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HTTP 411 Length Required means the server that received your request would not accept a body without a defined Content-Length. The usual trigger is a POST, PUT, or upload sent with no length or with Transfer-Encoding: chunked to a strict origin or proxy. Fix it by identifying the hop that generated the response, sending an exact byte count when the body size is known, or configuring the relevant reverse proxy to use fixed-length forwarding. Do not “solve” 411 by guessing a length or by setting Content-Length: 0 on a request that has data.
What the 411 Length Required error means
HTTP 411 is a client-error status. MDN defines it as a response in which “the server refused to accept the request without a defined Content-Length header.” The status describes the request framing, not the size of the payload. A server can accept a very large request when its length is declared, and reject a tiny request when the length is absent.
HTTP/1.1 can frame a request body in two relevant ways:
| Framing | What the receiver sees | Why it can produce 411 |
|---|---|---|
Content-Length: N |
A decimal byte count followed by exactly that many bytes | Normally accepted when the count is correct and within configured limits |
Transfer-Encoding: chunked |
Data arrives as a sequence of chunks, so there is no one overall length in the request headers | Some servers, gateways, and older applications insist on a fixed length and reject the request |
| No body framing | The request has a body but neither a usable length nor an accepted transfer coding | The receiving server may answer 411 rather than try to determine where the body ends |
RFC 7230 allows a server to reject a request that contains a message body but no Content-Length with 411. It also recommends that a sender include a valid length when the size is known, because services that understand HTTP may still reject chunked requests for compatibility reasons. See the IETF RFC 7230 and the MDN 411 reference for the protocol definitions.
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Find the component that actually returned 411
The first repair step is attribution. A browser, API client, CDN, load balancer, client-facing Nginx, Apache, or the application behind a proxy can each generate a response that looks similar. Changing the wrong layer leaves the error unchanged and can introduce buffering or latency elsewhere.
- Capture the outgoing request. Record the method, whether a body is present, the exact
Content-Length,Transfer-Encoding,Expect, and the response status and headers. A command-line trace, API-client export, or packet capture is useful as long as it shows the headers actually sent on the wire. - Capture the request at every proxy hop. Compare what leaves the client with what reaches Nginx, Apache, a load balancer, and the origin. A proxy may remove, add, or replace framing headers.
- Inspect the response
Serverand related headers. They can identify the responding layer, but treat them as clues rather than proof; headers may be changed or hidden. - Repeat the request directly to the origin. Use the same method, body, and authentication where possible. If direct origin access succeeds but the proxied path returns 411, focus on the intermediary. If both fail, inspect the origin’s request parser and logs.
- Check logs at the suspected hop. Nginx access and error logs, Apache logs, load-balancer logs, and application logs should be correlated by timestamp, request ID, and path.
A CDN-generated-looking page does not establish that the CDN caused the error. The provider’s documentation says its 411 response can be proxied from the origin. Follow the request to the source that emitted the status; the provider’s 411 troubleshooting page describes this distinction.
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When the body length is known
Serialize the body first, count its bytes, and send that decimal count in one Content-Length header. “Bytes” matters: a UTF-8 character can occupy more than one byte, so counting source-language characters can produce a mismatch. The number must describe the encoded wire representation, not an estimate, a character count, or a file’s uncompressed size when compression changes what is sent.
- Send one valid
Content-Lengthvalue. - Make the body contain exactly that many bytes.
- Do not also send a non-identity
Transfer-Encoding. - Confirm that any middleware has not re-encoded, compressed, or modified the body after the count was calculated.
When the body is streamed and its size is unknown
You have two sound choices: buffer the body until its length can be calculated, or make the receiving hop and upstream application accept chunked requests. Buffering consumes memory or disk and can delay the request; accepting chunked encoding may require changes to an old server or application. Never guess a length. A guessed value can cause truncation, request desynchronization, or rejection.
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When both framing headers appear
Do not send Content-Length together with a non-identity Transfer-Encoding. Under RFC 7230 framing rules, transfer encoding governs how the message is delimited and the Content-Length value is ignored. Conflicting headers are also a security risk because different intermediaries may parse the request differently. Remove the conflicting header and make the sender use exactly one framing method.
