[][src]Crate data_encoding

Efficient and customizable data-encoding functions

This crate provides little-endian ASCII base-conversion encodings for bases of size 2, 4, 8, 16, 32, and 64. It supports:

  • padded and unpadded encodings
  • canonical encodings (e.g. trailing bits are checked)
  • in-place encoding and decoding functions
  • partial decoding functions (e.g. for error recovery)
  • character translation (e.g. for case-insensitivity)
  • most and least significant bit-order
  • ignoring characters when decoding (e.g. for skipping newlines)
  • wrapping the output when encoding

The performance of the encoding and decoding functions are similar to existing implementations (see how to run the benchmarks on github).

This is the library documentation. If you are looking for the binary, see the installation instructions on github.


This crate provides predefined encodings as constants. These constants are of type Encoding. This type provides encoding and decoding functions with in-place or allocating variants. Here is an example using the allocating encoding function of base64:

use data_encoding::BASE64;
assert_eq!(BASE64.encode(b"Hello world"), "SGVsbG8gd29ybGQ=");

Here is an example using the in-place decoding function of base32:

use data_encoding::BASE32;
let input = b"JBSWY3DPEB3W64TMMQ======";
let mut output = vec![0; BASE32.decode_len(input.len()).unwrap()];
let len = BASE32.decode_mut(input, &mut output).unwrap();
assert_eq!(&output[0 .. len], b"Hello world");

You are not limited to the predefined encodings. You may define your own encodings (with the same correctness and performance properties as the predefined ones) using the Specification type:

use data_encoding::Specification;
let hex = {
    let mut spec = Specification::new();
assert_eq!(hex.encode(b"hello"), "68656c6c6f");

If you use the lazy_static crate, you can define a global encoding:

This example is not tested
lazy_static! {
    static ref HEX: Encoding = {
        let mut spec = Specification::new();

You may also use the macro library to define a compile-time custom encoding:

This example is not tested
const HEX: Encoding = new_encoding!{
    symbols: "0123456789abcdef",
    translate_from: "ABCDEF",
    translate_to: "abcdef",
const BASE64: Encoding = new_encoding!{
    symbols: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
    padding: '=',


The base16, base32, base32hex, base64, and base64url predefined encodings are conform to RFC4648.

In general, the encoding and decoding functions satisfy the following properties:

  • They are deterministic: their output only depends on their input
  • They have no side-effects: they do not modify a hidden mutable state
  • They are correct: encoding then decoding gives the initial data
  • They are canonical (unless is_canonical returns false): decoding then encoding gives the initial data

This last property is usually not satisfied by common base64 implementations (like the rustc-serialize crate, the base64 crate, or the base64 GNU program). This is a matter of choice and this crate has made the choice to let the user choose. Support for canonical encoding as described by the RFC is provided. But it is also possible to disable checking trailing bits, to add characters translation, to decode concatenated padded inputs, and to ignore some characters.

Since the RFC specifies the encoding function on all inputs and the decoding function on all possible encoded outputs, the differences between implementations come from the decoding function which may be more or less permissive. In this crate, the decoding function of canonical encodings rejects all inputs that are not a possible output of the encoding function. Here are some concrete examples of decoding differences between this crate, the rustc-serialize crate, the base64 crate, and the base64 GNU program:

Input data-encoding rustc base64 GNU base64
AAB= Trailing(2) [0, 0] [0, 0] \x00\x00
AA\nB= Length(4) [0, 0] Length \x00\x00
AAB Length(0) [0, 0] [0, 0] Invalid input
A\rA\nB= Length(4) [0, 0] Err(1) Invalid input
-_\r\n Symbol(0) [251] Err(0) Invalid input
AA==AA== [0, 0] Err Err(2) \x00\x00

We can summarize these discrepancies as follows:

Discrepancy data-encoding rustc base64 GNU base64
Check trailing bits Yes No No No
Ignored characters None \r and \n None \n
Translated characters None -_ mapped to +/ None None
Check padding Yes No No Yes
Support concatenated input Yes No No Yes

This crate permits to disable checking trailing bits. It permits to ignore some characters. It permits to translate characters. It permits to use unpadded encodings. However, for padded encodings, support for concatenated inputs cannot be disabled. This is simply because it doesn't make sense to use padding if it is not to support concatenated inputs.


The changelog describes the changes between v1 and v2. Here are the migration steps for common usage:

v1 v2
use data_encoding::baseNN use data_encoding::BASENN
baseNN::function BASENN.method
baseNN::function_nopad BASENN_NOPAD.method



Decoding error


Decoding error with partial result


Base-conversion encoding


Base-conversion specification


Specification error


How to translate characters when decoding


How to wrap the output when encoding



Order in which bits are read from a byte


Decoding error kind



Padded base32 encoding


Unpadded base32 encoding


Padded base32hex encoding


Unpadded base32hex encoding


DNSSEC base32 encoding


DNSCurve base32 encoding


Padded base64 encoding


Unpadded base64 encoding


MIME base64 encoding


Padded base64url encoding


Unpadded base64url encoding


Lowercase hexadecimal encoding


Lowercase hexadecimal encoding with case-insensitive decoding


Uppercase hexadecimal encoding


Uppercase hexadecimal encoding with case-insensitive decoding