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package netlink
import (
"encoding/binary"
"errors"
"fmt"
"math"
"github.com/josharian/native"
"github.com/mdlayher/netlink/nlenc"
)
// errInvalidAttribute specifies if an Attribute's length is incorrect.
var errInvalidAttribute = errors.New("invalid attribute; length too short or too large")
// An Attribute is a netlink attribute. Attributes are packed and unpacked
// to and from the Data field of Message for some netlink families.
type Attribute struct {
// Length of an Attribute, including this field and Type.
Length uint16
// The type of this Attribute, typically matched to a constant. Note that
// flags such as Nested and NetByteOrder must be handled manually when
// working with Attribute structures directly.
Type uint16
// An arbitrary payload which is specified by Type.
Data []byte
}
// marshal marshals the contents of a into b and returns the number of bytes
// written to b, including attribute alignment padding.
func (a *Attribute) marshal(b []byte) (int, error) {
if int(a.Length) < nlaHeaderLen {
return 0, errInvalidAttribute
}
nlenc.PutUint16(b[0:2], a.Length)
nlenc.PutUint16(b[2:4], a.Type)
n := copy(b[nlaHeaderLen:], a.Data)
return nlaHeaderLen + nlaAlign(n), nil
}
// unmarshal unmarshals the contents of a byte slice into an Attribute.
func (a *Attribute) unmarshal(b []byte) error {
if len(b) < nlaHeaderLen {
return errInvalidAttribute
}
a.Length = nlenc.Uint16(b[0:2])
a.Type = nlenc.Uint16(b[2:4])
if int(a.Length) > len(b) {
return errInvalidAttribute
}
switch {
// No length, no data
case a.Length == 0:
a.Data = make([]byte, 0)
// Not enough length for any data
case int(a.Length) < nlaHeaderLen:
return errInvalidAttribute
// Data present
case int(a.Length) >= nlaHeaderLen:
a.Data = make([]byte, len(b[nlaHeaderLen:a.Length]))
copy(a.Data, b[nlaHeaderLen:a.Length])
}
return nil
}
// MarshalAttributes packs a slice of Attributes into a single byte slice.
// In most cases, the Length field of each Attribute should be set to 0, so it
// can be calculated and populated automatically for each Attribute.
//
// It is recommend to use the AttributeEncoder type where possible instead of
// calling MarshalAttributes and using package nlenc functions directly.
func MarshalAttributes(attrs []Attribute) ([]byte, error) {
// Count how many bytes we should allocate to store each attribute's contents.
var c int
for _, a := range attrs {
c += nlaHeaderLen + nlaAlign(len(a.Data))
}
// Advance through b with idx to place attribute data at the correct offset.
var idx int
b := make([]byte, c)
for _, a := range attrs {
// Infer the length of attribute if zero.
if a.Length == 0 {
a.Length = uint16(nlaHeaderLen + len(a.Data))
}
// Marshal a into b and advance idx to show many bytes are occupied.
n, err := a.marshal(b[idx:])
if err != nil {
return nil, err
}
idx += n
}
return b, nil
}
// UnmarshalAttributes unpacks a slice of Attributes from a single byte slice.
//
// It is recommend to use the AttributeDecoder type where possible instead of calling
// UnmarshalAttributes and using package nlenc functions directly.
func UnmarshalAttributes(b []byte) ([]Attribute, error) {
ad, err := NewAttributeDecoder(b)
if err != nil {
return nil, err
}
// Return a nil slice when there are no attributes to decode.
if ad.Len() == 0 {
return nil, nil
}
attrs := make([]Attribute, 0, ad.Len())
for ad.Next() {
if ad.a.Length != 0 {
attrs = append(attrs, ad.a)
}
}
if err := ad.Err(); err != nil {
return nil, err
}
return attrs, nil
}
// An AttributeDecoder provides a safe, iterator-like, API around attribute
// decoding.
//
// It is recommend to use an AttributeDecoder where possible instead of calling
// UnmarshalAttributes and using package nlenc functions directly.
//
// The Err method must be called after the Next method returns false to determine
// if any errors occurred during iteration.
type AttributeDecoder struct {
// ByteOrder defines a specific byte order to use when processing integer
// attributes. ByteOrder should be set immediately after creating the
// AttributeDecoder: before any attributes are parsed.
//
// If not set, the native byte order will be used.
ByteOrder binary.ByteOrder
// The current attribute being worked on.
a Attribute
// The slice of input bytes and its iterator index.
b []byte
i int
length int
// Any error encountered while decoding attributes.
err error
}
// NewAttributeDecoder creates an AttributeDecoder that unpacks Attributes
// from b and prepares the decoder for iteration.
func NewAttributeDecoder(b []byte) (*AttributeDecoder, error) {
ad := &AttributeDecoder{
// By default, use native byte order.
