encoding/ebml

Go-EBML

A marshaler/unmarshaler for EBML.

It's quite simple to use:

func ExampleMarshal() {
	DoDad := new(struct {
		EbmlId      ebml.Id `ebml:"3f0000"`
		DoHickey    uint    `ebml:"4242"`
		ThingaMabob string  `ebml:"4243"`
		HumDinger   int     `ebml:"4244"`
	})

	DoDad.DoHickey = 70000
	DoDad.ThingaMabob = "huzah"
	DoDad.HumDinger = -92387

	b, _ := ebml.Marshal(*DoDad)
	fmt.Printf("0x%x\n", b)

	// Output:
	// 0x3f00009442428301117042438568757a6168424483fe971d
}

func ExampleUnmarshal() {
	data := []byte{
		0x3f, 0x00, 0x00, 0x94,
		0x42, 0x42, 0x83, 0x01, 0x11, 0x70,
		0x42, 0x43, 0x85, 0x68, 0x75, 0x7a, 0x61, 0x68,
		0x42, 0x44, 0x83, 0xfe, 0x97, 0x1d,
	}

	DoDad := new(struct {
		EbmlId      ebml.Id `ebml:"3f0000"`
		DoHickey    uint    `ebml:"4242"`
		ThingaMabob string  `ebml:"4243"`
		HumDinger   int     `ebml:"4244"`
	})

	ebml.Unmarshal(data, DoDad)
	fmt.Printf("%v\n", DoDad)
	// Output:
	// &{0 70000 huzah -92387}
}

Caveats

If an EBML DTD specifies a value as an unsigned integer, you must use a uint type. For example: the uint32 8388608 and int -8388608 may encode to identical 0x800000 24 bit arrays in an EBML stream.

EBML does not have a boolean type, but booleans are commonly defined in DTDs as zero or non-zero usigned integers.

Not Implemented

• Default values.

Every non-container MAY be assigned a default value. If so, its value will be added to the interpretation of the EBML data if no element with another value exists in the data.

As an example, consider this EBML DTD:

Weight := 4101 { WeightValue := 41a1 uint; WeightUnit := 41a2 string [ def:"kilogram" ]; }

If the Weight element only contains the WeightValue element, the WeightUnit element with value "kilogram" will be added when the information is semantically processed. A WeightUnit element with another value would of course override the default.

The default value can also be a symbol referring back to a previously seen symbol. If however no such symbol has been seen, i.e. it has not been encoded into the EBML data and has no default value, the element will not be added as a child on the semantic level.

Weight := 4101 { WeightValue := 41a1 uint; WeightUnit := 41a2 string [ def:WeightUnit ]; }