Idempotent Request IDs vs. create_new(true): Choosing the Right Retry Strategy for Tauri File Writes

Choosing the Optimal Retry Strategy

For typical Tauri projects, fs::OpenOptions::create_new(true) offers lower latency and simpler error handling than a persistent request ID store. It leverages the operating system's atomic file creation primitives, removing the need for an auxiliary database or state file to track request identifiers.

Comparing the Two Approaches

The choice depends on whether you need to prevent any overwrite or specifically prevent duplicate retries of the same logical operation.

Feature	create_new(true)	Request ID Store
Latency	Low (OS-level check)	Higher (Read/Write to store)
Complexity	Minimal (Standard Library)	Moderate (State management)
Scope	Per-file uniqueness	Per-operation uniqueness
Failure Mode	AlreadyExists error	Lookup miss/hit logic

Implementation Logic for create_new(true)

To implement this in a Tauri Rust command, use std::fs::OpenOptions. This ensures that if a retry occurs after a successful write (but before the frontend receives the ACK), the second attempt will fail immediately.

use std::fs::OpenOptions;
use std::io::Write;

#[tauri::command]
fn save_config(path: String, data: String) -> Result<String, String> {
    let mut file = OpenOptions::new()
        .write(true)
        .create_new(true) // Fails if file exists
        .open(&path)
        .map_err(|e| e.to_string())?;

    file.write_all(data.as_bytes()).map_err(|e| e.to_string())?;
    Ok("File created successfully".into())
}

Hybrid Approaches and Complexity

Combining create_new(true) with a persistent store is generally unnecessary for local file writes. The filesystem effectively acts as the persistent store. Adding a separate flag system introduces "dual-write" complexity, where the store and the filesystem could fall out of sync (e.g., the store marks a request as complete, but the OS fails to flush the file to disk).

Likely Explanation: The create_new(true) pattern is most effective when the filename is derived from the content or a unique transaction ID. If you are overwriting a single config.json, create_new will block all subsequent updates. In that specific case, a Request ID store is required to distinguish between a retry of an old write and a new legitimate update.

Verification and Diagnostics

To verify this behavior, simulate a network timeout by adding a std::thread::sleep after the write but before the return statement, then trigger a frontend retry. Ensure the second call returns an AlreadyExists error rather than overwriting the data.

Missing Detail: Are you writing to a fixed filename (e.g., settings.json) or generating unique filenames for each request? If the filename is fixed, create_new(true) is not viable for updates, and you must use the Request ID pattern.