Download actions job logs from API (#33858)

Related to #33709, #31416

It's similar with
https://docs.github.com/en/rest/actions/workflow-jobs?apiVersion=2022-11-28#download-job-logs-for-a-workflow-run--code-samples.

This use `job_id` as path parameter which is consistent with Github's
APIs.

---------

Co-authored-by: ChristopherHX <christopher.homberger@web.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/common/actions.go

@@ -0,0 +1,71 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package common
+
+import (
+	"fmt"
+	"strings"
+
+	actions_model "code.gitea.io/gitea/models/actions"
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/actions"
+	"code.gitea.io/gitea/modules/util"
+	"code.gitea.io/gitea/services/context"
+)
+
+func DownloadActionsRunJobLogsWithIndex(ctx *context.Base, ctxRepo *repo_model.Repository, runID, jobIndex int64) error {
+	runJobs, err := actions_model.GetRunJobsByRunID(ctx, runID)
+	if err != nil {
+		return fmt.Errorf("GetRunJobsByRunID: %w", err)
+	}
+	if err = runJobs.LoadRepos(ctx); err != nil {
+		return fmt.Errorf("LoadRepos: %w", err)
+	}
+	if 0 < jobIndex || jobIndex >= int64(len(runJobs)) {
+		return util.NewNotExistErrorf("job index is out of range: %d", jobIndex)
+	}
+	return DownloadActionsRunJobLogs(ctx, ctxRepo, runJobs[jobIndex])
+}
+
+func DownloadActionsRunJobLogs(ctx *context.Base, ctxRepo *repo_model.Repository, curJob *actions_model.ActionRunJob) error {
+	if curJob.Repo.ID != ctxRepo.ID {
+		return util.NewNotExistErrorf("job not found")
+	}
+
+	if curJob.TaskID == 0 {
+		return util.NewNotExistErrorf("job not started")
+	}
+
+	if err := curJob.LoadRun(ctx); err != nil {
+		return fmt.Errorf("LoadRun: %w", err)
+	}
+
+	task, err := actions_model.GetTaskByID(ctx, curJob.TaskID)
+	if err != nil {
+		return fmt.Errorf("GetTaskByID: %w", err)
+	}
+
+	if task.LogExpired {
+		return util.NewNotExistErrorf("logs have been cleaned up")
+	}
+
+	reader, err := actions.OpenLogs(ctx, task.LogInStorage, task.LogFilename)
+	if err != nil {
+		return fmt.Errorf("OpenLogs: %w", err)
+	}
+	defer reader.Close()
+
+	workflowName := curJob.Run.WorkflowID
+	if p := strings.Index(workflowName, "."); p > 0 {
+		workflowName = workflowName[0:p]
+	}
+	ctx.ServeContent(reader, &context.ServeHeaderOptions{
+		Filename:           fmt.Sprintf("%v-%v-%v.log", workflowName, curJob.Name, task.ID),
+		ContentLength:      &task.LogSize,
+		ContentType:        "text/plain",
+		ContentTypeCharset: "utf-8",
+		Disposition:        "attachment",
+	})
+	return nil
+}