Extract account migration sign feature to a module

This module can be used to compute account migration signature in other
objects besides Entities::AccountMigration. For instance this is to be
used in AccountMigration model of diaspora* web application.

lib/diaspora_federation/entities.rb

@@ -13,6 +13,7 @@ require "diaspora_federation/entities/related_entity"
 # abstract types
 require "diaspora_federation/entities/post"
 require "diaspora_federation/entities/signable"
+require "diaspora_federation/entities/account_migration/signable"
 require "diaspora_federation/entities/relayable"
 
 # types

lib/diaspora_federation/entities/account_migration.rb

@@ -5,7 +5,7 @@ module DiasporaFederation
     #
     # @see Validators::AccountMigrationValidator
     class AccountMigration < Entity
-      include Signable
+      include AccountMigration::Signable
 
       # @!attribute [r] author
       #   The old diaspora* ID of the person who changes their ID
@@ -23,16 +23,18 @@ module DiasporaFederation
       #   @return [String] signature
       property :signature, :string, default: nil
 
-      # @return [String] string representation of this object
-      def to_s
-        "AccountMigration:#{author}:#{profile.author}"
+      def old_user_id
+        author
       end
 
+      # @return [String] string representation of this object
+      alias to_s unique_migration_descriptor
+
       # Shortcut for calling super method with sensible arguments
       #
       # @see DiasporaFederation::Entities::Signable#verify_signature
       def verify_signature
-        super(profile.author, :signature)
+        super(signer_id, :signature)
       end
 
       # Calls super and additionally does signature verification for the instantiated entity.
@@ -44,9 +46,12 @@ module DiasporaFederation
 
       private
 
-      # @see DiasporaFederation::Entities::Signable#signature_data
-      def signature_data
-        to_s
+      def new_user_id
+        profile.author
+      end
+
+      def signer_id
+        new_user_id
       end
 
       def enriched_properties
@@ -59,10 +64,10 @@ module DiasporaFederation
       # @raise [NewPrivateKeyNotFound] if the new user's private key is not found
       # @return [String] A Base64 encoded signature of #signature_data with key
       def sign_with_new_key
-        privkey = DiasporaFederation.callbacks.trigger(:fetch_private_key, profile.author)
-        raise NewPrivateKeyNotFound, "author=#{profile.author} obj=#{self}" if privkey.nil?
+        privkey = DiasporaFederation.callbacks.trigger(:fetch_private_key, signer_id)
+        raise NewPrivateKeyNotFound, "signer=#{signer_id} obj=#{self}" if privkey.nil?
         sign_with_key(privkey).tap do
-          logger.info "event=sign status=complete signature=signature author=#{profile.author} obj=#{self}"
+          logger.info "event=sign status=complete signature=signature signer=#{signer_id} obj=#{self}"
         end
       end
 

lib/diaspora_federation/entities/account_migration/signable.rb

@@ -0,0 +1,24 @@
+module DiasporaFederation
+  module Entities
+    class AccountMigration < Entity
+      # AccountMigration::Signable is a module that encapsulates basic signature generation/verification flow for
+      # AccountMigration entity.
+      #
+      # It is possible that implementation of diaspora* protocol requires to compute the signature for the
+      # AccountMigration entity without instantiating the entity. In this case this module may be useful.
+      module Signable
+        include Entities::Signable
+
+        # @return [String] string which is uniquely represents migration occasion
+        def unique_migration_descriptor
+          "AccountMigration:#{old_identity}:#{new_identity}"
+        end
+
+        # @see DiasporaFederation::Entities::Signable#signature_data
+        def signature_data
+          unique_migration_descriptor
+        end
+      end
+    end
+  end
+end

spec/lib/diaspora_federation/entities/account_migration/signable_spec.rb

@@ -0,0 +1,39 @@
+module DiasporaFederation
+  describe Entities::AccountMigration::Signable do
+    let(:entity) { TestAMSignableEntity.new({}) }
+
+    class TestAMSignableEntity < Entity
+      include Entities::AccountMigration::Signable
+
+      property :my_signature, :string, default: nil
+
+      def old_identity
+        "old"
+      end
+
+      def new_identity
+        "new"
+      end
+
+      def freeze; end
+    end
+
+    it_behaves_like "a signable" do
+      let(:test_class) { TestAMSignableEntity }
+      let(:test_string) { "AccountMigration:old:new" }
+    end
+
+    describe "#unique_migration_descriptor" do
+      it "composes a string using #old_identity and #new_identity" do
+        expect(entity.unique_migration_descriptor).to eq("AccountMigration:old:new")
+      end
+    end
+
+    describe "#signature_data" do
+      it "delegates to #unique_migration_descriptor" do
+        expect(entity).to receive(:unique_migration_descriptor).and_return("test123")
+        expect(entity.signature_data).to eq("test123")
+      end
+    end
+  end
+end

spec/lib/diaspora_federation/entities/signable_spec.rb

@@ -1,9 +1,6 @@
 module DiasporaFederation
   describe Entities::Signable do
     TEST_STRING_VALUE = "abc123".freeze
-    let(:private_key) { OpenSSL::PKey::RSA.generate(1024) }
-    let(:test_string) { TEST_STRING_VALUE }
-    let(:test_signature) { sign_with_key(private_key, test_string) }
 
     class TestSignableEntity < Entity
       include Entities::Signable
@@ -27,51 +24,9 @@ module DiasporaFederation
       end
     end
 
