
 	return api.app.ReadFile(path)
 }
 
+func (api *PluginAPI) GetFile(fileId string) ([]byte, *model.AppError) {
+	return api.app.GetFile(fileId)
+}
+
 func (api *PluginAPI) UploadFile(data []byte, channelId string, filename string) (*model.FileInfo, *model.AppError) {
 	return api.app.UploadFile(data, channelId, filename)
 }

app/plugin_api_test.go

@@ -15,6 +15,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/plugin"
@@ -173,6 +174,31 @@ func TestPluginAPIUpdateUserStatus(t *testing.T) {
 	assert.Nil(t, status)
 }
 
+func TestPluginAPIGetFile(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+	api := th.SetupPluginAPI()
+
+	// check a valid file first
+	uploadTime := time.Date(2007, 2, 4, 1, 2, 3, 4, time.Local)
+	filename := "testGetFile"
+	fileData := []byte("Hello World")
+	info, err := th.App.DoUploadFile(uploadTime, th.BasicTeam.Id, th.BasicChannel.Id, th.BasicUser.Id, filename, fileData)
+	require.Nil(t, err)
+	defer func() {
+		<-th.App.Srv.Store.FileInfo().PermanentDelete(info.Id)
+		th.App.RemoveFile(info.Path)
+	}()
+
+	data, err1 := api.GetFile(info.Id)
+	require.Nil(t, err1)
+	assert.Equal(t, data, fileData)
+
+	// then checking invalid file
+	data, err = api.GetFile("../fake/testingApi")
+	require.NotNil(t, err)
+	require.Nil(t, data)
+}
 func TestPluginAPISavePluginConfig(t *testing.T) {
 	th := Setup().InitBasic()
 	defer th.TearDown()