/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "vm/Xdr.h"

#include "mozilla/Assertions.h"   // MOZ_ASSERT, MOZ_ASSERT_IF
#include "mozilla/EndianUtils.h"  // mozilla::NativeEndian
#include "mozilla/Result.h"       // mozilla::{Result, Ok, Err}, MOZ_TRY
#include "mozilla/Utf8.h"         // mozilla::Utf8Unit

#include <algorithm>    // std::transform
#include <stddef.h>     // size_t
#include <stdint.h>     // uint8_t, uint32_t, uintptr_t
#include <string>       // std::char_traits
#include <type_traits>  // std::is_same_v
#include <utility>      // std::move

#include "frontend/FrontendContext.h"  // FrontendContext
#include "js/Transcoding.h"  // JS::TranscodeResult, JS::TranscodeBuffer, JS::TranscodeRange
#include "js/UniquePtr.h"   // UniquePtr
#include "js/Utility.h"     // JS::FreePolicy, js_delete
#include "vm/JSContext.h"   // JSContext, ReportAllocationOverflow
#include "vm/StringType.h"  // JSString

using namespace js;

using mozilla::Utf8Unit;

#ifdef DEBUG
bool XDRCoderBase::validateResultCode(FrontendContext* fc,
                                      JS::TranscodeResult code) const {
  return fc->hadErrors() == bool(code == JS::TranscodeResult::Throw);
}
#endif

template <XDRMode mode>
XDRResult XDRState<mode>::codeChars(char* chars, size_t nchars) {
  return codeBytes(chars, nchars);
}

template <XDRMode mode>
XDRResult XDRState<mode>::codeChars(Latin1Char* chars, size_t nchars) {
  static_assert(sizeof(Latin1Char) == 1,
                "Latin1Char must be 1 byte for nchars below to be the "
                "proper count of bytes");
  static_assert(std::is_same_v<Latin1Char, unsigned char>,
                "Latin1Char must be unsigned char to C++-safely reinterpret "
                "the bytes generically copied below as Latin1Char");
  return codeBytes(chars, nchars);
}

template <XDRMode mode>
XDRResult XDRState<mode>::codeChars(Utf8Unit* units, size_t count) {
  if (count == 0) {
    return Ok();
  }

  if (mode == XDR_ENCODE) {
    uint8_t* ptr = buf->write(count);
    if (!ptr) {
      return fail(JS::TranscodeResult::Throw);
    }

    std::transform(units, units + count, ptr,
                   [](const Utf8Unit& unit) { return unit.toUint8(); });
  } else {
    const uint8_t* ptr = buf->read(count);
    if (!ptr) {
      return fail(JS::TranscodeResult::Failure_BadDecode);
    }

    std::transform(ptr, ptr + count, units,
                   [](const uint8_t& value) { return Utf8Unit(value); });
  }

  return Ok();
}

template <XDRMode mode>
XDRResult XDRState<mode>::codeChars(char16_t* chars, size_t nchars) {
  if (nchars == 0) {
    return Ok();
  }

  size_t nbytes = nchars * sizeof(char16_t);
  if (mode == XDR_ENCODE) {
    uint8_t* ptr = buf->write(nbytes);
    if (!ptr) {
      return fail(JS::TranscodeResult::Throw);
    }

    // |mozilla::NativeEndian| correctly handles writing into unaligned |ptr|.
    mozilla::NativeEndian::copyAndSwapToLittleEndian(ptr, chars, nchars);
  } else {
    const uint8_t* ptr = buf->read(nbytes);
    if (!ptr) {
      return fail(JS::TranscodeResult::Failure_BadDecode);
    }

    // |mozilla::NativeEndian| correctly handles reading from unaligned |ptr|.
    mozilla::NativeEndian::copyAndSwapFromLittleEndian(chars, ptr, nchars);
  }
  return Ok();
}

template <XDRMode mode, typename CharT>
static XDRResult XDRCodeCharsZ(XDRState<mode>* xdr,
                               XDRTranscodeString<CharT>& buffer) {
  MOZ_ASSERT_IF(mode == XDR_ENCODE, !buffer.empty());
  MOZ_ASSERT_IF(mode == XDR_DECODE, buffer.empty());

  using OwnedString = js::UniquePtr<CharT[], JS::FreePolicy>;
  OwnedString owned;

  static_assert(JSString::MAX_LENGTH <= INT32_MAX,
                "String length must fit in int32_t");

  uint32_t length = 0;
  CharT* chars = nullptr;

  if (mode == XDR_ENCODE) {
    chars = const_cast<CharT*>(buffer.template ref<const CharT*>());

    // Set a reasonable limit on string length.
    size_t lengthSizeT = std::char_traits<CharT>::length(chars);
    if (lengthSizeT > JSString::MAX_LENGTH) {
      ReportAllocationOverflow(xdr->fc());
      return xdr->fail(JS::TranscodeResult::Throw);
    }
    length = static_cast<uint32_t>(lengthSizeT);
  }
  MOZ_TRY(xdr->codeUint32(&length));

  if (mode == XDR_DECODE) {
    owned =
        xdr->fc()->getAllocator()->template make_pod_array<CharT>(length + 1);
    if (!owned) {
      return xdr->fail(JS::TranscodeResult::Throw);
    }
    chars = owned.get();
  }

  MOZ_TRY(xdr->codeChars(chars, length));
  if (mode == XDR_DECODE) {
    // Null-terminate and transfer ownership to caller.
    owned[length] = '\0';
    buffer.template construct<OwnedString>(std::move(owned));
  }

  return Ok();
}

template <XDRMode mode>
XDRResult XDRState<mode>::codeCharsZ(XDRTranscodeString<char>& buffer) {
  return XDRCodeCharsZ(this, buffer);
}

template <XDRMode mode>
XDRResult XDRState<mode>::codeCharsZ(XDRTranscodeString<char16_t>& buffer) {
  return XDRCodeCharsZ(this, buffer);
}

template class js::XDRState<XDR_ENCODE>;
template class js::XDRState<XDR_DECODE>;