nats-io/nats-server · error

compression negotiation error

Error message

compression negotiation error

What it means

Placeholder error for the leaf-node WebSocket compression negotiation path: when the connection requested permessage-deflate, the server's response headers are inspected with wsPMCExtensionSupport and this branch fires when the negotiated extension parameters (e.g. server/client no-context-takeover) are not acceptable.

Source

Thrown at server/leafnode.go:3689

	if err == nil &&
		(resp.StatusCode != 101 ||
			!strings.EqualFold(resp.Header.Get("Upgrade"), "websocket") ||
			!strings.EqualFold(resp.Header.Get("Connection"), "upgrade") ||
			resp.Header.Get("Sec-Websocket-Accept") != wsAcceptKey(wsKey)) {

		err = fmt.Errorf("invalid websocket connection")
	}
	// Check compression extension...
	if err == nil && c.ws.compress {
		// Check that not only permessage-deflate extension is present, but that
		// we also have server and client no context take over.
		srvCompress, noCtxTakeover := wsPMCExtensionSupport(resp.Header, false)

		// If server does not support compression, then simply disable it in our side.
		if !srvCompress {
			c.ws.compress = false
		} else if !noCtxTakeover {
			err = fmt.Errorf("compression negotiation error")
		}
	}
	// Same for no masking...
	if err == nil && noMasking {
		// Check if server accepts no masking
		if resp.Header.Get(wsNoMaskingHeader) != wsNoMaskingValue {
			// Nope, need to mask our writes as any client would do.
			c.ws.maskwrite = true
		}
	}
	if resp != nil {
		resp.Body.Close()
	}
	if err != nil {
		return nil, ReadError, err
	}
	c.Debugf("Leafnode compression=%v masking=%v", c.ws.compress, c.ws.maskwrite)

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Disable WebSocket compression on the leaf node connection if the peer does not negotiate permessage-deflate correctly
2. Upgrade the peer NATS server so both sides agree on no-context-takeover parameters
3. Inspect the 101 response headers to see which compression parameter mismatched

When it happens

Trigger: Thrown at server/leafnode.go:3689 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/6f7355f3abbb042b. Report an issue: GitHub.