process: add from_std to ChildStd* (#4045)

tokio/src/process/mod.rs

@@ -225,9 +225,9 @@ pub struct Command {
 
 pub(crate) struct SpawnedChild {
     child: imp::Child,
-    stdin: Option<imp::ChildStdin>,
-    stdout: Option<imp::ChildStdout>,
-    stderr: Option<imp::ChildStderr>,
+    stdin: Option<imp::ChildStdio>,
+    stdout: Option<imp::ChildStdio>,
+    stderr: Option<imp::ChildStdio>,
 }
 
 impl Command {
@@ -1151,7 +1151,7 @@ impl Child {
 /// handle of a child process asynchronously.
 #[derive(Debug)]
 pub struct ChildStdin {
-    inner: imp::ChildStdin,
+    inner: imp::ChildStdio,
 }
 
 /// The standard output stream for spawned children.
@@ -1160,7 +1160,7 @@ pub struct ChildStdin {
 /// handle of a child process asynchronously.
 #[derive(Debug)]
 pub struct ChildStdout {
-    inner: imp::ChildStdout,
+    inner: imp::ChildStdio,
 }
 
 /// The standard error stream for spawned children.
@@ -1169,7 +1169,52 @@ pub struct ChildStdout {
 /// handle of a child process asynchronously.
 #[derive(Debug)]
 pub struct ChildStderr {
-    inner: imp::ChildStderr,
+    inner: imp::ChildStdio,
+}
+
+impl ChildStdin {
+    /// Create an asynchronous `ChildStdin` from a synchronous one.
+    ///
+    /// # Errors
+    ///
+    /// This method may fail if an error is encountered when setting the pipe to
+    /// non-blocking mode, or when registering the pipe with the runtime's IO
+    /// driver.
+    pub fn from_std(inner: std::process::ChildStdin) -> io::Result<Self> {
+        Ok(Self {
+            inner: imp::stdio(inner)?,
+        })
+    }
+}
+
+impl ChildStdout {
+    /// Create an asynchronous `ChildStderr` from a synchronous one.
+    ///
+    /// # Errors
+    ///
+    /// This method may fail if an error is encountered when setting the pipe to
+    /// non-blocking mode, or when registering the pipe with the runtime's IO
+    /// driver.
+    pub fn from_std(inner: std::process::ChildStdout) -> io::Result<Self> {
+        Ok(Self {
+            inner: imp::stdio(inner)?,
+        })
+    }
+}
+
+impl ChildStderr {
+    /// Create an asynchronous `ChildStderr` from a synchronous one.
+    ///
+    /// # Errors
+    ///
+    /// This method may fail if an error is encountered when setting the pipe to
+    /// non-blocking mode, or when registering the pipe with the runtime's IO
+    /// driver.
+    pub fn from_std(inner: std::process::ChildStderr) -> io::Result<Self> {
+        Ok(Self {
+            inner: imp::stdio(inner)?,
+        })
+    }
 }
 
 impl AsyncWrite for ChildStdin {

tokio/src/process/unix/mod.rs

@@ -101,9 +101,9 @@ impl fmt::Debug for Child {
 
 pub(crate) fn spawn_child(cmd: &mut std::process::Command) -> io::Result<SpawnedChild> {
     let mut child = cmd.spawn()?;
-    let stdin = stdio(child.stdin.take())?;
-    let stdout = stdio(child.stdout.take())?;
-    let stderr = stdio(child.stderr.take())?;
+    let stdin = child.stdin.take().map(stdio).transpose()?;
+    let stdout = child.stdout.take().map(stdio).transpose()?;
+    let stderr = child.stderr.take().map(stdio).transpose()?;
 
     let signal = signal(SignalKind::child())?;
 
@@ -213,9 +213,7 @@ impl Source for Pipe {
     }
 }
 
-pub(crate) type ChildStdin = PollEvented<Pipe>;
-pub(crate) type ChildStdout = PollEvented<Pipe>;
-pub(crate) type ChildStderr = PollEvented<Pipe>;
+pub(crate) type ChildStdio = PollEvented<Pipe>;
 
 fn set_nonblocking<T: AsRawFd>(fd: &mut T, nonblocking: bool) -> io::Result<()> {
     unsafe {
@@ -240,18 +238,13 @@ fn set_nonblocking<T: AsRawFd>(fd: &mut T, nonblocking: bool) -> io::Result<()>
     Ok(())
 }
 
-fn stdio<T>(option: Option<T>) -> io::Result<Option<PollEvented<Pipe>>>
+pub(super) fn stdio<T>(io: T) -> io::Result<PollEvented<Pipe>>
 where
     T: IntoRawFd,
 {
-    let io = match option {
-        Some(io) => io,
-        None => return Ok(None),
-    };
-
     // Set the fd to nonblocking before we pass it to the event loop
     let mut pipe = Pipe::from(io);
     set_nonblocking(&mut pipe, true)?;
 
-    Ok(Some(PollEvented::new(pipe)?))
+    PollEvented::new(pipe)
 }

tokio/src/process/windows.rs

@@ -67,9 +67,9 @@ unsafe impl Send for Waiting {}
 
 pub(crate) fn spawn_child(cmd: &mut StdCommand) -> io::Result<SpawnedChild> {
     let mut child = cmd.spawn()?;
-    let stdin = stdio(child.stdin.take());
-    let stdout = stdio(child.stdout.take());
-    let stderr = stdio(child.stderr.take());
+    let stdin = child.stdin.take().map(stdio).transpose()?;
+    let stdout = child.stdout.take().map(stdio).transpose()?;
+    let stderr = child.stderr.take().map(stdio).transpose()?;
 
     Ok(SpawnedChild {
         child: Child {
@@ -167,20 +167,14 @@ unsafe extern "system" fn callback(ptr: PVOID, _timer_fired: BOOLEAN) {
     let _ = complete.take().unwrap().send(());
 }
 
-pub(crate) type ChildStdin = PollEvented<NamedPipe>;
-pub(crate) type ChildStdout = PollEvented<NamedPipe>;
-pub(crate) type ChildStderr = PollEvented<NamedPipe>;
+pub(crate) type ChildStdio = PollEvented<NamedPipe>;
 
-fn stdio<T>(option: Option<T>) -> Option<PollEvented<NamedPipe>>
+pub(super) fn stdio<T>(io: T) -> io::Result<PollEvented<NamedPipe>>
 where
     T: IntoRawHandle,
 {
-    let io = match option {
-        Some(io) => io,
-        None => return None,
-    };
     let pipe = unsafe { NamedPipe::from_raw_handle(io.into_raw_handle()) };
-    PollEvented::new(pipe).ok()
+    PollEvented::new(pipe)
 }
 
 pub(crate) fn convert_to_stdio(io: PollEvented<NamedPipe>) -> io::Result<Stdio> {