Fix error fetching non-existing log tail

A task can exist in the database but not have any log stored on disk yet.
This is now returned as `204 No Content` instead of an internal server
error.

The web interface is also adjusted to cope with this.

internal/manager/api_impl/jobs.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"os"
 
 	"github.com/labstack/echo/v4"
 
@@ -197,13 +198,23 @@ func (f *Flamenco) FetchTaskLogTail(e echo.Context, taskID string) error {
 		logger.Error().Err(err).Msg("error fetching task")
 		return sendAPIError(e, http.StatusInternalServerError, "error fetching task: %v", err)
 	}
+	logger = logger.With().Str("job", dbTask.Job.UUID).Logger()
 
 	tail, err := f.logStorage.Tail(dbTask.Job.UUID, taskID)
 	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			logger.Debug().Msg("task tail unavailable, task has no log on disk")
+			return e.NoContent(http.StatusNoContent)
+		}
 		logger.Error().Err(err).Msg("unable to fetch task log tail")
 		return sendAPIError(e, http.StatusInternalServerError, "error fetching task log tail: %v", err)
 	}
 
+	if tail == "" {
+		logger.Debug().Msg("task tail unavailable, on-disk task log is empty")
+		return e.NoContent(http.StatusNoContent)
+	}
+
 	logger.Debug().Msg("fetched task tail")
 	return e.String(http.StatusOK, tail)
 }

internal/manager/api_impl/jobs_test.go

@@ -4,7 +4,9 @@ package api_impl
 
 import (
 	"errors"
+	"fmt"
 	"net/http"
+	"os"
 	"testing"
 	"time"
 
@@ -187,3 +189,46 @@ func TestSetJobStatus_happy(t *testing.T) {
 
 	assertResponseEmpty(t, echoCtx)
 }
+
+func TestFetchTaskLogTail(t *testing.T) {
+	mockCtrl := gomock.NewController(t)
+	defer mockCtrl.Finish()
+
+	mf := newMockedFlamenco(mockCtrl)
+
+	jobID := "18a9b096-d77e-438c-9be2-74397038298b"
+	taskID := "2e020eee-20f8-4e95-8dcf-65f7dfc3ebab"
+	dbJob := persistence.Job{
+		UUID:     jobID,
+		Name:     "test job",
+		Status:   api.JobStatusActive,
+		Settings: persistence.StringInterfaceMap{},
+		Metadata: persistence.StringStringMap{},
+	}
+	dbTask := persistence.Task{
+		UUID: taskID,
+		Job:  &dbJob,
+		Name: "test task",
+	}
+
+	// The task can be found, but has no on-disk task log.
+	// This should not cause any error, but instead be returned as "no content".
+	mf.persistence.EXPECT().FetchTask(gomock.Any(), taskID).Return(&dbTask, nil)
+	mf.logStorage.EXPECT().Tail(jobID, taskID).
+		Return("", fmt.Errorf("wrapped error: %w", os.ErrNotExist))
+
+	echoCtx := mf.prepareMockedRequest(nil)
+	err := mf.flamenco.FetchTaskLogTail(echoCtx, taskID)
+	assert.NoError(t, err)
+	assertResponseEmpty(t, echoCtx)
+
+	// Check that a 204 No Content is also returned when the task log file on disk exists, but is empty.
+	mf.persistence.EXPECT().FetchTask(gomock.Any(), taskID).Return(&dbTask, nil)
+	mf.logStorage.EXPECT().Tail(jobID, taskID).
+		Return("", fmt.Errorf("wrapped error: %w", os.ErrNotExist))
+
+	echoCtx = mf.prepareMockedRequest(nil)
+	err = mf.flamenco.FetchTaskLogTail(echoCtx, taskID)
+	assert.NoError(t, err)
+	assertResponseEmpty(t, echoCtx)
+}

internal/manager/task_logs/task_logs_test.go

@@ -84,9 +84,13 @@ func TestLogTail(t *testing.T) {
 	jobID := "25c5a51c-e0dd-44f7-9f87-74f3d1fbbd8c"
 	taskID := "20ff9d06-53ec-4019-9e2e-1774f05f170a"
 
-	err := s.Write(zerolog.Nop(), jobID, taskID, "Just a single line")
-	assert.NoError(t, err)
 	contents, err := s.Tail(jobID, taskID)
+	assert.ErrorIs(t, err, os.ErrNotExist)
+	assert.Equal(t, "", contents)
+
+	err = s.Write(zerolog.Nop(), jobID, taskID, "Just a single line")
+	assert.NoError(t, err)
+	contents, err = s.Tail(jobID, taskID)
 	assert.NoError(t, err)
 	assert.Equal(t, "Just a single line\n", string(contents))
 

web/app/src/stores/tasklog.js

@@ -50,6 +50,8 @@ export const useTaskLog = defineStore('taskLog', {
      * @param {string} logChunk
      */
     addChunk(logChunk) {
+      if (!logChunk) return;
+
       const lines = logChunk.trimEnd().split('\n');
       if (lines.length == 0)
         return;