Bug Report: Inconsistent URL construction with url_prefix

[gyash1512]

Summary

When configuring the Y-Sweet server with a url_prefix, the generated WebSocket URL and HTTP baseUrl are constructed inconsistently.

• baseUrl correctly preserves the path prefix
• url (WebSocket) drops the prefix, leading to incorrect connection URLs

---

Steps to Reproduce

1. Configure the Y-Sweet server with:

   url_prefix = "https://example.domain.com/ysweet/"

2. Make a request to:

   /doc/{doc_id}/auth
   

3. Observe the returned url and baseUrl fields in the response

---

Expected Behavior

Both URLs should preserve the /ysweet/ path prefix:

{
  "url": "wss://example.domain.com/ysweet/d/{doc_id}/ws",
  "baseUrl": "https://example.domain.com/ysweet/d/{doc_id}"
}

---

Actual Behavior

The WebSocket URL drops the path prefix, while the base URL is correct:

{
  "url": "wss://example.domain.com/d/{doc_id}/ws",
  "baseUrl": "https://example.domain.com/ysweet/d/{doc_id}"
}

---

Root Cause

The issue originates in the auth_doc function in
crates/y-sweet/src/server.rs (around lines 777–796).

WebSocket URL construction (problematic)

let url = if let Some(url_prefix) = &server_state.url_prefix {
    let mut url = url_prefix.clone();
    let scheme = if url.scheme() == "https" { "wss" } else { "ws" };
    url.set_scheme(scheme).unwrap();
    url = url.join(&format!("/d/{doc_id}/ws")).unwrap(); // ❌ Replaces entire path
    url.to_string()
} else {
    format!("ws://{host}/d/{doc_id}/ws")
};

• url.join("/d/...") treats the argument as an absolute path
• This replaces the existing /ysweet/ path entirely

Base URL construction (correct)

let base_url = if let Some(url_prefix) = &server_state.url_prefix {
    let mut url_prefix = url_prefix.to_string();
    if !url_prefix.ends_with('/') {
        url_prefix = format!("{url_prefix}/");
    }
    format!("{url_prefix}d/{doc_id}") // ✅ Appends to existing path
} else {
    format!("http://{host}/d/{doc_id}")
};

---

Suggested Fix

Construct the WebSocket URL using the same append-style approach as baseUrl instead of url.join():

let url = if let Some(url_prefix) = &server_state.url_prefix {
    let mut url_prefix = url_prefix.to_string();
    if !url_prefix.ends_with('/') {
        url_prefix = format!("{url_prefix}/");
    }

    let scheme = if url_prefix.starts_with("https") { "wss" } else { "ws" };
    let url_prefix = url_prefix
        .replace("https://", "")
        .replace("http://", "");

    format!("{scheme}://{url_prefix}d/{doc_id}/ws")
} else {
    format!("ws://{host}/d/{doc_id}/ws")
};

---

Impact

• WebSocket connections fail when Y-Sweet is deployed behind a reverse proxy or sub-path
• Breaks setups using path-based routing (e.g., /ysweet/)

I would be happy to open a PR or help with the fix