Merge branch '23584-triggering-builds-from-webhooks' into 'master'

Add ref parameter for triggering builds with gitlab webhook from other project.

Currently GitLab can trigger builds from external tools like curl.
But there is no way to trigger builds with webhook from another GitLab project.
Executing webhook like `/projects/:id/trigger/builds?token=TOKEN&ref=master` results in such message from server:
```
400 No builds created
```

Problem is the ref from request body takes precedence of the ref from query string.
System tries to trigger build for nonexistent branch instead of `master`.
This is the feature of the Grape framework used to build GitLab api.

This MR adds optional `ref` parameter into the api url:
```
/projects/:id/ref/:ref/trigger/builds?token=TOKEN
```

This will lead that the ref in the url will have precedence of the ref inside request body.

This solution provides compatibility with current API urls.

Closes #23584

See merge request !7022

6 files changed, 61 insertions, 4 deletions

diff --git a/app/helpers/triggers_helper.rb b/app/helpers/triggers_helper.rb
index 8cad994d10f..c41181bab3d 100644
--- a/app/helpers/triggers_helper.rb
+++ b/app/helpers/triggers_helper.rb
@@ -1,5 +1,9 @@
 module TriggersHelper
-  def builds_trigger_url(project_id)
-    "#{Settings.gitlab.url}/api/v3/projects/#{project_id}/trigger/builds"
+  def builds_trigger_url(project_id, ref: nil)
+    if ref.nil?
+      "#{Settings.gitlab.url}/api/v3/projects/#{project_id}/trigger/builds"
+    else
+      "#{Settings.gitlab.url}/api/v3/projects/#{project_id}/ref/#{ref}/trigger/builds"
+    end
   end
 end
diff --git a/app/views/projects/triggers/index.html.haml b/app/views/projects/triggers/index.html.haml
index f6e0b0a7c8a..6e5dd1b196d 100644
--- a/app/views/projects/triggers/index.html.haml
+++ b/app/views/projects/triggers/index.html.haml
@@ -76,6 +76,16 @@
               script:
                 - "curl -X POST -F token=TOKEN -F ref=REF_NAME #{builds_trigger_url(@project.id)}"
         %h5.prepend-top-default
+          Use webhook
+
+        %p.light
+          Add the following webhook to another project for Push and Tag push events.
+          The project will be rebuilt at the corresponding event.
+
+        %pre
+          :plain
+             #{builds_trigger_url(@project.id, ref: 'REF_NAME')}?token=TOKEN
+        %h5.prepend-top-default
           Pass build variables
 
         %p.light
@@ -83,10 +93,18 @@
           %code variables[VARIABLE]=VALUE
           to an API request. Variable values can be used to distinguish between triggered builds and normal builds.
 
-        %pre.append-bottom-0
+          With cURL:
+
+        %pre
           :plain
             curl -X POST \
                  -F token=TOKEN \
                  -F "ref=REF_NAME" \
                  -F "variables[RUN_NIGHTLY_BUILD]=true" \
                  #{builds_trigger_url(@project.id)}
+        %p.light
+          With webhook:
+
+        %pre.append-bottom-0
+          :plain
+             #{builds_trigger_url(@project.id, ref: 'REF_NAME')}?token=TOKEN&variables[RUN_NIGHTLY_BUILD]=true
diff --git a/changelogs/unreleased/23584-triggering-builds-from-webhooks.yml b/changelogs/unreleased/23584-triggering-builds-from-webhooks.yml
new file mode 100644
index 00000000000..59e0d851366
--- /dev/null
+++ b/changelogs/unreleased/23584-triggering-builds-from-webhooks.yml
@@ -0,0 +1,4 @@
+---
+title: Make it possible to trigger builds from webhooks
+merge_request: 7022
+author: Dmitry Poray
diff --git a/doc/ci/triggers/README.md b/doc/ci/triggers/README.md
index 84048f1d25f..cf7c55f75f2 100644
--- a/doc/ci/triggers/README.md
+++ b/doc/ci/triggers/README.md
@@ -58,6 +58,22 @@ below.
 See the [Examples](#examples) section for more details on how to actually
 trigger a rebuild.
 
+## Trigger a build from webhook
+
+> Introduced in GitLab 8.14.
+
+To trigger a build from webhook of another project you need to add the following
+webhook url for Push and Tag push events:
+
+```
+https://gitlab.example.com/api/v3/projects/:id/ref/:ref/trigger/builds?token=TOKEN
+```
+
+> **Note**:
+- `ref` should be passed as part of url in order to take precedence over `ref`
+  from webhook body that designates the branchref that fired the trigger in the source repository.
+- `ref` should be url encoded if contains slashes.
+
 ## Pass build variables to a trigger
 
 You can pass any number of arbitrary variables in the trigger API call and they
@@ -169,6 +185,14 @@ curl --request POST \
   https://gitlab.example.com/api/v3/projects/9/trigger/builds
 ```
 
+### Using webhook to trigger builds
+
+You can add the following webhook to another project in order to trigger a build:
+
+```
+https://gitlab.example.com/api/v3/projects/9/ref/master/trigger/builds?token=TOKEN&variables[UPLOAD_TO_S3]=true
+```
+
 ### Using cron to trigger nightly builds
 
 Whether you craft a script or just run cURL directly, you can trigger builds
diff --git a/lib/api/triggers.rb b/lib/api/triggers.rb
index 9a4f1cd342f..569598fbd2c 100644
--- a/lib/api/triggers.rb
+++ b/lib/api/triggers.rb
@@ -12,7 +12,7 @@ module API
         requires :token, type: String, desc: 'The unique token of trigger'
         optional :variables, type: Hash, desc: 'The list of variables to be injected into build'
       end
-      post ":id/trigger/builds" do
+      post ":id/(ref/:ref/)trigger/builds" do
         project = Project.find_with_namespace(params[:id]) || Project.find_by(id: params[:id])
         trigger = Ci::Trigger.find_by_token(params[:token].to_s)
         not_found! unless project && trigger
diff --git a/spec/requests/api/triggers_spec.rb b/spec/requests/api/triggers_spec.rb
index 8ba2eccf66c..c890a51ae42 100644
--- a/spec/requests/api/triggers_spec.rb
+++ b/spec/requests/api/triggers_spec.rb
@@ -54,6 +54,13 @@ describe API::API do
         expect(pipeline.builds.size).to eq(5)
       end
 
+      it 'creates builds on webhook from other gitlab repository and branch' do
+        expect do
+          post api("/projects/#{project.id}/ref/master/trigger/builds?token=#{trigger_token}"), { ref: 'refs/heads/other-branch' }
+        end.to change(project.builds, :count).by(5)
+        expect(response).to have_http_status(201)
+      end
+
       it 'returns bad request with no builds created if there\'s no commit for that ref' do
         post api("/projects/#{project.id}/trigger/builds"), options.merge(ref: 'other-branch')
         expect(response).to have_http_status(400)