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//! # nom-derive //! //! [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](./LICENSE-MIT) //! [![Apache License 2.0](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](./LICENSE-APACHE) //! [![docs.rs](https://docs.rs/nom-derive/badge.svg)](https://docs.rs/nom-derive) //! [![Build Status](https://travis-ci.org/chifflier/nom-derive.svg?branch=master)](https://travis-ci.org/chifflier/nom-derive) //! [![Crates.io Version](https://img.shields.io/crates/v/nom-derive.svg)](https://crates.io/crates/nom-derive) //! //! ## Overview //! //! nom-derive is a custom derive attribute, to derive [nom] parsers automatically from the structure definition. //! //! It is not meant to replace [nom], but to provide a quick and easy way to generate parsers for //! structures, especially for simple structures. This crate aims at simplifying common cases. //! In some cases, writing the parser manually will remain more efficient. //! //! - [API documentation](https://docs.rs/nom-derive) //! - [Documentation of `Nom` attribute](https://docs.rs/nom-derive/latest/nom_derive/derive.Nom.html). This is the main //! documentation for this crate, with all possible options and many examples. //! //! *Feedback welcome !* //! //! ## `#[derive(Nom)]` //! //! This crate exposes a single custom-derive macro `Nom` which //! implements `parse` for the struct it is applied to. //! //! The goal of this project is that: //! //! * `derive(Nom)` should be enough for you to derive [nom] parsers for simple //! structures easily, without having to write it manually //! * it allows overriding any parsing method by your own //! * it allows using generated parsing functions along with handwritten parsers and //! combining them without efforts //! //! `nom-derive` adds declarative parsing to `nom`. It also allows mixing with //! procedural parsing easily, making writing parsers for byte-encoded formats //! very easy. //! //! For example: //! //! ```rust //! use nom_derive::Nom; //! //! #[derive(Nom)] //! struct S { //! a: u32, //! b: u16, //! c: u16 //! } //! ``` //! //! This adds a static method `parse` to `S`, with the following signature: //! ```rust,ignore //! impl S { //! pub fn parse(i: &[u8]) -> nom::IResult(&[u8], S); //! } //! ``` //! //! To parse input, just call `let res = S::parse(input);`. //! //! For extensive documentation of all attributes and examples, see the //! [Nom derive //! attribute](https://docs.rs/nom-derive/latest/nom_derive/derive.Nom.html) //! documentation. //! //! Many examples are provided, and more can be found in the [project //! tests](https://github.com/rust-bakery/nom-derive/tree/master/tests). //! //! ## Debug tips //! //! * If the generated parser does not compile, add `#[nom(DebugDerive)]` to the structure. //! It will dump the generated parser to `stderr`. //! * If the generated parser fails at runtime, try adding `#[nom(Debug)]` to the structure or //! to fields. It wraps subparsers in `dbg_dmp` and will print the field name and input to //! `stderr` if the parser fails. //! //! [nom]: https://github.com/geal/nom extern crate proc_macro; extern crate proc_macro2; extern crate syn; #[macro_use] extern crate quote; use proc_macro::TokenStream; use syn::*; use syn::export::Span; mod config; mod meta; mod parsertree; mod structs; mod enums; use structs::{get_pre_post_exec, parse_struct}; use enums::impl_nom_enums; /// The `Nom` derive automatically generates a `parse` function for the structure /// using [nom] parsers. It will try to infer parsers for primitive of known /// types, but also allows you to specify parsers using custom attributes. /// /// Deriving parsers supports `struct` and `enum` types. /// /// Many examples are provided, and more can be found in the [project /// tests](https://github.com/rust-bakery/nom-derive/tree/master/tests). /// /// [nom]: https://github.com/Geal/nom /// /// # Attributes /// /// Derived parsers can be controlled using the `nom` attribute, with