proxy-range-header-forwarding

Proxy Range Header Forwarding for Video Streaming

Problem

A proxy/edge service (Fastly Compute, Cloudflare Workers, custom reverse proxy) sits between clients and object storage. Some routes correctly forward HTTP Range headers to the storage backend, but other routes (added later or by different developers) construct backend requests from scratch without forwarding Range headers. This causes iOS AVPlayer to fail because it probes with Range: bytes=0-1 and rejects responses where the body size doesn't match the requested range.

Context / Trigger Conditions

• iOS error: CoreMediaErrorDomain error -12939 - byte range length mismatch - should be length 2 is length N
• PlatformException(VideoError, Failed to load video: Operation Stopped)
• curl -H "Range: bytes=0-1" on the failing URL returns 200 with Content-Length equal to full file size
• The same curl test on a different URL path to the same storage returns 206 with Content-Length: 2
• The proxy/edge code has multiple route handlers that independently construct backend requests
• Response headers include Accept-Ranges: bytes (misleadingly advertising support)

Root Cause Pattern

In proxy architectures, each route handler independently constructs requests to the storage backend. It's common for the "original" handler to properly forward Range headers while variant handlers (quality variants, thumbnails, transcoded versions) build requests from scratch without considering Range.

// BROKEN: Handler ignores client Range header
fn handle_variant(req: Request, path: &str) -> Response {
    let gcs_path = resolve_variant(path);
    let backend_req = Request::new(Method::GET, &gcs_url);  // No Range header!
    backend_req.send("storage")
}

// WORKING: Handler forwards Range header
fn handle_original(req: Request, path: &str) -> Response {
    let range = req.get_header("Range");  // Extracts Range
    let backend_req = Request::new(Method::GET, &gcs_url);
    if let Some(r) = range {
        backend_req.set_header("Range", r);  // Forwards it
    }
    backend_req.send("storage")
}