provide a framework for shell builtins

5 files changed, 180 insertions, 34 deletions

diff --git a/src/builtins.rs b/src/builtins.rs
new file mode 100644
index 0000000..f4c8c44
--- /dev/null
+++ b/src/builtins.rs
@@ -0,0 +1,71 @@
+use snafu::{ResultExt, Snafu};
+
+#[derive(Debug, Snafu)]
+pub enum Error {
+    #[snafu(display("unknown builtin {}", cmd))]
+    UnknownBuiltin { cmd: String },
+
+    #[snafu(display("failed to cd to {}: {}", dir, source))]
+    Chdir { dir: String, source: nix::Error },
+
+    #[snafu(display("cd requires a directory to be given"))]
+    ChdirParams,
+}
+
+pub fn exec(cmd: &str, args: &[String]) -> Result<Builtin, Error> {
+    Builtin::new(cmd, args)
+}
+
+pub struct Builtin {
+    cmd: String,
+    args: Vec<String>,
+    done: bool,
+}
+
+impl Builtin {
+    fn new(cmd: &str, args: &[String]) -> Result<Self, Error> {
+        match cmd {
+            "cd" => Ok(Builtin {
+                cmd: cmd.to_string(),
+                args: args.to_vec(),
+                done: false,
+            }),
+            _ => Err(Error::UnknownBuiltin {
+                cmd: cmd.to_string(),
+            }),
+        }
+    }
+}
+
+#[must_use = "streams do nothing unless polled"]
+impl futures::stream::Stream for Builtin {
+    type Item = crate::eval::CommandEvent;
+    type Error = Error;
+
+    fn poll(&mut self) -> futures::Poll<Option<Self::Item>, Self::Error> {
+        if self.done {
+            return Ok(futures::Async::Ready(None));
+        }
+
+        self.done = true;
+        let res = match self.cmd.as_ref() {
+            "cd" => cd(&self.args),
+            _ => Err(Error::UnknownBuiltin {
+                cmd: self.cmd.clone(),
+            }),
+        };
+        res.map(|_| {
+            futures::Async::Ready(Some(
+                crate::eval::CommandEvent::BuiltinExit,
+            ))
+        })
+    }
+}
+
+fn cd(args: &[String]) -> Result<(), Error> {
+    if let Some(dir) = args.get(0) {
+        nix::unistd::chdir(dir.as_str()).context(Chdir { dir: dir.clone() })
+    } else {
+        Err(Error::ChdirParams)
+    }
+}
diff --git a/src/eval.rs b/src/eval.rs
new file mode 100644
index 0000000..a46045a
--- /dev/null
+++ b/src/eval.rs
@@ -0,0 +1,85 @@
+use futures::stream::Stream;
+use snafu::{ResultExt, Snafu};
+
+#[derive(Debug, Snafu)]
+pub enum Error {
+    #[snafu(display("failed to parse command line '{}': {}", line, source))]
+    ParserError {
+        line: String,
+        source: crate::parser::Error,
+    },
+
+    #[snafu(display("failed to find command `{}`: {}", cmd, source))]
+    CommandError {
+        cmd: String,
+        source: crate::process::Error,
+    },
+
+    #[snafu(display("failed to run builtin command `{}`: {}", cmd, source))]
+    BuiltinExecution {
+        cmd: String,
+        source: crate::builtins::Error,
+    },
+
+    #[snafu(display("failed to run executable `{}`: {}", cmd, source))]
+    ProcessExecution {
+        cmd: String,
+        source: crate::process::Error,
+    },
+}
+
+pub fn eval(line: &str) -> Result<Eval, Error> {
+    Eval::new(line)
+}
+
+pub enum CommandEvent {
+    Output(Vec<u8>),
+    ProcessExit(std::process::ExitStatus),
+    BuiltinExit,
+}
+
+pub struct Eval {
+    stream: Box<
+        dyn futures::stream::Stream<Item = CommandEvent, Error = Error>
+            + Send,
+    >,
+}
+
+impl Eval {
+    fn new(line: &str) -> Result<Self, Error> {
+        let (cmd, args) =
+            crate::parser::parse(line).context(ParserError { line })?;
+        let builtin_stream = crate::builtins::exec(&cmd, &args);
+        let stream: Box<
+            dyn futures::stream::Stream<Item = CommandEvent, Error = Error>
+                + Send,
+        > = if let Ok(s) = builtin_stream {
+            Box::new(s.map_err(move |e| Error::BuiltinExecution {
+                cmd: cmd.clone(),
+                source: e,
+            }))
+        } else {
+            let process_stream = crate::process::spawn(&cmd, &args);
+            match process_stream {
+                Ok(s) => {
+                    Box::new(s.map_err(move |e| Error::ProcessExecution {
+                        cmd: cmd.clone(),
+                        source: e,
+                    }))
+                }
+                Err(e) => return Err(e).context(CommandError { cmd }),
+            }
+        };
+        Ok(Eval { stream })
+    }
+}
+
+#[must_use = "streams do nothing unless polled"]
+impl futures::stream::Stream for Eval {
+    type Item = CommandEvent;
+    type Error = Error;
+
+    fn poll(&mut self) -> futures::Poll<Option<Self::Item>, Self::Error> {
+        self.stream.poll()
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index d283021..3656616 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,5 @@
+mod builtins;
+mod eval;
 mod parser;
 mod process;
 mod readline;
diff --git a/src/process.rs b/src/process.rs
index 9d6582c..d059803 100644
--- a/src/process.rs
+++ b/src/process.rs
@@ -12,12 +12,6 @@ pub enum Error {
     #[snafu(display("failed to spawn process for `{}`: {}", cmd, source))]
     SpawnProcess { cmd: String, source: std::io::Error },
 
