nginx protocol_error ai_generated true

upstream sent invalid Content-Length: -1 while reading response header from upstream

ID: nginx/upstream-sent-invalid-content-length-negative

Also available as: JSON · Markdown

90%Fix Rate

85%Confidence

1Evidence

2025-02-01First Seen

Version Compatibility

Version	Status	Introduced	Deprecated	Notes
nginx 1.24.0	active	—	—	—
nginx 1.25.3	active	—	—	—
nginx 1.26.0	active	—	—	—

Root Cause

Upstream server returns a negative Content-Length value in the HTTP response, which violates HTTP specification.

generic

Official Documentation

https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_ignore_headers

Workarounds

85% success Use proxy_ignore_headers to ignore the Content-Length header from upstream: location / { proxy_pass http://upstream; proxy_ignore_headers Content-Length; }
```
Use proxy_ignore_headers to ignore the Content-Length header from upstream:
  location / {
      proxy_pass http://upstream;
      proxy_ignore_headers Content-Length;
  }
```
95% success Fix the upstream application to emit a valid Content-Length (non-negative integer). For example, in a Python Flask app: from flask import Response @app.route('/data') def data(): body = 'hello' return Response(body, headers={'Content-Length': str(len(body))})
```
Fix the upstream application to emit a valid Content-Length (non-negative integer). For example, in a Python Flask app:
  from flask import Response
  @app.route('/data')
  def data():
      body = 'hello'
      return Response(body, headers={'Content-Length': str(len(body))})
```

中文步骤

Use proxy_ignore_headers to ignore the Content-Length header from upstream:
  location / {
      proxy_pass http://upstream;
      proxy_ignore_headers Content-Length;
  }

Fix the upstream application to emit a valid Content-Length (non-negative integer). For example, in a Python Flask app:
  from flask import Response
  @app.route('/data')
  def data():
      body = 'hello'
      return Response(body, headers={'Content-Length': str(len(body))})

Dead Ends

Common approaches that don't work:

Add proxy_buffering off; 90% fail
Buffering does not fix an invalid header value from upstream.
Increase proxy_buffer_size 100% fail
This addresses header size, not header validity.
Restart nginx 100% fail
Restarting does not change the upstream behavior.