rust-lang/rust · error · io::Error

must specify at least one of read, write, or append access

Error message

must specify at least one of read, write, or append access

What it means

Windows counterpart of error 214. In get_access_mode() (windows.rs:279-284), when no access mode (read/write/append/access_mode) and no creation flag is set, there is no valid disposition to request, so the open is rejected as InvalidInput.

Source

Thrown at library/std/src/sys/fs/windows.rs:280

        match (self.read, self.write, self.append, self.access_mode) {
            (.., Some(mode)) => Ok(mode),
            (true, false, false, None) => Ok(c::GENERIC_READ),
            (false, true, false, None) => Ok(c::GENERIC_WRITE),
            (true, true, false, None) => Ok(c::GENERIC_READ | c::GENERIC_WRITE),
            (false, _, true, None) => Ok(c::FILE_GENERIC_WRITE & !c::FILE_WRITE_DATA),
            (true, _, true, None) => {
                Ok(c::GENERIC_READ | (c::FILE_GENERIC_WRITE & !c::FILE_WRITE_DATA))
            }
            (false, false, false, None) => {
                // If no access mode is set, check if any creation flags are set
                // to provide a more descriptive error message
                if self.create || self.create_new || self.truncate {
                    Err(io::Error::new(
                        io::ErrorKind::InvalidInput,
                        "creating or truncating a file requires write or append access",
                    ))
                } else {
                    Err(io::Error::new(
                        io::ErrorKind::InvalidInput,
                        "must specify at least one of read, write, or append access",
                    ))
                }
            }
        }
    }

    fn get_cmode_disposition(&self) -> io::Result<(u32, u32)> {
        match (self.write, self.append) {
            (true, false) => {}
            (false, false) => {
                if self.truncate || self.create || self.create_new {
                    return Err(io::Error::new(
                        io::ErrorKind::InvalidInput,
                        "creating or truncating a file requires write or append access",
                    ));
                }

View on GitHub (pinned to 7088e4b63a)

Solutions

Add at least one of .read(true), .write(true), or .append(true).
Use File::open(p) for plain reading.

Example fix

// before
std::fs::OpenOptions::new().open("f")?;
// after
std::fs::OpenOptions::new().read(true).open("f")?

Defensive patterns

Strategy: validation

Try / catch

match std::fs::OpenOptions::new().open(p) {
    Ok(f) => f,
    Err(e) if e.kind() == std::io::ErrorKind::InvalidInput => {
        return Err(e); // set read/write/append
    }
    Err(e) => return Err(e),
}

Prevention

Never call .open() on an OpenOptions with no access flag.
Prefer File::open / File::create for common cases.

When it happens

Trigger: `OpenOptions::new().open(p)` on Windows with no access or creation setters.

Common situations: Forgetting to set any mode; expecting a read default.

Related errors

AI-assisted analysis of rust-lang/rust@7088e4b63a (2026-08-10). Data as JSON: /api/errors/fa9850efd368450c. Report an issue: GitHub.