Fix the client request first
Known-size JSON with curl
For a small JSON request, serialize the exact payload and let curl send it as a fixed-length body:
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curl -X POST https://example.test/api
-H 'Content-Type: application/json'
--data-binary "$body"curl normally computes the length for --data-binary. Avoid options, wrappers, or HTTP libraries that force chunked streaming when the destination requires a fixed length. For a file or generated payload, make sure the bytes are final before the request begins and verify that any transformation performed by the client is included in the count.
Application-code checklist
Use your HTTP library’s fixed-length request mode when the serialized body is available. The safe sequence is:
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- Build the logical object or text.
- Encode it exactly as the client will transmit it, commonly UTF-8 for JSON.
- Measure the encoded byte array or buffer.
- Pass that buffer and its byte count to the library’s fixed-length API.
- Inspect the emitted request in a trace to confirm one matching
Content-Lengthand no chunked transfer coding.
Do not add Content-Length: 0 merely because a server requested a length. That header is correct only for a genuinely empty body. If the request contains data, zero creates a length mismatch and may cause the server or a proxy to read no body, truncate it, or reject it.
Resolve 411 on Nginx
Understand what Nginx’s directive controls
Nginx provides chunked_transfer_encoding on|off, whose default is on. The directive controls Nginx’s transfer behavior when it sends a response or forwards data; it does not repair a client that has already sent an invalid or incorrect Content-Length. Nginx documents that disabling chunked transfer can help when communicating with software that does not support chunked encoding. Read the current Nginx HTTP core module documentation for directive context and version details.
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Put the directive only in the http, server, or location context that serves the incompatible endpoint. A narrow location prevents streaming APIs and unrelated uploads from being buffered or changed unnecessarily.
location /legacy-upstream/ {
chunked_transfer_encoding off;
proxy_pass http://legacy_backend;
}- Identify the path whose upstream returns 411.
- Place
chunked_transfer_encoding off;in that location, or in the smallest suitable parent context. - Validate the configuration with your normal Nginx configuration-test command before reloading.
- Reload Nginx, reproduce with a small fixed-length request, and compare the request received by the upstream.
- Review access and error logs, then test the real payload and any streaming endpoints that share the configuration.
Turning the directive off globally can force buffering or other transfer changes for endpoints designed to stream. If memory use, temporary-disk use, latency, or timeout behavior worsens, roll back the broad setting and keep the compatibility rule local to the legacy route.
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When the problem is a broken HTTP/1.0 backend response
A related but different failure occurs when a backend sends a chunked response while speaking HTTP/1.0. Nginx’s FAQ says that this violates the HTTP specification and recommends correcting the backend or using a newer Nginx version that handles the errant behavior. That advice concerns a malformed backend response; it is not a substitute for fixing a client request that lacks a length. See the Nginx chunked-encoding FAQ when packet captures show this HTTP/1.0 response pattern.
Resolve 411 with Apache httpd and mod_proxy
How mod_proxy chooses request framing
Apache’s mod_proxy sends a request body either with chunked transfer encoding or with a Content-Length header. For an upstream that responds 411, set the proxy-sendcl environment variable so the proxy sends a fixed length. The opposite setting, proxy-sendchunked, forces chunked encoding and is appropriate only when the upstream accepts it.
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Example for a legacy upstream
<Location "/legacy-upstream/">
ProxyPass "http://legacy-backend/"
SetEnv proxy-sendcl 1
</Location>- Scope the rule to the proxied path that requires fixed-length requests.
- Set
proxy-sendclfor that location. - Check the Apache configuration, reload gracefully, and reproduce the request.
- Inspect the upstream-facing capture or logs to verify that Apache sends one correct
Content-Length. - Measure temporary-disk use and latency with realistic payloads, especially large uploads.
HTTP/1.0 and keep-alive compatibility controls
If logs or a packet capture show that the origin requires HTTP/1.0 or has broken keep-alive behavior, Apache documents force-proxy-request-1.0 and proxy-nokeepalive as compatibility controls. Use them only for the demonstrated protocol mismatch. They change the proxy connection behavior; they do not create a correct request length and therefore cannot replace proxy-sendcl or a properly framed client request.
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Distinguish 411 from upload-size errors
Do not change body-size limits as a first response to 411. Nginx’s client_max_body_size and Apache’s request-body limits govern how large a body may be. Exceeding such a limit normally produces HTTP 413 (Payload Too Large), not 411 (Length Required). Raising a limit can increase exposure to large uploads while leaving missing or conflicting framing untouched.
