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Diffstat (limited to 'src/lib.rs')
| -rw-r--r-- | src/lib.rs | 229 |
1 files changed, 164 insertions, 65 deletions
@@ -1,100 +1,124 @@ -//! # Getting started +//! Correct, fast, and configurable [base64][] decoding and encoding. Base64 +//! transports binary data efficiently in contexts where only plain text is +//! allowed. //! -//! 1. Perhaps one of the preconfigured engines in [engine::general_purpose] will suit, e.g. -//! [engine::general_purpose::STANDARD_NO_PAD]. -//! - These are re-exported in [prelude] with a `BASE64_` prefix for those who prefer to -//! `use base64::prelude::*` or equivalent, e.g. [prelude::BASE64_STANDARD_NO_PAD] -//! 1. If not, choose which alphabet you want. Most usage will want [alphabet::STANDARD] or [alphabet::URL_SAFE]. -//! 1. Choose which [Engine] implementation you want. For the moment there is only one: [engine::GeneralPurpose]. -//! 1. Configure the engine appropriately using the engine's `Config` type. -//! - This is where you'll select whether to add padding (when encoding) or expect it (when -//! decoding). If given the choice, prefer no padding. -//! 1. Build the engine using the selected alphabet and config. +//! [base64]: https://developer.mozilla.org/en-US/docs/Glossary/Base64 //! -//! For more detail, see below. +//! # Usage //! -//! ## Alphabets +//! Use an [`Engine`] to decode or encode base64, configured with the base64 +//! alphabet and padding behavior best suited to your application. //! -//! An [alphabet::Alphabet] defines what ASCII symbols are used to encode to or decode from. +//! ## Engine setup //! -//! Constants in [alphabet] like [alphabet::STANDARD] or [alphabet::URL_SAFE] provide commonly used -//! alphabets, but you can also build your own custom [alphabet::Alphabet] if needed. +//! There is more than one way to encode a stream of bytes as “base64”. +//! Different applications use different encoding +//! [alphabets][alphabet::Alphabet] and +//! [padding behaviors][engine::general_purpose::GeneralPurposeConfig]. //! -//! ## Engines +//! ### Encoding alphabet //! -//! Once you have an `Alphabet`, you can pick which `Engine` you want. A few parts of the public -//! API provide a default, but otherwise the user must provide an `Engine` to use. +//! Almost all base64 [alphabets][alphabet::Alphabet] use `A-Z`, `a-z`, and +//! `0-9`, which gives nearly 64 characters (26 + 26 + 10 = 62), but they differ +//! in their choice of their final 2. //! -//! See [Engine] for more. +//! Most applications use the [standard][alphabet::STANDARD] alphabet specified +//! in [RFC 4648][rfc-alphabet]. If that’s all you need, you can get started +//! quickly by using the pre-configured +//! [`STANDARD`][engine::general_purpose::STANDARD] engine, which is also available +//! in the [`prelude`] module as shown here, if you prefer a minimal `use` +//! footprint. //! -//! ## Config +#![cfg_attr(feature = "alloc", doc = "```")] +#![cfg_attr(not(feature = "alloc"), doc = "```ignore")] +//! use base64::prelude::*; //! -//! In addition to an `Alphabet`, constructing an `Engine` also requires an [engine::Config]. Each -//! `Engine` has a corresponding `Config` implementation since different `Engine`s may offer different -//! levels of configurability. +//! # fn main() -> Result<(), base64::DecodeError> { +//! assert_eq!(BASE64_STANDARD.decode(b"+uwgVQA=")?, b"\xFA\xEC\x20\x55\0"); +//! assert_eq!(BASE64_STANDARD.encode(b"\xFF\xEC\x20\x55\0"), "/+wgVQA="); +//! # Ok(()) +//! # } +//! ``` //! -//! # Encoding +//! [rfc-alphabet]: https://datatracker.ietf.org/doc/html/rfc4648#section-4 //! -//! Several different encoding methods on [Engine] are available to you depending on your desire for -//! convenience vs performance. +//! Other common alphabets are available in the [`alphabet`] module. //! -//! | Method | Output | Allocates | -//! | ------------------------ | ---------------------------- | ------------------------------ | -//! | [Engine::encode] | Returns a new `String` | Always | -//! | [Engine::encode_string] | Appends to provided `String` | Only if `String` needs to grow | -//! | [Engine::encode_slice] | Writes to provided `&[u8]` | Never - fastest | +//! #### URL-safe alphabet //! -//! All of the encoding methods will pad as per the engine's config. +//! The standard alphabet uses `+` and `/` as its two non-alphanumeric tokens, +//! which cannot be safely used in URL’s without encoding them as `%2B` and +//! `%2F`. //! -//! # Decoding +//! To avoid that, some applications use a [“URL-safe” alphabet][alphabet::URL_SAFE], +//! which uses `-` and `_` instead. To use that alternative alphabet, use the +//! [`URL_SAFE`][engine::general_purpose::URL_SAFE] engine. This example doesn't +//! use [`prelude`] to show what a more explicit `use` would look like. //! -//! Just as for encoding, there are different decoding methods available. +#![cfg_attr(feature = "alloc", doc = "```")] +#![cfg_attr(not(feature = "alloc"), doc = "```ignore")] +//! use base64::{engine::general_purpose::URL_SAFE, Engine as _}; //! -//! | Method | Output | Allocates | -//! | ------------------------ | ----------------------------- | ------------------------------ | -//! | [Engine::decode] | Returns a new `Vec<u8>` | Always | -//! | [Engine::decode_vec] | Appends to provided `Vec<u8>` | Only if `Vec` needs to grow | -//! | [Engine::decode_slice] | Writes to provided `&[u8]` | Never - fastest | +//! # fn main() -> Result<(), base64::DecodeError> { +//! assert_eq!(URL_SAFE.decode(b"-uwgVQA=")?, b"\xFA\xEC\x20\x55\0"); +//! assert_eq!(URL_SAFE.encode(b"\xFF\xEC\x20\x55\0"), "_-wgVQA="); +//! # Ok(()) +//! # } +//! ``` //! -//! Unlike encoding, where all possible input is valid, decoding can fail (see [DecodeError]). +//! ### Padding characters //! -//! Input can be invalid because it has invalid characters or invalid padding. The nature of how -//! padding is checked depends on the engine's config. -//! Whitespace in the input is invalid, just like any other non-base64 byte. +//! Each base64 character represents 6 bits (2⁶ = 64) of the original binary +//! data, and every 3 bytes of input binary data will encode to 4 base64 +//! characters (8 bits × 3 = 6 bits × 4 = 24 bits). //! -//! # `Read` and `Write` +//! When the input is not an even multiple of 3 bytes in length, [canonical][] +//! base64 encoders insert padding characters at the end, so that the output +//! length is always a multiple of 4: //! -//! To decode a [std::io::Read] of b64 bytes, wrap a reader (file, network socket, etc) with -//! [read::DecoderReader]. +//! [canonical]: https://datatracker.ietf.org/doc/html/rfc4648#section-3.5 //! -//! To write raw bytes and have them b64 encoded on the fly, wrap a [std::io::Write] with -//! [write::EncoderWriter]. +#![cfg_attr(feature = "alloc", doc = "```")] +#![cfg_attr(not(feature = "alloc"), doc = "```ignore")] +//! use base64::{engine::general_purpose::STANDARD, Engine as _}; //! -//! There is some performance overhead (15% or so) because of the necessary buffer shuffling -- -//! still fast enough that almost nobody cares. Also, these implementations do not heap allocate. +//! assert_eq!(STANDARD.encode(b""), ""); +//! assert_eq!(STANDARD.encode(b"f"), "Zg=="); +//! assert_eq!(STANDARD.encode(b"fo"), "Zm8="); +//! assert_eq!(STANDARD.encode(b"foo"), "Zm9v"); +//! ``` //! -//! # `Display` +//! Canonical encoding ensures that base64 encodings will be exactly the same, +//! byte-for-byte, regardless of input length. But the `=` padding characters +//! aren’t necessary for decoding, and they may be omitted by using a +//! [`NO_PAD`][engine::general_purpose::NO_PAD] configuration: //! -//! See [display] for how to transparently base64 data via a `Display` implementation. +#![cfg_attr(feature = "alloc", doc = "```")] +#![cfg_attr(not(feature = "alloc"), doc = "```ignore")] +//! use base64::{engine::general_purpose::STANDARD_NO_PAD, Engine as _}; //! -//! # Examples +//! assert_eq!(STANDARD_NO_PAD.encode(b""), ""); +//! assert_eq!(STANDARD_NO_PAD.encode(b"f"), "Zg"); +//! assert_eq!(STANDARD_NO_PAD.encode(b"fo"), "Zm8"); +//! assert_eq!