a sub-attribute. /// For example, `#[nom(Value)]`. /// /// Most combinators support using literal strings `#[nom(Count="4")]` or /// parenthesized values `#[nom(Count(4))]` /// /// To specify multiple attributes, use a comma-separated list: `#[nom(Debug, Count="4")]`. /// /// The available attributes are: /// /// | Attribute | Supports | Description /// |-----------|------------------|------------ /// | [AlignAfter](#alignment-and-padding) | fields | skip bytes until aligned to a multiple of the provided value, after parsing value /// | [AlignBefore](#alignment-and-padding) | fields | skip bytes until aligned to a multiple of the provided value, before parsing value /// | [BigEndian](#byteorder) | all | Set the endianness to big endian /// | [Cond](#conditional-values) | fields | Used on an `Option<T>` to read a value of type `T` only if the condition is met /// | [Complete](#complete) | fields | Transforms Incomplete into Error /// | [Count](#count) | fields | Set the expected number of items to parse /// | [Debug](#debug) | all | Print error message and input if parser fails (at runtime) /// | [DebugDerive](#debugderive) | top-level | Print the generated code to stderr during build /// | [Default](#default) | fields | Do not parse, set a field to the default value for the type /// | [ErrorIf](#verifications) | fields | Before parsing, check condition is true and return an error if false. /// | [Exact](#exact) | top-level | Check that input was entirely consumed by parser /// | [If](#conditional-values) | fields | Similar to `Cond` /// | [Ignore](#default) | fields | An alias for `default` /// | [InputName](#input-name) | top-level | Change the internal name of input /// | [LittleEndian](#byteorder) | all | Set the endianness to little endian /// | [Map](#map) | fields | Parse field, then apply a function /// | [Move](#alignment-and-padding) | fields | add the specified offset to current position, before parsing /// | [MoveAbs](#alignment-and-padding) | fields | go to the specified absoluted position, before parsing /// | [Parse](#custom-parsers) | fields | Use a custom parser function for reading from a file /// | [PreExec](#preexec) | all | Execute Rust code before parsing field or struct /// | [PostExec](#postexec) | all | Execute Rust code after parsing field or struct /// | [Selector](#deriving-parser-for-enum) | all | Used to specify the value matching an enum variant /// | [SkipAfter](#alignment-and-padding) | fields | skip the specified number of bytes, after parsing /// | [SkipBefore](#alignment-and-padding) | fields | skip the specified number of bytes, before parsing /// | [Take](#take) | fields | Take `n` bytes of input /// | [Value](#value) | fields | Store result of evaluated expression in field /// | [Verify](#verifications) | fields | After parsing, check that condition is true and return an error if false. /// /// See below for examples. /// /// # Deriving parsers for `Struct` /// /// Import the `Nom` derive attribute: /// /// ```rust /// use nom_derive::Nom; /// ``` /// and add it to structs or enums. /// /// For simple structures, the parsers are automatically generated: /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S { /// a: u32, /// b: u16, /// c: u16 /// } /// /// # fn main() { /// # let input = b"\x00\x00\x00\x01\x12\x34\x56\x78"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[8..],S{a:1,b:0x1234,c:0x5678}))); /// # } /// ``` /// /// This also work for tuple structs: /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug, PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S(u32); /// # /// # fn main() { /// # let input = b"\x00\x00\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[4..],S(1)))); /// # } /// ``` /// /// ## Byteorder /// /// By default, integers are parsed are big endian. /// /// The `LittleEndian` attribute can be applied to a struct to change all integer parsers: /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug, PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(LittleEndian)] /// struct LittleEndianStruct { /// a: u32, /// b: u16, /// c: u16 /// } /// /// # fn main() { /// let input = b"\x00\x00\x00\x01\x12\x34\x56\x78"; /// let res = LittleEndianStruct::parse(input); /// assert_eq!