Why required request headers e.g. strings - are not treated as missing if they are blank?

[memoricab]

Hello

When I read the below comments I understand that if a header is blank it is treated as missing regardless of thinking of the Key-Value concept.

For example, when we request a string header, even it is a blank string the controller does not respond as a bad request.

if the header is missing in the request, maybe I am assuming for this condition that a blank string does not mean missing header?
I wish we could somehow mention that regardless of the value it checks only the presence of the key of the header.

spring-framework/spring-web/src/main/java/org/springframework/web/bind/annotation/RequestHeader.java

Lines 63 to 71 in 0cbea29

	* Whether the header is required.
	* <p>Defaults to {@code true}, leading to an exception being thrown
	* if the header is missing in the request. Switch this to
	* {@code false} if you prefer a {@code null} value if the header is
	* not present in the request.
	* <p>Alternatively, provide a {@link #defaultValue}, which implicitly
	* sets this flag to {@code false}.
	*/
	boolean required() default true;

Disclosure:
I am aware of Spring 5.3+, for type conversions it works very well, but in my case is without type conversion. i.e. requesting string header and no type conversion.

[rstoyanchev]

The header is indeed considered present but without a value. In the case where type conversion is required, it can "hide" the original empty value, and hence the change in 5.3 with #23939. We could improve the Javadoc for this.

[rstoyanchev]

As to the question, why empty is not treated as missing, it really depends on your use case and perspective. There have been many discussions on the subject, and changing behavior will only lead to regressions for others.

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