aria2 - The ultra fast download utility¶

Disclaimer¶

This program comes with no warranty. You must use this program at your own risk.

Introduction¶

aria2 is a utility for downloading files. The supported protocols are HTTP(S), FTP, SFTP, BitTorrent, and Metalink. aria2 can download a file from multiple sources/protocols and tries to utilize your maximum download bandwidth. It supports downloading a file from HTTP(S)/FTP/SFTP and BitTorrent at the same time, while the data downloaded from HTTP(S)/FTP/SFTP is uploaded to the BitTorrent swarm. Using Metalink’s chunk checksums, aria2 automatically validates chunks of data while downloading a file like BitTorrent.

The project page is located at https://aria2.github.io/.

See aria2 Online Manual (Russian translation, Portuguese translation) to learn how to use aria2.

Features¶

Here is a list of features:

• Command-line interface

• Download files through HTTP(S)/FTP/SFTP/BitTorrent

• Segmented downloading

• Metalink version 4 (RFC 5854) support(HTTP/FTP/SFTP/BitTorrent)

• Metalink version 3.0 support(HTTP/FTP/SFTP/BitTorrent)

• Metalink/HTTP (RFC 6249) support

• HTTP/1.1 implementation

• HTTP Proxy support

• HTTP BASIC authentication support

• HTTP Proxy authentication support

• Well-known environment variables for proxy: http_proxy, https_proxy, ftp_proxy, all_proxy and no_proxy

• HTTP gzip, deflate content encoding support

• Verify peer using given trusted CA certificate in HTTPS

• Client certificate authentication in HTTPS

• Chunked transfer encoding support

• Load Cookies from file using the Firefox3 format, Chromium/Google Chrome and the Mozilla/Firefox (1.x/2.x)/Netscape format.

• Save Cookies in the Mozilla/Firefox (1.x/2.x)/Netscape format.

• Custom HTTP Header support

• Persistent Connections support

• FTP/SFTP through HTTP Proxy

• Download/Upload speed throttling

• BitTorrent extensions: Fast extension, DHT, PEX, MSE/PSE, Multi-Tracker, UDP tracker

• BitTorrent WEB-Seeding. aria2 requests chunks more than piece size to reduce the request overhead. It also supports pipelined requests with piece size.

• BitTorrent Local Peer Discovery

• Rename/change the directory structure of BitTorrent downloads completely

• JSON-RPC (over HTTP and WebSocket)/XML-RPC interface

• Run as a daemon process

• Selective download in multi-file torrent/Metalink

• Chunk checksum validation in Metalink

• Can disable segmented downloading in Metalink

• Netrc support

• Configuration file support

• Download URIs found in a text file or stdin and the destination directory and output file name can be specified optionally

• Parameterized URI support

• IPv6 support with Happy Eyeballs

• Disk cache to reduce disk activity

Versioning and release schedule¶

We use 3 numbers for aria2 version: MAJOR.MINOR.PATCH. We will ship MINOR update on 15th of every month. We may skip a release if we have no changes since the last release. The feature and documentation freeze happens 10 days before the release day (5th day of the month) for translation teams. We will raise an issue about the upcoming release around that day.

We may release PATCH releases between regular releases if we have security issues.

MAJOR version will stay at 1 for the time being.

How to get source code¶

We maintain the source code at Github: https://github.com/aria2/aria2

To get the latest source code, run following command:

$ git clone https://github.com/aria2/aria2.git

This will create aria2 directory in your current directory and source files are stored there.

Dependency¶

A user can have one of the following configurations for SSL and crypto libraries:

• OpenSSL

• GnuTLS + libgcrypt

• GnuTLS + libnettle

• Apple TLS (OSX only)

• Windows TLS (Windows only)

You can disable BitTorrent and Metalink support by providing --disable-bittorrent and --disable-metalink to the configure script respectively.

In order to enable async DNS support, you need c-ares.

• c-ares: http://c-ares.haxx.se/

How to build¶

aria2 is primarily written in C++. Initially it was written based on C++98/C++03 standard features. We are now migrating aria2 to C++11 standard. The current source code requires C++11 aware compiler. For well-known compilers, such as g++ and clang, the -std=c++11 or -std=c++0x flag must be supported.