(res, Ok((&input[8..], /// LittleEndianStruct{a:0x0100_0000,b:0x3412,c:0x7856})) /// ); /// # } /// ``` /// /// The `BigEndian` and `LittleEndian` attributes can be specified for struct fields. /// If both per-struct and per-field attributes are present, the more specific wins. /// /// For example, the all fields of the following struct will be parsed as big-endian, /// except `b`: /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(BigEndian)] /// struct MixedEndianStruct { /// a: u32, /// #[nom(LittleEndian)] /// b: u16, /// c: u16 /// } /// /// # fn main() { /// # let input = b"\x00\x00\x00\x01\x12\x34\x56\x78"; /// # let res = MixedEndianStruct::parse(input); /// # assert_eq!(res, Ok((&input[8..], /// # MixedEndianStruct{a:0x1,b:0x3412,c:0x5678})) /// # ); /// # } /// ``` /// /// # Deriving and Inferring Parsers /// /// `nom-derive` is also able to infer parsers for some usual types: integers, `Option`, `Vec`, etc. /// /// If the parser cannot be inferred, a default function will be called. It is also possible to /// override this using the `Parse` attribute. /// /// Following sections give more details. /// /// ## Option types /// /// If a field is an `Option<T>`, the generated parser is `opt(complete(T::parse))` /// /// For ex: /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S { /// a: Option<u32> /// } /// /// # fn main() { /// let input = b"\x00\x00\x00\x01"; /// let res = S::parse(input); /// assert_eq!(res, Ok((&input[4..],S{a:Some(1)}))); /// # } /// ``` /// /// ## Vec types /// /// If a field is an `Vec<T>`, the generated parser is `many0(complete(T::parse))` /// /// For ex: /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S { /// a: Vec<u16> /// } /// /// # fn main() { /// let input = b"\x00\x00\x00\x01"; /// let res = S::parse(input); /// assert_eq!(res, Ok((&input[4..],S{a:vec![0,1]}))); /// # } /// ``` /// /// ## Count /// /// The `Count(n)` attribute can be used to specify the number of items to parse. /// /// Notes: /// - the subparser is inferred as usual (item type must be `Vec< ... >`) /// - the number of items (`n`) can be any expression, and will be cast to `usize` /// /// For ex: /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S { /// a: u16, /// #[nom(Count="a")] /// b: Vec<u16> /// } /// # /// # fn main() { /// # let input = b"\x00\x01\x12\x34"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[4..],S{a:1, b:vec![0x1234]}))); /// # } /// ``` /// /// ## Take /// /// The `Take="n"` attribute can be used to take `n` bytes of input. /// /// Notes: /// - the number of items (`n`) can be any expression, and will be cast to `usize` /// /// For ex: /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S<'a> { /// a: u16, /// #[nom(Take="1")] /// b: &'a [u8], /// } /// # /// # fn main() { /// # let input = b"\x00\x01\x12\x34"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[3..],S{a:1, b:&[0x12]}))); /// # } /// ``` /// /// ## Default parsing function /// /// If a field with type `T` is not a primitive or known type, the generated parser is /// `T::parse(input)`. /// /// This function can be automatically derived, or specified as a method for the struct. /// In that case, the function must be a static method with the same API as a /// [nom] combinator, returning the wrapped struct when parsing succeeds. /// /// For example (using `Nom` derive): /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S2 { /// c: u16 /// } /// /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S { /// a: u16, /// b: S2 /// } /// # /// # fn main() { /// # let input = b"\x00\x00\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[4..],S{a:0,b:S2{c:1}}))); /// # } /// ``` /// /// Example (defining `parse` method): /// ```rust /// # use nom_derive::Nom; /// # use nom::{IResult,call,map}; /// # use nom::number::streaming::le_u16; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// // no Nom derive /// struct S2 { /// c: u16 /// } /// /// impl S2 { /// fn parse(i:&[u8]) -> IResult<&[u8],S2> { /// map!