ldx

ldx — A C library for reading Lingoes dictionary files (.ld2 / .ldx format).

ldx parses encrypted and compressed dictionary files produced by the Lingoes translator. It handles 3DES decryption of metadata, zlib block decompression, charset conversion, and XML parsing to extract dictionary entries and embedded resources.

Note ldx is, to the best of the author's knowledge, the first open-source library that fully parses .ld2 / .ldx files — including the encrypted metadata — across all major platforms (Linux, macOS, Windows). The LD2/LDX format has no public specification; every detail here was reverse-engineered from scratch.

If you use ldx in your project, please follow the terms of the MIT License. If you draw on ldx's parsing logic, reverse-engineering notes, or format documentation for your own implementation, please credit ldx and link back to this repository in your project.

Features

• Dictionary Info — Decrypts and parses the DictInfo XML (3DES-ECB → UTF-16LE → UTF-8 → libxml2)
• Glossary Entries — Iterates word + definition pairs with sort-order support and cross-references
• Embedded Resources — Extracts images, audio, CSS, and other resources from the RES section
• On-demand Decompression — Block-level zlib decompression with LRU cache (6 slots, 16KB per block)
• Cross-platform — Linux, macOS, Windows

Building

Prerequisites

• C compiler with C11 support
• CMake 3.14+
• zlib
• libxml2
• libiconv

Install Dependencies

macOS: All dependencies are included with Xcode Command Line Tools:

xcode-select --install

Ubuntu/Debian:

sudo apt-get install zlib1g-dev libxml2-dev

Fedora/RHEL:

sudo dnf install zlib-devel libxml2-devel libiconv-devel

Windows: Install dependencies using vcpkg:

vcpkg install zlib:x64-windows libxml2:x64-windows libiconv:x64-windows

Build from Source

# Clone the repository
git clone https://github.com/unidict/ldx.git
cd ldx

# Configure
mkdir build && cd build
cmake ..

# Build
cmake --build .

# Run tests
ctest --output-on-failure

# Install (optional)
sudo cmake --install

On Windows, add the vcpkg toolchain:

cmake -B build -DCMAKE_TOOLCHAIN_FILE=C:/vcpkg/scripts/buildsystems/vcpkg.cmake
cmake --build build --config Release
ctest --test-dir build -C Release

CMake Options

Option	Default	Description
LDX_BUILD_TESTS	ON	Build unit tests
BUILD_SHARED_LIBS	OFF	Build shared library instead of static

Quick Start

Open a Dictionary File

#include "ldx_reader.h"

int main() {
    ldx_reader *reader = ldx_reader_open("mydict.ld2");
    if (!reader) {
        fprintf(stderr, "Failed to open file\n");
        return 1;
    }

    // Get dictionary info
    const ldx_info *info = ldx_reader_get_info(reader);
    if (info) {
        printf("Name: %s\n", info->name ? info->name : "(null)");
        printf("From: %s\n", info->from_lang ? info->from_lang : "?");
        printf("To: %s\n", info->to_charset ? info->to_charset : "?");
        printf("Entries: %d\n", info->gls_count);
    }

    ldx_reader_close(reader);
    return 0;
}

Iterate Glossary Entries

ldx_gls_iter *iter = ldx_reader_gls_iter_create(reader,
    LDX_GLS_ENTRY_MODE_DEF_STRING);
const ldx_gls_entry *entry;

while ((entry = ldx_reader_gls_iter_next(iter)) != NULL) {
    printf("[%d] %s\n", entry->seq, entry->word);
    if (entry->definition) {
        printf("%s\n", entry->definition);
    }
}

ldx_reader_gls_iter_free(iter);

Iterate Resources

int res_count = ldx_reader_res_count(reader);
printf("Resources: %d\n", res_count);

ldx_res_iter *res_iter = ldx_reader_res_iter_create(reader,
    LDX_RES_ENTRY_MODE_DATA_BLOB);
const ldx_res_entry *res_entry;

while ((res_entry = ldx_reader_res_iter_next(res_iter)) != NULL) {
    printf("  %s (%zu bytes)\n", res_entry->name, res_entry->data_size);
}

ldx_reader_res_iter_free(res_iter);

Architecture

                    ldx_reader (top-level API)
                   /            |            \
              ldx_info      ldx_gls        ldx_res
           (decrypt+XML)  (entries)      (resources)
                |              |              |
          ldx_info_crypto  ldx_blockstore (shared)
          (custom 3DES)    (zlib + LRU cache)

• ldx_reader — Opens the file, parses the 88-byte header, scans sections
• ldx_info — Decrypts INFO section with 3DES-ECB, converts UTF-16LE to UTF-8, parses XML
• ldx_info_crypto — Self-contained 3DES implementation (no external crypto library)
• ldx_blockstore — Block-level zlib decompression with 6-slot LRU cache
• ldx_gls — Glossary reader: index/word/definition area navigation, charset conversion
• ldx_res — Resource reader: CellInfo navigation, data extraction

Thread Safety

ldx is not thread-safe. For concurrent access, create a separate reader per thread.

Platform Support

• Linux ✅
• macOS ✅
• Windows ✅ (MSVC, via vcpkg)

License

ldx is released under the MIT License. You are free to use, modify, and distribute it, provided you retain the copyright notice and license text.

Attribution & Derivative Works

Because the LD2/LDX format is undocumented, the parsing logic, crypto details, and format notes in this repository represent substantial original reverse-engineering effort. If your project borrows from or is derived from ldx — whether source code, algorithmic approach, or the format documentation under docs/ — please:

1. Keep the ldx copyright notice as required by the MIT License.
2. Add a visible note in your README or documentation stating that your work builds on ldx, with a link to https://github.com/unidict/ldx.

MIT License

Copyright (c) 2026 kejinlu <kejinlu@gmail.com> (ldx project)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Acknowledgments

ldx incorporates the following third-party components:

• zlib by Jean-loup Gailly and Mark Adler (zlib License)
• libxml2 by GNOME Project (MIT License)
• libiconv by GNU Project (LGPL License)
• Unity Test Framework by ThrowTheSwitch (MIT License)

See Also

• LD2/LDX File Format Specification