Definition and delineation of tasks within the scanner

Also defines primitives for the processor.

processor/scanner/src/scan.rs

@@ -0,0 +1,73 @@
+use serai_db::{Db, DbTxn};
+
+use primitives::{Id, Block};
+
+// TODO: Localize to ScanDb?
+use crate::{db::ScannerDb, ScannerFeed};
+
+struct ScanForOutputsTask<D: Db, S: ScannerFeed> {
+  db: D,
+  feed: S,
+}
+
+#[async_trait::async_trait]
+impl<D: Db, S: ScannerFeed> ContinuallyRan for ScanForOutputsTask<D, S> {
+  async fn run_instance(&mut self) -> Result<(), String> {
+    // Fetch the safe to scan block
+    let latest_scannable = ScannerDb::<S>::latest_scannable_block(&self.db).expect("ScanForOutputsTask run before writing the start block");
+    // Fetch the next block to scan
+    let next_to_scan = ScannerDb::<S>::next_to_scan_for_outputs_block(&self.db).expect("ScanForOutputsTask run before writing the start block");
+
+    for b in next_to_scan ..= latest_scannable {
+      let block = match self.feed.block_by_number(b).await {
+        Ok(block) => block,
+        Err(e) => Err(format!("couldn't fetch block {b}: {e:?}"))?,
+      };
+
+      // Check the ID of this block is the expected ID
+      {
+        let expected = ScannerDb::<S>::block_id(b).expect("scannable block didn't have its ID saved");
+        if block.id() != expected {
+          panic!("finalized chain reorganized from {} to {} at {}", hex::encode(expected), hex::encode(block.id()), b);
+        }
+      }
+
+      log::info!("scanning block: {} ({b})", hex::encode(block.id()));
+
+      let keys = ScannerDb::<S>::keys(&self.db).expect("scanning for a blockchain without any keys set");
+      // Remove all the retired keys
+      while let Some(retire_at) = keys[0].retirement_block_number {
+        if retire_at <= b {
+          keys.remove(0);
+        }
+      }
+      assert!(keys.len() <= 2);
+
+      // Scan for each key
+      for key in keys {
+        // If this key has yet to active, skip it
+        if key.activation_block_number > b {
+          continue;
+        }
+
+        let mut outputs = vec![];
+        for output in network.scan_for_outputs(&block, key).awaits {
+          assert_eq!(output.key(), key);
+          // TODO: Check for dust
+          outputs.push(output);
+        }
+      }
+
+      let mut txn = self.db.txn();
+      // Update the latest scanned block
+      ScannerDb::<S>::set_next_to_scan_for_outputs_block(&mut txn, b + 1);
+      // TODO: If this had outputs, yield them and mark this block notable
+      /*
+        A block is notable if it's an activation, had outputs, or a retirement block.
+      */
+      txn.commit();
+    }
+
+    Ok(())
+  }
+}