spl: Add shared memory api

CHANGELOG.md

@@ -13,6 +13,7 @@ incremented for features.
 
 * cli: Embed workspace programs into local validator genesis when testing.
 * cli: Stream program logs to `.anchor/program-logs` directory when testing.
+* spl: Add shared memory api.
 
 ## [0.2.0] - 2021-02-08
 

spl/Cargo.toml

@@ -9,3 +9,4 @@ description = "CPI clients for SPL programs"
 [dependencies]
 anchor-lang = { path = "../lang", version = "0.2.0", features = ["derive"] }
 spl-token = { version = "3.0.1", features = ["no-entrypoint"] }
+solana-program = "=1.5.0"

spl/src/lib.rs

@@ -1 +1,2 @@
+pub mod shmem;
 pub mod token;

spl/src/shmem.rs

@@ -0,0 +1,49 @@
+//! CPI API for interacting with the SPL shared memory
+//! [program](https://github.com/solana-labs/solana-program-library/tree/master/shared-memory).
+
+use anchor_lang::{Accounts, CpiContext};
+use solana_program::account_info::AccountInfo;
+use solana_program::declare_id;
+use solana_program::entrypoint::ProgramResult;
+use solana_program::instruction::{AccountMeta, Instruction};
+use solana_program::program;
+
+// TODO: update this once the final shared memory program gets released.
+//       shmem4EWT2sPdVGvTZCzXXRAURL9G5vpPxNwSeKhHUL.
+declare_id!("DynWy94wrWp5RimU49creYMQ5py3Up8BBNS4VA73VCpi");
+
+/// `ret` writes the given `data` field to the shared memory account
+/// acting as a return value that can be used across CPI.
+/// The caleee should use this to write data into the shared memory account.
+/// The caler should use the account directly to pull out and interpret the
+/// bytes. Shared memory serialization is not specified and is up to the
+/// caller and callee.
+pub fn ret<'a, 'b, 'c, 'info>(
+    ctx: CpiContext<'a, 'b, 'c, 'info, Ret<'info>>,
+    data: Vec<u8>,
+) -> ProgramResult {
+    let instruction = Instruction {
+        program_id: *ctx.program.key,
+        accounts: vec![AccountMeta::new(*ctx.accounts.buffer.key, false)],
+        data,
+    };
+    let mut accounts = vec![ctx.accounts.buffer];
+    accounts.push(ctx.program.clone());
+    program::invoke(&instruction, &accounts)
+}
+
+#[derive(Accounts)]
+pub struct Ret<'info> {
+    #[account(mut)]
+    pub buffer: AccountInfo<'info>,
+}
+
+// A set of accounts that can be used with shared memory.
+#[derive(Accounts)]
+pub struct Shmem<'info> {
+    // Shared memory account to write the return value into.
+    #[account(mut, "shmem.owner == shmem_program.key")]
+    pub shmem: AccountInfo<'info>,
+    #[account("shmem_program.key == &ID")]
+    pub shmem_program: AccountInfo<'info>,
+}