Speed up wallet synchronization, especially re-syncs of large wallets:
- Incremental address discovery: known indices from the previous sync
(NextReceiveIndex/NextChangeIndex) are fetched in a single parallel
burst instead of sequential gap-limit rounds, cutting round-trips from
O(used/gapLimit) to ~O(1). Receive and change chains scan in parallel.
- Merge tx download and Merkle verification into one parallel phase
(no barrier between them); the per-call semaphore is dropped in favor
of the transport-level in-flight gate.
- Persist verified block headers (SyncCache.BlockHeaders, height -> hex):
immutable once stored, so blockchain.block.header round-trips for
already-verified proofs are eliminated on later syncs.
- RetryOnBusyAsync with exponential backoff around server calls, treating
-101/-102 and "server busy"/"excessive resource usage" as transient.
Wire the new PreloadCaches/ExportCaches signatures through the desktop
view model and the CLI sync command.
Three interrelated fixes for sync reliability on large wallets:
1. Prevent -101 "excessive resource usage":
ScanChainAsync uses GetHistoryAsync for discovery instead of
SubscribeScripthashAsync. Subscriptions are limited to the gap window
only (≤ 2×gapLimit addresses), so the session subscription count stays
constant regardless of wallet history size — eliminating -101 on
wallets with 1000+ historical addresses.
2. Persist and resume tx cache across sessions and disconnects:
WalletSynchronizer gains ExportCaches() and PreloadCaches(). On every
successful sync (and on partial failure) the downloaded raw tx hex and
verified Merkle heights are written to SyncCache.RawTxHex/VerifiedAt
in the wallet file. On reconnect or app restart the new synchronizer
is pre-populated from disk so only new transactions are downloaded.
_synchronizer is always nulled on reconnect (new client = new instance)
while caches survive via the wallet file.
3. Auto-connect with multi-server fallback and retry:
ConnectAndSync iterates BuildServerCandidates() (current server first,
then all KnownServers in order) and stops at the first that responds.
_autoReconnect and _syncFailed are set in OpenLoaded() so the keepalive
timer (20 s) retries automatically on any failure — connection error,
-101 mid-download, or timeout. PersistPartialTxCache() saves whatever
was downloaded so each retry resumes from its checkpoint.
Tab bar: replace plain Header strings with icon+label StackPanels
(≡ ↑ ↓ ⊙ ⊕); style TabStrip with UniformGrid so all five tabs share
the full width equally; center content and add touch padding. Icons
are visible only on mobile (IsMobile binding); desktop keeps text only.
Server settings overlay: dual layout for host/port/TLS input (vertical
on mobile: host full-width, port+TLS side by side) and for action
buttons (stacked full-width on mobile). Known-server list item shows
host on one line and tcp/ssl ports on the line below on mobile.
Connection status bar: simplify to "connesso" / "non connesso" —
remove the "a host:port" suffix from the connected state and
consolidate all disconnected/error/cert-changed states to conn.none.
davide