ByteOrder: native.Endian,
b: b,
}
var err error
ad.length, err = ad.available()
if err != nil {
return nil, err
}
return ad, nil
}
// Next advances the decoder to the next netlink attribute. It returns false
// when no more attributes are present, or an error was encountered.
func (ad *AttributeDecoder) Next() bool {
if ad.err != nil {
// Hit an error, stop iteration.
return false
}
// Exit if array pointer is at or beyond the end of the slice.
if ad.i >= len(ad.b) {
return false
}
if err := ad.a.unmarshal(ad.b[ad.i:]); err != nil {
ad.err = err
return false
}
// Advance the pointer by at least one header's length.
if int(ad.a.Length) < nlaHeaderLen {
ad.i += nlaHeaderLen
} else {
ad.i += nlaAlign(int(ad.a.Length))
}
return true
}
// Type returns the Attribute.Type field of the current netlink attribute
// pointed to by the decoder.
//
// Type masks off the high bits of the netlink attribute type which may contain
// the Nested and NetByteOrder flags. These can be obtained by calling TypeFlags.
func (ad *AttributeDecoder) Type() uint16 {
// Mask off any flags stored in the high bits.
return ad.a.Type & attrTypeMask
}
// TypeFlags returns the two high bits of the Attribute.Type field of the current
// netlink attribute pointed to by the decoder.
//
// These bits of the netlink attribute type are used for the Nested and NetByteOrder
// flags, available as the Nested and NetByteOrder constants in this package.
func (ad *AttributeDecoder) TypeFlags() uint16 {
return ad.a.Type & ^attrTypeMask
}
// Len returns the number of netlink attributes pointed to by the decoder.
func (ad *AttributeDecoder) Len() int { return ad.length }
// count scans the input slice to count the number of netlink attributes
// that could be decoded by Next().
func (ad *AttributeDecoder) available() (int, error) {
var count int
for i := 0; i < len(ad.b); {
// Make sure there's at least a header's worth
// of data to read on each iteration.
if len(ad.b[i:]) < nlaHeaderLen {
return 0, errInvalidAttribute
}
// Extract the length of the attribute.
l := int(nlenc.Uint16(ad.b[i : i+2]))
// Ignore zero-length attributes.
if l != 0 {
count++
}
// Advance by at least a header's worth of bytes.
if l < nlaHeaderLen {
l = nlaHeaderLen
}
i += nlaAlign(l)
}
return count, nil
}
// data returns the Data field of the current Attribute pointed to by the decoder.
func (ad *AttributeDecoder) data() []byte { return ad.a.Data }
// Err returns the first error encountered by the decoder.
func (ad *AttributeDecoder) Err() error { return ad.err }
// Bytes returns the raw bytes of the current Attribute's data.
func (ad *AttributeDecoder) Bytes() []byte {
src := ad.data()
dest := make([]byte, len(src))
copy(dest, src)
return dest
}
// String returns the string representation of the current Attribute's data.
func (ad *AttributeDecoder) String() string {
if ad.err != nil {
return ""
}
return nlenc.String(ad.data())
}
// Uint8 returns the uint8 representation of the current Attribute's data.
func (ad *AttributeDecoder) Uint8() uint8 {
if ad.err != nil {
return 0
}
b := ad.data()
if len(b) != 1 {
ad.err = fmt.Errorf("netlink: attribute %d is not a uint8; length: %d", ad.Type(), len(b))
return 0
}
return uint8(b[0])
}
// Uint16 returns the uint16 representation of the current Attribute's data.
func (ad *AttributeDecoder) Uint16() uint16 {
if ad.err != nil {
return 0
}
b := ad.data()
if len(b) != 2 {
ad.err = fmt.Errorf("netlink: attribute %d is not a uint16; length: %d", ad.Type(), len(b))
return 0
}
return ad.ByteOrder.Uint16(b)
}
// Uint32 returns the uint32 representation of the current Attribute's data.
func (ad *AttributeDecoder) Uint32() uint32 {
if ad.err != nil {
return 0
}
b := ad.data()
if len(b) != 4 {
ad.err = fmt.Errorf("netlink: attribute %d is not a uint32; length: %d", ad.Type(), len(b))
return 0
}
return ad.ByteOrder.Uint32(b)
}
// Uint64 returns the uint64 representation of the current Attribute's data.
