Resolve "Expand API: Render an arbitrary Markdown document"

8 files changed, 184 insertions, 3 deletions

diff --git a/changelogs/unreleased/19861-expand-api-render-an-arbitrary-markdown-document.yml b/changelogs/unreleased/19861-expand-api-render-an-arbitrary-markdown-document.yml
new file mode 100644
index 00000000000..a97e8a2b5cc
--- /dev/null
+++ b/changelogs/unreleased/19861-expand-api-render-an-arbitrary-markdown-document.yml
@@ -0,0 +1,5 @@
+---
+title: Add API endpoint to render markdown text
+merge_request: 18926
+author: "@blackst0ne"
+type: added
diff --git a/doc/api/README.md b/doc/api/README.md
index e777fc63d2b..194907accc7 100644
--- a/doc/api/README.md
+++ b/doc/api/README.md
@@ -33,6 +33,7 @@ following locations:
 - [Jobs](jobs.md)
 - [Keys](keys.md)
 - [Labels](labels.md)
+- [Markdown](markdown.md)
 - [Merge Requests](merge_requests.md)
 - [Project milestones](milestones.md)
 - [Group milestones](group_milestones.md)
diff --git a/doc/api/markdown.md b/doc/api/markdown.md
new file mode 100644
index 00000000000..f406838e887
--- /dev/null
+++ b/doc/api/markdown.md
@@ -0,0 +1,29 @@
+# Markdown API
+
+> [Introduced][ce-18926] in GitLab 11.0.
+
+Available only in APIv4.
+
+## Render an arbitrary Markdown document
+
+```
+POST /api/v4/markdown
+```
+
+| Attribute | Type    | Required      | Description                                |
+| --------- | ------- | ------------- | ------------------------------------------ |
+| `text`    | string  | yes           | The markdown text to render                |
+| `gfm`     | boolean | no (optional) | Render text using GitLab Flavored Markdown. Default is `false` |
+| `project` | string  | no (optional) | Use `project` as a context when creating references using GitLab Flavored Markdown. [Authentication](README.html#authentication) is required if a project is not public.  |
+
+```bash
+curl --header Content-Type:application/json --data '{"text":"Hello world! :tada:", "gfm":true, "project":"group_example/project_example"}' https://gitlab.example.com/api/v4/markdown
+```
+
+Response example:
+
+```json
+{ "html": "<p dir=\"auto\">Hello world! <gl-emoji title=\"party popper\" data-name=\"tada\" data-unicode-version=\"6.0\">🎉</gl-emoji></p>" }
+```
+
+[ce-18926]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18926
diff --git a/lib/api/api.rb b/lib/api/api.rb
index 2fbeaaffcfe..de20b2b8e67 100644
--- a/lib/api/api.rb
+++ b/lib/api/api.rb
@@ -140,6 +140,7 @@ module API
     mount ::API::Keys
     mount ::API::Labels
     mount ::API::Lint
+    mount ::API::Markdown
     mount ::API::Members
     mount ::API::MergeRequestDiffs
     mount ::API::MergeRequests
diff --git a/lib/api/markdown.rb b/lib/api/markdown.rb
new file mode 100644
index 00000000000..b9ed68aa584
--- /dev/null
+++ b/lib/api/markdown.rb
@@ -0,0 +1,33 @@
+module API
+  class Markdown < Grape::API
+    params do
+      requires :text, type: String, desc: "The markdown text to render"
+      optional :gfm, type: Boolean, desc: "Render text using GitLab Flavored Markdown"
+      optional :project, type: String, desc: "The full path of a project to use as the context when creating references using GitLab Flavored Markdown"
+    end
+    resource :markdown do
+      desc "Render markdown text" do
+        detail "This feature was introduced in GitLab 11.0."
+      end
+      post do
+        # Explicitly set CommonMark as markdown engine to use.
+        # Remove this set when https://gitlab.com/gitlab-org/gitlab-ce/issues/43011 is done.
+        context = { markdown_engine: :common_mark, only_path: false }
+
+        if params[:project]
+          project = Project.find_by_full_path(params[:project])
+
+          not_found!("Project") unless can?(current_user, :read_project, project)
+
+          context[:project] = project
+        else
+          context[:skip_project_check] = true
+        end
+
+        context[:pipeline] = params[:gfm] ? :full : :plain_markdown
+
+        { html: Banzai.render(params[:text], context) }
+      end
+    end
+  end
+end
diff --git a/lib/banzai/filter/reference_filter.rb b/lib/banzai/filter/reference_filter.rb
index b9d5ecf70ec..2f023f4f242 100644
--- a/lib/banzai/filter/reference_filter.rb
+++ b/lib/banzai/filter/reference_filter.rb
@@ -73,7 +73,7 @@ module Banzai
       #
       # Note that while the key might exist, its value could be nil!
       def validate
-        needs :project
+        needs :project unless skip_project_check?
       end
 
