go-sfv

Go implementation for RFC 9651 Structured Field Values for HTTP (SFV).

Synopsis

Decoding Structured Field Values

h := make(http.Header)
// Decoding Items
item, err := sfv.DecodeItem(h.Values("Example-Hdr"))
switch val := item.Value.(type) {
case int64:             // Integers
case float64:           // Decimals
case string:            // Strings
case sfv.Token:         // Tokens
case bool:              // Booleans
case time.Time:         // Dates
case sfv.DisplayString: // Display Strings
}

// Decoding Lists
list, err := sfv.DecodeList(h.Values("Example-Hdr"))

// Decoding Dictionaries
dict, err := sfv.DecodeDictionary(h.Values("Example-Hdr"))

Encoding Structured Field Values

// Encoding Items
val, err := sfv.EncodeItem(item)

// Encoding Lists
val, err := sfv.EncodeList(list)

// Encoding Dictionaries
val, err := sfv.EncodeDictionary(dict)

Supported Data Types

SFV types are mapped to Go types as described in this section. Note that only Lists(sfv.List), Dictionaries(sfv.Dictionary), and Items (sfv.Item) can be in a top-level.

Values of Items

The sfv.Value is defined as the following:

type Value any

The actual type might be one of them:

Type of SFV	Example of SFV	Type in Go	Example in Go
Integer	10	int64	int64(10)
Decimal	3.14	float64	float64(3.14)
String	"hello"	string	"hello"
Token	x	sfv.Token	sfv.Token("x")
Byte Seq	:AQID:	[]byte	[]byte{1, 2, 3}
Boolean	?1	bool	true
Date	@1659578233	time.Time	time.Unix(1659578233, 0)
DisplayString	%"f%c3%bc%c3%bc"	sfv.DisplayString	sfv.DisplayString("füü")
Inner List	(1 2)	sfv.InnerList	sfv.InnerList{}

Parameters of Items

Parameters are ordered map of key-value pairs, however Go's map types are unordered. So sfv.Parameters is defined by a slice of sfv.Parameter that is a key-value pair.

type Parameter struct {
	Key   string
	Value Value
}

type Parameters []Parameter

Lists

Lists are decoded to sfv.List.

type List []Item

Inner Lists

Inner Lists are decoded to sfv.InnerList.

type InnerList []Item

Note that sfv.InnerList can't contain sfv.InnerList itself.

// Encoding this will fail.
innerList := sfv.InnerList{
    {
        Value: sfv.InnerList{},
    },
}

Dictionaries

Dictionaries are ordered maps of key-value pairs, however Go's map types are unordered. So sfv.Dictionary is defined by a slice of sfv.DictMember that is a key-value pair.

type DictMember struct {
	Key  string
	Item Item
}

type Dictionary []DictMember

References

• RFC 9651 Structured Field Values for HTTP
• Structured Field Values による Header Field の構造化
• IETF RFC における ABNF と Parsing Algorithm の関係