Integrate SPV cross-validation checks into the headers thread

And keep the latest validation status on the store cache.

NOTE: This commit depends on a rust-bitcoin fork with serializable uint types.
A PR was sent upstream: rust-bitcoin/rust-bitcoin#511

subprojects/gdk_rust/Cargo.toml

@@ -12,7 +12,7 @@ crate-type = ["staticlib"]
 android_log = ["android_logger"]
 
 [dependencies]
-bitcoin = { version = "0.25", features = [ "use-serde" ] }
+bitcoin = { version = "0.25.2", features = [ "use-serde" ] }
 rand = "0.7.3"
 gdk-electrum = { path = "gdk_electrum", features = ["android_log"] }
 gdk-common = { path = "gdk_common" }
@@ -39,3 +39,6 @@ panic = 'abort'
 opt-level = 'z'
 codegen-units = 1
 incremental = false
+
+[patch.crates-io]
+bitcoin = { git = "https://github.com/shesek/rust-bitcoin", branch = "0.25.2-uint-serde", features = [ "use-serde" ] }

subprojects/gdk_rust/gdk_electrum/Cargo.toml

@@ -31,3 +31,6 @@ lazy_static = "1.4.0"
 # remember to update secp256k1 deps if increasing this one, unfortunately we can't use the rexported one from bitcoin because we need recovery feature
 bitcoin = { version = "0.25", features = [ "use-serde" ] }
 elements = { version = "0.13", features = ["serde-feature"] }
+
+[patch.crates-io]
+bitcoin = { git = "https://github.com/shesek/rust-bitcoin", branch = "0.25.2-uint-serde", features = [ "use-serde" ] }

subprojects/gdk_rust/gdk_electrum/src/interface.rs

@@ -10,6 +10,7 @@ use gdk_common::model::{AddressAmount, Balances, GetTransactionsOpt, SPVVerifyRe
 use hex;
 use log::{info, trace};
 use rand::Rng;
+use serde::{Deserialize, Serialize};
 
 use gdk_common::mnemonic::Mnemonic;
 use gdk_common::model::{AddressPointer, CreateTransaction, Settings, TransactionMeta};
@@ -41,7 +42,7 @@ pub struct WalletCtx {
     pub change_max_deriv: u32,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Serialize, Deserialize, Debug)]
 pub enum ElectrumUrl {
     Tls(String, bool), // the bool value indicates if the domain name should be validated
     Plaintext(String),

subprojects/gdk_rust/gdk_electrum/src/lib.rs

@@ -52,6 +52,7 @@ use crate::headers::bitcoin::HeadersChain;
 use crate::headers::liquid::Verifier;
 use crate::headers::ChainOrVerifier;
 use crate::pin::PinManager;
+use crate::spv::SpvCrossValidator;
 use aes::Aes256;
 use bitcoin::blockdata::constants::DIFFCHANGE_INTERVAL;
 use block_modes::block_padding::Pkcs7;
@@ -66,6 +67,8 @@ use std::hash::Hasher;
 use std::sync::{mpsc, Arc, RwLock};
 use std::thread::JoinHandle;
 
+const CROSS_VALIDATION_RATE: u8 = 4; // Once every 4 thread loop runs, or roughly 28 seconds
+
 type Aes256Cbc = Cbc<Aes256, Pkcs7>;
 
 pub struct Syncer {
@@ -82,6 +85,7 @@ pub struct Tipper {
 pub struct Headers {
     pub store: Store,
     pub checker: ChainOrVerifier,
+    pub cross_validator: Option<SpvCrossValidator>,
 }
 
 #[derive(Clone)]
@@ -420,9 +424,12 @@ impl Session<Error> for ElectrumSession {
                 }
             };
 
+            let cross_validator = SpvCrossValidator::from_network(&self.network)?;
+
             let mut headers = Headers {
                 store: store.clone(),
                 checker,
+                cross_validator,
             };
 
             let headers_url = self.url.clone();
@@ -431,6 +438,7 @@ impl Session<Error> for ElectrumSession {
             let chunk_size = DIFFCHANGE_INTERVAL as usize;
             let headers_handle = thread::spawn(move || {
                 info!("starting headers thread");
+                let mut round = 0u8;
 
                 'outer: loop {
                     if wait_or_close(&r, sync_interval) {
@@ -477,6 +485,12 @@ impl Session<Error> for ElectrumSession {
                             }
                             Err(e) => warn!("error in getting proofs {:?}", e),
                         }
+
+                        if round % CROSS_VALIDATION_RATE == 0 {
+                            headers.cross_validate();
+                        }
+
+                        round = round.wrapping_add(1);
                     }
                 }
             });
@@ -993,6 +1007,18 @@ impl Headers {
         }
         Ok(())
     }
+
+    pub fn cross_validate(&mut self) {
+        if let (Some(cross_validator), ChainOrVerifier::Chain(chain)) =
+            (&mut self.cross_validator, &self.checker)
+        {
+            let result = cross_validator.validate(chain);
+            debug!("cross validation result: {:?}", result);
+
+            let mut store = self.store.write().unwrap();
+            store.cache.cross_validation_result = Some(result);
+        }
+    }
 }
 
 #[derive(Default)]

subprojects/gdk_rust/gdk_electrum/src/spv.rs

@@ -1,5 +1,6 @@
 use log::warn;
 use rand::seq::SliceRandom;
+use serde::{Deserialize, Serialize};
 use std::str::FromStr;
 
 use bitcoin::blockdata::constants::{max_target, DIFFCHANGE_INTERVAL, DIFFCHANGE_TIMESPAN};
@@ -18,7 +19,6 @@ const MAX_CHUNK_SIZE: u32 = 200;
 const MAX_FORK_DEPTH: u32 = DIFFCHANGE_INTERVAL * 3;
 const SERVERS_PER_ROUND: usize = 3;
 
-// XXX when to run - add to existing headers thread?
 // XXX how to alert when something's up
 
 #[derive(Debug)]
@@ -27,7 +27,7 @@ pub struct SpvCrossValidator {
     last_result: CrossValidationResult,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Serialize, Deserialize, Debug)]
 pub enum CrossValidationResult {
     Valid,
 

subprojects/gdk_rust/gdk_electrum/src/store.rs

@@ -1,3 +1,4 @@
+use crate::spv::CrossValidationResult;
 use crate::Error;
 use aes_gcm_siv::aead::{generic_array::GenericArray, AeadInPlace, NewAead};
 use aes_gcm_siv::Aes256GcmSiv;
@@ -71,6 +72,9 @@ pub struct RawCache {
 
     /// registry icons last modified, used when making the http request
     pub icons_last_modified: String,
+
+    /// the result of the last spv cross-validation execution
+    pub cross_validation_result: Option<CrossValidationResult>,
 }
 
 /// RawStore contains data that are not extractable from xpub+blockchain