core: route view_image through a sandbox-backed fs helper

codex-rs/fs-ops/BUILD.bazel

@@ -0,0 +1,6 @@
+load("//:defs.bzl", "codex_rust_crate")
+
+codex_rust_crate(
+    name = "fs-ops",
+    crate_name = "codex_fs_ops",
+)

codex-rs/fs-ops/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "codex-fs-ops"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[lib]
+name = "codex_fs_ops"
+path = "src/lib.rs"
+
+[lints]
+workspace = true
+
+[dependencies]
+anyhow = { workspace = true }
+base64 = { workspace = true }
+serde = { workspace = true, features = ["derive"] }
+serde_json = { workspace = true }
+
+[dev-dependencies]
+pretty_assertions = { workspace = true }
+tempfile = { workspace = true }

codex-rs/fs-ops/src/command.rs

@@ -0,0 +1,38 @@
+use std::ffi::OsString;
+use std::path::PathBuf;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum FsCommand {
+    ReadFile { path: PathBuf },
+}
+
+pub fn parse_command_from_args(
+    mut args: impl Iterator<Item = OsString>,
+) -> Result<FsCommand, String> {
+    let Some(operation) = args.next() else {
+        return Err("missing operation".to_string());
+    };
+    let Some(operation) = operation.to_str() else {
+        return Err("operation must be valid UTF-8".to_string());
+    };
+    let Some(path) = args.next() else {
+        return Err(format!("missing path for operation `{operation}`"));
+    };
+    if args.next().is_some() {
+        return Err(format!(
+            "unexpected extra arguments for operation `{operation}`"
+        ));
+    }
+
+    let path = PathBuf::from(path);
+    match operation {
+        "read" => Ok(FsCommand::ReadFile { path }),
+        _ => Err(format!(
+            "unsupported filesystem operation `{operation}`; expected `read`"
+        )),
+    }
+}
+
+#[cfg(test)]
+#[path = "command_tests.rs"]
+mod tests;

codex-rs/fs-ops/src/command_tests.rs

@@ -0,0 +1,16 @@
+use super::FsCommand;
+use super::parse_command_from_args;
+use pretty_assertions::assert_eq;
+
+#[test]
+fn parse_read_command() {
+    let command = parse_command_from_args(["read", "/tmp/example.png"].into_iter().map(Into::into))
+        .expect("command should parse");
+
+    assert_eq!(
+        command,
+        FsCommand::ReadFile {
+            path: "/tmp/example.png".into(),
+        }
+    );
+}

codex-rs/fs-ops/src/constants.rs

@@ -0,0 +1,3 @@
+/// Special argv[1] flag used when the Codex executable self-invokes to run the
+/// internal sandbox-backed filesystem helper path.
+pub const CODEX_CORE_FS_OPS_ARG1: &str = "--codex-run-as-fs-ops";

codex-rs/fs-ops/src/error.rs

@@ -0,0 +1,70 @@
+use serde::Deserialize;
+use serde::Serialize;
+use std::io::ErrorKind;
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum FsErrorKind {
+    NotFound,
+    PermissionDenied,
+    IsADirectory,
+    InvalidData,
+    Other,
+}
+
+impl From<ErrorKind> for FsErrorKind {
+    fn from(value: ErrorKind) -> Self {
+        match value {
+            ErrorKind::NotFound => Self::NotFound,
+            ErrorKind::PermissionDenied => Self::PermissionDenied,
+            ErrorKind::IsADirectory => Self::IsADirectory,
+            ErrorKind::InvalidData => Self::InvalidData,
+            _ => Self::Other,
+        }
+    }
+}
+
+impl FsErrorKind {
+    pub fn to_io_error_kind(&self) -> ErrorKind {
+        match self {
+            Self::NotFound => ErrorKind::NotFound,
+            Self::PermissionDenied => ErrorKind::PermissionDenied,
+            Self::IsADirectory => ErrorKind::IsADirectory,
+            Self::InvalidData => ErrorKind::InvalidData,
+            Self::Other => ErrorKind::Other,
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct FsError {
+    pub kind: FsErrorKind,
+    pub message: String,
+    pub raw_os_error: Option<i32>,
+}
+
+impl std::fmt::Display for FsError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&self.message)
+    }
+}
+
+impl FsError {
+    pub fn to_io_error(&self) -> std::io::Error {
+        if let Some(raw_os_error) = self.raw_os_error {
+            std::io::Error::from_raw_os_error(raw_os_error)
+        } else {
+            std::io::Error::new(self.kind.to_io_error_kind(), self.message.clone())
+        }
+    }
+}
+
+impl From<std::io::Error> for FsError {
+    fn from(error: std::io::Error) -> Self {
+        Self {
+            kind: error.kind().into(),
+            message: error.to_string(),
+            raw_os_error: error.raw_os_error(),
+        }
+    }
+}

