src/__support/File/file.cpp

//===--- Implementation of a platform independent file data structure -----===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "file.h"

#include "src/__support/CPP/new.h"
#include "src/__support/CPP/span.h"
#include "src/errno/libc_errno.h" // For error macros

#include <stdio.h>
#include <stdlib.h>

namespace LIBC_NAMESPACE {

FileIOResult File::write_unlocked(const void *data, size_t len) {
  if (!write_allowed()) {
    err = true;
    return {0, EBADF};
  }

  prev_op = FileOp::WRITE;

  if (bufmode == _IONBF) { // unbuffered.
    size_t ret_val =
        write_unlocked_nbf(static_cast<const uint8_t *>(data), len);
    flush_unlocked();
    return ret_val;
  } else if (bufmode == _IOFBF) { // fully buffered
    return write_unlocked_fbf(static_cast<const uint8_t *>(data), len);
  } else /*if (bufmode == _IOLBF) */ { // line buffered
    return write_unlocked_lbf(static_cast<const uint8_t *>(data), len);
  }
}

FileIOResult File::write_unlocked_nbf(const uint8_t *data, size_t len) {
  if (pos > 0) { // If the buffer is not empty
    // Flush the buffer
    const size_t write_size = pos;
    auto write_result = platform_write(this, buf, write_size);
    pos = 0; // Buffer is now empty so reset pos to the beginning.
    // If less bytes were written than expected, then an error occurred.
    if (write_result < write_size) {
      err = true;
      // No bytes from data were written, so return 0.
      return {0, write_result.error};
    }
  }

  auto write_result = platform_write(this, data, len);
  if (write_result < len)
    err = true;
  return write_result;
}

FileIOResult File::write_unlocked_fbf(const uint8_t *data, size_t len) {
  const size_t init_pos = pos;
  const size_t bufspace = bufsize - pos;

  // If data is too large to be buffered at all, then just write it unbuffered.
  if (len > bufspace + bufsize)
    return write_unlocked_nbf(data, len);

  // we split |data| (conceptually) using the split point. Then we handle the
  // two pieces separately.
  const size_t split_point = len < bufspace ? len : bufspace;

  // The primary piece is the piece of |data| we want to write to the buffer
  // before flushing. It will always fit into the buffer, since the split point
  // is defined as being min(len, bufspace), and it will always exist if len is
  // non-zero.
  cpp::span<const uint8_t> primary(data, split_point);

  // The second piece is the remainder of |data|. It is written to the buffer if
  // it fits, or written directly to the output if it doesn't. If the primary
  // piece fits entirely in the buffer, the remainder may be nothing.
  cpp::span<const uint8_t> remainder(
      static_cast<const uint8_t *>(data) + split_point, len - split_point);

  cpp::span<uint8_t> bufref(static_cast<uint8_t *>(buf), bufsize);

  // Copy the first piece into the buffer.
  // TODO: Replace the for loop below with a call to internal memcpy.
  for (size_t i = 0; i < primary.size(); ++i)
    bufref[pos + i] = primary[i];
  pos += primary.size();

  // If there is no remainder, we can return early, since the first piece has
  // fit completely into the buffer.
  if (remainder.size() == 0)
    return len;

  // We need to flush the buffer now, since there is still data and the buffer
  // is full.
  const size_t write_size = pos;

  auto buf_result = platform_write(this, buf, write_size);
  size_t bytes_written = buf_result.value;

  pos = 0; // Buffer is now empty so reset pos to the beginning.
  // If less bytes were written than expected, then an error occurred. Return
  // the number of bytes that have been written from |data|.
  if (buf_result.has_error() || bytes_written < write_size) {
    err = true;
    return {bytes_written <= init_pos ? 0 : bytes_written - init_pos,
            buf_result.error};
  }

  // The second piece is handled basically the same as the first, although we
  // know that if the second piece has data in it then the buffer has been
  // flushed, meaning that pos is always 0.
  if (remainder.size() < bufsize) {
    // TODO: Replace the for loop below with a call to internal memcpy.
    for (size_t i = 0; i < remainder.size(); ++i)
      bufref[i] = remainder[i];
    pos = remainder.size();
  } else {

    auto result = platform_write(this, remainder.data(), remainder.size());
    size_t bytes_written = buf_result.value;

    // If less bytes were written than expected, then an error occurred. Return
    // the number of bytes that have been written from |data|.
    if (result.has_error() || bytes_written < remainder.size()) {
      err = true;
      return {primary.size() + bytes_written, result.error};
    }
  }

  return len;
}

FileIOResult File::write_unlocked_lbf(const uint8_t *data, size_t len) {
  constexpr uint8_t NEWLINE_CHAR = '\n';
  size_t last_newline = len;
  for (size_t i = len; i >= 1; --i) {
    if (data[i - 1] == NEWLINE_CHAR) {
      last_newline = i - 1;
      break;
    }
  }

