solana_program_log/

logger.rs

use core::{
    cmp::min, mem::MaybeUninit, ops::Deref, ptr::copy_nonoverlapping, slice::from_raw_parts,
};
#[cfg(any(target_os = "solana", target_arch = "bpf"))]
use solana_define_syscall::definitions::{sol_log_, sol_remaining_compute_units};

/// Bytes for a truncated `str` log message.
const TRUNCATED_SLICE: [u8; 3] = [b'.', b'.', b'.'];

/// Byte representing a truncated log.
const TRUNCATED: u8 = b'@';

/// An uninitialized byte.
const UNINIT_BYTE: MaybeUninit<u8> = MaybeUninit::uninit();

/// Logger to efficiently format log messages.
///
/// The logger is a fixed size buffer that can be used to format log messages
/// before sending them to the log output. Any type that implements the `Log`
/// trait can be appended to the logger.
pub struct Logger<const BUFFER: usize> {
    // Byte buffer to store the log message.
    buffer: [MaybeUninit<u8>; BUFFER],

    // Length of the log message.
    len: usize,
}

impl<const BUFFER: usize> Default for Logger<BUFFER> {
    #[inline]
    fn default() -> Self {
        Self {
            buffer: [UNINIT_BYTE; BUFFER],
            len: 0,
        }
    }
}

impl<const BUFFER: usize> Deref for Logger<BUFFER> {
    type Target = [u8];

    fn deref(&self) -> &Self::Target {
        // SAFETY: the slice is created from the buffer up to the length
        // of the message.
        unsafe { from_raw_parts(self.buffer.as_ptr() as *const _, self.len) }
    }
}

impl<const BUFFER: usize> Logger<BUFFER> {
    /// Append a value to the logger.
    #[inline(always)]
    pub fn append<T: Log>(&mut self, value: T) -> &mut Self {
        self.append_with_args(value, &[]);
        self
    }

    /// Append a value to the logger with formatting arguments.
    #[inline]
    pub fn append_with_args<T: Log>(&mut self, value: T, args: &[Argument]) -> &mut Self {
        if self.is_full() {
            if BUFFER > 0 {
                // SAFETY: the buffer is checked to be full.
                unsafe {
                    let last = self.buffer.get_unchecked_mut(BUFFER - 1);
                    last.write(TRUNCATED);
                }
            }
        } else {
            self.len += value.write_with_args(&mut self.buffer[self.len..], args);

            if self.len > BUFFER {
                // Indicates that the buffer is full.
                self.len = BUFFER;
                // SAFETY: the buffer length is checked to greater than `BUFFER`.
                unsafe {
                    let last = self.buffer.get_unchecked_mut(BUFFER - 1);
                    last.write(TRUNCATED);
                }
            }
        }

        self
    }

    /// Log the message in the buffer.
    #[inline(always)]
    pub fn log(&self) {
        log_message(self);
    }

    /// Clear the message buffer.
    #[inline(always)]
    pub fn clear(&mut self) {
        self.len = 0;
    }

    /// Check whether the log buffer is at the maximum length or not.
    #[inline(always)]
    pub fn is_full(&self) -> bool {
        self.len == BUFFER
    }

    /// Get the remaining space in the log buffer.
    #[inline(always)]
    pub fn remaining(&self) -> usize {
        BUFFER - self.len
    }
}

/// Log a message.
#[inline(always)]
pub fn log_message(message: &[u8]) {
    #[cfg(any(target_os = "solana", target_arch = "bpf"))]
    // SAFETY: the message is always a valid pointer to a slice of bytes
    // and `sol_log_` is a syscall.
    unsafe {
        sol_log_(message.as_ptr(), message.len() as u64);
    }
    #[cfg(all(not(any(target_os = "solana", target_arch = "bpf")), feature = "std"))]
    {
        let message = core::str::from_utf8(message).unwrap();
        std::println!("{message}");
    }

    #[cfg(all(
        not(any(target_os = "solana", target_arch = "bpf")),
        not(feature = "std")
    ))]
    core::hint::black_box(message);
}

