feat: access ActivityPub client through interfaces to facilitate mocking in unit tests (#4853)

Was facing issues while writing unit tests for federation code. Mocks weren't catching all network calls, because was being out of scope of the mocking infra. Plus, I think we can have more granular tests.

This PR puts the client behind an interface, that can be retrieved from `ctx`. Context doesn't require initialization, as it defaults to the implementation available in-tree. It may be overridden when required (like testing).

## Mechanism

1. Get client factory from `ctx` (factory contains network and crypto parameters that are needed)
2. Initialize client with sender's keys and the receiver's public key
3. Use client as before.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/4853
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Aravinth Manivannan <realaravinth@batsense.net>
Co-committed-by: Aravinth Manivannan <realaravinth@batsense.net>

6 files changed, 140 insertions, 25 deletions

diff --git a/.deadcode-out b/.deadcode-out
index 555797e2ed..91ef32cdf4 100644
--- a/.deadcode-out
+++ b/.deadcode-out
@@ -93,6 +93,10 @@ code.gitea.io/gitea/models/user
 	GetUserEmailsByNames
 	GetUserNamesByIDs
 
+code.gitea.io/gitea/modules/activitypub
+	NewContext
+	Context.APClientFactory
+
 code.gitea.io/gitea/modules/assetfs
 	Bindata
 
diff --git a/modules/activitypub/client.go b/modules/activitypub/client.go
index f07d3bc7d6..064d8984c1 100644
--- a/modules/activitypub/client.go
+++ b/modules/activitypub/client.go
@@ -56,35 +56,23 @@ func containsRequiredHTTPHeaders(method string, headers []string) error {
 }
 
 // Client struct
-type Client struct {
+type ClientFactory struct {
 	client      *http.Client
 	algs        []httpsig.Algorithm
 	digestAlg   httpsig.DigestAlgorithm
 	getHeaders  []string
 	postHeaders []string
-	priv        *rsa.PrivateKey
-	pubID       string
 }
 
 // NewClient function
-func NewClient(ctx context.Context, user *user_model.User, pubID string) (c *Client, err error) {
+func NewClientFactory() (c *ClientFactory, err error) {
 	if err = containsRequiredHTTPHeaders(http.MethodGet, setting.Federation.GetHeaders); err != nil {
 		return nil, err
 	} else if err = containsRequiredHTTPHeaders(http.MethodPost, setting.Federation.PostHeaders); err != nil {
 		return nil, err
 	}
 
-	priv, err := GetPrivateKey(ctx, user)
-	if err != nil {
-		return nil, err
-	}
-	privPem, _ := pem.Decode([]byte(priv))
-	privParsed, err := x509.ParsePKCS1PrivateKey(privPem.Bytes)
-	if err != nil {
-		return nil, err
-	}
-
-	c = &Client{
+	c = &ClientFactory{
 		client: &http.Client{
 			Transport: &http.Transport{
 				Proxy: proxy.Proxy(),
@@ -95,10 +83,47 @@ func NewClient(ctx context.Context, user *user_model.User, pubID string) (c *Cli
 		digestAlg:   httpsig.DigestAlgorithm(setting.Federation.DigestAlgorithm),
 		getHeaders:  setting.Federation.GetHeaders,
 		postHeaders: setting.Federation.PostHeaders,
+	}
+	return c, err
+}
+
+type APClientFactory interface {
+	WithKeys(ctx context.Context, user *user_model.User, pubID string) (APClient, error)
+}
+
+// Client struct
+type Client struct {
+	client      *http.Client
+	algs        []httpsig.Algorithm
+	digestAlg   httpsig.DigestAlgorithm
+	getHeaders  []string
+	postHeaders []string
+	priv        *rsa.PrivateKey
+	pubID       string
+}
+
+// NewRequest function
+func (cf *ClientFactory) WithKeys(ctx context.Context, user *user_model.User, pubID string) (APClient, error) {
+	priv, err := GetPrivateKey(ctx, user)
+	if err != nil {
+		return nil, err
+	}
+	privPem, _ := pem.Decode([]byte(priv))
+	privParsed, err := x509.ParsePKCS1PrivateKey(privPem.Bytes)
+	if err != nil {
+		return nil, err
+	}
+
+	c := Client{
+		client:      cf.client,
+		algs:        cf.algs,
+		digestAlg:   cf.digestAlg,
+		getHeaders:  cf.getHeaders,
+		postHeaders: cf.postHeaders,
 		priv:        privParsed,
 		pubID:       pubID,
 	}
-	return c, err
+	return &c, nil
 }
 
