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soypat
39 lines
1.9 KiB
Go
39 lines
1.9 KiB
Go
package ipv4
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const (
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sizeHeader = 20
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)
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// ToS represents the Traffic Class (a.k.a Type of Service). It is 8 bits long. 6 MSB are Differentiated Services; 2 LSB are Explicit Congenstion Notification.
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type ToS uint8
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// DS returns the top 6 bits of the IPv4 ToS holding the Differentiated Services field
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// which is used to classify packets.
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func (tos ToS) DS() uint8 { return uint8(tos) >> 2 }
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// ECN is the Explicit Congestion Notification which provides congestion control and non-congestion control traffic.
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func (tos ToS) ECN() uint8 { return uint8(tos & 0b11) }
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// Flags holds fragmentation field data of an IPv4 header. It is 16 bits long.
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type Flags uint16
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// IsEvil returns true if evil bit set as per [RFC3514].
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//
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// [RFC3514]: https://datatracker.ietf.org/doc/html/rfc3514
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func (f Flags) IsEvil() bool { return f&2000 != 0 }
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// DontFragment specifies whether the datagram can not be fragmented.
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// This can be used when sending packets to a host that does not have resources to perform reassembly of fragments.
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// If the DontFragment(DF) flag is set, and fragmentation is required to route the packet, then the packet is dropped.
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func (f Flags) DontFragment() bool { return f&0x4000 != 0 }
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// MoreFragments is cleared for unfragmented packets.
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// For fragmented packets, all fragments except the last have the MF flag set.
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// The last fragment has a non-zero Fragment Offset field, so it can still be differentiated from an unfragmented packet.
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func (f Flags) MoreFragments() bool { return f&0x8000 != 0 }
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// FragmentOffset specifies the offset of a particular fragment relative to the beginning of the original unfragmented IP datagram.
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// Fragments are specified in units of 8 bytes, which is why fragment lengths are always a multiple of 8; except the last, which may be smaller.
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// The fragmentation offset value for the first fragment is always 0.
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func (f Flags) FragmentOffset() uint16 { return uint16(f) & 0x1fff }
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