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es compression

ES Compression: A Compression Framework for Dart #
Description #
Compression framework for Dart providing FFI implementations for Brotli, Lz4, Zstd (Zstandard) with ready-to-use prebuilt binaries
for Win/Linux/Mac.
This work is an inspired port of the Unified Compression Framework from the VAST Platform (VA Smalltalk) language
and development environment.
See the Design Document for detailed
information on how this package was designed and implemented.
Below is a simple example of what an encode/decode would look like:
import 'dart:convert';
import 'package:es_compression/brotli.dart';
import 'package:es_compression/lz4.dart';
import 'package:es_compression/zstd.dart';

/// Brotli, Lz4, Zstd usage example
void main() {
final bytes = utf8.encode('Hello Dart');
for (final codec in [brotli, lz4, zstd]) {
final encoded = codec.encode(bytes);
final decoded = codec.decode(encoded);
print(utf8.decode(decoded));
}
}
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Executables #
In the bin subdirectory, the following executables are provided.

Executable
Source
Description

escompress
es_compress.dart
Encode/Decode files using brotli, gzip, lz4 and zstd

If you want to use escompress on the command line,
install it using pub global activate:
> pub global activate es_compression
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escompress #
escompress is a program that will encode/decode files using brotli, gzip, lz4 or zstd.
The user provides the input and output file names from the command line.
By default, the file extension of either the input or output file name is used to determine which algorithm and
encode/decode mode to use.
The user can provide additional command line arguments to make these decisions explicitly.
Some examples are provided below.
Examples
Encode input.txt to output.lz4 using Lz4 compression:
> escompress -i"input.txt" -o"output.lz4"
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Encode input.txt to output.lz4 using Lz4 compression at compression level 3:
> escompress -l 3 -i"input.txt" -o"output.lz4"
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Decode input.brotli to output.txt using Brotli compression:
> escompress -i"input.brotli" -o"output.txt"
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Encode input.txt to output.compressed using Zstd compression:
> escompress -e -a zstd -i"input.txt" -o"output.compressed"
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Decode input.compressed to output.txt using GZip compression:
> escompress -d -a gzip -i"input.compressed" -o"output.txt"
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Print help:
> escompress -h
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Examples #
In the example subdirectory, the following examples are provided to demonstrate usage of the converters and the
framework.

Example
Description

brotli_example.dart
Encode/Decode in one-shot and streaming modes using the Brotli FFI-based implementation

lz4_example.dart
Encode/Decode in one-shot and streaming modes using the Lz4 FFI-based implementation

rle_example.dart
A simple RLE compression example designed to show how build custom codecs

zstd_example.dart
Encode/Decode in one-shot and streaming modes using the Zstd FFI-based implementation

To run (brotli shown below):
> dart example/brotli_example.dart
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Tests #
In the test subdirectory, the following tests are provided for the compression framework and encoder/decoder
implementations.

Test
Description

benchmarks_test.dart
Test benchmarks defined in benchmark subdirectory

brotli_test.dart
Test encoding/decode of the Brotli FFI-based implementation

buffer_test.dart
Test CodecBuffer and friends in the compression framework

escompress_test.dart
Test escompress binary in the bin subdirectory

examples_test.dart
Test examples defined in the example subdirectory

lz4_test.dart
Test encoding/decode of the Lz4 FFI-based implementation

zstd_test.dart
Test encoding/decode of the Zstd FFI-based implementation

To run test suite:
> pub run test
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Benchmarks #
In the benchmark subdirectory, the following benchmarks are provided to help understand encoder/decoder performance
and tradeoffs involved with parameters like buffer sizing.