/// Remaining CUs.
#[inline(always)]
pub fn remaining_compute_units() -> u64 {
    #[cfg(any(target_os = "solana", target_arch = "bpf"))]
    // SAFETY: `sol_remaining_compute_units` is a syscall that returns the remaining compute units.
    unsafe {
        sol_remaining_compute_units()
    }
    #[cfg(not(any(target_os = "solana", target_arch = "bpf")))]
    core::hint::black_box(0u64)
}

/// Formatting arguments.
///
/// Arguments can be used to specify additional formatting options for the log message.
/// Note that types might not support all arguments.
#[non_exhaustive]
pub enum Argument {
    /// Number of decimal places to display for numbers.
    ///
    /// This is only applicable for numeric types.
    Precision(u8),

    /// Truncate the output at the end when the specified maximum number of characters
    /// is exceeded.
    ///
    /// This is only applicable for `str` types.
    TruncateEnd(usize),

    /// Truncate the output at the start when the specified maximum number of characters
    /// is exceeded.
    ///
    /// This is only applicable for `str` types.
    TruncateStart(usize),
}

/// Trait to specify the log behavior for a type.
///
/// # Safety
///
/// The implementation must ensure that the value returned by any of the methods correctly
/// reflects the actual number of bytes written to the buffer. Returning a value greater
/// than the number of bytes written to the buffer will result in undefined behavior, since
/// it will lead to reading uninitialized memory from the buffer.
pub unsafe trait Log {
    #[inline(always)]
    fn debug(&self, buffer: &mut [MaybeUninit<u8>]) -> usize {
        self.debug_with_args(buffer, &[])
    }

    #[inline(always)]
    fn debug_with_args(&self, buffer: &mut [MaybeUninit<u8>], args: &[Argument]) -> usize {
        self.write_with_args(buffer, args)
    }

    #[inline(always)]
    fn write(&self, buffer: &mut [MaybeUninit<u8>]) -> usize {
        self.write_with_args(buffer, &[])
    }

    fn write_with_args(&self, buffer: &mut [MaybeUninit<u8>], parameters: &[Argument]) -> usize;
}

/// Implement the log trait for unsigned integer types.
macro_rules! impl_log_for_unsigned_integer {
    ( $type:tt ) => {
        unsafe impl Log for $type {
            #[inline]
            fn write_with_args(&self, buffer: &mut [MaybeUninit<u8>], args: &[Argument]) -> usize {
                // The maximum number of digits that the type can have.
                const MAX_DIGITS: usize = $type::MAX.ilog10() as usize + 1;

                if buffer.is_empty() {
                    return 0;
                }

                match *self {
                    // Handle zero as a special case.
                    0 => {
                        // SAFETY: the buffer is checked to be non-empty.
                        unsafe {
                            buffer.get_unchecked_mut(0).write(b'0');
                        }
                        1
                    }
                    mut value => {
                        let mut digits = [UNINIT_BYTE; MAX_DIGITS];
                        let mut offset = MAX_DIGITS;

                        while value > 0 {
                            let remainder = value % 10;
                            value /= 10;
                            offset -= 1;
                            // SAFETY: the offset is always within the bounds of the array since
                            // `offset` is initialized with the maximum number of digits that
                            // the type can have and decremented on each iteration; `remainder`
                            // is always less than 10.
                            unsafe {
                                digits
                                    .get_unchecked_mut(offset)
                                    .write(b'0' + remainder as u8);
                            }
                        }

                        let precision = if let Some(Argument::Precision(p)) = args
                            .iter()
                            .find(|arg| matches!(arg, Argument::Precision(_)))
                        {
                            *p as usize
                        } else {
                            0
                        };

                        let written = MAX_DIGITS - offset;
                        let length = buffer.len();

                        // Space required with the specified precision. We might need
                        // to add leading zeros and a decimal point, but this is only
                        // if the precision is greater than zero.
                        let required = match precision {
                            0 => written,
                            // decimal point
                            _precision if precision < written => written + 1,
                            // decimal point + one leading zero
                            _ => precision + 2,
                        };
                        // Determines whether the value will be truncated or not.
                        let is_truncated = required > length;
                        // Cap the number of digits to write to the buffer length.
                        let digits_to_write = min(MAX_DIGITS - offset, length);

                        // SAFETY: the length of both `digits` and `buffer` arrays are guaranteed
                        // to be within bounds and the `digits_to_write` value is capped to the
                        // length of the `buffer`.
                        unsafe {
                            let source = digits.as_ptr().add(offset);
                            let ptr = buffer.as_mut_ptr();

