electrum: login_user: prevent AccountGapsDisallowed

Subaccounts created at login come from the cache/store so in theory
they can't have gaps. But if for any reason we see a gap here, we
should not error and prevent login since it might lock a user out of
its wallet.

GA_create_subaccount will still error if there is a gap.

Author: LeoComandini

src/ga_auth_handlers.cpp

@@ -530,6 +530,8 @@ namespace sdk {
             // Fall through to create the subaccount
         }
 
+        // This is an actual subaccount creation, do not allow the caller to set this flag
+        m_details.erase("is_already_created");
         // Create the subaccount
         m_result = m_session->create_subaccount(m_details, m_subaccount, m_subaccount_xpub);
         // Ensure the server created the subaccount number we expected

src/ga_rust.cpp

@@ -108,7 +108,9 @@ namespace sdk {
         const std::vector<uint32_t>& pointers, const std::vector<std::string>& bip32_xpubs)
     {
         // Note we only register each loaded subaccount once.
-        const nlohmann::json details({ { "name", std::string() } });
+        // Subaccount to register has already been created, so we
+        // set a flag to avoid the checks on the (sub)account gaps.
+        const nlohmann::json details({ { "name", std::string() }, { "is_already_created", true } });
         for (size_t i = 0; i < pointers.size(); ++i) {
             const auto pointer = pointers.at(i);
             if (!m_user_pubkeys->have_subaccount(pointer)) {

subprojects/gdk_rust/gdk_common/src/model.rs

@@ -206,6 +206,8 @@ pub struct CreateAccountOpt {
     pub xpub: Option<ExtendedPubKey>,
     #[serde(default)]
     pub discovered: bool,
+    #[serde(default)]
+    pub is_already_created: bool,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone)]

subprojects/gdk_rust/gdk_electrum/src/lib.rs

@@ -418,6 +418,7 @@ impl ElectrumSession {
                 name: "".to_string(),
                 xpub: Some(xpub),
                 discovered: false,
+                is_already_created: true,
             })?;
         }
 
@@ -818,7 +819,7 @@ impl ElectrumSession {
             let account = accounts
                 .get(&last_account)
                 .ok_or_else(|| Error::InvalidSubaccount(last_account))?;
-            if !account.has_transactions()? {
+            if !opt.is_already_created && !account.has_transactions()? {
                 bail!(Error::AccountGapsDisallowed);
             }
         }

subprojects/gdk_rust/gdk_test/src/electrum_session_ext.rs

@@ -58,6 +58,7 @@ impl ElectrumSessionExt for ElectrumSession {
                 name: "".to_string(),
                 xpub: Some(xpub),
                 discovered: false,
+                is_already_created: true,
             };
             self.create_subaccount(opt).unwrap();
         }