Use read method to get request body in Conan

The method 'string' does not exist for Unicorn::TeeInput
causing Conan upload_urls endpoints to fail when reading
request.body.string.

changelogs/unreleased/246741-conan-unicorn-bug.yml

+---
+title: Use 'read' method to get request body in Conan to fix uploads when using Unicorn
+merge_request: 41801
+author:
+type: fixed

lib/api/helpers/packages/conan/api_helpers.rb

@@ -140,7 +140,7 @@ module API
           end
 
           def file_names
-            json_payload = Gitlab::Json.parse(request.body.string)
+            json_payload = Gitlab::Json.parse(request.body.read)
 
             bad_request!(nil) unless json_payload.is_a?(Hash)
 

spec/requests/api/conan_packages_spec.rb

@@ -383,6 +383,16 @@ RSpec.describe API::ConanPackages do
       end
     end
 
+    shared_examples 'successful response when using Unicorn' do
+      context 'on Unicorn', :unicorn do
+        it 'returns successfully' do
+          subject
+
+          expect(response).to have_gitlab_http_status(:ok)
+        end
+      end
+    end
+
     describe 'GET /api/v4/packages/conan/v1/conans/:package_name/package_version/:package_username/:package_channel' do
       let(:recipe_path) { package.conan_recipe_path }
 
@@ -478,6 +488,7 @@ RSpec.describe API::ConanPackages do
 
       it_behaves_like 'rejects invalid recipe'
       it_behaves_like 'rejects invalid upload_url params'
+      it_behaves_like 'successful response when using Unicorn'
 
       it 'returns a set of upload urls for the files requested' do
         subject
@@ -541,6 +552,7 @@ RSpec.describe API::ConanPackages do
 
       it_behaves_like 'rejects invalid recipe'
       it_behaves_like 'rejects invalid upload_url params'
+      it_behaves_like 'successful response when using Unicorn'
 
       it 'returns a set of upload urls for the files requested' do
         expected_response = {