                            // Copy the number to the buffer if no precision is specified.
                            if precision == 0 {
                                copy_nonoverlapping(source, ptr, digits_to_write);
                            }
                            // If padding is needed to satisfy the precision, add leading zeros
                            // and a decimal point.
                            else if precision >= digits_to_write {
                                // Prefix.
                                (ptr as *mut u8).write(b'0');

                                if length > 2 {
                                    (ptr.add(1) as *mut u8).write(b'.');
                                    let padding = min(length - 2, precision - digits_to_write);

                                    // Precision padding.
                                    (ptr.add(2) as *mut u8).write_bytes(b'0', padding);

                                    let current = 2 + padding;

                                    // If there is still space, copy (part of) the number.
                                    if current < length {
                                        let remaining = min(digits_to_write, length - current);

                                        // Number part.
                                        copy_nonoverlapping(source, ptr.add(current), remaining);
                                    }
                                }
                            }
                            // No padding is needed, calculate the integer and fractional
                            // parts and add a decimal point.
                            else {
                                let integer_part = digits_to_write - precision;

                                // Integer part of the number.
                                copy_nonoverlapping(source, ptr, integer_part);

                                // Decimal point.
                                (ptr.add(integer_part) as *mut u8).write(b'.');
                                let current = integer_part + 1;

                                // If there is still space, copy (part of) the remaining.
                                if current < length {
                                    let remaining = min(precision, length - current);

                                    // Fractional part of the number.
                                    copy_nonoverlapping(
                                        source.add(integer_part),
                                        ptr.add(current),
                                        remaining,
                                    );
                                }
                            }
                        }

                        let written = min(required, length);

                        // There might not have been space.
                        if is_truncated {
                            // SAFETY: `written` is capped to the length of the buffer and
                            // the required length (`required` is always greater than zero);
                            // `buffer` is guaranteed  to have a length of at least 1.
                            unsafe {
                                buffer.get_unchecked_mut(written - 1).write(TRUNCATED);
                            }
                        }

                        written
                    }
                }
            }
        }
    };
}

// Supported unsigned integer types.
impl_log_for_unsigned_integer!(u8);
impl_log_for_unsigned_integer!(u16);
impl_log_for_unsigned_integer!(u32);
impl_log_for_unsigned_integer!(u64);
impl_log_for_unsigned_integer!(usize);
#[cfg(not(target_arch = "bpf"))]
impl_log_for_unsigned_integer!(u128);

/// Implement the log trait for the signed integer types.
macro_rules! impl_log_for_signed {
    ( $type:tt ) => {
        unsafe impl Log for $type {
            #[inline]
            fn write_with_args(&self, buffer: &mut [MaybeUninit<u8>], args: &[Argument]) -> usize {
                if buffer.is_empty() {
                    return 0;
                }

                match *self {
                    // Handle zero as a special case.
                    0 => {
                        // SAFETY: the buffer is checked to be non-empty.
                        unsafe {
                            buffer.get_unchecked_mut(0).write(b'0');
                        }
                        1
                    }
                    value => {
                        let mut prefix = 0;

                        if *self < 0 {
                            if buffer.len() == 1 {
                                // SAFETY: the buffer is checked to be non-empty.
                                unsafe {
                                    buffer.get_unchecked_mut(0).write(TRUNCATED);
                                }
                                // There is no space for the number, so just return.
                                return 1;
                            }

                            // SAFETY: the buffer is checked to be non-empty.
                            unsafe {
                                buffer.get_unchecked_mut(0).write(b'-');
                            }
                            prefix += 1;
                        };

                        prefix
                            + $type::unsigned_abs(value)
                                .write_with_args(&mut buffer[prefix..], args)
                    }
                }
            }
        }
    };
}

// Supported signed integer types.
impl_log_for_signed!(i8);
impl_log_for_signed!(i16);
impl_log_for_signed!(i32);
impl_log_for_signed!(i64);
impl_log_for_signed!(isize);
#[cfg(not(target_arch = "bpf"))]
impl_log_for_signed!(i128);

