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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224
//! Implements an interface for writing the Nix archive format (NAR).
//!
//! NAR files (and their hashed representations) are used in C++ Nix for
//! addressing fixed-output derivations and a variety of other things.
//!
//! NAR files can be output to any type that implements [`Write`], and content
//! can be read from any type that implementes [`BufRead`].
//!
//! Writing a single file might look like this:
//!
//! ```rust
//! # use std::io::BufReader;
//! # let some_file: Vec<u8> = vec![0, 1, 2, 3, 4];
//!
//! // Output location to write the NAR to.
//! let mut sink: Vec<u8> = Vec::new();
//!
//! // Instantiate writer for this output location.
//! let mut nar = nix_compat::nar::writer::open(&mut sink)?;
//!
//! // Acquire metadata for the single file to output, and pass it in a
//! // `BufRead`-implementing type.
//!
//! let executable = false;
//! let size = some_file.len() as u64;
//! let mut reader = BufReader::new(some_file.as_slice());
//! nar.file(executable, size, &mut reader)?;
//! # Ok::<(), std::io::Error>(())
//! ```
use crate::nar::wire;
use std::io::{
self, BufRead,
ErrorKind::{InvalidInput, UnexpectedEof},
Write,
};
/// Convenience type alias for types implementing [`Write`].
pub type Writer<'a> = dyn Write + Send + 'a;
/// Create a new NAR, writing the output to the specified writer.
pub fn open<'a, 'w: 'a>(writer: &'a mut Writer<'w>) -> io::Result<Node<'a, 'w>> {
let mut node = Node { writer };
node.write(&wire::TOK_NAR)?;
Ok(node)
}
/// Single node in a NAR file.
///
/// A NAR can be thought of as a tree of nodes represented by this type. Each
/// node can be a file, a symlink or a directory containing other nodes.
pub struct Node<'a, 'w: 'a> {
writer: &'a mut Writer<'w>,
}
impl<'a, 'w> Node<'a, 'w> {
fn write(&mut self, data: &[u8]) -> io::Result<()> {
self.writer.write_all(data)
}
fn pad(&mut self, n: u64) -> io::Result<()> {
match (n & 7) as usize {
0 => Ok(()),
n => self.write(&[0; 8][n..]),
}
}
/// Make this node a symlink.
pub fn symlink(mut self, target: &[u8]) -> io::Result<()> {
debug_assert!(
target.len() <= wire::MAX_TARGET_LEN,
"target.len() > {}",
wire::MAX_TARGET_LEN
);
debug_assert!(!target.is_empty(), "target is empty");
debug_assert!(!target.contains(&0), "target contains null byte");
self.write(&wire::TOK_SYM)?;
self.write(&target.len().to_le_bytes())?;
self.write(target)?;
self.pad(target.len() as u64)?;
self.write(&wire::TOK_PAR)?;
Ok(())
}
/// Make this node a single file.
pub fn file(mut self, executable: bool, size: u64, reader: &mut dyn BufRead) -> io::Result<()> {
self.write(if executable {
&wire::TOK_EXE
} else {
&wire::TOK_REG
})?;
self.write(&size.to_le_bytes())?;
let mut need = size;
while need != 0 {
let data = reader.fill_buf()?;
if data.is_empty() {
return Err(UnexpectedEof.into());
}
let n = need.min(data.len() as u64) as usize;
self.write(&data[..n])?;
need -= n as u64;
reader.consume(n);
}
// bail if there's still data left in the passed reader.
// This uses the same code as [BufRead::has_data_left] (unstable).
if reader.fill_buf().map(|b| !b.is_empty())? {
return Err(io::Error::new(
InvalidInput,
"reader contained more data than specified size",
));
}
self.pad(size)?;
self.write(&wire::TOK_PAR)?;
Ok(())
}
/// Make this node a directory, the content of which is set using the
/// resulting [`Directory`] value.
///
/// It is the caller's responsibility to invoke [`Directory::close`],
/// or invalid archives will be produced silently.
pub fn directory(mut self) -> io::Result<Directory<'a, 'w>> {
self.write(&wire::TOK_DIR)?;
Ok(Directory::new(self))
}
}
#[cfg(debug_assertions)]
type Name = Vec<u8>;
#[cfg(not(debug_assertions))]
type Name = ();
fn into_name(_name: &[u8]) -> Name {
#[cfg(debug_assertions)]
_name.to_owned()
}
/// Content of a NAR node that represents a directory.
pub struct Directory<'a, 'w> {
node: Node<'a, 'w>,
prev_name: Option<Name>,
}
impl<'a, 'w> Directory<'a, 'w> {
fn new(node: Node<'a, 'w>) -> Self {
Self {
node,
prev_name: None,
}
}
/// Add an entry to the directory.
///
/// The entry is simply another [`Node`], which can then be filled like the
/// root of a NAR (including, of course, by nesting directories).
///
/// It is the caller's responsibility to ensure that directory entries are
/// written in order of ascending name. If this is not ensured, this method
/// may panic or silently produce invalid archives.
pub fn entry(&mut self, name: &[u8]) -> io::Result<Node<'_, 'w>> {
debug_assert!(
name.len() <= wire::MAX_NAME_LEN,
"name.len() > {}",
wire::MAX_NAME_LEN
);
debug_assert!(!name.is_empty(), "name is empty");
debug_assert!(!name.contains(&0), "name contains null byte");
debug_assert!(!name.contains(&b'/'), "name contains {:?}", '/');
debug_assert!(name != b".", "name == {:?}", ".");
debug_assert!(name != b"..", "name == {:?}", "..");
match self.prev_name {
None => {
self.prev_name = Some(into_name(name));
}
Some(ref mut _prev_name) => {
#[cfg(debug_assertions)]
{
use bstr::ByteSlice;
assert!(
&**_prev_name < name,
"misordered names: {:?} >= {:?}",
_prev_name.as_bstr(),
name.as_bstr()
);
name.clone_into(_prev_name);
}
self.node.write(&wire::TOK_PAR)?;
}
}
self.node.write(&wire::TOK_ENT)?;
self.node.write(&name.len().to_le_bytes())?;
self.node.write(name)?;
self.node.pad(name.len() as u64)?;
self.node.write(&wire::TOK_NOD)?;
Ok(Node {
writer: &mut *self.node.writer,
})
}
/// Close a directory and write terminators for the directory to the NAR.
///
/// **Important:** This *must* be called when all entries have been written
/// in a directory, otherwise the resulting NAR file will be invalid.
pub fn close(mut self) -> io::Result<()> {
if self.prev_name.is_some() {
self.node.write(&wire::TOK_PAR)?;
}
self.node.write(&wire::TOK_PAR)?;
Ok(())
}
}