| // Copyright 2019 The gVisor Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| package header |
| |
| import ( |
| "encoding/binary" |
| "errors" |
| "fmt" |
| "math" |
| "time" |
| |
| "gvisor.dev/gvisor/pkg/tcpip" |
| ) |
| |
| const ( |
| // NDPSourceLinkLayerAddressOptionType is the type of the Source Link Layer |
| // Address option, as per RFC 4861 section 4.6.1. |
| NDPSourceLinkLayerAddressOptionType = 1 |
| |
| // NDPTargetLinkLayerAddressOptionType is the type of the Target Link Layer |
| // Address option, as per RFC 4861 section 4.6.1. |
| NDPTargetLinkLayerAddressOptionType = 2 |
| |
| // NDPLinkLayerAddressSize is the size of a Source or Target Link Layer |
| // Address option for an Ethernet address. |
| NDPLinkLayerAddressSize = 8 |
| |
| // NDPPrefixInformationType is the type of the Prefix Information |
| // option, as per RFC 4861 section 4.6.2. |
| NDPPrefixInformationType = 3 |
| |
| // ndpPrefixInformationLength is the expected length, in bytes, of the |
| // body of an NDP Prefix Information option, as per RFC 4861 section |
| // 4.6.2 which specifies that the Length field is 4. Given this, the |
| // expected length, in bytes, is 30 becuase 4 * lengthByteUnits (8) - 2 |
| // (Type & Length) = 30. |
| ndpPrefixInformationLength = 30 |
| |
| // ndpPrefixInformationPrefixLengthOffset is the offset of the Prefix |
| // Length field within an NDPPrefixInformation. |
| ndpPrefixInformationPrefixLengthOffset = 0 |
| |
| // ndpPrefixInformationFlagsOffset is the offset of the flags byte |
| // within an NDPPrefixInformation. |
| ndpPrefixInformationFlagsOffset = 1 |
| |
| // ndpPrefixInformationOnLinkFlagMask is the mask of the On-Link Flag |
| // field in the flags byte within an NDPPrefixInformation. |
| ndpPrefixInformationOnLinkFlagMask = (1 << 7) |
| |
| // ndpPrefixInformationAutoAddrConfFlagMask is the mask of the |
| // Autonomous Address-Configuration flag field in the flags byte within |
| // an NDPPrefixInformation. |
| ndpPrefixInformationAutoAddrConfFlagMask = (1 << 6) |
| |
| // ndpPrefixInformationReserved1FlagsMask is the mask of the Reserved1 |
| // field in the flags byte within an NDPPrefixInformation. |
| ndpPrefixInformationReserved1FlagsMask = 63 |
| |
| // ndpPrefixInformationValidLifetimeOffset is the start of the 4-byte |
| // Valid Lifetime field within an NDPPrefixInformation. |
| ndpPrefixInformationValidLifetimeOffset = 2 |
| |
| // ndpPrefixInformationPreferredLifetimeOffset is the start of the |
| // 4-byte Preferred Lifetime field within an NDPPrefixInformation. |
| ndpPrefixInformationPreferredLifetimeOffset = 6 |
| |
| // ndpPrefixInformationReserved2Offset is the start of the 4-byte |
| // Reserved2 field within an NDPPrefixInformation. |
| ndpPrefixInformationReserved2Offset = 10 |
| |
| // ndpPrefixInformationReserved2Length is the length of the Reserved2 |
| // field. |
| // |
| // It is 4 bytes. |
| ndpPrefixInformationReserved2Length = 4 |
| |
| // ndpPrefixInformationPrefixOffset is the start of the Prefix field |
| // within an NDPPrefixInformation. |
| ndpPrefixInformationPrefixOffset = 14 |
| |
| // NDPRecursiveDNSServerOptionType is the type of the Recursive DNS |
| // Server option, as per RFC 8106 section 5.1. |
| NDPRecursiveDNSServerOptionType = 25 |
| |
| // ndpRecursiveDNSServerLifetimeOffset is the start of the 4-byte |
| // Lifetime field within an NDPRecursiveDNSServer. |
| ndpRecursiveDNSServerLifetimeOffset = 2 |
| |
| // ndpRecursiveDNSServerAddressesOffset is the start of the addresses |
| // for IPv6 Recursive DNS Servers within an NDPRecursiveDNSServer. |
| ndpRecursiveDNSServerAddressesOffset = 6 |
| |
| // minNDPRecursiveDNSServerLength is the minimum NDP Recursive DNS |
| // Server option's length field value when it contains at least one |
| // IPv6 address. |
| minNDPRecursiveDNSServerLength = 3 |
| |
| // lengthByteUnits is the multiplier factor for the Length field of an |