-    #[snafu(display("failed to parse command line '{}': {}", line, source))]
-    ParserError {
-        line: String,
-        source: crate::parser::Error,
-    },
-
     #[snafu(display("failed to write to pty: {}", source))]
     WriteToPty { source: std::io::Error },
 
@@ -40,13 +34,8 @@ pub enum Error {
     IntoRawMode { source: std::io::Error },
 }
 
-pub fn spawn(line: &str) -> Result<RunningProcess, Error> {
-    RunningProcess::new(line)
-}
-
-pub enum ProcessEvent {
-    Output(Vec<u8>),
-    Exit(std::process::ExitStatus),
+pub fn spawn(cmd: &str, args: &[String]) -> Result<RunningProcess, Error> {
+    RunningProcess::new(cmd, args)
 }
 
 pub struct RunningProcess {
@@ -62,14 +51,12 @@ pub struct RunningProcess {
 }
 
 impl RunningProcess {
-    fn new(line: &str) -> Result<Self, Error> {
+    fn new(cmd: &str, args: &[String]) -> Result<Self, Error> {
         let pty =
             tokio_pty_process::AsyncPtyMaster::open().context(OpenPty)?;
 
-        let (cmd, args) =
-            crate::parser::parse(line).context(ParserError { line })?;
-        let process = std::process::Command::new(cmd.clone())
-            .args(&args)
+        let process = std::process::Command::new(cmd)
+            .args(args)
             .spawn_pty_async(&pty)
             .context(SpawnProcess { cmd })?;
 
@@ -92,7 +79,7 @@ impl RunningProcess {
 
 #[must_use = "streams do nothing unless polled"]
 impl futures::stream::Stream for RunningProcess {
-    type Item = ProcessEvent;
+    type Item = crate::eval::CommandEvent;
     type Error = Error;
 
     fn poll(&mut self) -> futures::Poll<Option<Self::Item>, Self::Error> {
@@ -141,7 +128,7 @@ impl futures::stream::Stream for RunningProcess {
                             acc
                         });
                     return Ok(futures::Async::Ready(Some(
-                        ProcessEvent::Output(bytes),
+                        crate::eval::CommandEvent::Output(bytes),
                     )));
                 }
                 Ok(futures::Async::NotReady) => {
@@ -162,7 +149,7 @@ impl futures::stream::Stream for RunningProcess {
                 Ok(futures::Async::Ready(status)) => {
                     self.exit_done = true;
                     return Ok(futures::Async::Ready(Some(
-                        ProcessEvent::Exit(status),
+                        crate::eval::CommandEvent::ProcessExit(status),
                     )));
                 }
                 Ok(futures::Async::NotReady) => {
diff --git a/src/repl.rs b/src/repl.rs
index af87a0f..53e897c 100644
--- a/src/repl.rs
+++ b/src/repl.rs
@@ -9,7 +9,7 @@ enum Error {
     ReadError { source: crate::readline::Error },
 
     #[snafu(display("error during eval: {}", source))]
-    EvalError { source: crate::process::Error },
+    EvalError { source: crate::eval::Error },
 
     #[snafu(display("error during print: {}", source))]
     PrintError { source: std::io::Error },
@@ -24,25 +24,26 @@ pub fn repl() {
         let repl = read().and_then(|line| {
             eprint!("running '{}'\r\n", line);
             eval(&line).fold(None, |acc, event| match event {
-                crate::process::ProcessEvent::Output(out) => {
-                    match print(&out) {
-                        Ok(()) => futures::future::ok(acc),
-                        Err(e) => futures::future::err(e),
-                    }
+                crate::eval::CommandEvent::Output(out) => match print(&out) {
+                    Ok(()) => futures::future::ok(acc),
+                    Err(e) => futures::future::err(e),
+                },
+                crate::eval::CommandEvent::ProcessExit(status) => {
+                    futures::future::ok(Some(format!("{}", status)))
                 }
-                crate::process::ProcessEvent::Exit(status) => {
-                    futures::future::ok(Some(status))
+                crate::eval::CommandEvent::BuiltinExit => {
+                    futures::future::ok(Some(format!("success")))
                 }
             })
         });
 
         Some(repl.then(move |res| match res {
             Ok(Some(status)) => {
-                eprint!("process exited with status {}\r\n", status);
+                eprint!("command exited: {}\r\n", status);
                 return Ok((done, false));
             }
             Ok(None) => {
-                eprint!("process exited weirdly?\r\n");
+                eprint!("command exited weirdly?\r\n");
                 return Ok((done, false));
             }
             Err(Error::ReadError {
@@ -52,7 +53,7 @@ pub fn repl() {
             }
             Err(Error::EvalError {
                 source:
-                    crate::process::Error::ParserError {
+                    crate::eval::Error::ParserError {
                         source: crate::parser::Error::CommandRequired,
                         line: _,
                     },
@@ -81,9 +82,9 @@ fn read() -> impl futures::future::Future<Item = String, Error = Error> {
 
 fn eval(
     line: &str,
-) -> impl futures::stream::Stream<Item = crate::process::ProcessEvent, Error = Error>
+) -> impl futures::stream::Stream<Item = crate::eval::CommandEvent, Error = Error>
 {
-    crate::process::spawn(line)
+    crate::eval::eval(line)
         .into_future()
         .flatten_stream()
         .map_err(|e| Error::EvalError { source: e })