fix(message-buffer): address PR feedback from 779, update tests (#784)

* fix(message-buffer): address PR feedback from 779, update tests

Add new unit test for reading with cursor, update test setup

* refactor(message-buffer): refactor test methods, add big endian doc on MessageBuffer

Author: swimricky

message_buffer/Cargo.lock

@@ -19,3 +19,6 @@ default = []
 anchor-lang = { version = "0.27.0" }
 # needed for the new #[account(zero_copy)] in anchor 0.27.0
 bytemuck = { version = "1.4.0", features = ["derive", "min_const_generics"]}
+
+[dev-dependencies]
+byteorder = "1.4.3"

message_buffer/programs/message_buffer/Cargo.toml

@@ -75,6 +75,9 @@ pub fn create_buffer<'info>(
             *message_buffer = MessageBuffer::new(bump);
         }
         loader.exit(&crate::ID)?;
+    } else {
+        // FIXME: change this to be emit!(Event)
+        msg!("Buffer account already initialized");
     }
 
     Ok(())

message_buffer/programs/message_buffer/src/instructions/create_buffer.rs

@@ -1,6 +1,5 @@
 use {
     crate::{
-        instructions::verify_message_buffer,
         state::*,
         MessageBufferError,
         MESSAGE,
@@ -23,7 +22,7 @@ pub fn delete_buffer<'info>(
         .whitelist
         .is_allowed_program_auth(&allowed_program_auth)?;
 
-    verify_message_buffer(message_buffer_account_info)?;
+    MessageBuffer::check_discriminator(message_buffer_account_info)?;
 
     let expected_key = Pubkey::create_program_address(
         &[

message_buffer/programs/message_buffer/src/instructions/delete_buffer.rs

@@ -1,13 +1,6 @@
-use {
-    crate::{
-        state::MessageBuffer,
-        MessageBufferError,
-    },
-    anchor_lang::{
-        prelude::*,
-        system_program,
-        Discriminator,
-    },
+use anchor_lang::{
+    prelude::*,
+    system_program,
 };
 pub use {
     create_buffer::*,
@@ -23,34 +16,12 @@ mod put_all;
 mod resize_buffer;
 
 // String constants for deriving PDAs.
+//
 // An authorized program's message buffer will have PDA seeds [authorized_program_pda, MESSAGE, base_account_key],
-// where authorized_program_pda is the
+// where authorized_program_pda is the where `allowed_program_auth`
+// is the whitelisted pubkey who authorized this call.
 pub const MESSAGE: &str = "message";
-pub const FUND: &str = "fund";
-
 
 pub fn is_uninitialized_account(ai: &AccountInfo) -> bool {
     ai.data_is_empty() && ai.owner == &system_program::ID
 }
-
-/// Verify message buffer account is initialized and has the correct discriminator.
-///
-/// Note: manually checking because using anchor's `AccountLoader.load()`
-/// will panic since the `AccountInfo.data_len()` will not match the
-/// size of the `MessageBuffer` since the `MessageBuffer` struct does not
-/// include the messages.
-pub fn verify_message_buffer(message_buffer_account_info: &AccountInfo) -> Result<()> {
-    if is_uninitialized_account(message_buffer_account_info) {
-        return err!(MessageBufferError::MessageBufferUninitialized);
-    }
-    let data = message_buffer_account_info.try_borrow_data()?;
-    if data.len() < MessageBuffer::discriminator().len() {
-        return Err(ErrorCode::AccountDiscriminatorNotFound.into());
-    }
-
-    let disc_bytes = &data[0..8];
-    if disc_bytes != &MessageBuffer::discriminator() {
-        return Err(ErrorCode::AccountDiscriminatorMismatch.into());
-    }
-    Ok(())
-}

message_buffer/programs/message_buffer/src/instructions/mod.rs

@@ -1,6 +1,5 @@
 use {
     crate::{
-        instructions::verify_message_buffer,
         state::*,
         MessageBufferError,
     },
@@ -20,7 +19,7 @@ pub fn put_all<'info>(
         .first()
         .ok_or(MessageBufferError::MessageBufferNotProvided)?;
 
-    verify_message_buffer(message_buffer_account_info)?;
+    MessageBuffer::check_discriminator(message_buffer_account_info)?;
 
     let account_data = &mut message_buffer_account_info.try_borrow_mut_data()?;
     let header_end_index = mem::size_of::<MessageBuffer>() + 8;

message_buffer/programs/message_buffer/src/instructions/put_all.rs

@@ -1,6 +1,5 @@
 use {
     crate::{
-        instructions::verify_message_buffer,
         state::*,
         MessageBufferError,
         MESSAGE,
@@ -30,7 +29,7 @@ pub fn resize_buffer<'info>(
     ctx.accounts
         .whitelist
         .is_allowed_program_auth(&allowed_program_auth)?;
-    verify_message_buffer(message_buffer_account_info)?;
+    MessageBuffer::check_discriminator(message_buffer_account_info)?;
 
     require_gte!(
         target_size,
@@ -62,7 +61,10 @@ pub fn resize_buffer<'info>(
         MessageBufferError::InvalidPDA
     );
 
-    if target_size_delta > 0 {
+    // allow for delta == 0 in case Rent requirements have changed
+    // and additional lamports need to be transferred.
+    // the realloc step will be a no-op in this case.
+    if target_size_delta >= 0 {
         let target_rent = Rent::get()?.minimum_balance(target_size);
         if message_buffer_account_info.lamports() < target_rent {
             system_program::transfer(