codex-rs/fs-ops/src/lib.rs

@@ -0,0 +1,13 @@
+mod command;
+mod constants;
+mod error;
+mod runner;
+
+pub use command::FsCommand;
+pub use command::parse_command_from_args;
+pub use constants::CODEX_CORE_FS_OPS_ARG1;
+pub use error::FsError;
+pub use error::FsErrorKind;
+pub use runner::execute;
+pub use runner::run_from_args;
+pub use runner::write_error;

codex-rs/fs-ops/src/runner.rs

@@ -0,0 +1,55 @@
+use crate::FsCommand;
+use crate::FsError;
+use crate::parse_command_from_args;
+use anyhow::Context;
+use anyhow::Result;
+use std::ffi::OsString;
+use std::io::Read;
+use std::io::Write;
+
+pub fn run_from_args(
+    args: impl Iterator<Item = OsString>,
+    stdin: &mut impl Read,
+    stdout: &mut impl Write,
+    stderr: &mut impl Write,
+) -> Result<()> {
+    let command = match parse_command_from_args(args) {
+        Ok(command) => command,
+        Err(error) => {
+            writeln!(stderr, "{error}").context("failed to write fs helper usage error")?;
+            anyhow::bail!("{error}");
+        }
+    };
+
+    if let Err(error) = execute(command, stdin, stdout) {
+        write_error(stderr, &error)?;
+        anyhow::bail!("{error}");
+    }
+
+    Ok(())
+}
+
+pub fn execute(
+    command: FsCommand,
+    _stdin: &mut impl Read,
+    stdout: &mut impl Write,
+) -> Result<(), FsError> {
+    match command {
+        FsCommand::ReadFile { path } => {
+            let mut file = std::fs::File::open(path).map_err(FsError::from)?;
+            std::io::copy(&mut file, stdout)
+                .map(|_| ())
+                .map_err(FsError::from)
+        }
+    }
+}
+
+pub fn write_error(stderr: &mut impl Write, error: &FsError) -> Result<()> {
+    serde_json::to_writer(&mut *stderr, error).context("failed to serialize fs error")?;
+    writeln!(stderr).context("failed to terminate fs error with newline")?;
+    Ok(())
+}
+
+#[cfg(test)]
+#[path = "runner_tests.rs"]
+mod tests;

codex-rs/fs-ops/src/runner_tests.rs

@@ -0,0 +1,76 @@
+use super::execute;
+use crate::FsCommand;
+use crate::FsErrorKind;
+use crate::run_from_args;
+use pretty_assertions::assert_eq;
+use tempfile::tempdir;
+
+#[test]
+fn run_from_args_streams_file_bytes_to_stdout() {
+    let tempdir = tempdir().expect("tempdir");
+    let path = tempdir.path().join("image.bin");
+    let expected = b"hello\x00world".to_vec();
+    std::fs::write(&path, &expected).expect("write test file");
+
+    let mut stdout = Vec::new();
+    let mut stderr = Vec::new();
+    let mut stdin = std::io::empty();
+    run_from_args(
+        ["read", path.to_str().expect("utf-8 test path")]
+            .into_iter()
+            .map(Into::into),
+        &mut stdin,
+        &mut stdout,
+        &mut stderr,
+    )
+    .expect("read should succeed");
+
+    assert_eq!(stdout, expected);
+    assert_eq!(stderr, Vec::<u8>::new());
+}
+
+#[test]
+fn read_reports_directory_error() {
+    let tempdir = tempdir().expect("tempdir");
+    let mut stdout = Vec::new();
+    let mut stdin = std::io::empty();
+
+    let error = execute(
+        FsCommand::ReadFile {
+            path: tempdir.path().to_path_buf(),
+        },
+        &mut stdin,
+        &mut stdout,
+    )
+    .expect_err("reading a directory should fail");
+
+    #[cfg(target_os = "windows")]
+    assert_eq!(error.kind, FsErrorKind::PermissionDenied);
+    #[cfg(not(target_os = "windows"))]
+    assert_eq!(error.kind, FsErrorKind::IsADirectory);
+}
+
+#[test]
+fn run_from_args_serializes_errors_to_stderr() {
+    let tempdir = tempdir().expect("tempdir");
+    let missing = tempdir.path().join("missing.txt");
+    let mut stdout = Vec::new();
+    let mut stderr = Vec::new();
+    let mut stdin = std::io::empty();
+
+    let result = run_from_args(
+        ["read", missing.to_str().expect("utf-8 test path")]
+            .into_iter()
+            .map(Into::into),
+        &mut stdin,
+        &mut stdout,
+        &mut stderr,
+    );
+
+    assert!(result.is_err(), "missing file should fail");
+    assert_eq!(stdout, Vec::<u8>::new());
+
+    let error: crate::FsError = serde_json::from_slice(&stderr).expect("structured fs error");
+    assert_eq!(error.kind, FsErrorKind::NotFound);
+    assert!(error.raw_os_error.is_some());
+}