Added necessary comments to insecure, recommended, and secure closing account programs

programs/9-closing-accounts/insecure-still-still/src/lib.rs

@@ -1,38 +1,42 @@
 use anchor_lang::prelude::*;
-use std::io::Write;
 use std::ops::DerefMut;
 
 declare_id!("Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS");
 
 #[program]
-pub mod closing_accounts_insecure_still_still {
+pub mod closing_accounts_insecure_still {
     use super::*;
 
     pub fn close(ctx: Context<Close>) -> ProgramResult {
         let account = ctx.accounts.account.to_account_info();
 
         let dest_starting_lamports = ctx.accounts.destination.lamports();
 
+        // Transfer all lamports from the account being closed to the destination.
         **ctx.accounts.destination.lamports.borrow_mut() = dest_starting_lamports
             .checked_add(account.lamports())
             .unwrap();
+
+        // Set the lamports of the account being closed to zero.
         **account.lamports.borrow_mut() = 0;
 
+        // Zero out the account's data.
         let mut data = account.try_borrow_mut_data()?;
         for byte in data.deref_mut().iter_mut() {
             *byte = 0;
         }
 
-        let dst: &mut [u8] = &mut data;
-        let mut cursor = std::io::Cursor::new(dst);
-        cursor
-            .write_all(&anchor_lang::__private::CLOSED_ACCOUNT_DISCRIMINATOR)
-            .unwrap();
-
         Ok(())
     }
 }
 
+#[derive(Accounts)]
+pub struct Initialize<'info> {
+    #[account(zero)] // Ensure the account has zeroed data before use.
+    account: Account<'info, Data>,
+    authority: Signer<'info>,
+}
+
 #[derive(Accounts)]
 pub struct Close<'info> {
     account: Account<'info, Data>,

programs/9-closing-accounts/insecure-still/src/lib.rs

@@ -12,11 +12,15 @@ pub mod closing_accounts_insecure_still {
 
         let dest_starting_lamports = ctx.accounts.destination.lamports();
 
+        // Transfer all lamports from the account being closed to the destination.
         **ctx.accounts.destination.lamports.borrow_mut() = dest_starting_lamports
             .checked_add(account.lamports())
             .unwrap();
+
+        // Set the lamports of the account being closed to zero.
         **account.lamports.borrow_mut() = 0;
 
+        // Zero out the account's data.
         let mut data = account.try_borrow_mut_data()?;
         for byte in data.deref_mut().iter_mut() {
             *byte = 0;
@@ -28,7 +32,7 @@ pub mod closing_accounts_insecure_still {
 
 #[derive(Accounts)]
 pub struct Initialize<'info> {
-    #[account(zero)]
+    #[account(zero)] // Ensure the account has zeroed data before use.
     account: Account<'info, Data>,
     authority: Signer<'info>,
 }

programs/9-closing-accounts/insecure/src/lib.rs

@@ -7,11 +7,15 @@ pub mod closing_accounts_insecure {
     use super::*;
 
     pub fn close(ctx: Context<Close>) -> ProgramResult {
+        // Get the current balance of the destination account
         let dest_starting_lamports = ctx.accounts.destination.lamports();
 
+        // Transfer all lamports from the account being closed to the destination account
         **ctx.accounts.destination.lamports.borrow_mut() = dest_starting_lamports
             .checked_add(ctx.accounts.account.to_account_info().lamports())
             .unwrap();
+
+        // Set the balance of the closed account to zero
         **ctx.accounts.account.to_account_info().lamports.borrow_mut() = 0;
 
         Ok(())
@@ -21,7 +25,7 @@ pub mod closing_accounts_insecure {
 #[derive(Accounts)]
 pub struct Close<'info> {
     account: Account<'info, Data>,
-    destination: AccountInfo<'info>,
+    destination: AccountInfo<'info>, // The account to receive the lamports
 }
 
 #[account]

programs/9-closing-accounts/recommended/src/lib.rs

@@ -13,10 +13,11 @@ pub mod closing_accounts_recommended {
 
 #[derive(Accounts)]
 pub struct Close<'info> {
+    // Automatically transfer lamports from the account to the destination and close the account
     #[account(mut, close = destination)]
     account: Account<'info, Data>,
     #[account(mut)]
-    destination: AccountInfo<'info>,
+    destination: AccountInfo<'info>, // Receiver of the remaining lamports
 }
 
 #[account]

programs/9-closing-accounts/secure/src/lib.rs

@@ -13,16 +13,19 @@ pub mod closing_accounts_secure {
         let dest_starting_lamports = ctx.accounts.destination.lamports();
 
         let account = ctx.accounts.account.to_account_info();
+        // Transfer lamports from the account being closed to the destination account
         **ctx.accounts.destination.lamports.borrow_mut() = dest_starting_lamports
             .checked_add(account.lamports())
             .unwrap();
         **account.lamports.borrow_mut() = 0;
 
+        // Clear the account data
         let mut data = account.try_borrow_mut_data()?;
         for byte in data.deref_mut().iter_mut() {
             *byte = 0;
         }
 
+        // Write CLOSED_ACCOUNT_DISCRIMINATOR to mark the account as closed
         let dst: &mut [u8] = &mut data;
         let mut cursor = Cursor::new(dst);
         cursor.write_all(&CLOSED_ACCOUNT_DISCRIMINATOR).unwrap();
@@ -36,6 +39,7 @@ pub mod closing_accounts_secure {
         let data = account.try_borrow_data()?;
         assert!(data.len() > 8);
 
+        // Check if the account is already closed by inspecting the discriminator
         let mut discriminator = [0u8; 8];
         discriminator.copy_from_slice(&data[0..8]);
         if discriminator != CLOSED_ACCOUNT_DISCRIMINATOR {
@@ -44,6 +48,7 @@ pub mod closing_accounts_secure {
 
         let dest_starting_lamports = ctx.accounts.destination.lamports();
 
+        // Transfer remaining lamports from the account to the destination
         **ctx.accounts.destination.lamports.borrow_mut() = dest_starting_lamports
             .checked_add(account.lamports())
             .unwrap();
@@ -55,14 +60,14 @@ pub mod closing_accounts_secure {
 
 #[derive(Accounts)]
 pub struct Close<'info> {
-    account: Account<'info, Data>,
-    destination: AccountInfo<'info>,
+    account: Account<'info, Data>, // The account to be closed
+    destination: AccountInfo<'info>, // The account that receives the lamports
 }
 
 #[derive(Accounts)]
 pub struct ForceDefund<'info> {
-    account: AccountInfo<'info>,
-    destination: AccountInfo<'info>,
+    account: AccountInfo<'info>, // The already-closed account
+    destination: AccountInfo<'info>, // The account receiving any remaining lamports
 }
 
 #[account]