In order to build aria2 from the source package, you need following development packages (package name may vary depending on the distribution you use):

• libgnutls-dev (Required for HTTPS, BitTorrent, Checksum support)

• nettle-dev (Required for BitTorrent, Checksum support)

• libgmp-dev (Required for BitTorrent)

• libssh2-1-dev (Required for SFTP support)

• libc-ares-dev (Required for async DNS support)

• libxml2-dev (Required for Metalink support)

• zlib1g-dev (Required for gzip, deflate decoding support in HTTP)

• libsqlite3-dev (Required for Firefox3/Chromium cookie support)

• pkg-config (Required to detect installed libraries)

You can use libgcrypt-dev instead of nettle-dev and libgmp-dev:

• libgpg-error-dev (Required for BitTorrent, Checksum support)

• libgcrypt-dev (Required for BitTorrent, Checksum support)

You can use libssl-dev instead of libgnutls-dev, nettle-dev, libgmp-dev, libgpg-error-dev and libgcrypt-dev:

• libssl-dev (Required for HTTPS, BitTorrent, Checksum support)

You can use libexpat1-dev instead of libxml2-dev:

• libexpat1-dev (Required for Metalink support)

On Fedora you need the following packages: gcc, gcc-c++, kernel-devel, libgcrypt-devel, libxml2-devel, openssl-devel, gettext-devel, cppunit

If you downloaded source code from git repository, you have to install following packages to get autoconf macros:

• libxml2-dev

• libcppunit-dev

• autoconf

• automake

• autotools-dev

• autopoint

• libtool

And run following command to generate configure script and other files necessary to build the program:

$ autoreconf -i

Also you need Sphinx to build man page.

If you are building aria2 for Mac OS X, take a look at the makerelease-osx.mk GNU Make makefile.

The quickest way to build aria2 is first run configure script:

$ ./configure

To build statically linked aria2, use ARIA2_STATIC=yes command-line option:

$ ./configure ARIA2_STATIC=yes

After configuration is done, run make to compile the program:

$ make

See Cross-compiling Windows binary to create a Windows binary. See Cross-compiling Android binary to create an Android binary.

The configure script checks available libraries and enables as many features as possible except for experimental features not enabled by default.

Since 1.1.0, aria2 checks the certificate of HTTPS servers by default. If you build with OpenSSL or the recent version of GnuTLS which has gnutls_certificate_set_x509_system_trust() function and the library is properly configured to locate the system-wide CA certificates store, aria2 will automatically load those certificates at the startup. If it is not the case, I recommend to supply the path to the CA bundle file. For example, in Debian the path to CA bundle file is ‘/etc/ssl/certs/ca-certificates.crt’ (in ca-certificates package). This may vary depending on your distribution. You can give it to configure script using --with-ca-bundle option:

$ ./configure --with-ca-bundle='/etc/ssl/certs/ca-certificates.crt'
$ make

Without --with-ca-bundle option, you will encounter the error when accessing HTTPS servers because the certificate cannot be verified without CA bundle. In such case, you can specify the CA bundle file using aria2’s --ca-certificate option. If you don’t have CA bundle file installed, then the last resort is disable the certificate validation using --check-certificate=false.

Using the native OSX (AppleTLS) and/or Windows (WinTLS) implementation will automatically use the system certificate store, so --with-ca-bundle is not necessary and will be ignored when using these implementations.

By default, the bash_completion file named aria2c is installed to the directory $prefix/share/doc/aria2/bash_completion. To change the install directory of the file, use --with-bashcompletiondir option.

After a make the executable is located at src/aria2c.

aria2 uses CppUnit for automated unit testing. To run the unit test:

$ make check

Cross-compiling Windows binary¶

In this section, we describe how to build a Windows binary using a mingw-w64 (http://mingw-w64.org/doku.php) cross-compiler on Debian Linux. The MinGW (http://www.mingw.org/) may not be able to build aria2.

The easiest way to build Windows binary is use Dockerfile.mingw. See Dockerfile.mingw how to build binary. If you cannot use Dockerfile, then continue to read following paragraphs.

Basically, after compiling and installing depended libraries, you can do cross-compile just passing appropriate --host option and specifying CPPFLAGS, LDFLAGS and PKG_CONFIG_LIBDIR variables to configure. For convenience and lowering our own development cost, we provide easier way to configure the build settings.

mingw-config script is a configure script wrapper for mingw-w64. We use it to create official Windows build. This script assumes following libraries have been built for cross-compile:

• c-ares

• expat

• sqlite3

• zlib

• libssh2

• cppunit

Some environment variables can be adjusted to change build settings:

HOST

cross-compile to build programs to run on HOST. It defaults to i686-w64-mingw32. To build 64bit binary, specify x86_64-w64-mingw32.

PREFIX

Prefix to the directory where dependent libraries are installed. It defaults to /usr/local/$HOST. -I$PREFIX/include will be added to CPPFLAGS. -L$PREFIX/lib will be added to LDFLAGS. $PREFIX/lib/pkgconfig will be set to PKG_CONFIG_LIBDIR.

For example, to build 64bit binary do this:

$ HOST=x86_64-w64-mingw32 ./mingw-config

If you want libaria2 dll with --enable-libaria2, then don’t use ARIA2_STATIC=yes and prepare the DLL version of external libraries.

Cross-compiling Android binary¶

In this section, we describe how to build Android binary using Android NDK cross-compiler on Debian Linux.