| // NDP option. That is, the length field for NDP options is in units of |
| // 8 octets, as per RFC 4861 section 4.6. |
| lengthByteUnits = 8 |
| ) |
| |
| var ( |
| // NDPInfiniteLifetime is a value that represents infinity for the |
| // 4-byte lifetime fields found in various NDP options. Its value is |
| // (2^32 - 1)s = 4294967295s. |
| // |
| // This is a variable instead of a constant so that tests can change |
| // this value to a smaller value. It should only be modified by tests. |
| NDPInfiniteLifetime = time.Second * math.MaxUint32 |
| ) |
| |
| // NDPOptionIterator is an iterator of NDPOption. |
| // |
| // Note, between when an NDPOptionIterator is obtained and last used, no changes |
| // to the NDPOptions may happen. Doing so may cause undefined and unexpected |
| // behaviour. It is fine to obtain an NDPOptionIterator, iterate over the first |
| // few NDPOption then modify the backing NDPOptions so long as the |
| // NDPOptionIterator obtained before modification is no longer used. |
| type NDPOptionIterator struct { |
| // The NDPOptions this NDPOptionIterator is iterating over. |
| opts NDPOptions |
| } |
| |
| // Potential errors when iterating over an NDPOptions. |
| var ( |
| ErrNDPOptBufExhausted = errors.New("Buffer unexpectedly exhausted") |
| ErrNDPOptZeroLength = errors.New("NDP option has zero-valued Length field") |
| ErrNDPOptMalformedBody = errors.New("NDP option has a malformed body") |
| ErrNDPInvalidLength = errors.New("NDP option's Length value is invalid as per relevant RFC") |
| ) |
| |
| // Next returns the next element in the backing NDPOptions, or true if we are |
| // done, or false if an error occured. |
| // |
| // The return can be read as option, done, error. Note, option should only be |
| // used if done is false and error is nil. |
| func (i *NDPOptionIterator) Next() (NDPOption, bool, error) { |
| for { |
| // Do we still have elements to look at? |
| if len(i.opts) == 0 { |
| return nil, true, nil |
| } |
| |
| // Do we have enough bytes for an NDP option that has a Length |
| // field of at least 1? Note, 0 in the Length field is invalid. |
| if len(i.opts) < lengthByteUnits { |
| return nil, true, ErrNDPOptBufExhausted |
| } |
| |
| // Get the Type field. |
| t := i.opts[0] |
| |
| // Get the Length field. |
| l := i.opts[1] |
| |
| // This would indicate an erroneous NDP option as the Length |
| // field should never be 0. |
| if l == 0 { |
| return nil, true, ErrNDPOptZeroLength |
| } |
| |
| // How many bytes are in the option body? |
| numBytes := int(l) * lengthByteUnits |
| numBodyBytes := numBytes - 2 |
| |
| potentialBody := i.opts[2:] |
| |
| // This would indicate an erroenous NDPOptions buffer as we ran |
| // out of the buffer in the middle of an NDP option. |
| if left := len(potentialBody); left < numBodyBytes { |
| return nil, true, ErrNDPOptBufExhausted |
| } |
| |
| // Get only the options body, leaving the rest of the options |
| // buffer alone. |
| body := potentialBody[:numBodyBytes] |
| |
| // Update opts with the remaining options body. |
| i.opts = i.opts[numBytes:] |
| |
| switch t { |
| case NDPSourceLinkLayerAddressOptionType: |
| return NDPSourceLinkLayerAddressOption(body), false, nil |
| |
| case NDPTargetLinkLayerAddressOptionType: |
| return NDPTargetLinkLayerAddressOption(body), false, nil |
| |
| case NDPPrefixInformationType: |
| // Make sure the length of a Prefix Information option |
| // body is ndpPrefixInformationLength, as per RFC 4861 |
| // section 4.6.2. |
| if numBodyBytes != ndpPrefixInformationLength { |
| return nil, true, ErrNDPOptMalformedBody |
| } |
| |
| return NDPPrefixInformation(body), false, nil |
| |
| case NDPRecursiveDNSServerOptionType: |
| // RFC 8106 section 5.3.1 outlines that the RDNSS option |
| // must have a minimum length of 3 so it contains at |
| // least one IPv6 address. |
| if l < minNDPRecursiveDNSServerLength { |
| return nil, true, ErrNDPInvalidLength |
| } |
| |
| opt := NDPRecursiveDNSServer(body) |
