feat: get more last headers in the first proof of a newly connected peer

src/protocols/light_client/mod.rs

@@ -852,11 +852,35 @@ impl LightClientProtocol {
         }
         let builder = packed::GetLastStateProof::new_builder()
             .last_hash(last_header.header().hash())
-            .start_hash(start_hash)
-            .start_number(start_number.pack())
             .last_n_blocks(last_n_blocks.pack());
         let content = if last_number - start_number <= last_n_blocks {
-            builder.difficulty_boundary(start_total_difficulty.pack())
+            let last_n_headers = self.storage.get_last_n_headers();
+            let mut real_start_hash = start_hash;
+            let mut real_start_number = start_number;
+            // Find the number which satisfies that `last_number - number > last_n_blocks`.
+            // If not found, then choose the smallest number.
+            for (num, hash) in last_n_headers
+                .into_iter()
+                .rev()
+                // `skip_while` should do nothing, just for safety.
+                .skip_while(|(n, _)| *n >= start_number)
+            {
+                if real_start_number <= num {
+                    continue;
+                }
+                if last_number > num + last_n_blocks {
+                    break;
+                }
+                real_start_hash = hash;
+                real_start_number = num;
+                if last_number == num + last_n_blocks {
+                    break;
+                }
+            }
+            builder
+                .start_hash(real_start_hash)
+                .start_number(real_start_number.pack())
+                .difficulty_boundary(start_total_difficulty.pack())
         } else {
             let (difficulty_boundary, difficulties) = sampling::sample_blocks(
                 start_number,
@@ -866,6 +890,8 @@ impl LightClientProtocol {
                 last_n_blocks,
             );
             builder
+                .start_hash(start_hash)
+                .start_number(start_number.pack())
                 .difficulty_boundary(difficulty_boundary.pack())
                 .difficulties(difficulties.into_iter().map(|inner| inner.pack()).pack())
         }