seqs

seqs is what is commonly referred to as a userspace IP implementation. It handles:

• Ethernet protocol
• IP packet marshalling to sub-protocols:
  • ARP requests and responses
  • UDP packet handling
  • DHCP client requests and DHCP server
  • TCP connections over IP with support for multiple listeners on same port. These implement net.Conn and net.Listener interfaces. See stacks/tcpconn.go
  • HTTP: Algorithm to reuse heap memory between requests and avoid allocations. See httpx package
  • NTP client for resolving time offset to a NTP server

Example of use

// stack works by having access to Ethernet packet sending
// and processing. NIC is our physical link to the internet.
var NIC NetworkInterfaceCard = getNIC()

stack := stacks.NewPortStack(stacks.PortStackConfig{
    MAC:             MAC,
    MaxOpenPortsTCP: 1,
    MaxOpenPortsUDP: 1,
    MTU:             2048,
})
// stack.RecvEth should be called on receiving an ethernet packet. It should NOT block.
NIC.SetRecvEthHandle(stack.RecvEth)

// Static IP setting.
ip := netip.AddrFrom4([4]byte{192, 168, 1, 45}) 
stack.SetAddr(ip)

// Or can request an address via DHCP.
dhcpClient := stacks.NewDHCPClient(stack, dhcp.DefaultClientPort)
err = dhcpClient.BeginRequest(stacks.DHCPRequestConfig{
    RequestedAddr: netip.AddrFrom4([4]byte{192, 168, 1, 69}),
    Xid:           0x12345678,
    Hostname:      "tinygo-pico",
})
if err != nil {
    panic(err)
}

fmt.Println("Start DHCP...")
for !dhcpClient.Done() {
    doNICPoll(NIC)
    time.Sleep(time.Second / 10)
}

offeredIP := dhcpClient.Offer()
fmt.Println("got offer:", offeredIP)
stack.SetAddr(offeredIP)

How to use seqs

go mod download github.com/soypat/seqs@latest

History - Precursors to seqs

Before seqs there was:

• ether-swtch - First known instance of a (barely) working TCP/IP stack in Go working on embedded systems, circa June 2021. Could blink an Arduino UNO's LED via HTTP (!). Famously bad design, code, performance, readability.
• dgrams - Library prepared for Pico W's wifi chip. Already shows similarities with seqs. Circa May 2023.