( /// i, /// le_u16, // little-endian /// |c| S2{c} // return a struct S2 /// ) /// } /// } /// /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S { /// a: u16, /// b: S2 /// } /// # /// # fn main() { /// # let input = b"\x00\x00\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[4..],S{a:0,b:S2{c:256}}))); /// # } /// ``` /// /// ## Custom parsers /// /// Sometimes, the default parsers generated automatically are not those you /// want. /// /// The `Parse` custom attribute allows for specifying the parser that /// will be inserted in the nom parser. /// /// The parser is called with input as argument, so the signature of the parser /// must be equivalent to: /// /// ```rust,ignore /// fn parser(i: &[u8]) -> IResult<T> { /// // ... /// } /// ``` /// /// For example, to specify the parser of a field: /// /// ```rust /// # use nom_derive::Nom; /// # use nom::number::streaming::le_u16; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// #[nom(Parse="le_u16")] /// a: u16 /// } /// # /// # fn main() { /// # let input = b"\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[2..],S{a:256}))); /// # } /// ``` /// /// The `Parse` argument can be a complex expression: /// ```rust /// # use nom_derive::Nom; /// # use nom::combinator::cond; /// # use nom::number::streaming::be_u16; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// pub a: u8, /// #[nom(Parse="cond(a > 0,be_u16)")] /// pub b: Option<u16>, /// } /// # /// # fn main() { /// # let input = b"\x01\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[3..],S{a:1,b:Some(1)}))); /// # } /// ``` /// Note that you are responsible from providing correct code. /// /// ## Default /// /// If a field is marked as `Ignore` (or `Default`), it will not be parsed. /// Its value will be the default value for the field type. /// /// This is convenient if the structured has more fields than the serialized value. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// pub a: u8, /// #[nom(Ignore)] /// pub b: Option<u16>, /// } /// # /// # fn main() { /// # let input = b"\x01\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[1..],S{a:1,b:None}))); /// # } /// ``` /// /// ## Complete /// /// The `Complete` attribute transforms Incomplete into Error. /// /// Default is to use streaming parsers. /// /// ```rust /// # use nom_derive::Nom; /// # use nom::number::streaming::be_u8; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// pub a: u8, /// #[nom(Complete)] /// pub b: u64, /// } /// # /// # fn main() { /// # let input = b"\x01\x00\x01"; /// # let res = S::parse(input).expect_err("parse error"); /// # assert!(!res.is_incomplete()); /// # } /// ``` /// /// ## Map /// /// The `Map` attribute can be used to apply a function to the result /// of the parser. /// It is often used combined with the `Parse` attribute. /// /// ```rust /// # use nom_derive::Nom; /// # use nom::number::streaming::be_u8; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// pub a: u8, /// #[nom(Parse="be_u8", Map = "|x: u8| x.to_string()")] /// pub b: String, /// } /// # /// # fn main() { /// # let input = b"\x01\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[2..],S{a:1,b:"0".to_string()}))); /// # } /// ``` /// /// ## Conditional Values /// /// The `Cond` custom attribute allows for specifying a condition. /// The generated parser will use the `cond!` combinator, which calls the /// child parser only if the condition is met. /// The type with this attribute must be an `Option` type. