HttpHeaders.toSingleValueMap() is not case-insensitive

[OrangeDog]

The map returned by HttpHeaders.toSingleValueMap() is not case-insensitive.

This copy also ensures that collection-iterating methods like entrySet() are case-insensitive.

var response = restTemplate.getForEntity(uri, String.class);
assertTrue(response.getHeaders().containsHeader("date");  // passes
assertTrue(response.getHeaders().containsHeader("Date");  // passes
assertTrue(response.getHeaders().toSingleValueMap().keySet().contains("date");  // passes
assertTrue(response.getHeaders().toSingleValueMap().keySet().contains("Date");  // fails

Which case they're been normalised to depends on the request factory.

Tested with Spring Framework 7.0.2 (via Boot 4.0.1).

[bclozel]

Have you seen #36056 ?

Can you try with snapshots and report back please?

[OrangeDog]

I did not see that, but toSingleValueMap() is not returning a LinkedCaseInsensitiveMap in the first place:

System.out.println(restTemplate.getForEntity("/", String.class).getHeaders().toSingleValueMap().getClass())
// class java.util.LinkedHashMap