2.1.2. Dictionary Structured Field Members

2.1.2. Dictionary Structured Field Members

If a given field is known by the application to be a Dictionary Structured Field, an individual member in the value of that Dictionary is identified by using the parameter key and the Dictionary member key as a String value.

If multiple field values occur within a message, these values MUST be combined into a single Dictionary structure before serialization.

An individual member value of a Dictionary Structured Field is canonicalized by applying the serialization algorithm described in Section 4.1.2 of [STRUCTURED-FIELDS] on the member_value and its parameters, not including the Dictionary key itself. Specifically, the value is serialized as an Item or Inner List (the two possible values of a Dictionary member), with all parameters and possible subfields serialized using the strict serialization rules defined in Section 4 of [STRUCTURED-FIELDS] (or the applicable section of its extensions or updates).

Each parameterized key for a given field MUST NOT appear more than once in the signature base. Parameterized keys MAY appear in any order in the signature base, regardless of the order they occur in the source Dictionary.

If a Dictionary key is named as a covered component but it does not occur in the Dictionary, this MUST cause an error in the signature base generation.

The following are non-normative examples of canonicalized values for Dictionary Structured Field members, given the following example header field, whose value is known by the application to be a Dictionary:

Example-Dict: a=1, b=2;x=1;y=2, c=(a b c), d

The following example shows canonicalized values for different component identifiers of this field, presented using the signature base format discussed in Section 2.5:

"example-dict";key="a": 1 "example-dict";key="d": ?1 "example-dict";key="b": 2;x=1;y=2 "example-dict";key="c": (a b c)

Note that the value for key="c" has been reserialized according to the strict member_value algorithm, and the value for key="d" has been serialized as a Boolean value.