Use the status and the captured headers to separate the cases:
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| Observed symptom | Likely issue | Next action |
|---|---|---|
411 with no usable Content-Length |
Strict receiver requires fixed-length framing | Calculate and send the exact byte count, or configure the receiver to accept chunked data |
411 with Transfer-Encoding: chunked |
Receiver or upstream rejects chunked requests | Buffer and send a fixed length, or use Nginx/Apache compatibility controls |
| 411 with both framing headers | Conflicting request framing | Remove the conflict and send one valid method |
| 413 after framing is corrected | Body exceeds a configured size limit | Review the applicable size setting and intended upload policy |
| Works direct to origin but fails through a proxy | Intermediary rewrites or rejects framing | Compare hop-by-hop captures and scope the proxy fix |
Common mistakes and their consequences
- Setting
Content-Length: 0on a non-empty request: the receiver may treat the body as absent, truncate it, or reject the mismatch. - Sending both
Content-Lengthand chunked transfer coding: transfer coding governs framing, while intermediaries may still disagree about the ignored value. - Guessing a length for a stream: an incorrect count can leave unread bytes on a persistent connection or make the receiver wait for bytes that will never arrive.
- Disabling chunked encoding everywhere: streaming routes can become buffered, increasing memory or temporary-disk use and response latency.
- Changing upload-size limits to cure 411: this addresses a different status and can create an unnecessarily permissive upload policy.
- Blaming a CDN page automatically: the CDN may simply be relaying the origin’s 411. Trace the emitting hop before changing CDN or origin settings.
- Fixing only the browser or only the proxy: the request must be correctly framed at the hop that rejects it. A downstream proxy cannot infer a trustworthy length from a malformed upstream request without buffering and validating the body.
Verify the repair end to end
Use a two-stage test so a compatibility change is not mistaken for a complete fix.
- Start with a small deterministic body. Send a short JSON or text payload whose encoded bytes you can count.
- Check the client trace. Confirm the method, body presence, one correct
Content-Length, and no non-identityTransfer-Encoding. - Check each proxy hop. Ensure Nginx, Apache, the load balancer, and the origin receive the framing you expect; do not assume a proxy preserves headers.
- Compare direct and proxied requests. The same body and headers should produce the same result at the origin and through the public path.
- Test the real payload. Include its actual encoding, size, authentication, compression behavior, and any upload streaming code.
- Review logs and resource use. Look for retries, request truncation, temporary files, buffering delays, connection resets, and upstream timeouts.
- Exercise unrelated endpoints. Verify that streaming and large-upload routes did not inherit an overly broad Nginx or Apache compatibility rule.
- Keep a rollback ready. If fixed-length forwarding causes unacceptable buffering or disk use, revert the narrow directive and either make the upstream support chunked requests or redesign the client to know the length.
A practical decision guide
| Your situation | Preferred action | Trade-off to account for |
|---|---|---|
| JSON, form data, or a file is fully available before sending | Encode it, measure bytes, and send fixed-length framing | The body must not change after measurement |
| Client streams an unknown-size body to Nginx | Buffer and calculate a length, or make the upstream accept chunked requests | Buffering can consume memory or disk and add latency |
| Nginx proxies a legacy endpoint that rejects chunked data | Use chunked_transfer_encoding off; in the relevant location and reload after validation |
Do not apply it globally without testing streaming routes |
| Apache mod_proxy upstream returns 411 | Set proxy-sendcl 1 for the affected location |
Apache may spool large bodies to disk to determine length |
| Origin requires HTTP/1.0 or has broken keep-alive | Consider force-proxy-request-1.0 or proxy-nokeepalive only after evidence of that mismatch |
These controls do not replace correct body framing |
| Request contains conflicting framing headers | Remove the conflict and emit exactly one valid framing method | Retest every intermediary because parsing differences can persist in caches or gateways |
What to remember
411 is a framing failure at a particular receiving hop. Locate that hop before editing configuration. If the payload size is known, send the exact encoded byte count in Content-Length and omit conflicting transfer coding. If the payload is truly streamed, either buffer it or update the receiving path to accept chunked requests. Nginx exposes chunked_transfer_encoding; Apache mod_proxy exposes proxy-sendcl and proxy-sendchunked. Apply compatibility settings narrowly, validate the request at every hop, and test resource impact before keeping the change.
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