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

/* Copyright 2018 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use crate::{BinaryReader, FromReader, OperatorsReader, Result, SectionLimited, ValType};
use core::ops::Range;

/// A reader for the code section of a WebAssembly module.
pub type CodeSectionReader<'a> = SectionLimited<'a, FunctionBody<'a>>;

/// Represents a WebAssembly function body.
#[derive(Debug, Clone)]
pub struct FunctionBody<'a> {
    reader: BinaryReader<'a>,
}

impl<'a> FunctionBody<'a> {
    /// Constructs a new `FunctionBody` for the given data and offset.
    pub fn new(reader: BinaryReader<'a>) -> Self {
        Self { reader }
    }

    /// Gets a binary reader for this function body.
    pub fn get_binary_reader(&self) -> BinaryReader<'a> {
        self.reader.clone()
    }

    fn skip_locals(reader: &mut BinaryReader) -> Result<()> {
        let count = reader.read_var_u32()?;
        for _ in 0..count {
            reader.read_var_u32()?;
            reader.read::<ValType>()?;
        }
        Ok(())
    }

    /// Gets the locals reader for this function body.
    pub fn get_locals_reader(&self) -> Result<LocalsReader<'a>> {
        let mut reader = self.reader.clone();
        let count = reader.read_var_u32()?;
        Ok(LocalsReader { reader, count })
    }

    /// Gets the operators reader for this function body.
    pub fn get_operators_reader(&self) -> Result<OperatorsReader<'a>> {
        let mut reader = self.reader.clone();
        Self::skip_locals(&mut reader)?;
        Ok(OperatorsReader::new(reader))
    }

    /// Gets the range of the function body.
    pub fn range(&self) -> Range<usize> {
        self.reader.range()
    }

    /// Returns the body of this function as a list of bytes.
    ///
    /// Note that the returned bytes start with the function locals declaration.
    pub fn as_bytes(&self) -> &'a [u8] {
        self.reader.remaining_buffer()
    }
}

impl<'a> FromReader<'a> for FunctionBody<'a> {
    fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {
        let reader = reader.read_reader()?;
        Ok(FunctionBody { reader })
    }
}

/// A reader for a function body's locals.
pub struct LocalsReader<'a> {
    reader: BinaryReader<'a>,
    count: u32,
}

impl<'a> LocalsReader<'a> {
    /// Gets the count of locals in the function body.
    pub fn get_count(&self) -> u32 {
        self.count
    }

    /// Gets the original position of the reader.
    pub fn original_position(&self) -> usize {
        self.reader.original_position()
    }

    /// Reads an item from the reader.
    pub fn read(&mut self) -> Result<(u32, ValType)> {
        let count = self.reader.read()?;
        let value_type = self.reader.read()?;
        Ok((count, value_type))
    }
}

impl<'a> IntoIterator for LocalsReader<'a> {
    type Item = Result<(u32, ValType)>;
    type IntoIter = LocalsIterator<'a>;
    fn into_iter(self) -> Self::IntoIter {
        let count = self.count;
        LocalsIterator {
            reader: self,
            left: count,
            err: false,
        }
    }
}

/// An iterator over locals in a function body.
pub struct LocalsIterator<'a> {
    reader: LocalsReader<'a>,
    left: u32,
    err: bool,
}

impl<'a> Iterator for LocalsIterator<'a> {
    type Item = Result<(u32, ValType)>;
    fn next(&mut self) -> Option<Self::Item> {
        if self.err || self.left == 0 {
            return None;
        }
        let result = self.reader.read();
        self.err = result.is_err();
        self.left -= 1;
        Some(result)
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        let count = self.reader.get_count() as usize;
        (count, Some(count))
    }
}