| if len(opt.Addresses()) == 0 { |
| return nil, true, ErrNDPOptMalformedBody |
| } |
| |
| return opt, false, nil |
| |
| default: |
| // We do not yet recognize the option, just skip for |
| // now. This is okay because RFC 4861 allows us to |
| // skip/ignore any unrecognized options. However, |
| // we MUST recognized all the options in RFC 4861. |
| // |
| // TODO(b/141487990): Handle all NDP options as defined |
| // by RFC 4861. |
| } |
| } |
| } |
| |
| // NDPOptions is a buffer of NDP options as defined by RFC 4861 section 4.6. |
| type NDPOptions []byte |
| |
| // Iter returns an iterator of NDPOption. |
| // |
| // If check is true, Iter will do an integrity check on the options by iterating |
| // over it and returning an error if detected. |
| // |
| // See NDPOptionIterator for more information. |
| func (b NDPOptions) Iter(check bool) (NDPOptionIterator, error) { |
| it := NDPOptionIterator{opts: b} |
| |
| if check { |
| for it2 := it; true; { |
| if _, done, err := it2.Next(); err != nil || done { |
| return it, err |
| } |
| } |
| } |
| |
| return it, nil |
| } |
| |
| // Serialize serializes the provided list of NDP options into o. |
| // |
| // Note, b must be of sufficient size to hold all the options in s. See |
| // NDPOptionsSerializer.Length for details on the getting the total size |
| // of a serialized NDPOptionsSerializer. |
| // |
| // Serialize may panic if b is not of sufficient size to hold all the options |
| // in s. |
| func (b NDPOptions) Serialize(s NDPOptionsSerializer) int { |
| done := 0 |
| |
| for _, o := range s { |
| l := paddedLength(o) |
| |
| if l == 0 { |
| continue |
| } |
| |
| b[0] = o.Type() |
| |
| // We know this safe because paddedLength would have returned |
| // 0 if o had an invalid length (> 255 * lengthByteUnits). |
| b[1] = uint8(l / lengthByteUnits) |
| |
| // Serialize NDP option body. |
| used := o.serializeInto(b[2:]) |
| |
| // Zero out remaining (padding) bytes, if any exists. |
| for i := used + 2; i < l; i++ { |
| b[i] = 0 |
| } |
| |
| b = b[l:] |
| done += l |
| } |
| |
| return done |
| } |
| |
| // NDPOption is the set of functions to be implemented by all NDP option types. |
| type NDPOption interface { |
| fmt.Stringer |
| |
| // Type returns the type of the receiver. |
| Type() uint8 |
| |
| // Length returns the length of the body of the receiver, in bytes. |
| Length() int |
| |
| // serializeInto serializes the receiver into the provided byte |
| // buffer. |
| // |
| // Note, the caller MUST provide a byte buffer with size of at least |
| // Length. Implementers of this function may assume that the byte buffer |
| // is of sufficient size. serializeInto MAY panic if the provided byte |
| // buffer is not of sufficient size. |
| // |
| // serializeInto will return the number of bytes that was used to |
| // serialize the receiver. Implementers must only use the number of |
| // bytes required to serialize the receiver. Callers MAY provide a |
| // larger buffer than required to serialize into. |
| serializeInto([]byte) int |
| } |
| |
| // paddedLength returns the length of o, in bytes, with any padding bytes, if |
| // required. |
| func paddedLength(o NDPOption) int { |
| l := o.Length() |
| |
| if l == 0 { |
| return 0 |
| } |
| |
| // Length excludes the 2 Type and Length bytes. |
| l += 2 |
| |
| // Add extra bytes if needed to make sure the option is |
| // lengthByteUnits-byte aligned. We do this by adding lengthByteUnits-1 |
| // to l and then stripping off the last few LSBits from l. This will |
| // make sure that l is rounded up to the nearest unit of |
| // lengthByteUnits. This works since lengthByteUnits is a power of 2 |
| // (= 8). |
| mask := lengthByteUnits - 1 |
| l += mask |
| l &^= mask |
| |
| if l/lengthByteUnits > 255 { |
| // Should never happen because an option can only have a max |
| // value of 255 for its Length field, so just return 0 so this |
| // option does not get serialized. |
