spl_shared_memory/
lib.rs

1#![deny(missing_docs)]
2//! Shared memory program for the Solana blockchain.
3//
4// Useful for returning data from cross-program invoked programs to the invoker.
5//
6// This program is highly optimized for its particular use case and does not
7// implement the typical `process_instruction` entrypoint.
8
9extern crate solana_program;
10use arrayref::{array_refs, mut_array_refs};
11use solana_program::{
12    declare_id, entrypoint::MAX_PERMITTED_DATA_INCREASE, entrypoint::SUCCESS,
13    program_error::ProgramError, pubkey::Pubkey,
14};
15use std::{
16    mem::{align_of, size_of},
17    ptr::read,
18    slice::{from_raw_parts, from_raw_parts_mut},
19};
20
21declare_id!("shmem4EWT2sPdVGvTZCzXXRAURL9G5vpPxNwSeKhHUL");
22
23/// A more efficient `copy_from_slice` implementation.
24fn fast_copy(mut src: &[u8], mut dst: &mut [u8]) {
25    while src.len() >= 8 {
26        #[allow(clippy::ptr_offset_with_cast)]
27        let (src_word, src_rem) = array_refs![src, 8; ..;];
28        #[allow(clippy::ptr_offset_with_cast)]
29        let (dst_word, dst_rem) = mut_array_refs![dst, 8; ..;];
30        *dst_word = *src_word;
31        src = src_rem;
32        dst = dst_rem;
33    }
34    unsafe {
35        std::ptr::copy_nonoverlapping(src.as_ptr(), dst.as_mut_ptr(), src.len());
36    }
37}
38
39/// Deserializes only the particular input parameters that the shared memory
40/// program uses.  For more information about the format of the serialized input
41/// parameters see `solana_sdk::entrypoint::deserialize`
42unsafe fn deserialize_input_parameters<'a>(
43    input: *mut u8,
44) -> Result<(&'a mut [u8], &'a [u8]), u64> {
45    // Only one account expected
46    let num_accounts = read(input as *const u64);
47    if num_accounts == 0 {
48        return Err(ProgramError::NotEnoughAccountKeys.into());
49    } else if num_accounts > 1 {
50        return Err(ProgramError::InvalidArgument.into());
51    }
52
53    // Offset to the first (and only) account's data length
54    let data_len_offset = size_of::<u64>()
55        + size_of::<u8>()
56        + size_of::<u8>()
57        + size_of::<u8>()
58        + size_of::<u8>()
59        + size_of::<u32>()
60        + size_of::<Pubkey>()
61        + size_of::<Pubkey>()
62        + size_of::<u64>();
63
64    let account_data_len = read(input.add(data_len_offset) as *const usize);
65    let data_ptr = input.add(data_len_offset + size_of::<u64>());
66    let account_data = from_raw_parts_mut(data_ptr, account_data_len);
67
68    // Offset from the account data pointer to the instruction's data length
69    let instruction_len_offset = account_data_len
70        + MAX_PERMITTED_DATA_INCREASE
71        + (account_data_len as *const u8).align_offset(align_of::<u128>())
72        + size_of::<u64>();
73
74    let instruction_data_len = read(data_ptr.add(instruction_len_offset) as *const usize);
75    let instruction_data = from_raw_parts(
76        data_ptr.add(instruction_len_offset + size_of::<u64>()),
77        instruction_data_len,
78    );
79
80    Ok((account_data, instruction_data))
81}
82
83/// This program expects one account and writes instruction data into the
84/// account's data.  The first 8 bytes of the instruction data contain the
85/// little-endian offset into the account data.  The rest of the instruction
86/// data is written into the account data starting at that offset.
87///
88/// This program uses the raw Solana runtime's entrypoint which takes a pointer
89/// to serialized input parameters.  For more information about the format of
90/// the serialized input parameters see `solana_sdk::entrypoint::deserialize`
91///
92/// # Safety
93#[no_mangle]
94pub unsafe extern "C" fn entrypoint(input: *mut u8) -> u64 {
95    match deserialize_input_parameters(input) {
96        Ok((account_data, instruction_data)) => {
97            if instruction_data.len() < 8 {
98                return ProgramError::AccountDataTooSmall.into();
99            }
100            #[allow(clippy::ptr_offset_with_cast)]
101            let (offset, content) = array_refs![instruction_data, 8; ..;];
102            let offset = usize::from_le_bytes(*offset);
103            if account_data.len() < offset + content.len() {
104                return ProgramError::AccountDataTooSmall.into();
105            }
106            let data_ptr = account_data.as_mut_ptr() as usize;
107            let data = from_raw_parts_mut((data_ptr + offset) as *mut u8, content.len());
108            fast_copy(content, data);
109        }
110        Err(err) => return err,
111    }
112    SUCCESS
113}
spl_shared_memory/lib.rs

spl_shared_memory/
lib.rs