Benchmark
Description

brotli_benchmark.dart
Benchmark encoding/decode of the Brotli FFI-based implementation

gzip_benchmark.dart
Benchmark encoding/decode of the GZip implementation from the Dart SDK

lz4_benchmark.dart
Benchmark encoding/decode of the Lz4 FFI-based implementation

zstd_benchmark.dart
Benchmark encoding/decode of the Zstd FFI-based implementation

To run (lz4 shown below):
> dart benchmark/lz4_benchmark.dart
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Deployment #
FFI-based implementations will need access to the low-level shared libraries (i.e. .dll, .so, .dylib).
This package offers a flexible library loader that can be customized for end-user deployment needs.
By default, the resolution order is:

Environment Variable
Package-Relative
Script-Relative
OS-Dependent

User Provided Resolution: The user can override the above resolution with a user provided library path. The different
strategies for locating shared libraries are described below.
Environment Variable Resolution #
An environment variable can be defined that provides the path to the shared library. This is either the path to the shared
library file or the directory which should contain the filename of the form es{algo}_{os}{bitness}.{ext}. For example,
the filename for lz4 on 64-bit windows would be eslz4_win64.dll.

Codec
Environment Variable

brotli
BROTLI_LIBRARY_PATH

lz4
LZ4_LIBRARY_PATH

zstd
ZSTD_LIBRARY_PATH

Package-Relative Resolution #
Prebuilt shared libraries for Win/Linux/Mac are provided in the blob directory of each FFI codec implementation. These
have been built by the package maintainer using the blob_builder
tool.
The distributed shared libs for a codec named 'xxx' is expected to be located in lib/src/xxx/blobs by default.
Script-Relative Resolution #
An attempt is made to find the shared library in the same directory as the running script. The name of the shared library
is expected to be of the form es{algo}_{os}{bitness}.{ext}. For example, the filename for zstd on 64-bit linux would
be eszstd_linux64.dll.
OS-Dependent Resolution #
A call to DynamicLibrary.open() is made for the filename of the form es{algo}_{os}{bitness}.{ext} which will use
the resolution rules for the operating system.
User Provided Resolution #
Users of this package have the option to override the library path early in the program.
Provided FFI Codecs have static getters/setters for the libraryPath. Users should be sure set the libraryPath
early before the first use. A StateError will be thrown if a user attempts to set the libraryPath more than once.
final codec = ZstdCodec.libraryPath = '/path/to/shared/library.so';
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Code Signing #
Windows
Provided dlls are digitally signed with an MS authenticode certificate owned by Instantiations, Inc.
Linux
N/A
Mac
Provided dylibs are not currently signed, and recent versions of OSX will refuse to load them unless you allow
it from the Security & Privacy dialog.
The build scripts have been provided blob_builder
and gives you access to build and sign them yourself, if desired.
Instantiations may sign the libraries in the future, and if so, it will be noted in the changelog and here.
Tools #
In the tool subdirectory, the following tools are provided.
Blob Builder #
blob_builder is a cmake-based build
generator which builds all the prebuilt shared libraries and copies them to their appropriate location in the dart library.
The maintainers use this tool to update the prebuilt shared libraries.
It can also be used to build custom versions of the various libraries by making adjustments to CMake variables that
define the version level information.
Prebuilt shared libraries for Win/Linux/Mac are provided in the blobs directory for each FFI codec implementation.
The distributed shared libs for a codec named xxx is expected to be located in lib/src/xxx/blobs.
There are instructions in the main CMakeLists.txt
file that describe how to run the tool.
Framework #
Initial codecs provided by this library use FFI-based implementations. However, the framework easily allows for pure
dart implementations for use within a front-end web context. rle_example.dart
shows a simple example of how to accomplish this.
The GZipCodec from dart:io served as a great starting point for understanding how to put the VAST Platform framework
abstractions in terms of Dart codecs, converters, filters, sinks.
The major compression framework abstractions are:

CodecConverter - Connects the compression framework to Converter in dart:convert.
CodecFilter - Direct processing of byte data and provides low-level compression implementation and hooks.
CodecSink - A type of ByteConversionSink for efficient transmission of byte data.
CodecBuffer - A buffer with a streaming API that is backed by either native
or dart heap bytes.

Features and bugs #
Please file feature requests and bugs at the issue tracker.
They will be reviewed and addressed on a best-effort basis by Instantiations, Inc.
About Us #
Since 1988, Instantiations has been building software to meet the diverse and evolutionary needs of our customers. We've now added Dart and Flutter to our toolbox.
For more information about our custom development or consulting services with Dart, Flutter, and other languages, please visit: https://www.instantiations.com/services/