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# frozen_string_literal: true
# Released under the MIT License.
# Copyright, 2020-2025, by Samuel Williams.
module Protocol
module HTTP
module Header
# The `etag` header represents the entity tag for a resource.
#
# The `etag` header provides a unique identifier for a specific version of a resource, typically used for cache validation or conditional requests. It can be either a strong or weak validator as defined in RFC 9110.
class ETag < String
# Parses a raw header value.
#
# @parameter value [String] a raw header value.
# @returns [ETag] a new instance.
def self.parse(value)
self.new(value)
end
# Coerces a value into a parsed header object.
#
# @parameter value [String] the value to coerce.
# @returns [ETag] a parsed header object.
def self.coerce(value)
self.new(value.to_s)
end
# Replaces the current value of the `etag` header.
#
# @parameter value [String] a raw header value for the `etag` header.
def << value
replace(value)
end
# Checks whether the `etag` is a weak validator.
#
# Weak validators indicate semantically equivalent content but may not be byte-for-byte identical.
#
# @returns [Boolean] whether the `etag` is weak.
def weak?
self.start_with?("W/")
end
# Whether this header is acceptable in HTTP trailers.
# ETag headers can safely appear in trailers as they provide cache validation metadata.
# @returns [Boolean] `true`, as ETag headers are metadata that can be computed after response generation.
def self.trailer?
true
end
end
end
end
end
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