func (ad *AttributeDecoder) Uint64() uint64 {
if ad.err != nil {
return 0
}
b := ad.data()
if len(b) != 8 {
ad.err = fmt.Errorf("netlink: attribute %d is not a uint64; length: %d", ad.Type(), len(b))
return 0
}
return ad.ByteOrder.Uint64(b)
}
// Int8 returns the Int8 representation of the current Attribute's data.
func (ad *AttributeDecoder) Int8() int8 {
if ad.err != nil {
return 0
}
b := ad.data()
if len(b) != 1 {
ad.err = fmt.Errorf("netlink: attribute %d is not a int8; length: %d", ad.Type(), len(b))
return 0
}
return int8(b[0])
}
// Int16 returns the Int16 representation of the current Attribute's data.
func (ad *AttributeDecoder) Int16() int16 {
if ad.err != nil {
return 0
}
b := ad.data()
if len(b) != 2 {
ad.err = fmt.Errorf("netlink: attribute %d is not a int16; length: %d", ad.Type(), len(b))
return 0
}
return int16(ad.ByteOrder.Uint16(b))
}
// Int32 returns the Int32 representation of the current Attribute's data.
func (ad *AttributeDecoder) Int32() int32 {
if ad.err != nil {
return 0
}
b := ad.data()
if len(b) != 4 {
ad.err = fmt.Errorf("netlink: attribute %d is not a int32; length: %d", ad.Type(), len(b))
return 0
}
return int32(ad.ByteOrder.Uint32(b))
}
// Int64 returns the Int64 representation of the current Attribute's data.
func (ad *AttributeDecoder) Int64() int64 {
if ad.err != nil {
return 0
}
b := ad.data()
if len(b) != 8 {
ad.err = fmt.Errorf("netlink: attribute %d is not a int64; length: %d", ad.Type(), len(b))
return 0
}
return int64(ad.ByteOrder.Uint64(b))
}
// Flag returns a boolean representing the Attribute.
func (ad *AttributeDecoder) Flag() bool {
if ad.err != nil {
return false
}
b := ad.data()
if len(b) != 0 {
ad.err = fmt.Errorf("netlink: attribute %d is not a flag; length: %d", ad.Type(), len(b))
return false
}
return true
}
// Do is a general purpose function which allows access to the current data
// pointed to by the AttributeDecoder.
//
// Do can be used to allow parsing arbitrary data within the context of the
// decoder. Do is most useful when dealing with nested attributes, attribute
// arrays, or decoding arbitrary types (such as C structures) which don't fit
// cleanly into a typical unsigned integer value.
//
// The function fn should not retain any reference to the data b outside of the
// scope of the function.
func (ad *AttributeDecoder) Do(fn func(b []byte) error) {
if ad.err != nil {
return
}
b := ad.data()
if err := fn(b); err != nil {
ad.err = err
}
}
// Nested decodes data into a nested AttributeDecoder to handle nested netlink
// attributes. When calling Nested, the Err method does not need to be called on
// the nested AttributeDecoder.
//
// The nested AttributeDecoder nad inherits the same ByteOrder setting as the
// top-level AttributeDecoder ad.
func (ad *AttributeDecoder) Nested(fn func(nad *AttributeDecoder) error) {
// Because we are wrapping Do, there is no need to check ad.err immediately.
ad.Do(func(b []byte) error {
nad, err := NewAttributeDecoder(b)
if err != nil {
return err
}
nad.ByteOrder = ad.ByteOrder
if err := fn(nad); err != nil {
return err
}
return nad.Err()
})
}
// An AttributeEncoder provides a safe way to encode attributes.
//
// It is recommended to use an AttributeEncoder where possible instead of
// calling MarshalAttributes or using package nlenc directly.
//
// Errors from intermediate encoding steps are returned in the call to
// Encode.
type AttributeEncoder struct {
// ByteOrder defines a specific byte order to use when processing integer
// attributes. ByteOrder should be set immediately after creating the
// AttributeEncoder: before any attributes are encoded.
//
// If not set, the native byte order will be used.