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// pub a: u8, /// #[nom(Cond="a == 1")] /// pub b: Option<u16>, /// } /// # /// # fn main() { /// # let input = b"\x01\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[3..],S{a:1,b:Some(1)}))); /// # } /// ``` /// /// ## Value /// /// The `Value` attribute does not parse data. It is used to store the result /// of the evaluated expression in the variable. /// /// Previous fields can be used in the expression. /// /// ```rust /// # use nom_derive::Nom; /// # use nom::number::streaming::be_u8; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// pub a: u8, /// #[nom(Value = "a.to_string()")] /// pub b: String, /// } /// # /// # fn main() { /// # let input = b"\x01\x00\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[1..],S{a:1,b:"1".to_string()}))); /// # } /// ``` /// /// ## Verifications /// /// The `Verify` custom attribute allows for specifying a verifying function. /// The generated parser will use the `verify` combinator, which calls the /// child parser only if is verifies a condition (and otherwise raises an error). /// /// The argument used in verify function is passed as a reference. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// #[nom(Verify="*a == 1")] /// pub a: u8, /// } /// # /// # fn main() { /// # let input = b"\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[1..],S{a:1}))); /// # } /// ``` /// /// The `ErrorIf` checks the provided condition, and return an error if the /// test returns false. /// The condition is tested before any parsing occurs for this field, and does not /// change the input pointer. /// /// Error has type `ErrorKind::Verify` (nom). /// /// The argument used in verify function is passed as a reference. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// pub a: u8, /// #[nom(ErrorIf(a != 1))] /// pub b: u8, /// } /// # /// # fn main() { /// # let input = b"\x01\x02"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[2..],S{a:1, b:2}))); /// # } /// ``` /// /// ## Exact /// /// The `Exact` custom attribute adds a verification after parsing the entire element. /// It succeeds if the input has been entirely consumed by the parser. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(Exact)] /// struct S{ /// pub a: u8, /// } /// # /// # fn main() { /// # let input = b"\x01\x01"; /// # let res = S::parse(&input[1..]); /// # assert!(res.is_ok()); /// # let res = S::parse(input); /// # assert!(res.is_err()); /// # } /// ``` /// /// ## PreExec /// /// The `PreExec` custom attribute executes the provided code before parsing /// the field or structure. /// /// This attribute can be specified multiple times. Statements will be executed in order. /// /// Note that the current input can be accessed, as a regular variable (see [InputName](#input-name)). /// If you create a new variable with the same name, it will be used as input (resulting in /// side-effects). /// /// Expected value: a valid Rust statement /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// #[nom(PreExec="let sz = i.len();")] /// pub a: u8, /// #[nom(Value(sz))] /// pub sz: usize, /// } /// # /// # fn main() { /// # let input = b"\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[1..],S{a:1, sz:1}))); /// # } /// ``` /// /// ## PostExec /// /// The `PostExec` custom attribute executes the provided code after parsing /// the field or structure. /// /// This attribute can be specified multiple times. Statements will be executed in order. /// /// Note that the current input can be accessed, as a regular variable (see [InputName](#input-name)). /// If you create a new variable with the same name, it will be used as input (resulting in /// side-effects). /// /// Expected value: a valid Rust statement /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// #[nom(PostExec="let b = a + 1;")] /// pub a: u8, /// #[nom(Value(b))] /// pub b: u8, /// } /// # /// # fn main() { /// # let input = b"\x01"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[1..],S{a:1, b:2}))); /// # } /// ``` /// /// If applied to the top-level element, the statement is executing after the entire element /// is parsed. /// /// If parsing a structure, the built structure is available in the `struct_def` variable. /// /// If parsing an enum, the built structure is available in the `enum_def` variable. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(PartialEq)] // for assert_eq! /// #[derive(Debug)] /// #[derive(Nom)] /// #[nom(PostExec(println!("parsing done: {:?}", struct_def);))] /// struct S{ /// pub a: u8, /// pub b: u8, /// } /// # /// # fn main() { /// # let input = b"\x01\x02"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[2..],S{a:1, b:2}))); /// # } /// ``` /// /// ## Alignment and Padding /// /// - `AlignAfter`/`AlignBefore`: skip bytes until aligned to a multiple of the provided value /// Alignment is calculated to the start of the original parser input /// - `SkipAfter`/`SkipBefore`: skip the specified number of bytes /// - `Move`: add the speficied offset to current position, before parsing. Offset can be negative. /// - `MoveAbs`: go to specified absolute position (relative to the start of original parser /// input), before parsing /// /// If multiple directives are provided, they are applied in order of appearance of the /// attribute. /// /// If the new position would be before the start of the slice or beyond its end, /// an error is raised (`TooLarge` or `Incomplete`, depending on the case). /// /// Expected value: a valid Rust value (immediate value, or expression) /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// struct S{ /// pub a: u8, /// #[nom(AlignBefore(4))] /// pub b: u8, /// } /// # /// # fn main() { /// # let input = b"\x01\x00\x00\x00\x02"; /// # let res = S::parse(input); /// # assert_eq!(res, Ok((&input[5..],S{a:1, b:2}))); /// # } /// ``` /// /// # Deriving parsers for `Enum` /// /// The `Nom` attribute can also used to generate parser for `Enum` types. /// The generated parser will used a value (called *selector*) to determine /// which attribute variant is parsed. /// Named and unnamed enums are supported. /// /// In addition of `derive(Nom)`, a `Selector` attribute must be used: /// - on the structure, to specify the type of selector to match /// - on each variant, to specify the value associated with this variant. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(Selector="u8")] /// pub enum U1{ /// #[nom(Selector="0")] Field1(u32), /// #[nom(Selector="1")] Field2(Option<u32>), /// } /// # /// # fn main() { /// # let input = b"\x00\x00\x00\x02"; /// # let res = U1::parse(input, 0); /// # assert_eq!(res, Ok((&input[4..],U1::Field1(2)))); /// # } /// ``` /// /// The generated function will look like: /// /// <pre> /// impl U1{ /// pub fn parse(i:&[u8), selector: u8) -> IResult<&[u8],U1> { /// match selector { /// ... /// } /// } /// } /// </pre> /// /// It can be called either directly (`U1::parse(n)`) or using nom /// (`call!(U1::parse,n)`). /// /// The selector can be a primitive type (`u8`), or any other type implementing the `PartialEq` /// trait. /// /// ```rust /// # use nom_derive::Nom; /// # /// #[derive(Debug,PartialEq,Eq,Clone,Copy,Nom)] /// pub struct MessageType(pub u8); /// /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(Selector="MessageType")] /// pub enum U1{ /// #[nom(Selector="MessageType(0)")] Field1(u32), /// #[nom(Selector="MessageType(1)")] Field2(Option<u32>), /// } /// /// // Example of call from a struct: /// #[derive(Nom)] /// pub struct S1{ /// pub msg_type: MessageType, /// #[nom(Parse="{ |i| U1::parse(i, msg_type) }")] /// pub msg_value: U1 /// } /// # /// # fn main() { /// # let input = b"\x00\x00\x00\x02"; /// # let res = U1::parse(input, MessageType(0)); /// # assert_eq!(res, Ok((&input[4..],U1::Field1(2)))); /// # } /// ``` /// /// ## Default case /// /// By default, if no value of the selector matches the input value, a nom error /// `ErrorKind::Switch` is raised. This can be changed by using `_` as selector /// value for one the variants. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(Selector="u8")] /// pub enum U2{ /// #[nom(Selector="0")] Field1(u32), /// #[nom(Selector="_")] Field2(u32), /// } /// # /// # fn main() { /// # let input = b"\x00\x00\x00\x02"; /// # let res = U2::parse(input, 123); /// # assert_eq!