1 files changed, 76 insertions, 0 deletions
diff --git a/app/services/import/validate_remote_git_endpoint_service.rb b/app/services/import/validate_remote_git_endpoint_service.rb
new file mode 100644
index 00000000000..afccb5373a9
--- /dev/null
+++ b/app/services/import/validate_remote_git_endpoint_service.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module Import
+  class ValidateRemoteGitEndpointService
+    # Validates if the remote endpoint is a valid GIT repository
+    # Only smart protocol is supported
+    # Validation rules are taken from https://git-scm.com/docs/http-protocol#_smart_clients
+
+    GIT_SERVICE_NAME = "git-upload-pack"
+    GIT_EXPECTED_FIRST_PACKET_LINE = "# service=#{GIT_SERVICE_NAME}"
+    GIT_BODY_MESSAGE_REGEXP = /^[0-9a-f]{4}#{GIT_EXPECTED_FIRST_PACKET_LINE}/.freeze
+    # https://github.com/git/git/blob/master/Documentation/technical/protocol-common.txt#L56-L59
+    GIT_PROTOCOL_PKT_LEN = 4
+    GIT_MINIMUM_RESPONSE_LENGTH = GIT_PROTOCOL_PKT_LEN + GIT_EXPECTED_FIRST_PACKET_LINE.length
+    EXPECTED_CONTENT_TYPE = "application/x-#{GIT_SERVICE_NAME}-advertisement"
+
+    def initialize(params)
+      @params = params
+    end
+
+    def execute
+      uri = Gitlab::Utils.parse_url(@params[:url])
+
+      return ServiceResponse.error(message: "#{@params[:url]} is not a valid URL") unless uri
+
+      uri.fragment = nil
+      url = Gitlab::Utils.append_path(uri.to_s, "/info/refs?service=#{GIT_SERVICE_NAME}")
+
+      response_body = ''
+      result = nil
+      Gitlab::HTTP.try_get(url, stream_body: true, follow_redirects: false, basic_auth: auth) do |fragment|
+        response_body += fragment
+        next if response_body.length < GIT_MINIMUM_RESPONSE_LENGTH
+
+        result = if status_code_is_valid(fragment) && content_type_is_valid(fragment) && response_body_is_valid(response_body)
+                   :success
+                 else
+                   :error
+                 end
+
+        # We are interested only in the first chunks of the response
+        # So we're using stream_body: true and breaking when receive enough body
+        break
+      end
+
+      if result == :success
+        ServiceResponse.success
+      else
+        ServiceResponse.error(message: "#{uri} is not a valid HTTP Git repository")
+      end
+    end
+
+    private
+
+    def auth
+      unless @params[:user].to_s.blank?
+        {
+          username: @params[:user],
+          password: @params[:password]
+        }
+      end
+    end
+
+    def status_code_is_valid(fragment)
+      fragment.http_response.code == '200'
+    end
+
+    def content_type_is_valid(fragment)
+      fragment.http_response['content-type'] == EXPECTED_CONTENT_TYPE
+    end
+
+    def response_body_is_valid(response_body)
+      response_body.match?(GIT_BODY_MESSAGE_REGEXP)
+    end
+  end
+end