1 files changed, 94 insertions, 0 deletions
diff --git a/src/commands.rs b/src/commands.rs
index a2b6004..5e2af91 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -17,8 +17,14 @@
 // * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
 // *************************************************************************
 
+use std::borrow;
+use std::env;
+use std::ffi;
 use std::fmt;
+use std::io;
 use std::mem;
+use std::path;
+use std::process;
 use std::result;
 use std::thread;
 use std::time;
@@ -980,6 +986,94 @@ pub fn pws_status(ctx: &mut ExecCtx<'_>, all: bool) -> Result<()> {
   })
 }
 
+/// Resolve an extension provided by name to an actual path.
+///
+/// Extensions are (executable) files that have the "nitrocli-" prefix
+/// and are discoverable via the `PATH` environment variable.
+pub(crate) fn resolve_extension(
+  path_var: &ffi::OsStr,
+  ext_name: &ffi::OsStr,
+) -> Result<path::PathBuf> {
+  let mut bin_name = ffi::OsString::from("nitrocli-");
+  bin_name.push(ext_name);
+
+  // The std::env module has several references to the PATH environment
+  // variable, indicating that this name is considered platform
+  // independent from their perspective. We do the same.
+  for dir in env::split_paths(path_var) {
+    let mut bin_path = dir.clone();
+    bin_path.push(&bin_name);
+    // Note that we deliberately do not check whether the file we found
+    // is executable. If it is not we will just fail later on with a
+    // permission denied error. The reasons for this behavior are two
+    // fold:
+    // 1) Checking whether a file is executable in Rust is painful (as
+    //    of 1.37 there exists the PermissionsExt trait but it is
+    //    available only for Unix based systems).
+    // 2) It is considered a better user experience to show an extension
+    //    that we found (we list them in the help text) even if it later
+    //    turned out to be not usable over not showing it and silently
+    //    doing nothing -- mostly because anything residing in PATH
+    //    should be executable anyway and given that its name also
+    //    starts with nitrocli- we are pretty sure that's a bug on the
+    //    user's side.
+    if bin_path.is_file() {
+      return Ok(bin_path);
+    }
+  }
+
+  let err = if let Some(name) = bin_name.to_str() {
+    format!("extension {} not found", name).into()
+  } else {
+    borrow::Cow::from("extension not found")
+  };
+  Err(io::Error::new(io::ErrorKind::NotFound, err).into())
+}
+
+/// Run an extension.
+pub fn extension(ctx: &mut ExecCtx<'_>, args: Vec<ffi::OsString>) -> Result<()> {
+  // Note that while `Command` would actually honor PATH by itself, we
+  // do not want that behavior because it would circumvent the execution
+  // context we use for testing. As such, we need to do our own search.
+  let mut args = args.into_iter();
+  let ext_name = args
+    .next()
+    .ok_or_else(|| Error::from("no extension specified"))?;
+  let path_var = ctx
+    .path
+    .as_ref()
+    .ok_or_else(|| Error::from("PATH variable not present"))?;
+  let ext_path = resolve_extension(&path_var, &ext_name)?;
+
+  // Note that theoretically we could just exec the extension and be
+  // done. However, the problem with that approach is that it makes
+  // testing extension support much more nasty, because the test process
+  // would be overwritten in the process, requiring us to essentially
+  // fork & exec nitrocli beforehand -- which is much more involved from
+  // a cargo test context.
+  let mut cmd = process::Command::new(&ext_path);
+
+  if let Some(model) = ctx.model {
+    let _ = cmd.args(&["--model", model.as_ref()]);
+  };
+
+  let out = cmd
+    // TODO: We may want to take this path from the command execution
+    //       context.
+    .args(&["--nitrocli", &env::current_exe()?.to_string_lossy()])
+    .args(&["--verbosity", &ctx.verbosity.to_string()])
+    .args(args)
+    .output()?;
+  ctx.stdout.write_all(&out.stdout)?;
+  ctx.stderr.write_all(&out.stderr)?;
+
+  if out.status.success() {
+    Ok(())
+  } else {
+    Err(Error::ExtensionFailed(ext_path, out.status.code()))
+  }
+}
+
 #[cfg(test)]
 mod tests {
   use super::*;