1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173

//! A WebAssembly encoder.
//!
//! The main builder is the [`Module`]. You can build a section with a
//! section-specific builder, like [`TypeSection`] or [`ImportSection`], and
//! then add it to the module with [`Module::section`]. When you are finished
//! building the module, call either [`Module::as_slice`] or [`Module::finish`]
//! to get the encoded bytes. The former gives a shared reference to the
//! underlying bytes as a slice, while the latter gives you ownership of them as
//! a vector.
//!
//! # Example
//!
//! If we wanted to build this module:
//!
//! ```wasm
//! (module
//!   (type (func (param i32 i32) (result i32)))
//!   (func (type 0)
//!     local.get 0
//!     local.get 1
//!     i32.add)
//!   (export "f" (func 0)))
//! ```
//!
//! then we would do this:
//!
//! ```
//! use wasm_encoder::{
//!     CodeSection, ExportKind, ExportSection, Function, FunctionSection, Instruction,
//!     Module, TypeSection, ValType,
//! };
//!
//! let mut module = Module::new();
//!
//! // Encode the type section.
//! let mut types = TypeSection::new();
//! let params = vec![ValType::I32, ValType::I32];
//! let results = vec![ValType::I32];
//! types.function(params, results);
//! module.section(&types);
//!
//! // Encode the function section.
//! let mut functions = FunctionSection::new();
//! let type_index = 0;
//! functions.function(type_index);
//! module.section(&functions);
//!
//! // Encode the export section.
//! let mut exports = ExportSection::new();
//! exports.export("f", ExportKind::Func, 0);
//! module.section(&exports);
//!
//! // Encode the code section.
//! let mut codes = CodeSection::new();
//! let locals = vec![];
//! let mut f = Function::new(locals);
//! f.instruction(&Instruction::LocalGet(0));
//! f.instruction(&Instruction::LocalGet(1));
//! f.instruction(&Instruction::I32Add);
//! f.instruction(&Instruction::End);
//! codes.function(&f);
//! module.section(&codes);
//!
//! // Extract the encoded Wasm bytes for this module.
//! let wasm_bytes = module.finish();
//!
//! // We generated a valid Wasm module!
//! assert!(wasmparser::validate(&wasm_bytes).is_ok());
//! ```

#![deny(missing_docs, missing_debug_implementations)]

mod component;
mod core;
mod raw;

pub use self::component::*;
pub use self::core::*;
pub use self::raw::*;

/// Implemented by types that can be encoded into a byte sink.
pub trait Encode {
    /// Encode the type into the given byte sink.
    fn encode(&self, sink: &mut Vec<u8>);
}

impl<T: Encode + ?Sized> Encode for &'_ T {
    fn encode(&self, sink: &mut Vec<u8>) {
        T::encode(self, sink)
    }
}

impl<T: Encode> Encode for [T] {
    fn encode(&self, sink: &mut Vec<u8>) {
        self.len().encode(sink);
        for item in self {
            item.encode(sink);
        }
    }
}

impl Encode for [u8] {
    fn encode(&self, sink: &mut Vec<u8>) {
        self.len().encode(sink);
        sink.extend(self);
    }
}

impl Encode for str {
    fn encode(&self, sink: &mut Vec<u8>) {
        self.len().encode(sink);
        sink.extend_from_slice(self.as_bytes());
    }
}

impl Encode for usize {
    fn encode(&self, sink: &mut Vec<u8>) {
        assert!(*self <= u32::max_value() as usize);
        (*self as u32).encode(sink)
    }
}

impl Encode for u32 {
    fn encode(&self, sink: &mut Vec<u8>) {
        leb128::write::unsigned(sink, (*self).into()).unwrap();
    }
}

impl Encode for i32 {
    fn encode(&self, sink: &mut Vec<u8>) {
        leb128::write::signed(sink, (*self).into()).unwrap();
    }
}

impl Encode for u64 {
    fn encode(&self, sink: &mut Vec<u8>) {
        leb128::write::unsigned(sink, *self).unwrap();
    }
}

impl Encode for i64 {
    fn encode(&self, sink: &mut Vec<u8>) {
        leb128::write::signed(sink, *self).unwrap();
    }
}

fn encoding_size(n: u32) -> usize {
    let mut buf = [0u8; 5];
    leb128::write::unsigned(&mut &mut buf[..], n.into()).unwrap()
}

fn encode_section(sink: &mut Vec<u8>, count: u32, bytes: &[u8]) {
    (encoding_size(count) + bytes.len()).encode(sink);
    count.encode(sink);
    sink.extend(bytes);
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn it_encodes_an_empty_module() {
        let bytes = Module::new().finish();
        assert_eq!(bytes, [0x00, b'a', b's', b'm', 0x01, 0x00, 0x00, 0x00]);
    }

    #[test]
    fn it_encodes_an_empty_component() {
        let bytes = Component::new().finish();
        assert_eq!(bytes, [0x00, b'a', b's', b'm', 0x0a, 0x00, 0x01, 0x00]);
    }
}