/// Implement the log trait for the `&str` type.
unsafe impl Log for &str {
    #[inline]
    fn debug_with_args(&self, buffer: &mut [MaybeUninit<u8>], _args: &[Argument]) -> usize {
        if buffer.is_empty() {
            return 0;
        }
        // SAFETY: the buffer is checked to be non-empty.
        unsafe {
            buffer.get_unchecked_mut(0).write(b'"');
        }

        let mut offset = 1;
        offset += self.write(&mut buffer[offset..]);

        match buffer.len() - offset {
            0 => {
                // SAFETY: the buffer is guaranteed to be within `offset` bounds.
                unsafe {
                    buffer.get_unchecked_mut(offset - 1).write(TRUNCATED);
                }
            }
            _ => {
                // SAFETY: the buffer is guaranteed to be within `offset` bounds.
                unsafe {
                    buffer.get_unchecked_mut(offset).write(b'"');
                }
                offset += 1;
            }
        }

        offset
    }

    #[inline]
    fn write_with_args(&self, buffer: &mut [MaybeUninit<u8>], args: &[Argument]) -> usize {
        // There are 4 different cases to consider:
        //
        // 1. No arguments were provided, so the entire string is copied to the buffer if it fits;
        //    otherwise, the buffer is filled as many characters as possible and the last character
        //    is set to `TRUNCATED`.
        //
        // Then cases only applicable when precision formatting is used:
        //
        // 2. The buffer is large enough to hold the entire string: the string is copied to the
        //    buffer and the length of the string is returned.
        //
        // 3. The buffer is smaller than the string, but large enough to hold the prefix and part
        //    of the string: the prefix and part of the string are copied to the buffer. The length
        //    returned is `prefix` + number of characters copied.
        //
        // 4. The buffer is smaller than the string and the prefix: the buffer is filled with the
        //    prefix and the last character is set to `TRUNCATED`. The length returned is the length
        //    of the buffer.
        //
        // The length of the message is determined by whether a precision formatting was used or
        // not, and the length of the buffer.

        let (size, truncate_end) = match args
            .iter()
            .find(|arg| matches!(arg, Argument::TruncateEnd(_) | Argument::TruncateStart(_)))
        {
            Some(Argument::TruncateEnd(size)) => (*size, Some(true)),
            Some(Argument::TruncateStart(size)) => (*size, Some(false)),
            _ => (buffer.len(), None),
        };

        // Handles the write of the `str` to the buffer.
        //
        // - `destination`: pointer to the buffer where the string will be copied. This is always
        //   the a pointer to the log buffer, but it could de in a different offset depending on
        //   whether the truncated slice is copied or not.
        //
        // - `source`: pointer to the string that will be copied. This could either be a pointer
        //   to the `str` itself or `TRUNCATE_SLICE`).
        //
        // - `length_to_write`: number of characters from `source` that will be copied.
        //
        // - `written_truncated_slice_length`: number of characters copied from `TRUNCATED_SLICE`.
        //   This is used to determine the total number of characters copied to the buffer.
        //
        // - `truncated`: indicates whether the `str` was truncated or not. This is used to set
        //   the last character of the buffer to `TRUNCATED`.
        let (destination, source, length_to_write, written_truncated_slice_length, truncated) =
            // No truncate arguments were provided, so the entire `str` is copied to the buffer
            // if it fits; otherwise indicates that the `str` was truncated.
            if truncate_end.is_none() {
                let length = min(size, self.len());
                (
                    buffer.as_mut_ptr(),
                    self.as_ptr(),
                    length,
                    0,
                    length != self.len(),
                )
            } else {
                let max_length = min(size, buffer.len());
                let ptr = buffer.as_mut_ptr();

                // The buffer is large enough to hold the entire `str`, so no need to use the
                // truncate args.
                if max_length >= self.len() {
                    (ptr, self.as_ptr(), self.len(), 0, false)
                }
                // The buffer is large enough to hold the truncated slice and part of the string.
                // In this case, the characters from the start or end of the string are copied to
                // the buffer together with the `TRUNCATED_SLICE`.
                else if max_length > TRUNCATED_SLICE.len() {
                    // Number of characters that can be copied to the buffer.
                    let length = max_length - TRUNCATED_SLICE.len();
                    // SAFETY: the `ptr` is always within `length` bounds.
                    unsafe {
                        let (offset, source, destination) = if truncate_end == Some(true) {
                            (length, self.as_ptr(), ptr)
                        } else {
                            (
                                0,
                                self.as_ptr().add(self.len() - length),
                                ptr.add(TRUNCATED_SLICE.len()),
                            )
                        };
                        // Copy the truncated slice to the buffer.
                        copy_nonoverlapping(
                            TRUNCATED_SLICE.as_ptr(),
                            ptr.add(offset) as *mut _,
                            TRUNCATED_SLICE.len(),
                        );

