1 files changed, 71 insertions, 0 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)
+    }
+}