Merge pull request Blockstream#5 from mempool/fix/difficulty_f64

REST: Return an f64 for difficulty from the block value endpoint

Author: softsimon

src/rest.rs

@@ -69,7 +69,7 @@ struct BlockValue {
     #[cfg(not(feature = "liquid"))]
     bits: u32,
     #[cfg(not(feature = "liquid"))]
-    difficulty: u64,
+    difficulty: f64,
 
     #[cfg(feature = "liquid")]
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -78,7 +78,7 @@ struct BlockValue {
 
 impl BlockValue {
     #[cfg_attr(feature = "liquid", allow(unused_variables))]
-    fn new(blockhm: BlockHeaderMeta, network: Network) -> Self {
+    fn new(blockhm: BlockHeaderMeta) -> Self {
         let header = blockhm.header_entry.header();
         BlockValue {
             id: header.block_hash().to_hex(),
@@ -106,14 +106,35 @@ impl BlockValue {
             #[cfg(not(feature = "liquid"))]
             nonce: header.nonce,
             #[cfg(not(feature = "liquid"))]
-            difficulty: header.difficulty(bitcoin::Network::from(network)),
+            difficulty: difficulty_new(header),
 
             #[cfg(feature = "liquid")]
             ext: Some(json!(header.ext)),
         }
     }
 }
 
+/// Calculate the difficulty of a BlockHeader
+/// using Bitcoin Core code ported to Rust.
+///
+/// https://github.com/bitcoin/bitcoin/blob/v25.0/src/rpc/blockchain.cpp#L75-L97
+#[cfg_attr(feature = "liquid", allow(dead_code))]
+fn difficulty_new(bh: &bitcoin::BlockHeader) -> f64 {
+    let mut n_shift = bh.bits >> 24 & 0xff;
+    let mut d_diff = (0x0000ffff as f64) / ((bh.bits & 0x00ffffff) as f64);
+
+    while n_shift < 29 {
+        d_diff *= 256.0;
+        n_shift += 1;
+    }
+    while n_shift > 29 {
+        d_diff /= 256.0;
+        n_shift -= 1;
+    }
+
+    d_diff
+}
+
 #[derive(Serialize, Deserialize)]
 struct TransactionValue {
     txid: Txid,
@@ -681,7 +702,7 @@ fn handle_request(
                 .chain()
                 .get_block_with_meta(&hash)
                 .ok_or_else(|| HttpError::not_found("Block not found".to_string()))?;
-            let block_value = BlockValue::new(blockhm, config.network_type);
+            let block_value = BlockValue::new(blockhm);
             json_response(block_value, TTL_LONG)
         }
         (&Method::GET, Some(&"block"), Some(hash), Some(&"status"), None, None) => {
@@ -1325,7 +1346,7 @@ fn blocks(
         current_hash = blockhm.header_entry.header().prev_blockhash;
 
         #[allow(unused_mut)]
-        let mut value = BlockValue::new(blockhm, config.network_type);
+        let mut value = BlockValue::new(blockhm);
 
         #[cfg(feature = "liquid")]
         {
@@ -1533,4 +1554,128 @@ mod tests {
 
         assert!(err.is_err());
     }
+
+    #[test]
+    fn test_difficulty_new() {
+        use super::difficulty_new;
+
+        let vectors = [
+            (
+                // bits in header
+                0x17053894,
+                // expected output (Rust)
+                53911173001054.586,
+                // Block hash where found (for getblockheader)
+                "0000000000000000000050b050758dd2ccb0ba96ad5e95db84efd2f6c05e4e90",
+                // difficulty returned by Bitcoin Core v25
+                "53911173001054.59",
+            ),
+            (
+                0x1a0c2a12,
+                1379192.2882280778,
+                "0000000000000bc7636ffbc1cf90cf4a2674de7fcadbc6c9b63d31f07cb3c2c2",
+                "1379192.288228078",
+            ),
+            (
+                0x19262222,
+                112628548.66634709,
+                "000000000000000996b1f06771a81bcf7b15c5f859b6f8329016f01b0442ca72",
+                "112628548.6663471",
+            ),
+            (
+                0x1d00c428,
+                1.3050621315915245,
+                "0000000034014d731a3e1ad6078662ce19b08179dcc7ec0f5f717d4b58060736",
+                "1.305062131591525",
+            ),
+            (
+                0,
+                f64::INFINITY,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking edge cases]",
+            ),
+            (
+                0x00000001,
+                4.523059468369196e74,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking edge cases]",
+            ),
+            (
+                0x1d00ffff,
+                1.0,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking MAX_TARGET]",
+            ),
+            (
+                0x1c7fff80,
+                2.0,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking MAX_TARGET >> 1]",
+            ),
+            (
+                0x1b00ffff,
+                65536.0,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking MAX_TARGET >> 16]",
+            ),
+            (
+                0x1a7fff80,
+                131072.0,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking MAX_TARGET >> 17]",
+            ),
+            (
+                0x1d01fffe,
+                0.5,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking MAX_TARGET << 1]",
+            ),
+            (
+                0x1f000080,
+                0.007812380790710449,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking 2**255]",
+            ),
+            (
+                0x1e00ffff,
+                0.00390625, // 2.0**-8
+                "[No Blockhash]",
+                "[No Core difficulty, just checking MAX_TARGET << 8]",
+            ),
+            (
+                0x1e00ff00,
+                0.0039215087890625,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking MAX_TARGET << 8 - two `f` chars]",
+            ),
+            (
+                0x1f0000ff,
+                0.0039215087890625,
+                "[No Blockhash]",
+                "[No Core difficulty, just checking MAX_TARGET << 8]",
+            ),
+        ];
+
+        let to_bh = |b| bitcoin::BlockHeader {
+            version: 1,
+            prev_blockhash: "0000000000000000000000000000000000000000000000000000000000000000"
+                .parse()
+                .unwrap(),
+            merkle_root: "0000000000000000000000000000000000000000000000000000000000000000"
+                .parse()
+                .unwrap(),
+            time: 0,
+            bits: b,
+            nonce: 0,
+        };
+
+        for (bits, expected, hash, core_difficulty) in vectors {
+            let result = difficulty_new(&to_bh(bits));
+            assert_eq!(
+                result, expected,
+                "Block {} difficulty is {} but Core difficulty is {}",
+                hash, result, core_difficulty,
+            );
+        }
+    }
 }