Runtime diagnostics

Runtime diagnostics (raised by your generated SDK)

One code is different from every other on this page: it is emitted into your SDK and raised by your own application at call time, not by glotto while generating. If you are looking for it in glotto generate output you will not find it there — it appears in your application’s logs or as an exception at the call site.

Code	Meaning
`GLOTTO_RESTRICTED_HEADER`	You passed a per-call header whose name the SDK’s HTTP transport controls, so the SDK cannot send your value. The message names the header. Rather than dropping it silently — leaving you to discover from a packet capture that it never went out — the SDK refuses the call before any request is sent, so it has no server-side effect.

Which names are refused depends on the language, because the transports genuinely differ and we would rather not take a capability away from one SDK to match another’s limitation:

SDK	Refused	Sent normally
Java, Kotlin (JVM)	`Content-Length`, `Host`, `Connection`, `Upgrade`, `Expect`	—
Go	`Content-Length`, `Host`	`Connection`, `Upgrade`, `Expect`
All other languages	—	all of the above

The Java and Kotlin list is java.net.http’s own restricted set. That JDK exposes a jdk.httpclient.allowRestrictedHeaders system property which can re-enable individual names; the generated SDK deliberately does not consult it, because an SDK whose accepted headers changed with a JVM flag would be harder to reason about than one that is consistently strict.

Setting one of these headers is usually unnecessary. Content-Length is computed from the body you pass; Host follows from your configured base URL. If you need to reach a different host, change the client’s base URL rather than the header.

You can also see this code at generation time. If your spec declares one of these names as a required header parameter, or sets one as an auto_populate constant, generation refuses instead — emitting an SDK whose every call throws would not be something a caller could fix.