internal/godoc/codec/doc.go - pkgsite - Git at Google

 // Copyright 2020 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 /*
 Package codec implements the general-purpose part of an encoder for Go
 values. It relies on code generation rather than reflection so it is
 significantly faster than reflection-based encoders like gob. It also
 preserves sharing among struct pointers (but not other forms of sharing, like
 other pointer types or sub-slices). These features are sufficient for
 encoding the structures of the go/ast package, which is its sole purpose.

 Encoding Scheme

 Every encoded value begins with a single byte that describes what (if
 anything) follows. There is enough information to skip over the value, since
 the decoder must be able to do that if it encounters a struct field it
 doesn't know.

 Most of the values of that initial byte can be devoted to small unsigned
 integers. For example, the number 17 is represented by the single byte 17.
 Only a few byte values have special meaning.

 The nil code indicates that the value is nil. We don't absolutely need this:
 we could always represent the nil value for a type as something that couldn't
 be mistaken for an encoded value of that type. For instance, we could use 0
 for nil in the case of slices (which always begin with the nValues code), and
 for pointers to numbers like *int, we could use something like "nBytes 0".
 But it is simpler to have a reserved value for nil.

 The nBytes code indicates that an unsigned integer N is encoded next,
 followed by N bytes of data. This is used to represent strings and byte
 slices, as well numbers bigger than can fit into the initial byte. For
 example, the string "hi" is represented as:
   nBytes 2 'h' 'i'

 Unsigned integers that can't fit into the initial byte are encoded as byte
 sequences of length 4 or 8, holding little-endian uint32 or uint64 values. We
 use uint32s where possible to save space. We could have saved more space by
 also considering 16-byte numbers, or using a variable-length encoding like
 varints or gob's representation, but it didn't seem worth the additional
 complexity.

 The nValues code is for sequences of values whose size is known beforehand,
 like a Go slice or array. The slice []string{"hi", "bye"} is encoded as
   nValues 2 nBytes 2 'h' 'i' nBytes 3 'b' 'y' 'e'

 The ref code is used to refer to an earlier encoded value. It is followed by
 a uint denoting the index data of the value to use.

 The start and end codes delimit a value whose length is unknown beforehand.
 It is used for structs.
 */
 package codec
	// Copyright 2020 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	/*
	Package codec implements the general-purpose part of an encoder for Go
	values. It relies on code generation rather than reflection so it is
	significantly faster than reflection-based encoders like gob. It also
	preserves sharing among struct pointers (but not other forms of sharing, like
	other pointer types or sub-slices). These features are sufficient for
	encoding the structures of the go/ast package, which is its sole purpose.

	Encoding Scheme

	Every encoded value begins with a single byte that describes what (if
	anything) follows. There is enough information to skip over the value, since
	the decoder must be able to do that if it encounters a struct field it
	doesn't know.

	Most of the values of that initial byte can be devoted to small unsigned
	integers. For example, the number 17 is represented by the single byte 17.
	Only a few byte values have special meaning.

	The nil code indicates that the value is nil. We don't absolutely need this:
	we could always represent the nil value for a type as something that couldn't
	be mistaken for an encoded value of that type. For instance, we could use 0
	for nil in the case of slices (which always begin with the nValues code), and
	for pointers to numbers like *int, we could use something like "nBytes 0".
	But it is simpler to have a reserved value for nil.

	The nBytes code indicates that an unsigned integer N is encoded next,
	followed by N bytes of data. This is used to represent strings and byte
	slices, as well numbers bigger than can fit into the initial byte. For
	example, the string "hi" is represented as:
	nBytes 2 'h' 'i'

	Unsigned integers that can't fit into the initial byte are encoded as byte
	sequences of length 4 or 8, holding little-endian uint32 or uint64 values. We
	use uint32s where possible to save space. We could have saved more space by
	also considering 16-byte numbers, or using a variable-length encoding like
	varints or gob's representation, but it didn't seem worth the additional
	complexity.

	The nValues code is for sequences of values whose size is known beforehand,
	like a Go slice or array. The slice []string{"hi", "bye"} is encoded as
	nValues 2 nBytes 2 'h' 'i' nBytes 3 'b' 'y' 'e'

	The ref code is used to refer to an earlier encoded value. It is followed by
	a uint denoting the index data of the value to use.

	The start and end codes delimit a value whose length is unknown beforehand.
	It is used for structs.
	*/
	package codec