Support path parameter for repository download via API

This adds support for only downloading parts of a repository using the API.

Changelog: added

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/28827

doc/api/repositories.md

@@ -126,6 +126,7 @@ Supported attributes:
 ## Get file archive
 
 > Support for [including Git LFS blobs](../topics/git/lfs/index.md#lfs-objects-in-project-archives) was [introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/15079) in GitLab 13.5.
+> Support for downloading a subfolder was [introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/28827) in GitLab 14.4.
 
 Get an archive of the repository. This endpoint can be accessed without
 authentication if the repository is publicly accessible.
@@ -147,11 +148,12 @@ Supported attributes:
 |:------------|:---------------|:---------|:----------------------|
 | `id`        | integer/string | yes      | The ID or [URL-encoded path of the project](index.md#namespaced-path-encoding) owned by the authenticated user. |
 | `sha`       | string         | no       | The commit SHA to download. A tag, branch reference, or SHA can be used. This defaults to the tip of the default branch if not specified. |
+| `path`      | string         | no       | The subpath of the repository to download. This defaults to the whole repository (empty string).  |
 
 Example request:
 
 ```shell
-curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.com/api/v4/projects/<project_id>/repository/archive?sha=<commit_sha>"
+curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.com/api/v4/projects/<project_id>/repository/archive?sha=<commit_sha>&path=<path>"
 ```
 
 ## Compare branches, tags or commits

lib/api/repositories.rb

@@ -101,6 +101,7 @@ module API
       params do
         optional :sha, type: String, desc: 'The commit sha of the archive to be downloaded'
         optional :format, type: String, desc: 'The archive format'
+        optional :path, type: String, desc: 'Subfolder of the repository to be downloaded'
       end
       get ':id/repository/archive', requirements: { format: Gitlab::PathRegex.archive_formats_regex } do
         if archive_rate_limit_reached?(current_user, user_project)
@@ -109,7 +110,7 @@ module API
 
         not_acceptable! if Gitlab::HotlinkingDetector.intercept_hotlinking?(request)
 
-        send_git_archive user_project.repository, ref: params[:sha], format: params[:format], append_sha: true
+        send_git_archive user_project.repository, ref: params[:sha], format: params[:format], append_sha: true, path: params[:path]
       rescue StandardError
         not_found!('File')
       end

spec/requests/api/repositories_spec.rb

@@ -305,6 +305,18 @@ RSpec.describe API::Repositories do
         end
       end
 
+      it 'returns only a part of the repository with path set' do
+        path = 'bar'
+        get api("#{route}?path=#{path}", current_user)
+
+        expect(response).to have_gitlab_http_status(:ok)
+
+        type, params = workhorse_send_data
+
+        expect(type).to eq('git-archive')
+        expect(params['ArchivePath']).to match(/#{project.path}\-[^\.]+\-#{path}\.tar.gz/)
+      end
+
       it 'rate limits user when thresholds hit' do
         allow(::Gitlab::ApplicationRateLimiter).to receive(:throttled?).and_return(true)