  // If there is no newline, treat this as fully buffered.
  if (last_newline == len) {
    return write_unlocked_fbf(data, len);
  }

  // we split |data| (conceptually) using the split point. Then we handle the
  // two pieces separately.
  const size_t split_point = last_newline + 1;

  // The primary piece is everything in |data| up to the newline. It's written
  // unbuffered to the output.
  cpp::span<const uint8_t> primary(data, split_point);

  // The second piece is the remainder of |data|. It is written fully buffered,
  // meaning it may stay in the buffer if it fits.
  cpp::span<const uint8_t> remainder(
      static_cast<const uint8_t *>(data) + split_point, len - split_point);

  size_t written = 0;

  written = write_unlocked_nbf(primary.data(), primary.size());
  if (written < primary.size()) {
    err = true;
    return written;
  }

  flush_unlocked();

  written += write_unlocked_fbf(remainder.data(), remainder.size());
  if (written < len) {
    err = true;
    return written;
  }

  return len;
}

FileIOResult File::read_unlocked(void *data, size_t len) {
  if (!read_allowed()) {
    err = true;
    return {0, EBADF};
  }

  prev_op = FileOp::READ;

  cpp::span<uint8_t> bufref(static_cast<uint8_t *>(buf), bufsize);
  cpp::span<uint8_t> dataref(static_cast<uint8_t *>(data), len);

  // Because read_limit is always greater than equal to pos,
  // available_data is never a wrapped around value.
  size_t available_data = read_limit - pos;
  if (len <= available_data) {
    // TODO: Replace the for loop below with a call to internal memcpy.
    for (size_t i = 0; i < len; ++i)
      dataref[i] = bufref[i + pos];
    pos += len;
    return len;
  }

  // Copy all of the available data.
  // TODO: Replace the for loop with a call to internal memcpy.
  for (size_t i = 0; i < available_data; ++i)
    dataref[i] = bufref[i + pos];
  read_limit = pos = 0; // Reset the pointers.
  // Update the dataref to reflect that fact that we have already
  // copied |available_data| into |data|.
  dataref = cpp::span<uint8_t>(dataref.data() + available_data,
                               dataref.size() - available_data);

  size_t to_fetch = len - available_data;
  if (to_fetch > bufsize) {
    auto result = platform_read(this, dataref.data(), to_fetch);
    size_t fetched_size = result.value;
    if (result.has_error() || fetched_size < to_fetch) {
      if (!result.has_error())
        eof = true;
      else
        err = true;
      return {available_data + fetched_size, result.has_error()};
    }
    return len;
  }

  // Fetch and buffer another buffer worth of data.
  auto result = platform_read(this, buf, bufsize);
  size_t fetched_size = result.value;
  read_limit += fetched_size;
  size_t transfer_size = fetched_size >= to_fetch ? to_fetch : fetched_size;
  for (size_t i = 0; i < transfer_size; ++i)
    dataref[i] = bufref[i];
  pos += transfer_size;
  if (result.has_error() || fetched_size < to_fetch) {
    if (!result.has_error())
      eof = true;
    else
      err = true;
  }
  return {transfer_size + available_data, result.error};
}

int File::ungetc_unlocked(int c) {
  // There is no meaning to unget if:
  // 1. You are trying to push back EOF.
  // 2. Read operations are not allowed on this file.
  // 3. The previous operation was a write operation.
  if (c == EOF || !read_allowed() || (prev_op == FileOp::WRITE))
    return EOF;

  cpp::span<uint8_t> bufref(static_cast<uint8_t *>(buf), bufsize);
  if (read_limit == 0) {
    // If |read_limit| is zero, it can mean three things:
    //   a. This file was just created.
    //   b. The previous operation was a seek operation.
    //   c. The previous operation was a read operation which emptied
    //      the buffer.
    // For all the above cases, we simply write |c| at the beginning
    // of the buffer and bump |read_limit|. Note that |pos| will also
    // be zero in this case, so we don't need to adjust it.
    bufref[0] = static_cast<unsigned char>(c);
    ++read_limit;
  } else {
    // If |read_limit| is non-zero, it means that there is data in the buffer
    // from a previous read operation. Which would also mean that |pos| is not
    // zero. So, we decrement |pos| and write |c| in to the buffer at the new
    // |pos|. If too many ungetc operations are performed without reads, it
    // can lead to (pos == 0 but read_limit != 0). We will just error out in
    // such a case.
    if (pos == 0)
      return EOF;
    --pos;
    bufref[pos] = static_cast<unsigned char>(c);
  }

  eof = false; // There is atleast one character that can be read now.
  err = false; // This operation was a success.
  return c;
}

