feat(templates): allow managing git based templates [EE-2600] (#7855)

Co-authored-by: itsconquest <william.conquest@portainer.io>
Co-authored-by: oscarzhou <oscar.zhou@portainer.io>
Co-authored-by: Chaim Lev-Ari <chiptus@users.noreply.github.com>

api/http/handler/gitops/git_repo_file_preview.go

@@ -0,0 +1,89 @@
+package gitops
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+
+	"github.com/asaskevich/govalidator"
+	httperror "github.com/portainer/libhttp/error"
+	"github.com/portainer/libhttp/request"
+	"github.com/portainer/libhttp/response"
+	gittypes "github.com/portainer/portainer/api/git/types"
+)
+
+type fileResponse struct {
+	FileContent string
+}
+
+type repositoryFilePreviewPayload struct {
+	Repository string `json:"repository" example:"https://github.com/openfaas/faas" validate:"required"`
+	Reference  string `json:"reference" example:"refs/heads/master"`
+	Username   string `json:"username" example:"myGitUsername"`
+	Password   string `json:"password" example:"myGitPassword"`
+	// Path to file whose content will be read
+	TargetFile string `json:"targetFile" example:"docker-compose.yml"`
+	// TLSSkipVerify skips SSL verification when cloning the Git repository
+	TLSSkipVerify bool `example:"false"`
+}
+
+func (payload *repositoryFilePreviewPayload) Validate(r *http.Request) error {
+	if govalidator.IsNull(payload.Repository) || !govalidator.IsURL(payload.Repository) {
+		return errors.New("Invalid repository URL. Must correspond to a valid URL format")
+	}
+
+	if govalidator.IsNull(payload.Reference) {
+		payload.Reference = "refs/heads/main"
+	}
+
+	if govalidator.IsNull(payload.TargetFile) {
+		return errors.New("Invalid target filename.")
+	}
+
+	return nil
+}
+
+// @id GitOperationRepoFilePreview
+// @summary preview the content of target file in the git repository
+// @description Retrieve the compose file content based on git repository configuration
+// @description **Access policy**: authenticated
+// @tags gitops
+// @security ApiKeyAuth
+// @security jwt
+// @produce json
+// @param body body repositoryFilePreviewPayload true "Template details"
+// @success 200 {object} fileResponse "Success"
+// @failure 400 "Invalid request"
+// @failure 500 "Server error"
+// @router /gitops/repo/file/preview [post]
+func (handler *Handler) gitOperationRepoFilePreview(w http.ResponseWriter, r *http.Request) *httperror.HandlerError {
+	var payload repositoryFilePreviewPayload
+	err := request.DecodeAndValidateJSONPayload(r, &payload)
+	if err != nil {
+		return httperror.BadRequest("Invalid request payload", err)
+	}
+
+	projectPath, err := handler.fileService.GetTemporaryPath()
+	if err != nil {
+		return httperror.InternalServerError("Unable to create temporary folder", err)
+	}
+
+	err = handler.gitService.CloneRepository(projectPath, payload.Repository, payload.Reference, payload.Username, payload.Password, payload.TLSSkipVerify)
+	if err != nil {
+		if err == gittypes.ErrAuthenticationFailure {
+			return httperror.BadRequest("Invalid git credential", err)
+		}
+
+		newErr := fmt.Errorf("unable to clone git repository: %w", err)
+		return httperror.InternalServerError(newErr.Error(), newErr)
+	}
+
+	defer handler.fileService.RemoveDirectory(projectPath)
+
+	fileContent, err := handler.fileService.GetFileContent(projectPath, payload.TargetFile)
+	if err != nil {
+		return httperror.InternalServerError("Unable to retrieve custom template file from disk", err)
+	}
+
+	return response.JSON(w, &fileResponse{FileContent: string(fileContent)})
+}