(STANDARD_NO_PAD.encode(b"foo"), "Zm9v"); +//! ``` //! -//! ## Using predefined engines +//! The pre-configured `NO_PAD` engines will reject inputs containing padding +//! `=` characters. To encode without padding and still accept padding while +//! decoding, create an [engine][engine::general_purpose::GeneralPurpose] with +//! that [padding mode][engine::DecodePaddingMode]. //! #![cfg_attr(feature = "alloc", doc = "```")] #![cfg_attr(not(feature = "alloc"), doc = "```ignore")] -//! use base64::{Engine as _, engine::general_purpose}; -//! -//! let orig = b"data"; -//! let encoded: String = general_purpose::STANDARD_NO_PAD.encode(orig); -//! assert_eq!("ZGF0YQ", encoded); -//! assert_eq!(orig.as_slice(), &general_purpose::STANDARD_NO_PAD.decode(encoded).unwrap()); -//! -//! // or, URL-safe -//! let encoded_url = general_purpose::URL_SAFE_NO_PAD.encode(orig); +//! # use base64::{engine::general_purpose::STANDARD_NO_PAD, Engine as _}; +//! assert_eq!(STANDARD_NO_PAD.decode(b"Zm8="), Err(base64::DecodeError::InvalidPadding)); //! ``` //! -//! ## Custom alphabet, config, and engine +//! ### Further customization +//! +//! Decoding and encoding behavior can be customized by creating an +//! [engine][engine::GeneralPurpose] with an [alphabet][alphabet::Alphabet] and +//! [padding configuration][engine::GeneralPurposeConfig]: //! #![cfg_attr(feature = "alloc", doc = "```")] #![cfg_attr(not(feature = "alloc"), doc = "```ignore")] @@ -117,6 +141,81 @@ //! //! ``` //! +//! ## Memory allocation +//! +//! The [decode][Engine::decode()] and [encode][Engine::encode()] engine methods +//! allocate memory for their results – `decode` returns a `Vec<u8>` and +//! `encode` returns a `String`. To instead decode or encode into a buffer that +//! you allocated, use one of the alternative methods: +//! +//! #### Decoding +//! +//! | Method | Output | Allocates memory | +//! | -------------------------- | ----------------------------- | ----------------------------- | +//! | [`Engine::decode`] | returns a new `Vec<u8>` | always | +//! | [`Engine::decode_vec`] | appends to provided `Vec<u8>` | if `Vec` lacks capacity | +//! | [`Engine::decode_slice`] | writes to provided `&[u8]` | never +//! +//! #### Encoding +//! +//! | Method | Output | Allocates memory | +//! | -------------------------- | ---------------------------- | ------------------------------ | +//! | [`Engine::encode`] | returns a new `String` | always | +//! | [`Engine::encode_string`] | appends to provided `String` | if `String` lacks capacity | +//! | [`Engine::encode_slice`] | writes to provided `&[u8]` | never | +//! +//! ## Input and output +//! +//! The `base64` crate can [decode][Engine::decode()] and +//! [encode][Engine::encode()] values in memory, or +//! [`DecoderReader`][read::DecoderReader] and +//! [`EncoderWriter`][write::EncoderWriter] provide streaming decoding and +//! encoding for any [readable][std::io::Read] or [writable][std::io::Write] +//! byte stream. +//! +//! #### Decoding +//! +#![cfg_attr(feature = "std", doc = "```")] +#![cfg_attr(not(feature = "std"), doc = "```ignore")] +//! # use std::io; +//! use base64::{engine::general_purpose::STANDARD, read::DecoderReader}; +//! +//! # fn main() -> Result<(), Box<dyn std::error::Error>> { +//! let mut input = io::stdin(); +//! let mut decoder = DecoderReader::new(&mut input, &STANDARD); +//! io::copy(&mut decoder, &mut io::stdout())?; +//! # Ok(()) +//! # } +//! ``` +//! +//! #### Encoding +//! +#![cfg_attr(feature = "std", doc = "```")] +#![cfg_attr(not(feature = "std"), doc = "```ignore")] +//! # use std::io; +//! use base64::{engine::general_purpose::STANDARD, write::EncoderWriter}; +//! +//! # fn main() -> Result<(), Box<dyn std::error::Error>> { +//! let mut output = io::stdout(); +//! let mut encoder = EncoderWriter::new(&mut output, &STANDARD); +//! io::copy(&mut io::stdin(), &mut encoder)?; +//! # Ok(()) +//! # } +//! ``` +//! +//! #### Display +//! +//! If you only need a base64 representation for implementing the +//! [`Display`][std::fmt::Display] trait, use +//! [`Base64Display`][display::Base64Display]: +//! +//! ``` +//! use base64::{display::Base64Display, engine::general_purpose::STANDARD}; +//! +//! let value = Base64Display::new(b"\0\x01\x02\x03", &STANDARD); +//! assert_eq!("base64: AAECAw==", format!("base64: {}", value)); +//! ``` +//! //! # Panics //! //! If length calculations result in overflowing `usize`, a panic will result. |