#21704 Validate header-setting options don't set multiple headers with different casing Issue created by huonw Currently the https://www.pantsbuild.org/prerelease/reference/global-options#remote_execution_headers and https://www.pantsbuild.org/prerelease/reference/global-options#remote_store_headers options allow setting a single header multiple times, just differing by casing, and getting potentially non-deterministic behaviour. For instance, both of these are setting the

example

header, but whether

a

or

b

is sent is likely to vary from run to run: [GLOBAL.remote_store_headers] EXAMPLE = "a" example = "b" We should validate the option only specifies a header with a single casing (i.e. emit an error like `` Found header

example

with multiple names: EXAMPLE, example. Choose one only one casing. ``), and normalise to lower case (this would allow simplifying the change in #21684) ---

```

Should this code also deal with multiple key/value pairs of varying case for a single header?

```

I ask because on the Rust side in headers_to_http_header_map the conversion should non-deterministically merge them or the "last" one in iteration order will overwrite. However, on the Python side, it would probably be good to validate

headers

and ensure that only key/value pair exists per header, so that the user gets a good error message.

Doing that would also allow normalizing

headers

before then checking for

user-agent

.

Thoughts?

Originally posted by @tdyas in #21684 (comment) pantsbuild/pants