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use std::fs::File;
use std::io::{self, Read};
use std::path::{Path, PathBuf};
use std::process::{self, Stdio};
use Result;
/// PreprocessorReader provides an `io::Read` impl to read kids output.
#[derive(Debug)]
pub struct PreprocessorReader {
cmd: PathBuf,
path: PathBuf,
child: process::Child,
done: bool,
}
impl PreprocessorReader {
/// Returns a handle to the stdout of the spawned preprocessor process for
/// `path`, which can be directly searched in the worker. When the returned
/// value is exhausted, the underlying process is reaped. If the underlying
/// process fails, then its stderr is read and converted into a normal
/// io::Error.
///
/// If there is any error in spawning the preprocessor command, then
/// return the corresponding error.
pub fn from_cmd_path(
cmd: PathBuf,
path: &Path,
) -> Result<PreprocessorReader> {
let child = process::Command::new(&cmd)
.arg(path)
.stdin(Stdio::from(File::open(path)?))
.stdout(Stdio::piped())
.stderr(Stdio::piped())
.spawn()
.map_err(|err| {
format!(
"error running preprocessor command '{}': {}",
cmd.display(),
err,
)
})?;
Ok(PreprocessorReader {
cmd: cmd,
path: path.to_path_buf(),
child: child,
done: false,
})
}
fn read_error(&mut self) -> io::Result<io::Error> {
let mut errbytes = vec![];
self.child.stderr.as_mut().unwrap().read_to_end(&mut errbytes)?;
let errstr = String::from_utf8_lossy(&errbytes);
let errstr = errstr.trim();
Ok(if errstr.is_empty() {
let msg = format!(
"preprocessor command failed: '{} {}'",
self.cmd.display(),
self.path.display(),
);
io::Error::new(io::ErrorKind::Other, msg)
} else {
let msg = format!(
"preprocessor command failed: '{} {}': {}",
self.cmd.display(),
self.path.display(),
errstr,
);
io::Error::new(io::ErrorKind::Other, msg)
})
}
}
impl io::Read for PreprocessorReader {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
if self.done {
return Ok(0);
}
let nread = self.child.stdout.as_mut().unwrap().read(buf)?;
if nread == 0 {
self.done = true;
// Reap the child now that we're done reading.
// If the command failed, report stderr as an error.
if !self.child.wait()?.success() {
return Err(self.read_error()?);
}
}
Ok(nread)
}
}