                        (destination, source, length, TRUNCATED_SLICE.len(), false)
                    }
                }
                // The buffer is smaller than the `PREFIX`: the buffer is filled with the `PREFIX`
                // and the last character is set to `TRUNCATED`.
                else {
                    (ptr, TRUNCATED_SLICE.as_ptr(), max_length, 0, true)
                }
            };

        if length_to_write > 0 {
            // SAFETY: the `destination` is always within `length_to_write` bounds.
            unsafe {
                copy_nonoverlapping(source, destination as *mut _, length_to_write);
            }

            // There might not have been space for all the value.
            if truncated {
                // SAFETY: the `destination` is always within `length_to_write` bounds.
                unsafe {
                    let last = buffer.get_unchecked_mut(length_to_write - 1);
                    last.write(TRUNCATED);
                }
            }
        }

        written_truncated_slice_length + length_to_write
    }
}

/// Implement the log trait for the slice type.
macro_rules! impl_log_for_slice {
    ( [$type:ident] ) => {
        unsafe impl<$type> Log for &[$type]
        where
            $type: Log
        {
            impl_log_for_slice!(@generate_write);
        }
    };
    ( [$type:ident; $size:ident] ) => {
        unsafe impl<$type, const $size: usize> Log for &[$type; $size]
        where
            $type: Log
        {
            impl_log_for_slice!(@generate_write);
        }
    };
    ( @generate_write ) => {
        #[inline]
        fn write_with_args(&self, buffer: &mut [MaybeUninit<u8>], _args: &[Argument]) -> usize {
            if buffer.is_empty() {
                return 0;
            }

            // Size of the buffer.
            let length = buffer.len();
            // SAFETY: the buffer is checked to be non-empty.
            unsafe {
                buffer.get_unchecked_mut(0).write(b'[');
            }

            let mut offset = 1;

            for value in self.iter() {
                if offset >= length {
                    // SAFETY: the buffer is checked to be non-empty and the `length`
                    // represents the buffer length.
                    unsafe {
                        buffer.get_unchecked_mut(length - 1).write(TRUNCATED);
                    }
                    offset = length;
                    break;
                }

                if offset > 1 {
                    if offset + 2 >= length {
                        // SAFETY: the buffer is checked to be non-empty and the `length`
                        // represents the buffer length.
                        unsafe {
                            buffer.get_unchecked_mut(length - 1).write(TRUNCATED);
                        }
                        offset = length;
                        break;
                    } else {
                        // SAFETY: the buffer is checked to be non-empty and the `offset`
                        // is smaller than the buffer length.
                        unsafe {
                            buffer.get_unchecked_mut(offset).write(b',');
                            buffer.get_unchecked_mut(offset + 1).write(b' ');
                        }
                        offset += 2;
                    }
                }

                offset += value.debug(&mut buffer[offset..]);
            }

            if offset < length {
                // SAFETY: the buffer is checked to be non-empty and the `offset`
                // is smaller than the buffer length.
                unsafe {
                    buffer.get_unchecked_mut(offset).write(b']');
                }
                offset += 1;
            }

            offset
        }
    };
}

// Supported slice types.
impl_log_for_slice!([T]);
impl_log_for_slice!([T; N]);

/// Implement the log trait for the `bool` type.
unsafe impl Log for bool {
    #[inline]
    fn debug_with_args(&self, buffer: &mut [MaybeUninit<u8>], args: &[Argument]) -> usize {
        let value = if *self { "true" } else { "false" };
        value.debug_with_args(buffer, args)
    }

    #[inline]
    fn write_with_args(&self, buffer: &mut [MaybeUninit<u8>], args: &[Argument]) -> usize {
        let value = if *self { "true" } else { "false" };
        value.write_with_args(buffer, args)
    }
}