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

use std::collections::VecDeque;
use std::io::IoSlice;

use bytes::{Buf, BufMut, Bytes, BytesMut};

#[derive(Debug)]
pub(crate) struct BufList<T> {
    bufs: VecDeque<T>,
}

impl<T: Buf> BufList<T> {
    #[inline]
    pub(crate) fn push(&mut self, buf: T) {
        debug_assert!(buf.has_remaining());
        self.bufs.push_back(buf);
    }

    #[inline]
    pub(crate) fn pop(&mut self) -> Option<T> {
        self.bufs.pop_front()
    }
}

impl<T: Buf> Buf for BufList<T> {
    #[inline]
    fn remaining(&self) -> usize {
        self.bufs.iter().map(|buf| buf.remaining()).sum()
    }

    #[inline]
    fn has_remaining(&self) -> bool {
        self.bufs.iter().any(|buf| buf.has_remaining())
    }

    #[inline]
    fn chunk(&self) -> &[u8] {
        self.bufs.front().map(Buf::chunk).unwrap_or_default()
    }

    #[inline]
    fn advance(&mut self, mut cnt: usize) {
        while cnt > 0 {
            {
                let front = &mut self.bufs[0];
                let rem = front.remaining();
                if rem > cnt {
                    front.advance(cnt);
                    return;
                } else {
                    front.advance(rem);
                    cnt -= rem;
                }
            }
            self.bufs.pop_front();
        }
    }

    #[inline]
    fn chunks_vectored<'t>(&'t self, dst: &mut [IoSlice<'t>]) -> usize {
        if dst.is_empty() {
            return 0;
        }
        let mut vecs = 0;
        for buf in &self.bufs {
            vecs += buf.chunks_vectored(&mut dst[vecs..]);
            if vecs == dst.len() {
                break;
            }
        }
        vecs
    }

    #[inline]
    fn copy_to_bytes(&mut self, len: usize) -> Bytes {
        // Our inner buffer may have an optimized version of copy_to_bytes, and if the whole
        // request can be fulfilled by the front buffer, we can take advantage.
        match self.bufs.front_mut() {
            Some(front) if front.remaining() == len => {
                let b = front.copy_to_bytes(len);
                self.bufs.pop_front();
                b
            }
            Some(front) if front.remaining() > len => front.copy_to_bytes(len),
            _ => {
                let rem = self.remaining();
                assert!(len <= rem, "`len` greater than remaining");
                let mut bm = BytesMut::with_capacity(len);
                if rem == len {
                    // .take() costs a lot more, so skip it if we don't need it
                    bm.put(self);
                } else {
                    bm.put(self.take(len));
                }
                bm.freeze()
            }
        }
    }
}

impl<T> Default for BufList<T> {
    fn default() -> Self {
        BufList {
            bufs: VecDeque::new(),
        }
    }
}

#[cfg(test)]
mod tests {
    use std::ptr;

    use super::*;

    fn hello_world_buf() -> BufList<Bytes> {
        BufList {
            bufs: vec![Bytes::from("Hello"), Bytes::from(" "), Bytes::from("World")].into(),
        }
    }

    #[test]
    fn to_bytes_shorter() {
        let mut bufs = hello_world_buf();
        let old_ptr = bufs.chunk().as_ptr();
        let start = bufs.copy_to_bytes(4);
        assert_eq!(start, "Hell");
        assert!(ptr::eq(old_ptr, start.as_ptr()));
        assert_eq!(bufs.chunk(), b"o");
        assert!(ptr::eq(old_ptr.wrapping_add(4), bufs.chunk().as_ptr()));
        assert_eq!(bufs.remaining(), 7);
    }

    #[test]
    fn to_bytes_eq() {
        let mut bufs = hello_world_buf();
        let old_ptr = bufs.chunk().as_ptr();
        let start = bufs.copy_to_bytes(5);
        assert_eq!(start, "Hello");
        assert!(ptr::eq(old_ptr, start.as_ptr()));
        assert_eq!(bufs.chunk(), b" ");
        assert_eq!(bufs.remaining(), 6);
    }

    #[test]
    fn to_bytes_longer() {
        let mut bufs = hello_world_buf();
        let start = bufs.copy_to_bytes(7);
        assert_eq!(start, "Hello W");
        assert_eq!(bufs.remaining(), 4);
    }

    #[test]
    fn one_long_buf_to_bytes() {
        let mut buf = BufList::default();
        buf.push(b"Hello World" as &[_]);
        assert_eq!(buf.copy_to_bytes(5), "Hello");
        assert_eq!(buf.chunk(), b" World");
    }

    #[test]
    #[should_panic(expected = "`len` greater than remaining")]
    fn buf_to_bytes_too_many() {
        hello_world_buf().copy_to_bytes(42);
    }
}