 // NewRequest function
@@ -185,3 +210,64 @@ func charLimiter(s string, limit int) string {
 	}
 	return s
 }
+
+type APClient interface {
+	newRequest(method string, b []byte, to string) (req *http.Request, err error)
+	Post(b []byte, to string) (resp *http.Response, err error)
+	Get(to string) (resp *http.Response, err error)
+	GetBody(uri string) ([]byte, error)
+}
+
+// contextKey is a value for use with context.WithValue.
+type contextKey struct {
+	name string
+}
+
+// clientFactoryContextKey is a context key. It is used with context.Value() to get the current Food for the context
+var (
+	clientFactoryContextKey                 = &contextKey{"clientFactory"}
+	_                       APClientFactory = &ClientFactory{}
+)
+
+// Context represents an activitypub client factory context
+type Context struct {
+	context.Context
+	e APClientFactory
+}
+
+func NewContext(ctx context.Context, e APClientFactory) *Context {
+	return &Context{
+		Context: ctx,
+		e:       e,
+	}
+}
+
+// APClientFactory represents an activitypub client factory
+func (ctx *Context) APClientFactory() APClientFactory {
+	return ctx.e
+}
+
+// provides APClientFactory
+type GetAPClient interface {
+	GetClientFactory() APClientFactory
+}
+
+// GetClientFactory will get an APClientFactory from this context or returns the default implementation
+func GetClientFactory(ctx context.Context) (APClientFactory, error) {
+	if e := getClientFactory(ctx); e != nil {
+		return e, nil
+	}
+	return NewClientFactory()
+}
+
+// getClientFactory will get an APClientFactory from this context or return nil
+func getClientFactory(ctx context.Context) APClientFactory {
+	if clientFactory, ok := ctx.(APClientFactory); ok {
+		return clientFactory
+	}
+	clientFactoryInterface := ctx.Value(clientFactoryContextKey)
+	if clientFactoryInterface != nil {
+		return clientFactoryInterface.(GetAPClient).GetClientFactory()
+	}
+	return nil
+}
diff --git a/modules/activitypub/client_test.go b/modules/activitypub/client_test.go
index dede579662..539fd012c7 100644
--- a/modules/activitypub/client_test.go
+++ b/modules/activitypub/client_test.go
@@ -64,14 +64,19 @@ Set up a user called "me" for all tests
 
 */
 
-func TestNewClientReturnsClient(t *testing.T) {
+func TestClientCtx(t *testing.T) {
 	require.NoError(t, unittest.PrepareTestDatabase())
 	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1})
 	pubID := "myGpgId"
-	c, err := NewClient(db.DefaultContext, user, pubID)
+	cf, err := NewClientFactory()
+	log.Debug("ClientFactory: %v\nError: %v", cf, err)
+	require.NoError(t, err)
+
+	c, err := cf.WithKeys(db.DefaultContext, user, pubID)
 
 	log.Debug("Client: %v\nError: %v", c, err)
 	require.NoError(t, err)
+	_ = NewContext(db.DefaultContext, cf)
 }
 
 /* TODO: bring this test to work or delete
@@ -109,7 +114,9 @@ func TestActivityPubSignedPost(t *testing.T) {
 	require.NoError(t, unittest.PrepareTestDatabase())
 	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1})
 	pubID := "https://example.com/pubID"
-	c, err := NewClient(db.DefaultContext, user, pubID)
+	cf, err := NewClientFactory()
+	require.NoError(t, err)
+	c, err := cf.WithKeys(db.DefaultContext, user, pubID)
 	require.NoError(t, err)
 
 	expected := "BODY"
diff --git a/services/federation/federation_service.go b/services/federation/federation_service.go
index a7d9b6ef80..4c6f5ca0ca 100644
--- a/services/federation/federation_service.go
+++ b/services/federation/federation_service.go
@@ -99,7 +99,11 @@ func ProcessLikeActivity(ctx context.Context, form any, repositoryID int64) (int
 
