Implement API to get single Project Remote Mirror

This change implements the `GET` API to retrieve a single projects
remote mirror.

Changelog: added
MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/82770

doc/api/remote_mirrors.md

@@ -51,6 +51,43 @@ NOTE:
 For security reasons, the `url` attribute is always scrubbed of username
 and password information.
 
+## Get a single project's remote mirror
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/82770) in GitLab 14.10.
+
+Returns a remote mirror and its statuses:
+
+```plaintext
+GET /projects/:id/remote_mirrors/:mirror_id
+```
+
+Example request:
+
+```shell
+curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/projects/42/remote_mirrors/101486"
+```
+
+Example response:
+
+```json
+{
+  "enabled": true,
+  "id": 101486,
+  "last_error": null,
+  "last_successful_update_at": "2020-01-06T17:32:02.823Z",
+  "last_update_at": "2020-01-06T17:32:02.823Z",
+  "last_update_started_at": "2020-01-06T17:31:55.864Z",
+  "only_protected_branches": true,
+  "keep_divergent_refs": true,
+  "update_status": "finished",
+  "url": "https://*****:*****@gitlab.com/gitlab-org/security/gitlab.git"
+}
+```
+
+NOTE:
+For security reasons, the `url` attribute is always scrubbed of username
+and password information.
+
 ## Create a pull mirror
 
 Learn how to [configure a pull mirror](projects.md#configure-pull-mirroring-for-a-project) using the Projects API.

lib/api/remote_mirrors.rb

@@ -25,6 +25,18 @@ module API
           with: Entities::RemoteMirror
       end
 
+      desc 'Get a single remote mirror' do
+        success Entities::RemoteMirror
+      end
+      params do
+        requires :mirror_id, type: String, desc: 'The ID of a remote mirror'
+      end
+      get ':id/remote_mirrors/:mirror_id' do
+        mirror = user_project.remote_mirrors.find(params[:mirror_id])
+
+        present mirror, with: Entities::RemoteMirror
+      end
+
       desc 'Create remote mirror for a project' do
         success Entities::RemoteMirror
       end

spec/requests/api/remote_mirrors_spec.rb

@@ -26,6 +26,26 @@ RSpec.describe API::RemoteMirrors do
     end
   end
 
+  describe 'GET /projects/:id/remote_mirrors/:mirror_id' do
+    let(:route) { "/projects/#{project.id}/remote_mirrors/#{mirror.id}" }
+    let(:mirror) { project.remote_mirrors.first }
+
+    it 'requires `admin_remote_mirror` permission' do
+      get api(route, developer)
+
+      expect(response).to have_gitlab_http_status(:unauthorized)
+    end
+
+    it 'returns at remote mirror' do
+      project.add_maintainer(user)
+
+      get api(route, user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(response).to match_response_schema('remote_mirror')
+    end
+  end
+
   describe 'POST /projects/:id/remote_mirrors' do
     let(:route) { "/projects/#{project.id}/remote_mirrors" }