| // |
| // Returning 0 here will make sure that this option does not get |
| // serialized when NDPOptions.Serialize is called with the |
| // NDPOptionsSerializer that holds this option, effectively |
| // skipping this option during serialization. Also note that |
| // a value of zero for the Length field in an NDP option is |
| // invalid so this is another sign to the caller that this NDP |
| // option is malformed, as per RFC 4861 section 4.6. |
| return 0 |
| } |
| |
| return l |
| } |
| |
| // NDPOptionsSerializer is a serializer for NDP options. |
| type NDPOptionsSerializer []NDPOption |
| |
| // Length returns the total number of bytes required to serialize. |
| func (b NDPOptionsSerializer) Length() int { |
| l := 0 |
| |
| for _, o := range b { |
| l += paddedLength(o) |
| } |
| |
| return l |
| } |
| |
| // NDPSourceLinkLayerAddressOption is the NDP Source Link Layer Option |
| // as defined by RFC 4861 section 4.6.1. |
| // |
| // It is the first X bytes following the NDP option's Type and Length field |
| // where X is the value in Length multiplied by lengthByteUnits - 2 bytes. |
| type NDPSourceLinkLayerAddressOption tcpip.LinkAddress |
| |
| // Type implements NDPOption.Type. |
| func (o NDPSourceLinkLayerAddressOption) Type() uint8 { |
| return NDPSourceLinkLayerAddressOptionType |
| } |
| |
| // Length implements NDPOption.Length. |
| func (o NDPSourceLinkLayerAddressOption) Length() int { |
| return len(o) |
| } |
| |
| // serializeInto implements NDPOption.serializeInto. |
| func (o NDPSourceLinkLayerAddressOption) serializeInto(b []byte) int { |
| return copy(b, o) |
| } |
| |
| // String implements fmt.Stringer.String. |
| func (o NDPSourceLinkLayerAddressOption) String() string { |
| return fmt.Sprintf("%T(%s)", o, tcpip.LinkAddress(o)) |
| } |
| |
| // EthernetAddress will return an ethernet (MAC) address if the |
| // NDPSourceLinkLayerAddressOption's body has at minimum EthernetAddressSize |
| // bytes. If the body has more than EthernetAddressSize bytes, only the first |
| // EthernetAddressSize bytes are returned as that is all that is needed for an |
| // Ethernet address. |
| func (o NDPSourceLinkLayerAddressOption) EthernetAddress() tcpip.LinkAddress { |
| if len(o) >= EthernetAddressSize { |
| return tcpip.LinkAddress(o[:EthernetAddressSize]) |
| } |
| |
| return tcpip.LinkAddress([]byte(nil)) |
| } |
| |
| // NDPTargetLinkLayerAddressOption is the NDP Target Link Layer Option |
| // as defined by RFC 4861 section 4.6.1. |
| // |
| // It is the first X bytes following the NDP option's Type and Length field |
| // where X is the value in Length multiplied by lengthByteUnits - 2 bytes. |
| type NDPTargetLinkLayerAddressOption tcpip.LinkAddress |
| |
| // Type implements NDPOption.Type. |
| func (o NDPTargetLinkLayerAddressOption) Type() uint8 { |
| return NDPTargetLinkLayerAddressOptionType |
| } |
| |
| // Length implements NDPOption.Length. |
| func (o NDPTargetLinkLayerAddressOption) Length() int { |
| return len(o) |
| } |
| |
| // serializeInto implements NDPOption.serializeInto. |
| func (o NDPTargetLinkLayerAddressOption) serializeInto(b []byte) int { |
| return copy(b, o) |
| } |
| |
| // String implements fmt.Stringer.String. |
| func (o NDPTargetLinkLayerAddressOption) String() string { |
| return fmt.Sprintf("%T(%s)", o, tcpip.LinkAddress(o)) |
| } |
| |
| // EthernetAddress will return an ethernet (MAC) address if the |
| // NDPTargetLinkLayerAddressOption's body has at minimum EthernetAddressSize |
| // bytes. If the body has more than EthernetAddressSize bytes, only the first |
| // EthernetAddressSize bytes are returned as that is all that is needed for an |
| // Ethernet address. |
| func (o NDPTargetLinkLayerAddressOption) EthernetAddress() tcpip.LinkAddress { |
| if len(o) >= EthernetAddressSize { |
| return tcpip.LinkAddress(o[:EthernetAddressSize]) |
| } |
| |
| return tcpip.LinkAddress([]byte(nil)) |
| } |
| |
