Serve pull request .diff files (#3293)

* Serve pull request .diff files

Closes #3259

* Add test for pull request redirection and .diff access

* Typo

* There's no need to test for pr.BaseRepo being nil after calling GetBaseRepo

routers/repo/pull.go

@@ -1,4 +1,6 @@
-// Copyright 2014 The Gogs Authors. All rights reserved.
+// Copyright 2018 The Gitea Authors.
+// Copyright 2014 The Gogs Authors.
+// All rights reserved.
 // Use of this source code is governed by a MIT-style
 // license that can be found in the LICENSE file.
 
@@ -991,3 +993,37 @@ func CleanUpPullRequest(ctx *context.Context) {
 
 	ctx.Flash.Success(ctx.Tr("repo.branch.deletion_success", fullBranchName))
 }
+
+// DownloadPullDiff render a pull's raw diff
+func DownloadPullDiff(ctx *context.Context) {
+	issue, err := models.GetIssueByIndex(ctx.Repo.Repository.ID, ctx.ParamsInt64(":index"))
+	if err != nil {
+		if models.IsErrIssueNotExist(err) {
+			ctx.Handle(404, "GetIssueByIndex", err)
+		} else {
+			ctx.Handle(500, "GetIssueByIndex", err)
+		}
+		return
+	}
+
+	// Redirect elsewhere if it's not a pull request
+	if !issue.IsPull {
+		ctx.Handle(404, "DownloadPullDiff",
+			fmt.Errorf("Issue is not a pull request"))
+		return
+	}
+
+	pr := issue.PullRequest
+
+	if err = pr.GetBaseRepo(); err != nil {
+		ctx.Handle(500, "GetBaseRepo", err)
+		return
+	}
+	patch, err := pr.BaseRepo.PatchPath(pr.Index)
+	if err != nil {
+		ctx.Handle(500, "PatchPath", err)
+		return
+	}
+
+	ctx.ServeFileContent(patch)
+}

routers/routes/routes.go

@@ -624,6 +624,7 @@ func RegisterRoutes(m *macaron.Macaron) {
 		}, repo.MustBeNotBare, context.RepoRef(), context.CheckUnit(models.UnitTypeCode))
 
 		m.Group("/pulls/:index", func() {
+			m.Get(".diff", repo.DownloadPullDiff)
 			m.Get("/commits", context.RepoRef(), repo.ViewPullCommits)
 			m.Get("/files", context.RepoRef(), repo.SetEditorconfigIfExists, repo.SetDiffViewStyle, repo.ViewPullFiles)
 			m.Post("/merge", reqRepoWriter, repo.MergePullRequest)