feat: decrypt secret-encrypted message edits

pkg/whatsmeow/service/secret_edit.go

@@ -0,0 +1,66 @@
+package whatsmeow_service
+
+// Decryption of secret-encrypted message EDITS.
+//
+// When a phone edits a message in a @lid-addressed chat, WhatsApp delivers the
+// edit as a `secretEncryptedMessage` (MESSAGE_EDIT): the new content is
+// encrypted with the "message secret" of the ORIGINAL message — a secret this
+// whatsmeow session already holds (it arrived inside the original message
+// itself). Without this handling, the encrypted event is forwarded to the
+// webhook as-is, so consumers learn THAT an edit happened but not WHAT changed.
+// This closes the loop: decrypt with the official primitive
+// (Client.DecryptSecretEncryptedMessage, which natively supports
+// EncSecretMessageEdit) and rewrite the event into the CANONICAL cleartext
+// shape (protocolMessage MESSAGE_EDIT + editedMessage) — the same shape
+// BuildEdit produces — so webhook consumers handle both paths identically.
+//
+// Kept in its own file (plus a single line at the handler call-site) on
+// purpose: rebasing over new evolution-go/whatsmeow releases stays trivial.
+
+import (
+	"context"
+
+	"go.mau.fi/whatsmeow/proto/waE2E"
+	"go.mau.fi/whatsmeow/types/events"
+	"google.golang.org/protobuf/proto"
+)
+
+// resolveSecretEncryptedEdit detects a secret-encrypted edit
+// (secretEncryptedMessage MESSAGE_EDIT) and, when decryption succeeds,
+// rewrites evt.Message into the canonical cleartext shape. Fail-open: on any
+// failure (missing secret, unsupported type, …) the event passes through
+// untouched — behavior falls back to what it was before this change (webhook
+// receives the encrypted payload).
+func (mycli *MyClient) resolveSecretEncryptedEdit(evt *events.Message) {
+	enc := evt.Message.GetSecretEncryptedMessage()
+	if enc == nil || enc.GetSecretEncType() != waE2E.SecretEncryptedMessage_MESSAGE_EDIT {
+		return
+	}
+	decrypted, err := mycli.WAClient.DecryptSecretEncryptedMessage(context.Background(), evt)
+	if err != nil {
+		// Without the original message's secret (e.g. the message predates this
+		// pairing) there is nothing to do — the consumer still receives the
+		// cleartext target (targetMessageKey) and can at least flag the message
+		// as edited.
+		mycli.loggerWrapper.GetLogger(mycli.userID).LogWarn("[%s] secret-edit: failed to decrypt edit of %s: %v", mycli.userID, enc.GetTargetMessageKey().GetID(), err)
+		return
+	}
+	mycli.loggerWrapper.GetLogger(mycli.userID).LogInfo("[%s] secret-edit: edit of %s decrypted — forwarding in cleartext", mycli.userID, enc.GetTargetMessageKey().GetID())
+	// Phones encrypt the FULL edit envelope (the plaintext is already a
+	// protocolMessage MESSAGE_EDIT with editedMessage inside) — use it as-is;
+	// re-wrapping would double the nesting. The fallback covers a plaintext
+	// that carries only the new content.
+	if pm := decrypted.GetProtocolMessage(); pm != nil &&
+		pm.GetType() == waE2E.ProtocolMessage_MESSAGE_EDIT && pm.GetEditedMessage() != nil {
+		evt.Message = decrypted
+		return
+	}
+	evt.Message = &waE2E.Message{
+		ProtocolMessage: &waE2E.ProtocolMessage{
+			Type:          waE2E.ProtocolMessage_MESSAGE_EDIT.Enum(),
+			Key:           enc.GetTargetMessageKey(),
+			EditedMessage: decrypted,
+			TimestampMS:   proto.Int64(evt.Info.Timestamp.UnixMilli()),
+		},
+	}
+}

pkg/whatsmeow/service/whatsmeow.go

@@ -1032,6 +1032,11 @@ func (mycli *MyClient) myEventHandler(rawEvt interface{}) {
 		postMap["event"] = "Message"
 		// Message received
 
+		// Secret-encrypted edits (secretEncryptedMessage MESSAGE_EDIT) become a
+		// cleartext protocolMessage when the original message's secret is known
+		// — see secret_edit.go.
+		mycli.resolveSecretEncryptedEdit(evt)
+
 		// Log message arrival with detailed info
 		messageSize := "unknown"
 		if evt.Message.GetDocumentMessage() != nil && evt.Message.GetDocumentMessage().FileLength != nil {