ByteOrder binary.ByteOrder
attrs []Attribute
err error
}
// NewAttributeEncoder creates an AttributeEncoder that encodes Attributes.
func NewAttributeEncoder() *AttributeEncoder {
return &AttributeEncoder{ByteOrder: native.Endian}
}
// Uint8 encodes uint8 data into an Attribute specified by typ.
func (ae *AttributeEncoder) Uint8(typ uint16, v uint8) {
if ae.err != nil {
return
}
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: []byte{v},
})
}
// Uint16 encodes uint16 data into an Attribute specified by typ.
func (ae *AttributeEncoder) Uint16(typ uint16, v uint16) {
if ae.err != nil {
return
}
b := make([]byte, 2)
ae.ByteOrder.PutUint16(b, v)
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: b,
})
}
// Uint32 encodes uint32 data into an Attribute specified by typ.
func (ae *AttributeEncoder) Uint32(typ uint16, v uint32) {
if ae.err != nil {
return
}
b := make([]byte, 4)
ae.ByteOrder.PutUint32(b, v)
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: b,
})
}
// Uint64 encodes uint64 data into an Attribute specified by typ.
func (ae *AttributeEncoder) Uint64(typ uint16, v uint64) {
if ae.err != nil {
return
}
b := make([]byte, 8)
ae.ByteOrder.PutUint64(b, v)
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: b,
})
}
// Int8 encodes int8 data into an Attribute specified by typ.
func (ae *AttributeEncoder) Int8(typ uint16, v int8) {
if ae.err != nil {
return
}
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: []byte{uint8(v)},
})
}
// Int16 encodes int16 data into an Attribute specified by typ.
func (ae *AttributeEncoder) Int16(typ uint16, v int16) {
if ae.err != nil {
return
}
b := make([]byte, 2)
ae.ByteOrder.PutUint16(b, uint16(v))
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: b,
})
}
// Int32 encodes int32 data into an Attribute specified by typ.
func (ae *AttributeEncoder) Int32(typ uint16, v int32) {
if ae.err != nil {
return
}
b := make([]byte, 4)
ae.ByteOrder.PutUint32(b, uint32(v))
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: b,
})
}
// Int64 encodes int64 data into an Attribute specified by typ.
func (ae *AttributeEncoder) Int64(typ uint16, v int64) {
if ae.err != nil {
return
}
b := make([]byte, 8)
ae.ByteOrder.PutUint64(b, uint64(v))
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: b,
})
}
// Flag encodes a flag into an Attribute specified by typ.
func (ae *AttributeEncoder) Flag(typ uint16, v bool) {
// Only set flag on no previous error or v == true.
if ae.err != nil || !v {
return
}
// Flags have no length or data fields.
ae.attrs = append(ae.attrs, Attribute{Type: typ})
}
// String encodes string s as a null-terminated string into an Attribute
// specified by typ.
func (ae *AttributeEncoder) String(typ uint16, s string) {
if ae.err != nil {
return
}
// Length checking, thanks ubiquitousbyte on GitHub.
if len(s) > math.MaxUint16-nlaHeaderLen {
ae.err = errors.New("string is too large to fit in a netlink attribute")
return
}
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: nlenc.Bytes(s),
})
}
// Bytes embeds raw byte data into an Attribute specified by typ.
func (ae *AttributeEncoder) Bytes(typ uint16, b []byte) {
if ae.err != nil {
return
}
if len(b) > math.MaxUint16-nlaHeaderLen {
ae.err = errors.New("byte slice is too large to fit in a netlink attribute")
return
}
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: b,
})
}
// Do is a general purpose function to encode arbitrary data into an attribute
// specified by typ.
//
// Do is especially helpful in encoding nested attributes, attribute arrays,
// or encoding arbitrary types (such as C structures) which don't fit cleanly
// into an unsigned integer value.
func (ae *AttributeEncoder) Do(typ uint16, fn func() ([]byte, error)) {
if ae.err != nil {
return
}
b, err := fn()
if err != nil {
ae.err = err
return
}
if len(b) > math.MaxUint16-nlaHeaderLen {
ae.err = errors.New("byte slice produced by Do is too large to fit in a netlink attribute")
return
}
ae.attrs = append(ae.attrs, Attribute{
Type: typ,
Data: b,
})
}
// Nested embeds data produced by a nested AttributeEncoder and flags that data
// with the Nested flag. When calling Nested, the Encode method should not be
// called on the nested AttributeEncoder.
//
// The nested AttributeEncoder nae inherits the same ByteOrder setting as the
// top-level AttributeEncoder ae.
func (ae *AttributeEncoder) Nested(typ uint16, fn func(nae *AttributeEncoder) error) {
// Because we are wrapping Do, there is no need to check ae.err immediately.
ae.Do(Nested|typ, func() ([]byte, error) {
nae := NewAttributeEncoder()
nae.ByteOrder = ae.ByteOrder
if err := fn(nae); err != nil {
return nil, err
}
return nae.Encode()
})
}
// Encode returns the encoded bytes representing the attributes.
func (ae *AttributeEncoder) Encode() ([]byte, error) {
if ae.err != nil {
return nil, ae.err
}
return MarshalAttributes(ae.attrs)
}
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