added paginated list of nodes

src/persistence.rs

@@ -108,6 +108,31 @@ impl FileManager {
         file.read_exact(&mut node_bytes).await?;
         Ok(Node::from_bytes(node_bytes))
     }
+
+    /// Returns 20 nodes from the disk.
+    /// Specify offset (the number of nodes to skip).
+    async fn get_page_of_20(&self, offset: u64) -> std::io::Result<Vec<Node>> {
+        let mut file = self.file.lock().await;
+        file.seek(SeekFrom::Start(
+            offset
+                .wrapping_mul(DATA_SIZE.try_into().unwrap_or(0)),
+        ))
+        .await?;
+        let mut nodes = Vec::new();
+        let mut count = 0;
+        loop {
+            let mut node_bytes = [0; DATA_SIZE];
+            if let Err(_) = file.read_exact(&mut node_bytes).await {
+                break;
+            };
+            nodes.push(Node::from_bytes(node_bytes));
+            count += 1;
+            if count == 20 {
+                break;
+            }
+        }
+        Ok(nodes)
+    }
 }
 
 #[cfg(test)]
@@ -287,4 +312,64 @@ mod tests {
         remove_file(get_test_file_name(function_name)).await?;
         Ok(())
     }
+
+    #[tokio::test]
+    async fn get_page_of_20_nodes() -> Result<()> {
+        let function_name = "get_page_of_20_nodes";
+        let manager = setup_test_file(function_name).await?;
+        let mut count = 0;
+        let mut nodes: Vec<Node> = Vec::new();
+        while count < 100 {
+            let node = get_random_node();
+            if count >= 23 && count < 43 {
+                nodes.push(node.clone());
+            }
+            manager.append_node(node).await?;
+            count += 1;
+        }
+        count = 23;
+        let mut r_nodes = manager.get_page_of_20(23).await?.into_iter();
+        for node in nodes.iter() {
+            let r_node = r_nodes.next().unwrap();
+            println!("{} {} {}", count, node.ip_as_string(), r_node.ip_as_string());
+            assert_eq!(node.ip_as_string(), r_node.ip_as_string());
+            assert_eq!(node.keypair, r_node.keypair);
+            count += 1;
+            if count == 44 {
+                break;
+            }
+        }
+        remove_file(get_test_file_name(function_name)).await?;
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn get_last_page() -> Result<()> {
+        let function_name = "get_last_page";
+        let manager = setup_test_file(function_name).await?;
+        let mut count = 0;
+        let mut nodes: Vec<Node> = Vec::new();
+        while count < 97 {
+            let node = get_random_node();
+            if count >= 90 {
+                nodes.push(node.clone());
+            }
+            manager.append_node(node).await?;
+            count += 1;
+        }
+        count = 23;
+        let mut r_nodes = manager.get_page_of_20(90).await?.into_iter();
+        for node in nodes.iter() {
+            let r_node = r_nodes.next().unwrap();
+            println!("{} {} {}", count, node.ip_as_string(), r_node.ip_as_string());
+            assert_eq!(node.ip_as_string(), r_node.ip_as_string());
+            assert_eq!(node.keypair, r_node.keypair);
+            count += 1;
+            if count == 44 {
+                break;
+            }
+        }
+        remove_file(get_test_file_name(function_name)).await?;
+        Ok(())
+    }
 }