At the time of this writing, Android NDK r20 should compile aria2 without errors.

android-config script is a configure script wrapper for Android build. We use it to create official Android build. This script assumes the following libraries have been built for cross-compile:

• c-ares

• openssl

• expat

• zlib

• libssh2

When building the above libraries, make sure that disable shared library and enable only static library. We are going to link those libraries statically.

android-config assumes that $ANDROID_HOME and $NDK environment variables are defined.

We currently use Android NDK r20. $NDK should point to the directory to Anroid NDK. The build tools will be found under $NDK/toolchains/llvm/prebuilt/linux-x86_64/bin/.

All the dependent libraries must be installed under $ANDROID_HOME/usr/local.

After android-config, run make to compile sources.

Building documentation¶

Sphinx is used to build the documentation. aria2 man pages will be build when you run make if they are not up-to-date. You can also build HTML version of aria2 man page by make html. The HTML version manual is also available at online (Russian translation, Portuguese translation).

BitTorrent¶

Metalink¶

The current implementation supports HTTP(S)/FTP/SFTP/BitTorrent. The other P2P protocols are ignored. Both Metalink4 (RFC 5854) and Metalink version 3.0 documents are supported.

For checksum verification, md5, sha-1, sha-224, sha-256, sha-384 and sha-512 are supported. If multiple hash algorithms are provided, aria2 uses stronger one. If whole file checksum verification fails, aria2 doesn’t retry the download and just exits with non-zero return code.

The supported user preferences are version, language, location, protocol and os.

If chunk checksums are provided in Metalink file, aria2 automatically validates chunks of data during download. This behavior can be turned off by a command-line option.

If signature is included in a Metalink file, aria2 saves it as a file after the completion of the download. The file name is download file name + “.sig”. If same file already exists, the signature file is not saved.

In Metalink4, multi-file torrent could appear in metalink:metaurl element. Since aria2 cannot download 2 same torrents at the same time, aria2 groups files in metalink:file element which has same BitTorrent metaurl and downloads them from a single BitTorrent swarm. This is basically multi-file torrent download with file selection, so the adjacent files which is not in Metalink document but shares same piece with selected file are also created.

If relative URI is specified in metalink:url or metalink:metaurl element, aria2 uses the URI of Metalink file as base URI to resolve the relative URI. If relative URI is found in Metalink file which is read from local disk, aria2 uses the value of --metalink-base-uri option as base URI. If this option is not specified, the relative URI will be ignored.

Metalink/HTTP¶

The current implementation only uses rel=duplicate links only. aria2 understands Digest header fields and check whether it matches the digest value from other sources. If it differs, drop connection. aria2 also uses this digest value to perform checksum verification after download finished. aria2 recognizes geo value. To tell aria2 which location you prefer, you can use --metalink-location option.

netrc¶

netrc support is enabled by default for HTTP(S)/FTP/SFTP. To disable netrc support, specify -n command-line option. Your .netrc file should have correct permissions(600).

WebSocket¶

The WebSocket server embedded in aria2 implements the specification defined in RFC 6455. The supported protocol version is 13.

libaria2¶

The libaria2 is a C++ library which offers aria2 functionality to the client code. Currently, libaria2 is not built by default. To enable libaria2, use --enable-libaria2 configure option. By default, only the shared library is built. To build static library, use --enable-static configure option as well. See libaria2 documentation to know how to use API.

References¶

• aria2 Online Manual

• https://aria2.github.io/

• RFC 959 FILE TRANSFER PROTOCOL (FTP)

• RFC 1738 Uniform Resource Locators (URL)

• RFC 2428 FTP Extensions for IPv6 and NATs

• RFC 2616 Hypertext Transfer Protocol – HTTP/1.1

• RFC 3659 Extensions to FTP

• RFC 3986 Uniform Resource Identifier (URI): Generic Syntax

• RFC 4038 Application Aspects of IPv6 Transition

• RFC 5854 The Metalink Download Description Format

• RFC 6249 Metalink/HTTP: Mirrors and Hashes

• RFC 6265 HTTP State Management Mechanism

• RFC 6266 Use of the Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP)

• RFC 6455 The WebSocket Protocol

• RFC 6555 Happy Eyeballs: Success with Dual-Stack Hosts

• The BitTorrent Protocol Specification

• BitTorrent: DHT Protocol

• BitTorrent: Fast Extension

• BitTorrent: IPv6 Tracker Extension

• BitTorrent: Extension for Peers to Send Metadata Files

• BitTorrent: Extension Protocol

• BitTorrent: Multitracker Metadata Extension

• BitTorrent: UDP Tracker Protocol for BitTorrent and BitTorrent udp-tracker protocol specification.

• BitTorrent: WebSeed - HTTP/FTP Seeding (GetRight style)

• BitTorrent: Private Torrents

• BitTorrent: BitTorrent DHT Extensions for IPv6

• BitTorrent: Message Stream Encryption

• Kademlia: A Peer-to-peer Information System Based on the XOR Metric