Feature: CPI Events API (coral-xyz#2438)

Co-authored-by: acheron <acheroncrypto@gmail.com>

CHANGELOG.md

@@ -17,6 +17,7 @@ The minor version will be incremented upon a breaking change and the patch versi
 - cli: Add support for Solidity programs. `anchor init` and `anchor new` take an option `--solidity` which creates solidity code rather than rust. `anchor build` and `anchor test` work accordingly ([#2421](https://github.com/coral-xyz/anchor/pull/2421))
 - bench: Add benchmarking for compute units usage ([#2466](https://github.com/coral-xyz/anchor/pull/2466))
 - cli: `idl set-buffer`, `idl set-authority` and `idl close` take an option `--print-only`. which prints transaction in a base64 Borsh compatible format but not sent to the cluster. It's helpful when managing authority under a multisig, e.g., a user can create a proposal for a `Custom Instruction` in SPL Governance ([#2486](https://github.com/coral-xyz/anchor/pull/2486)).
+- lang: Add `emit_cpi!` and `#[event_cpi]` macros(behind `event-cpi` feature flag) to store event logs in transaction metadata ([#2438](https://github.com/coral-xyz/anchor/pull/2438)).
 
 ### Fixes
 

cli/Cargo.toml

@@ -24,7 +24,7 @@ bincode = "1.3.3"
 syn = { version = "1.0.60", features = ["full", "extra-traits"] }
 anchor-lang = { path = "../lang", version = "0.27.0", package = "light-anchor-lang" }
 anchor-client = { path = "../client", version = "0.27.0", package = "light-anchor-client" }
-anchor-syn = { path = "../lang/syn", features = ["idl", "init-if-needed"], version = "0.27.0", package = "light-anchor-syn" }
+anchor-syn = { path = "../lang/syn", features = ["event-cpi", "idl", "init-if-needed"], version = "0.27.0", package = "light-anchor-syn" }
 serde_json = "1.0"
 shellexpand = "2.1.0"
 toml = "0.5.8"

lang/Cargo.toml

@@ -13,6 +13,7 @@ allow-missing-optionals = ["anchor-derive-accounts/allow-missing-optionals"]
 init-if-needed = ["anchor-derive-accounts/init-if-needed"]
 derive = []
 default = []
+event-cpi = ["anchor-attribute-event/event-cpi"]
 anchor-debug = [
     "anchor-attribute-access-control/anchor-debug",
     "anchor-attribute-account/anchor-debug",

lang/attribute/event/Cargo.toml

@@ -13,6 +13,7 @@ proc-macro = true
 
 [features]
 anchor-debug = ["anchor-syn/anchor-debug"]
+event-cpi = ["anchor-syn/event-cpi"]
 
 [dependencies]
 proc-macro2 = "1.0"

lang/attribute/event/src/lib.rs

@@ -1,5 +1,7 @@
 extern crate proc_macro;
 
+#[cfg(feature = "event-cpi")]
+use anchor_syn::parser::accounts::event_cpi::{add_event_cpi_accounts, EventAuthority};
 use quote::quote;
 use syn::parse_macro_input;
 
@@ -45,6 +47,14 @@ pub fn event(
     })
 }
 
+// EventIndex is a marker macro. It functionally does nothing other than
+// allow one to mark fields with the `#[index]` inert attribute, which is
+// used to add metadata to IDLs.
+#[proc_macro_derive(EventIndex, attributes(index))]
+pub fn derive_event(_item: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    proc_macro::TokenStream::from(quote! {})
+}
+
 /// Logs an event that can be subscribed to by clients.
 /// Uses the [`sol_log_data`](https://docs.rs/solana-program/latest/solana_program/log/fn.sol_log_data.html)
 /// syscall which results in the following log:
@@ -81,10 +91,127 @@ pub fn emit(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     })
 }
 