-    describe "#sign_with_key" do
-      it "produces a correct signature" do
-        signature = TestSignableEntity.new({}).sign_with_key(private_key)
-        expect(verify_signature(private_key.public_key, signature, test_string)).to be_truthy
-      end
-    end
-
-    describe "#verify_signature" do
-      it "doesn't raise if signature is correct" do
-        expect_callback(:fetch_public_key, "id@example.tld").and_return(private_key.public_key)
-
-        expect {
-          TestSignableEntity
-            .new(my_signature: test_signature)
-            .verify_signature("id@example.tld", :my_signature)
-        }.not_to raise_error
-      end
-
-      it "raises PublicKeyNotFound when key isn't provided" do
-        expect_callback(:fetch_public_key, "id@example.tld").and_return(nil)
-
-        expect {
-          TestSignableEntity
-            .new(my_signature: test_signature)
-            .verify_signature("id@example.tld", :my_signature)
-        }.to raise_error(Entities::Signable::PublicKeyNotFound)
-      end
-
-      it "raises SignatureVerificationFailed when signature isn't provided" do
-        expect_callback(:fetch_public_key, "id@example.tld").and_return(private_key.public_key)
-
-        expect {
-          TestSignableEntity.new({}).verify_signature("id@example.tld", :my_signature)
-        }.to raise_error(Entities::Signable::SignatureVerificationFailed)
-      end
-
-      it "raises SignatureVerificationFailed when signature is wrong" do
-        expect_callback(:fetch_public_key, "id@example.tld").and_return(private_key.public_key)
-
-        expect {
-          TestSignableEntity
-            .new(my_signature: "faked signature")
-            .verify_signature("id@example.tld", :my_signature)
-        }.to raise_error(Entities::Signable::SignatureVerificationFailed)
-      end
+    it_behaves_like "a signable" do
+      let(:test_class) { TestSignableEntity }
+      let(:test_string) { TEST_STRING_VALUE }
     end
   end
 end

spec/support/shared_signable_spec.rb

@@ -0,0 +1,51 @@
+shared_examples "a signable" do
+  let(:private_key) { OpenSSL::PKey::RSA.generate(1024) }
+  let(:test_signature) { sign_with_key(private_key, test_string) }
+
+  describe "#sign_with_key" do
+    it "produces a correct signature" do
+      signature = test_class.new({}).sign_with_key(private_key)
+      expect(verify_signature(private_key.public_key, signature, test_string)).to be_truthy
+    end
+  end
+
+  describe "#verify_signature" do
+    it "doesn't raise if signature is correct" do
+      expect_callback(:fetch_public_key, "id@example.tld").and_return(private_key.public_key)
+
+      expect {
+        test_class
+          .new(my_signature: test_signature)
+          .verify_signature("id@example.tld", :my_signature)
+      }.not_to raise_error
+    end
+
+    it "raises PublicKeyNotFound when key isn't provided" do
+      expect_callback(:fetch_public_key, "id@example.tld").and_return(nil)
+
+      expect {
+        test_class
+          .new(my_signature: test_signature)
+          .verify_signature("id@example.tld", :my_signature)
+      }.to raise_error(DiasporaFederation::Entities::Signable::PublicKeyNotFound)
+    end
+
+    it "raises SignatureVerificationFailed when signature isn't provided" do
+      expect_callback(:fetch_public_key, "id@example.tld").and_return(private_key.public_key)
+
+      expect {
+        test_class.new({}).verify_signature("id@example.tld", :my_signature)
+      }.to raise_error(DiasporaFederation::Entities::Signable::SignatureVerificationFailed)
+    end
+
+    it "raises SignatureVerificationFailed when signature is wrong" do
+      expect_callback(:fetch_public_key, "id@example.tld").and_return(private_key.public_key)
+
+      expect {
+        test_class
+          .new(my_signature: "faked signature")
+          .verify_signature("id@example.tld", :my_signature)
+      }.to raise_error(DiasporaFederation::Entities::Signable::SignatureVerificationFailed)
+    end
+  end
+end