divine-mobile: Skill for Claude Code

curl -I Sends HEAD, Not GET — Header Debugging Trap

Problem

When debugging HTTP response headers with curl -I or curl -sI, the response may show different header values than what actual GET requests receive. This is because -I sends a HEAD request, and server middleware that only processes GET requests will be skipped.

Context / Trigger Conditions

• Testing cache headers with curl -sI and seeing unexpected values
• Middleware that checks method == GET before setting headers (common in cache middleware)
• Headers appear correct in automated tests but wrong in manual curl testing
• Cache-Control, Surrogate-Control, or Surrogate-Key values don't match expectations
• Axum/Express/any framework middleware with method guards

Solution

Use curl -s -D - -o /dev/null instead of curl -I to get response headers from a GET request:

# WRONG — sends HEAD request, middleware may skip processing
curl -sI https://example.com/api/endpoint

# CORRECT — sends GET request, dumps headers, discards body
curl -s -D - -o /dev/null https://example.com/api/endpoint

If you need just specific headers:

curl -s -D - -o /dev/null https://example.com/api/endpoint | grep -iE 'cache-control|surrogate'

Verification

Compare output from both methods:

echo "=== HEAD (curl -I) ==="
curl -sI https://example.com/api/endpoint | grep cache-control

echo "=== GET (curl -D) ==="
curl -s -D - -o /dev/null https://example.com/api/endpoint | grep cache-control

If the values differ, your middleware has a GET-only guard (which is correct behavior).

Example

Axum middleware that only sets cache headers for GET requests:

async fn cache_middleware(request: Request, next: Next) -> Response {
    let method = request.method().clone();
    let mut response = next.run(request).await;

    // HEAD requests skip this — curl -I won't see these headers!
    if method != Method::GET {
        return response;
    }

    response.headers_mut().insert("cache-control", ...);
    response.headers_mut().insert("surrogate-control", ...);
    response
}