feat: Proper coinbase generation

signer/src/testing/dummy.rs

@@ -14,17 +14,7 @@ pub fn block<R: rand::RngCore + ?Sized>(config: &fake::Faker, rng: &mut R) -> bi
         .take(number_of_transactions)
         .collect();
 
-    // TODO(#213): Proper coinbase generation
-    let coinbase_script = bitcoin::script::Builder::new()
-        .push_slice([1, 2, 3, 4])
-        .into_script();
-
-    let mut coinbase_tx = tx(config, rng);
-    let mut coinbase_input = txin(config, rng);
-    coinbase_input.script_sig = coinbase_script;
-    coinbase_tx.input = vec![coinbase_input];
-
-    txdata.insert(0, coinbase_tx);
+    txdata.insert(0, coinbase_tx(config, rng));
 
     let header = bitcoin::block::Header {
         version: bitcoin::block::Version::TWO,
@@ -161,3 +151,25 @@ pub fn signature<R: rand::RngCore + ?Sized>(
 
     p256k1::ecdsa::Signature::new(&multipurpose_bytes, &secret_key).unwrap()
 }
+
+/// Coinbase transaction with random block height
+fn coinbase_tx<R: rand::RngCore + ?Sized>(
+    config: &fake::Faker,
+    rng: &mut R,
+) -> bitcoin::Transaction {
+    // Numbers below 17 are encoded differently which messes with the block height decoding
+    let min_block_height = 17;
+    let block_height_span = 10000;
+    let block_height =
+        config.fake_with_rng::<i64, _>(rng).abs() % block_height_span + min_block_height;
+    let coinbase_script = bitcoin::script::Builder::new()
+        .push_int(block_height)
+        .into_script();
+
+    let mut coinbase_tx = tx(config, rng);
+    let mut coinbase_input = txin(config, rng);
+    coinbase_input.script_sig = coinbase_script;
+    coinbase_tx.input = vec![coinbase_input];
+
+    coinbase_tx
+}