 func CreateFederationHostFromAP(ctx context.Context, actorID fm.ActorID) (*forgefed.FederationHost, error) {
 	actionsUser := user.NewActionsUser()
-	client, err := activitypub.NewClient(ctx, actionsUser, "no idea where to get key material.")
+	clientFactory, err := activitypub.GetClientFactory(ctx)
+	if err != nil {
+		return nil, err
+	}
+	client, err := clientFactory.WithKeys(ctx, actionsUser, "no idea where to get key material.")
 	if err != nil {
 		return nil, err
 	}
@@ -153,7 +157,11 @@ func GetFederationHostForURI(ctx context.Context, actorURI string) (*forgefed.Fe
 func CreateUserFromAP(ctx context.Context, personID fm.PersonID, federationHostID int64) (*user.User, *user.FederatedUser, error) {
 	// ToDo: Do we get a publicKeyId from server, repo or owner or repo?
 	actionsUser := user.NewActionsUser()
-	client, err := activitypub.NewClient(ctx, actionsUser, "no idea where to get key material.")
+	clientFactory, err := activitypub.GetClientFactory(ctx)
+	if err != nil {
+		return nil, nil, err
+	}
+	client, err := clientFactory.WithKeys(ctx, actionsUser, "no idea where to get key material.")
 	if err != nil {
 		return nil, nil, err
 	}
@@ -262,7 +270,11 @@ func SendLikeActivities(ctx context.Context, doer user.User, repoID int64) error
 		likeActivityList = append(likeActivityList, likeActivity)
 	}
 
-	apclient, err := activitypub.NewClient(ctx, &doer, doer.APActorID())
+	apclientFactory, err := activitypub.GetClientFactory(ctx)
+	if err != nil {
+		return err
+	}
+	apclient, err := apclientFactory.WithKeys(ctx, &doer, doer.APActorID())
 	if err != nil {
 		return err
 	}
diff --git a/tests/integration/api_activitypub_person_test.go b/tests/integration/api_activitypub_person_test.go
index f5cb1244af..55935e4ab6 100644
--- a/tests/integration/api_activitypub_person_test.go
+++ b/tests/integration/api_activitypub_person_test.go
@@ -98,7 +98,9 @@ func TestActivityPubPersonInbox(t *testing.T) {
 		user1, err := user_model.GetUserByName(ctx, username1)
 		require.NoError(t, err)
 		user1url := fmt.Sprintf("%s/api/v1/activitypub/user-id/1#main-key", srv.URL)
-		c, err := activitypub.NewClient(db.DefaultContext, user1, user1url)
+		cf, err := activitypub.GetClientFactory(ctx)
+		require.NoError(t, err)
+		c, err := cf.WithKeys(db.DefaultContext, user1, user1url)
 		require.NoError(t, err)
 		user2inboxurl := fmt.Sprintf("%s/api/v1/activitypub/user-id/2/inbox", srv.URL)
 
diff --git a/tests/integration/api_activitypub_repository_test.go b/tests/integration/api_activitypub_repository_test.go
index 5c97586b19..737f580061 100644
--- a/tests/integration/api_activitypub_repository_test.go
+++ b/tests/integration/api_activitypub_repository_test.go
@@ -140,7 +140,9 @@ func TestActivityPubRepositoryInboxValid(t *testing.T) {
 		}()
 		actionsUser := user.NewActionsUser()
 		repositoryID := 2
-		c, err := activitypub.NewClient(db.DefaultContext, actionsUser, "not used")
+		cf, err := activitypub.GetClientFactory(db.DefaultContext)
+		require.NoError(t, err)
+		c, err := cf.WithKeys(db.DefaultContext, actionsUser, "not used")
 		require.NoError(t, err)
 		repoInboxURL := fmt.Sprintf(
 			"%s/api/v1/activitypub/repository-id/%v/inbox",
@@ -232,7 +234,9 @@ func TestActivityPubRepositoryInboxInvalid(t *testing.T) {
 		}()
 		actionsUser := user.NewActionsUser()
 		repositoryID := 2
-		c, err := activitypub.NewClient(db.DefaultContext, actionsUser, "not used")
+		cf, err := activitypub.GetClientFactory(db.DefaultContext)
+		require.NoError(t, err)
+		c, err := cf.WithKeys(db.DefaultContext, actionsUser, "not used")
 		require.NoError(t, err)
 		repoInboxURL := fmt.Sprintf("%s/api/v1/activitypub/repository-id/%v/inbox",
 			srv.URL, repositoryID)