ErrorOr<int> File::seek(long offset, int whence) {
  FileLock lock(this);
  if (prev_op == FileOp::WRITE && pos > 0) {

    auto buf_result = platform_write(this, buf, pos);
    if (buf_result.has_error() || buf_result.value < pos) {
      err = true;
      return Error(buf_result.error);
    }
  } else if (prev_op == FileOp::READ && whence == SEEK_CUR) {
    // More data could have been read out from the platform file than was
    // required. So, we have to adjust the offset we pass to platform seek
    // function. Note that read_limit >= pos is always true.
    offset -= (read_limit - pos);
  }
  pos = read_limit = 0;
  prev_op = FileOp::SEEK;
  // Reset the eof flag as a seek might move the file positon to some place
  // readable.
  eof = false;
  auto result = platform_seek(this, offset, whence);
  if (!result.has_value())
    return Error(result.error());
  else
    return 0;
}

ErrorOr<long> File::tell() {
  FileLock lock(this);
  auto seek_target = eof ? SEEK_END : SEEK_CUR;
  auto result = platform_seek(this, 0, seek_target);
  if (!result.has_value() || result.value() < 0)
    return Error(result.error());
  long platform_offset = result.value();
  if (prev_op == FileOp::READ)
    return platform_offset - (read_limit - pos);
  else if (prev_op == FileOp::WRITE)
    return platform_offset + pos;
  else
    return platform_offset;
}

int File::flush_unlocked() {
  if (prev_op == FileOp::WRITE && pos > 0) {
    auto buf_result = platform_write(this, buf, pos);
    if (buf_result.has_error() || buf_result.value < pos) {
      err = true;
      return buf_result.error;
    }
    pos = 0;
  }
  // TODO: Add POSIX behavior for input streams.
  return 0;
}

int File::set_buffer(void *buffer, size_t size, int buffer_mode) {
  // We do not need to lock the file as this method should be called before
  // other operations are performed on the file.
  if (buffer != nullptr && size == 0)
    return EINVAL;

  switch (buffer_mode) {
  case _IOFBF:
  case _IOLBF:
  case _IONBF:
    break;
  default:
    return EINVAL;
  }

  if (buffer == nullptr && size != 0 && buffer_mode != _IONBF) {
    // We exclude the case of buffer_mode == _IONBF in this branch
    // because we don't need to allocate buffer in such a case.
    if (own_buf) {
      // This is one of the places where use a C allocation functon
      // as C++ does not have an equivalent of realloc.
      buf = reinterpret_cast<uint8_t *>(realloc(buf, size));
      if (buf == nullptr)
        return ENOMEM;
    } else {
      AllocChecker ac;
      buf = new (ac) uint8_t[size];
      if (!ac)
        return ENOMEM;
      own_buf = true;
    }
    bufsize = size;
    // TODO: Handle allocation failures.
  } else {
    if (own_buf)
      delete buf;
    if (buffer_mode != _IONBF) {
      buf = static_cast<uint8_t *>(buffer);
      bufsize = size;
    } else {
      // We don't need any buffer.
      buf = nullptr;
      bufsize = 0;
    }
    own_buf = false;
  }
  bufmode = buffer_mode;
  adjust_buf();
  return 0;
}

File::ModeFlags File::mode_flags(const char *mode) {
  // First character in |mode| should be 'a', 'r' or 'w'.
  if (*mode != 'a' && *mode != 'r' && *mode != 'w')
    return 0;

  // There should be exaclty one main mode ('a', 'r' or 'w') character.
  // If there are more than one main mode characters listed, then
  // we will consider |mode| as incorrect and return 0;
  int main_mode_count = 0;

  ModeFlags flags = 0;
  for (; *mode != '\0'; ++mode) {
    switch (*mode) {
    case 'r':
      flags |= static_cast<ModeFlags>(OpenMode::READ);
      ++main_mode_count;
      break;
    case 'w':
      flags |= static_cast<ModeFlags>(OpenMode::WRITE);
      ++main_mode_count;
      break;
    case '+':
      flags |= static_cast<ModeFlags>(OpenMode::PLUS);
      break;
    case 'b':
      flags |= static_cast<ModeFlags>(ContentType::BINARY);
      break;
    case 'a':
      flags |= static_cast<ModeFlags>(OpenMode::APPEND);
      ++main_mode_count;
      break;
    case 'x':
      flags |= static_cast<ModeFlags>(CreateType::EXCLUSIVE);
      break;
    default:
      return 0;
    }
  }

  if (main_mode_count != 1)
    return 0;

  return flags;
}

} // namespace LIBC_NAMESPACE