| // NDPPrefixInformation is the NDP Prefix Information option as defined by |
| // RFC 4861 section 4.6.2. |
| // |
| // The length, in bytes, of a valid NDP Prefix Information option body MUST be |
| // ndpPrefixInformationLength bytes. |
| type NDPPrefixInformation []byte |
| |
| // Type implements NDPOption.Type. |
| func (o NDPPrefixInformation) Type() uint8 { |
| return NDPPrefixInformationType |
| } |
| |
| // Length implements NDPOption.Length. |
| func (o NDPPrefixInformation) Length() int { |
| return ndpPrefixInformationLength |
| } |
| |
| // serializeInto implements NDPOption.serializeInto. |
| func (o NDPPrefixInformation) serializeInto(b []byte) int { |
| used := copy(b, o) |
| |
| // Zero out the Reserved1 field. |
| b[ndpPrefixInformationFlagsOffset] &^= ndpPrefixInformationReserved1FlagsMask |
| |
| // Zero out the Reserved2 field. |
| reserved2 := b[ndpPrefixInformationReserved2Offset:][:ndpPrefixInformationReserved2Length] |
| for i := range reserved2 { |
| reserved2[i] = 0 |
| } |
| |
| return used |
| } |
| |
| // String implements fmt.Stringer.String. |
| func (o NDPPrefixInformation) String() string { |
| return fmt.Sprintf("%T(O=%t, A=%t, PL=%s, VL=%s, Prefix=%s)", |
| o, |
| o.OnLinkFlag(), |
| o.AutonomousAddressConfigurationFlag(), |
| o.PreferredLifetime(), |
| o.ValidLifetime(), |
| o.Subnet()) |
| } |
| |
| // PrefixLength returns the value in the number of leading bits in the Prefix |
| // that are valid. |
| // |
| // Valid values are in the range [0, 128], but o may not always contain valid |
| // values. It is up to the caller to valdiate the Prefix Information option. |
| func (o NDPPrefixInformation) PrefixLength() uint8 { |
| return o[ndpPrefixInformationPrefixLengthOffset] |
| } |
| |
| // OnLinkFlag returns true of the prefix is considered on-link. On-link means |
| // that a forwarding node is not needed to send packets to other nodes on the |
| // same prefix. |
| // |
| // Note, when this function returns false, no statement is made about the |
| // on-link property of a prefix. That is, if OnLinkFlag returns false, the |
| // caller MUST NOT conclude that the prefix is off-link and MUST NOT update any |
| // previously stored state for this prefix about its on-link status. |
| func (o NDPPrefixInformation) OnLinkFlag() bool { |
| return o[ndpPrefixInformationFlagsOffset]&ndpPrefixInformationOnLinkFlagMask != 0 |
| } |
| |
| // AutonomousAddressConfigurationFlag returns true if the prefix can be used for |
| // Stateless Address Auto-Configuration (as specified in RFC 4862). |
| func (o NDPPrefixInformation) AutonomousAddressConfigurationFlag() bool { |
| return o[ndpPrefixInformationFlagsOffset]&ndpPrefixInformationAutoAddrConfFlagMask != 0 |
| } |
| |
| // ValidLifetime returns the length of time that the prefix is valid for the |
| // purpose of on-link determination. This value is relative to the send time of |
| // the packet that the Prefix Information option was present in. |
| // |
| // Note, a value of 0 implies the prefix should not be considered as on-link, |
| // and a value of infinity/forever is represented by |
| // NDPInfiniteLifetime. |
| func (o NDPPrefixInformation) ValidLifetime() time.Duration { |
| // The field is the time in seconds, as per RFC 4861 section 4.6.2. |
| return time.Second * time.Duration(binary.BigEndian.Uint32(o[ndpPrefixInformationValidLifetimeOffset:])) |
| } |
| |
| // PreferredLifetime returns the length of time that an address generated from |
| // the prefix via Stateless Address Auto-Configuration remains preferred. This |
| // value is relative to the send time of the packet that the Prefix Information |
| // option was present in. |
| // |
| // Note, a value of 0 implies that addresses generated from the prefix should |
| // no longer remain preferred, and a value of infinity is represented by |
| // NDPInfiniteLifetime. |
| // |
| // Also note that the value of this field MUST NOT exceed the Valid Lifetime |