(res, Ok((&input[4..],U2::Field2(2)))); /// # } /// ``` /// /// If the `_` selector is not the last variant, the generated code will use it /// as the last match to avoid unreachable code. /// /// ## Special case: specifying parsers for fields /// /// Sometimes, an unnamed field requires a custom parser. In that case, the /// *field* (not the variant) must be annotated with attribute `Parse`. /// /// Named fields: /// /// ```rust /// # use nom_derive::Nom; /// # use nom::bytes::streaming::take; /// # /// # #[derive(Debug,PartialEq,Eq,Clone,Copy,Nom)] /// # pub struct MessageType(pub u8); /// # /// #[derive(Nom)] /// #[nom(Selector="MessageType")] /// pub enum U3<'a>{ /// #[nom(Selector="MessageType(0)")] Field1{a:u32}, /// #[nom(Selector="MessageType(1)")] Field2{ /// #[nom(Parse="take(4 as usize)")] /// a: &'a[u8] /// }, /// } /// ``` /// /// Unnamed fields: /// /// ```rust /// # use nom_derive::Nom; /// # use nom::bytes::streaming::take; /// # /// # #[derive(Debug,PartialEq,Eq,Clone,Copy,Nom)] /// # pub struct MessageType(pub u8); /// # /// #[derive(Nom)] /// #[nom(Selector="MessageType")] /// pub enum U3<'a>{ /// #[nom(Selector="MessageType(0)")] Field1(u32), /// #[nom(Selector="MessageType(1)")] Field2( /// #[nom(Parse="take(4 as usize)")] &'a[u8] /// ), /// } /// ``` /// /// ## Special case: fieldless enums /// /// If the entire enum is fieldless (a list of constant integer values), a /// parser can be derived if /// - the `Enum` has a `repr(ty)` attribute, with `ty` an integer type /// - the `Enum` implements the `Eq` trait /// /// In that case, the `Selector` attribute must *not* be specified. /// /// ```rust /// # use nom_derive::Nom; /// # use nom::*; /// # use nom::number::streaming::be_u8; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[repr(u8)] /// #[derive(Eq,Nom)] /// pub enum U3{ /// A, /// B = 2, /// C /// } /// # /// # fn main() { /// # let empty : &[u8] = b""; /// # assert_eq!( /// # U3::parse(b"\x00"), /// # Ok((empty,U3::A)) /// # ); /// # assert!( /// # U3::parse(b"\x01").is_err() /// # ); /// # assert_eq!( /// # U3::parse(b"\x02"), /// # Ok((empty,U3::B)) /// # ); /// # } /// ``` /// /// The generated parser will parse an element of type `ty` (as Big Endian), try /// to match to enum values, and return an instance of `Enum` if it succeeds /// (wrapped in an `IResult`). /// /// For ex, `U3::parse(b"\x02")` will return `Ok((&b""[..],U3::B))`. /// /// ## Input Name /// /// Internally, the parser will use a variable to follow the input. /// By default, this variable is named `i`. /// /// This can cause problems, for example, if one field of the structure has the same name /// /// The internal variable name can be renamed using the `InputName` top-level attribute. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(InputName(aaa))] /// pub struct S { /// pub i: u8, /// } /// # /// # fn main() { /// # let empty : &[u8] = b""; /// # assert_eq!( /// # S::parse(b"\x00"), /// # Ok((empty, S{i:0})) /// # ); /// # } /// ``` /// /// Note that this variable can be used as usual, for ex. to peek data /// without advancing in the current stream, determining the length of /// remaining bytes, etc. /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(InputName(i))] /// pub struct S { /// pub a: u8, /// #[nom(Value(i.len()))] /// pub remaining_len: usize, /// } /// # /// # fn main() { /// # let empty : &[u8] = b""; /// # assert_eq!( /// # S::parse(b"\x00"), /// # Ok((empty, S{a:0, remaining_len:0})) /// # ); /// # } /// ``` /// /// **This can create side-effects**: if you create a variable with the same name /// as the input, it will shadow it. While this will is generally an error, it can /// sometimes be useful. /// /// For example, to skip 2 bytes of input: /// /// ```rust /// # use nom_derive::Nom; /// # /// # #[derive(Debug,PartialEq)] // for assert_eq! /// #[derive(Nom)] /// #[nom(InputName(i))] /// pub struct S { /// pub a: u8, /// // skip 2 bytes /// // XXX this will panic if input is smaller than 2 bytes at this points /// #[nom(PreExec(let i = &i[2..];))] /// pub b: u8, /// } /// # /// # fn main() { /// # let empty : &[u8] = b""; /// # assert_eq!