       # Iterates over all <a> and text() nodes in a document.
diff --git a/lib/banzai/pipeline/gfm_pipeline.rb b/lib/banzai/pipeline/gfm_pipeline.rb
index 8b2f05fffec..a1f24e8b093 100644
--- a/lib/banzai/pipeline/gfm_pipeline.rb
+++ b/lib/banzai/pipeline/gfm_pipeline.rb
@@ -42,9 +42,9 @@ module Banzai
       end
 
       def self.transform_context(context)
-        context.merge(
-          only_path: true,
+        context[:only_path] = true unless context.key?(:only_path)
 
+        context.merge(
           # EmojiFilter
           asset_host: Gitlab::Application.config.asset_host,
           asset_root: Gitlab.config.gitlab.base_url
diff --git a/spec/requests/api/markdown_spec.rb b/spec/requests/api/markdown_spec.rb
new file mode 100644
index 00000000000..a55796cf343
--- /dev/null
+++ b/spec/requests/api/markdown_spec.rb
@@ -0,0 +1,112 @@
+require "spec_helper"
+
+describe API::Markdown do
+  RSpec::Matchers.define_negated_matcher :exclude, :include
+
+  describe "POST /markdown" do
+    let(:user) {} # No-op. It gets overwritten in the contexts below.
+
+    before do
+      post api("/markdown", user), params
+    end
+
+    shared_examples "rendered markdown text without GFM" do
+      it "renders markdown text" do
+        expect(response).to have_http_status(201)
+        expect(response.headers["Content-Type"]).to eq("application/json")
+        expect(json_response).to be_a(Hash)
+        expect(json_response["html"]).to eq("<p>#{text}</p>")
+      end
+    end
+
+    shared_examples "404 Project Not Found" do
+      it "responses with 404 Not Found" do
+        expect(response).to have_http_status(404)
+        expect(response.headers["Content-Type"]).to eq("application/json")
+        expect(json_response).to be_a(Hash)
+        expect(json_response["message"]).to eq("404 Project Not Found")
+      end
+    end
+
+    context "when arguments are invalid" do
+      context "when text is missing" do
+        let(:params) { {} }
+
+        it "responses with 400 Bad Request" do
+          expect(response).to have_http_status(400)
+          expect(response.headers["Content-Type"]).to eq("application/json")
+          expect(json_response).to be_a(Hash)
+          expect(json_response["error"]).to eq("text is missing")
+        end
+      end
+
+      context "when project is not found" do
+        let(:params) { { text: "Hello world!", gfm: true, project: "Dummy project" } }
+
+        it_behaves_like "404 Project Not Found"
+      end
+    end
+
+    context "when arguments are valid" do
+      set(:project) { create(:project) }
+      set(:issue) { create(:issue, project: project) }
+      let(:text) { ":tada: Hello world! :100: #{issue.to_reference}" }
+
+      context "when not using gfm" do
+        context "without project" do
+          let(:params) { { text: text } }
+
+          it_behaves_like "rendered markdown text without GFM"
+        end
+
+        context "with project" do
+          let(:params) { { text: text, project: project.full_path } }
+
+          context "when not authorized" do
+            it_behaves_like "404 Project Not Found"
+          end
+
+          context "when authorized" do
+            let(:user) { project.owner }
+
+            it_behaves_like "rendered markdown text without GFM"
+          end
+        end
+      end
+
+      context "when using gfm" do
+        context "without project" do
+          let(:params) { { text: text, gfm: true } }
+
+          it "renders markdown text" do
+            expect(response).to have_http_status(201)
+            expect(response.headers["Content-Type"]).to eq("application/json")
+            expect(json_response).to be_a(Hash)
+            expect(json_response["html"]).to include("Hello world!")
+                                        .and include('data-name="tada"')
+                                        .and include('data-name="100"')
+                                        .and include("#1")
+                                        .and exclude("<a href=\"#{IssuesHelper.url_for_issue(issue.iid, project)}\"")
+                                        .and exclude("#1</a>")
+          end
+        end
+
+        context "with project" do
+          let(:params) { { text: text, gfm: true, project: project.full_path } }
+          let(:user) { project.owner }
+
+          it "renders markdown text" do
+            expect(response).to have_http_status(201)
+            expect(response.headers["Content-Type"]).to eq("application/json")
+            expect(json_response).to be_a(Hash)
+            expect(json_response["html"]).to include("Hello world!")
+                                        .and include('data-name="tada"')
+                                        .and include('data-name="100"')
+                                        .and include("<a href=\"#{IssuesHelper.url_for_issue(issue.iid, project)}\"")
+                                        .and include("#1</a>")
+          end
+        end
+      end
+    end
+  end
+end