-// EventIndex is a marker macro. It functionally does nothing other than
-// allow one to mark fields with the `#[index]` inert attribute, which is
-// used to add metadata to IDLs.
-#[proc_macro_derive(EventIndex, attributes(index))]
-pub fn derive_event(_item: proc_macro::TokenStream) -> proc_macro::TokenStream {
-    proc_macro::TokenStream::from(quote! {})
+/// Log an event by making a self-CPI that can be subscribed to by clients.
+///
+/// This way of logging events is more reliable than [`emit!`](emit!) because RPCs are less likely
+/// to truncate CPI information than program logs.
+///
+/// Uses a [`invoke_signed`](https://docs.rs/solana-program/latest/solana_program/program/fn.invoke_signed.html)
+/// syscall to store the event data in the ledger, which results in the data being stored in the
+/// transaction metadata.
+///
+/// This method requires the usage of an additional PDA to guarantee that the self-CPI is truly
+/// being invoked by the same program. Requiring this PDA to be a signer during `invoke_signed`
+/// syscall ensures that the program is the one doing the logging.
+///
+/// The necessary accounts are added to the accounts struct via [`#[event_cpi]`](event_cpi)
+/// attribute macro.
+///
+/// # Example
+///
+/// ```ignore
+/// use anchor_lang::prelude::*;
+///
+/// #[program]
+/// pub mod my_program {
+///     use super::*;
+///
+///     pub fn my_instruction(ctx: Context<MyInstruction>) -> Result<()> {
+///         emit_cpi!(MyEvent { data: 42 });
+///         Ok(())
+///     }
+/// }
+///
+/// #[event_cpi]
+/// #[derive(Accounts)]
+/// pub struct MyInstruction {}
+///
+/// #[event]
+/// pub struct MyEvent {
+///     pub data: u64,
+/// }
+/// ```
+///
+/// **NOTE:** This macro requires `ctx` to be in scope.
+///
+/// *Only available with `event-cpi` feature enabled.*
+#[cfg(feature = "event-cpi")]
+#[proc_macro]
+pub fn emit_cpi(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let event_struct = parse_macro_input!(input as syn::Expr);
+
+    let authority = EventAuthority::get();
+    let authority_name = authority.name_token_stream();
+    let authority_name_str = authority.name;
+    let authority_seeds = authority.seeds;
+
+    proc_macro::TokenStream::from(quote! {
+        {
+            let authority_info = ctx.accounts.#authority_name.to_account_info();
+            let authority_bump = *ctx.bumps.get(#authority_name_str).unwrap();
+
+            let disc = anchor_lang::event::EVENT_IX_TAG_LE;
+            let inner_data = anchor_lang::Event::data(&#event_struct);
+            let ix_data: Vec<u8> = disc.into_iter().chain(inner_data.into_iter()).collect();
+
+            let ix = anchor_lang::solana_program::instruction::Instruction::new_with_bytes(
+                crate::ID,
+                &ix_data,
+                vec![
+                    anchor_lang::solana_program::instruction::AccountMeta::new_readonly(
+                        *authority_info.key,
+                        true,
+                    ),
+                ],
+            );
+            anchor_lang::solana_program::program::invoke_signed(
+                &ix,
+                &[authority_info],
+                &[&[#authority_seeds, &[authority_bump]]],
+            )
+            .map_err(anchor_lang::error::Error::from)?;
+        }
+    })
+}
+
+/// An attribute macro to add necessary event CPI accounts to the given accounts struct.
+///
+/// Two accounts named `event_authority` and `program` will be appended to the list of accounts.
+///
+/// # Example
+///
+/// ```ignore
+/// #[event_cpi]
+/// #[derive(Accounts)]
+/// pub struct MyInstruction<'info> {
+///    pub signer: Signer<'info>,
+/// }
+/// ```
+///
+/// The code above will be expanded to:
+///
+/// ```ignore
+/// #[derive(Accounts)]
+/// pub struct MyInstruction<'info> {
+///    pub signer: Signer<'info>,
+///    /// CHECK: Only the event authority can invoke self-CPI
+///    #[account(seeds = [b"__event_authority"], bump)]
+///    pub event_authority: AccountInfo<'info>,
+///    /// CHECK: Self-CPI will fail if the program is not the current program
+///    pub program: AccountInfo<'info>,
+/// }
+/// ```
+///
+/// See [`emit_cpi!`](emit_cpi!) for a full example.
+///
+/// *Only available with `event-cpi` feature enabled.*
+#[cfg(feature = "event-cpi")]
+#[proc_macro_attribute]
+pub fn event_cpi(
+    _attr: proc_macro::TokenStream,
+    input: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    let accounts_struct = parse_macro_input!(input as syn::ItemStruct);
+    let accounts_struct = add_event_cpi_accounts(&accounts_struct).unwrap();
+    proc_macro::TokenStream::from(quote! {#accounts_struct})
 }