| // field to avoid preferring addresses that are no longer valid, for the |
| // purpose of Stateless Address Auto-Configuration. |
| func (o NDPPrefixInformation) PreferredLifetime() time.Duration { |
| // The field is the time in seconds, as per RFC 4861 section 4.6.2. |
| return time.Second * time.Duration(binary.BigEndian.Uint32(o[ndpPrefixInformationPreferredLifetimeOffset:])) |
| } |
| |
| // Prefix returns an IPv6 address or a prefix of an IPv6 address. The Prefix |
| // Length field (see NDPPrefixInformation.PrefixLength) contains the number |
| // of valid leading bits in the prefix. |
| // |
| // Hosts SHOULD ignore an NDP Prefix Information option where the Prefix field |
| // holds the link-local prefix (fe80::). |
| func (o NDPPrefixInformation) Prefix() tcpip.Address { |
| return tcpip.Address(o[ndpPrefixInformationPrefixOffset:][:IPv6AddressSize]) |
| } |
| |
| // Subnet returns the Prefix field and Prefix Length field represented in a |
| // tcpip.Subnet. |
| func (o NDPPrefixInformation) Subnet() tcpip.Subnet { |
| addrWithPrefix := tcpip.AddressWithPrefix{ |
| Address: o.Prefix(), |
| PrefixLen: int(o.PrefixLength()), |
| } |
| return addrWithPrefix.Subnet() |
| } |
| |
| // NDPRecursiveDNSServer is the NDP Recursive DNS Server option, as defined by |
| // RFC 8106 section 5.1. |
| // |
| // To make sure that the option meets its minimum length and does not end in the |
| // middle of a DNS server's IPv6 address, the length of a valid |
| // NDPRecursiveDNSServer must meet the following constraint: |
| // (Length - ndpRecursiveDNSServerAddressesOffset) % IPv6AddressSize == 0 |
| type NDPRecursiveDNSServer []byte |
| |
| // Type returns the type of an NDP Recursive DNS Server option. |
| // |
| // Type implements NDPOption.Type. |
| func (NDPRecursiveDNSServer) Type() uint8 { |
| return NDPRecursiveDNSServerOptionType |
| } |
| |
| // Length implements NDPOption.Length. |
| func (o NDPRecursiveDNSServer) Length() int { |
| return len(o) |
| } |
| |
| // serializeInto implements NDPOption.serializeInto. |
| func (o NDPRecursiveDNSServer) serializeInto(b []byte) int { |
| used := copy(b, o) |
| |
| // Zero out the reserved bytes that are before the Lifetime field. |
| for i := 0; i < ndpRecursiveDNSServerLifetimeOffset; i++ { |
| b[i] = 0 |
| } |
| |
| return used |
| } |
| |
| // String implements fmt.Stringer.String. |
| func (o NDPRecursiveDNSServer) String() string { |
| return fmt.Sprintf("%T(%s valid for %s)", o, o.Addresses(), o.Lifetime()) |
| } |
| |
| // Lifetime returns the length of time that the DNS server addresses |
| // in this option may be used for name resolution. |
| // |
| // Note, a value of 0 implies the addresses should no longer be used, |
| // and a value of infinity/forever is represented by NDPInfiniteLifetime. |
| // |
| // Lifetime may panic if o does not have enough bytes to hold the Lifetime |
| // field. |
| func (o NDPRecursiveDNSServer) Lifetime() time.Duration { |
| // The field is the time in seconds, as per RFC 8106 section 5.1. |
| return time.Second * time.Duration(binary.BigEndian.Uint32(o[ndpRecursiveDNSServerLifetimeOffset:])) |
| } |
| |
| // Addresses returns the recursive DNS server IPv6 addresses that may be |
| // used for name resolution. |
| // |
| // Note, some of the addresses returned MAY be link-local addresses. |
| // |
| // Addresses may panic if o does not hold valid IPv6 addresses. |
| func (o NDPRecursiveDNSServer) Addresses() []tcpip.Address { |
| l := len(o) |
| if l < ndpRecursiveDNSServerAddressesOffset { |
| return nil |
| } |
| |
| l -= ndpRecursiveDNSServerAddressesOffset |
| if l%IPv6AddressSize != 0 { |
| return nil |
| } |
| |
| buf := o[ndpRecursiveDNSServerAddressesOffset:] |
| var addrs []tcpip.Address |
| for len(buf) > 0 { |
| addr := tcpip.Address(buf[:IPv6AddressSize]) |
| if !IsV6UnicastAddress(addr) { |
| return nil |
| } |
| addrs = append(addrs, addr) |
| buf = buf[IPv6AddressSize:] |
| } |
| return addrs |
| } |