( /// # S::parse(b"\x00\x01\x02\x03"), /// # Ok((empty, S{a:0, b:3})) /// # ); /// # } /// ``` /// /// ## Limitations /// /// Except if the entire enum is fieldless (a list of constant integer values), /// unit fields are not supported. /// /// ## Debug /// /// Errors in generated parsers may be hard to understand and debug. /// /// The `Debug` attribute insert calls to nom's `dbg_dmp` function, which will print /// an error message and the input if the parser fails. This attribute can be applied to either /// fields, or at top-level (all sub-parsers will be wrapped). /// /// This helps resolving parse errors (at runtime). /// /// ```rust /// # use nom_derive::Nom; /// # /// #[derive(Nom)] /// pub struct S { /// pub a: u32, /// #[nom(Debug)] /// pub b: u64, /// } /// ``` /// /// ## DebugDerive /// /// The `DebugDerive` attribute, if applied to top-level, makes the generator print the /// generated code to `stderr`. /// /// This helps resolving compiler errors. /// /// ```rust /// # use nom_derive::Nom; /// # /// #[derive(Nom)] /// #[nom(DebugDerive)] /// pub struct S { /// pub a: u32, /// } /// ``` #[proc_macro_derive(Nom, attributes(nom))] pub fn nom(input: TokenStream) -> TokenStream { // Parse the input tokens into a syntax tree let ast = parse_macro_input!(input as DeriveInput); // Build the impl let gen = impl_nom(&ast, false); // Return the generated impl gen } fn impl_nom(ast: &syn::DeriveInput, debug_derive:bool) -> TokenStream { use crate::config::Config; // eprintln!("ast: {:#?}", ast); let struct_name = ast.ident.to_string(); // parse top-level attributes and prepare tokens for each field parser let meta = meta::parse_nom_top_level_attribute(&ast.attrs).expect("Parsing the 'nom' top level attribute failed"); let mut config = Config::from_meta_list(struct_name, &meta).expect("Could not build config"); config.debug_derive |= debug_derive; let (tl_pre, tl_post) = get_pre_post_exec(&meta, &config); // test if struct has a lifetime let s = match &ast.data { &syn::Data::Enum(_) => { return impl_nom_enums(ast, &config); }, &syn::Data::Struct(ref s) => parse_struct(s, &config), &syn::Data::Union(_) => panic!("Unions not supported"), }; // prepare tokens let generics = &ast.generics; let name = &ast.ident; let (idents, parser_tokens) : (Vec<_>,Vec<_>) = s.parsers.iter() .map(|sp| { let id = syn::Ident::new(&sp.name, Span::call_site()); (id, &sp.parser) }) .unzip(); let (pre, post) : (Vec<_>,Vec<_>) = s.parsers.iter() .map(|sp| { (sp.pre_exec.as_ref(), sp.post_exec.as_ref()) }) .unzip(); let idents2 = idents.clone(); // Code generation let struct_def = match s.unnamed { false => quote!{ ( #name { #(#idents2),* } ) }, true => quote!{ ( #name ( #(#idents2),* ) ) }, }; let input_name = syn::Ident::new(&config.input_name, Span::call_site()); let orig_input_name = syn::Ident::new(&("orig_".to_string() + &config.input_name), Span::call_site()); let tokens = quote! { impl#generics #name#generics { pub fn parse(#orig_input_name: &[u8]) -> nom::IResult<&[u8],#name> { let #input_name = #orig_input_name; #tl_pre #(#pre let (#input_name, #idents) = #parser_tokens (#input_name) ?; #post)* let struct_def = #struct_def; #tl_post Ok((#input_name, struct_def)) } } }; if config.debug_derive { eprintln!("tokens:\n{}", tokens); } tokens.into() } /// This derive macro behaves exactly like [Nom derive](derive.Nom.html), except it /// prints the generated parser on stderr. /// This is helpful for debugging generated parsers. #[deprecated( since = "0.6.0", note = "Please use the nom(DebugDerive) attribute instead" )] #[proc_macro_derive(NomDeriveDebug, attributes(nom))] pub fn nom_derive_debug(input: TokenStream) -> TokenStream { // Parse the input tokens into a syntax tree let ast = parse_macro_input!(input as DeriveInput); // Build the impl let gen = impl_nom(&ast, true); // Return the generated impl gen }