lang/src/error.rs

@@ -44,6 +44,11 @@ pub enum ErrorCode {
     #[msg("IDL account must be empty in order to resize, try closing first")]
     IdlAccountNotEmpty,
 
+    // Event instructions
+    /// 1500 - The program was compiled without `event-cpi` feature
+    #[msg("The program was compiled without `event-cpi` feature")]
+    EventInstructionStub = 1500,
+
     // Constraints
     /// 2000 - A mut constraint was violated
     #[msg("A mut constraint was violated")]

lang/src/event.rs

@@ -0,0 +1,3 @@
+// Sha256(anchor:event)[..8]
+pub const EVENT_IX_TAG: u64 = 0x1d9acb512ea545e4;
+pub const EVENT_IX_TAG_LE: [u8; 8] = EVENT_IX_TAG.to_le_bytes();

lang/src/lib.rs

@@ -38,6 +38,8 @@ mod common;
 pub mod context;
 pub mod error;
 #[doc(hidden)]
+pub mod event;
+#[doc(hidden)]
 pub mod idl;
 pub mod system_program;
 
@@ -48,6 +50,8 @@ pub use anchor_attribute_account::{account, declare_id, zero_copy};
 pub use anchor_attribute_constant::constant;
 pub use anchor_attribute_error::*;
 pub use anchor_attribute_event::{emit, event};
+#[cfg(feature = "event-cpi")]
+pub use anchor_attribute_event::{emit_cpi, event_cpi};
 pub use anchor_attribute_program::program;
 pub use anchor_derive_accounts::Accounts;
 pub use anchor_derive_space::InitSpace;
@@ -299,6 +303,8 @@ pub mod prelude {
         AccountsClose, AccountsExit, AnchorDeserialize, AnchorSerialize, Id, InitSpace, Key, Owner,
         ProgramData, Result, Space, ToAccountInfo, ToAccountInfos, ToAccountMetas,
     };
+    #[cfg(feature = "event-cpi")]
+    pub use super::{emit_cpi, event_cpi};
     pub use anchor_attribute_error::*;
     pub use borsh;
     pub use error::*;

lang/syn/Cargo.toml

@@ -16,6 +16,7 @@ hash = []
 default = []
 anchor-debug = []
 seeds = []
+event-cpi = []
 
 [dependencies]
 proc-macro2 = { version = "1.0", features=["span-locations"]}

lang/syn/src/codegen/program/dispatch.rs

@@ -27,9 +27,13 @@ pub fn generate(program: &Program) -> proc_macro2::TokenStream {
             }
         })
         .collect();
+
     let fallback_fn = gen_fallback(program).unwrap_or(quote! {
         Err(anchor_lang::error::ErrorCode::InstructionFallbackNotFound.into())
     });
+
+    let event_cpi_handler = generate_event_cpi_handler();
+
     quote! {
         /// Performs method dispatch.
         ///
@@ -67,17 +71,24 @@ pub fn generate(program: &Program) -> proc_macro2::TokenStream {
                 #(#global_dispatch_arms)*
                 anchor_lang::idl::IDL_IX_TAG_LE => {
                     // If the method identifier is the IDL tag, then execute an IDL
-                    // instruction, injected into all Anchor programs.
-                    if cfg!(not(feature = "no-idl")) {
+                    // instruction, injected into all Anchor programs unless they have
+                    // no-idl enabled
+                    #[cfg(not(feature = "no-idl"))]
+                    {
                         __private::__idl::__idl_dispatch(
                             program_id,
                             accounts,
                             &ix_data,
                         )
-                    } else {
+                    }
+                    #[cfg(feature = "no-idl")]
+                    {
                         Err(anchor_lang::error::ErrorCode::IdlInstructionStub.into())
                     }
                 }
+                anchor_lang::event::EVENT_IX_TAG_LE => {
+                    #event_cpi_handler
+                }
                 _ => {
                     #fallback_fn
                 }
@@ -96,3 +107,17 @@ pub fn gen_fallback(program: &Program) -> Option<proc_macro2::TokenStream> {
         }
     })
 }
+
+/// Generate the event-cpi instruction handler based on whether the `event-cpi` feature is enabled.
+pub fn generate_event_cpi_handler() -> proc_macro2::TokenStream {
+    #[cfg(feature = "event-cpi")]
+    quote! {
+        // `event-cpi` feature is enabled, dispatch self-cpi instruction
+        __private::__events::__event_dispatch(program_id, accounts, &ix_data)
+    }
+    #[cfg(not(feature = "event-cpi"))]
+    quote! {
+        // `event-cpi` feature is not enabled
+        Err(anchor_lang::error::ErrorCode::EventInstructionStub.into())
+    }
+}

lang/syn/src/codegen/program/handlers.rs

@@ -91,6 +91,8 @@ pub fn generate(program: &Program) -> proc_macro2::TokenStream {
         }
     };
 
+    let event_cpi_mod = generate_event_cpi_mod();
+
     let non_inlined_handlers: Vec<proc_macro2::TokenStream> = program
         .ixs
         .iter()
@@ -173,14 +175,14 @@ pub fn generate(program: &Program) -> proc_macro2::TokenStream {
                 #idl_accounts_and_functions
             }
 
-
-
             /// __global mod defines wrapped handlers for global instructions.
             pub mod __global {
                 use super::*;
 
                 #(#non_inlined_handlers)*
             }
+
+            #event_cpi_mod
         }
     }
 }
@@ -189,3 +191,49 @@ fn generate_ix_variant_name(name: String) -> proc_macro2::TokenStream {
     let n = name.to_camel_case();
     n.parse().unwrap()
 }
+
+/// Generate the event module based on whether the `event-cpi` feature is enabled.
+fn generate_event_cpi_mod() -> proc_macro2::TokenStream {
+    #[cfg(feature = "event-cpi")]
+    {
+        let authority = crate::parser::accounts::event_cpi::EventAuthority::get();
+        let authority_name = authority.name;
+        let authority_seeds = authority.seeds;
+
+        quote! {
+            /// __events mod defines handler for self-cpi based event logging
+            pub mod __events {
+                use super::*;
+
+                #[inline(never)]
+                pub fn __event_dispatch(
+                    program_id: &Pubkey,
+                    accounts: &[AccountInfo],
+                    event_data: &[u8],
+                ) -> anchor_lang::Result<()> {
+                    let given_event_authority = next_account_info(&mut accounts.iter())?;
+                    if !given_event_authority.is_signer {
+                        return Err(anchor_lang::error::Error::from(
+                            anchor_lang::error::ErrorCode::ConstraintSigner,
+                        )
+                        .with_account_name(#authority_name));
+                    }
+
+                    let (expected_event_authority, _) =
+                        Pubkey::find_program_address(&[#authority_seeds], &program_id);
+                    if given_event_authority.key() != expected_event_authority {
+                        return Err(anchor_lang::error::Error::from(
+                            anchor_lang::error::ErrorCode::ConstraintSeeds,
+                        )
+                        .with_account_name(#authority_name)
+                        .with_pubkeys((given_event_authority.key(), expected_event_authority)));
+                    }
+
+                    Ok(())
+                }
+            }
+        }
+    }
+    #[cfg(not(feature = "event-cpi"))]
+    quote! {}
+}