tailscale/tailcat

like netcat, but over Tailscale's data plane, without Tailscale's control plane

Go★ 9,548+256 that day#7 on trending

Analyzed November 14, 2026 at e00cdde (main) with jscpd v5 in 0.8s.

C55/100

Project health22,136 lines of code (M)

Duplication78

3.1% in go, c-header, javascript, c, bash, nix

Dead coden/a

the languages dead code reads are under 5% of the code

Complexity39

72.4%

The score is jscpd's own --health model: markup, data and text left out, tests kept. The numbers below are the trending scan's.

0.7%duplicated code · 93 of 13,308 lines

9clones in code

43code files of 100 scanned

2.81%duplicated over all files · 65 clones

Most complex files

Dead code 0% unused · 0 findings

No dead code found — everything here is reachable.

The code number leaves out tests, fixtures, docs, examples, data files, styles, translations and vendored code.

Largest clones in the code

19 lines in 2 placesgo131 tokens

tailcat.go:652–670tailcat.go:2011–2029

652sys := &lb.sys
653bus := eventbus.New()
654sys.Set(bus)
655sys.Set(health.NewTracker(bus))
656
657netMon, err := netmon.New(bus, func(format string, args ...any) {
658    logf(format, args...)
659})
660if err != nil {
661    lb.Close() // closes the subsystems started so far

First 10 of 19 lines.

11 lines in 2 placesgo90 tokens

cmd/libtailcat/main.go:148–158cmd/libtailcat/main.go:165–175

148func tc_conn_read(id C.tc_handle, token C.tc_token, ptr unsafe.Pointer, size C.size_t, count *C.size_t, err **C.char) C.int32_t {
149    return guard(err, func() error {
150        if count == nil {
151            return capi.ErrArgument
152        }
153        *count = 0
154        b, err := buffer(ptr, size)
155        if err != nil {
156            return err
157        }

First 10 of 11 lines.

11 lines in 2 placesgo88 tokens

tailcat.go:2338–2348tailcat.go:2366–2376

2338func (c *Client) DialTCP(ctx context.Context, ap netip.AddrPort) (net.Conn, error) {
2339    if err := c.up(ctx); err != nil {
2340        return nil, err
2341    }
2342    if ap.Addr().Is4() {
2343        a := nat64PrefixBytes
2344        a4 := ap.Addr().As4()
2345        copy(a[12:], a4[:])
2346        ap = netip.AddrPortFrom(netip.AddrFrom16(a), ap.Port())
2347    }

First 10 of 11 lines.

6 more

10 lines in 2 placesgo86 tokens
tailcat.go:750–759 tailcat.go:2073–2081
9 lines in 2 placesgo75 tokens
cmd/tailcat/tailcat.go:1979–1987 cmd/tailcat/tailcat.go:2061–2070
12 lines in 2 placesgo69 tokens
tailcat.go:693–704 tailcat.go:2047–2058
9 lines in 2 placesgo67 tokens
cmd/tailcat/tailcat.go:807–815 cmd/tailcat/tailcat.go:1341–1349
6 lines in 2 placesgo64 tokens
tailcat.go:719–724 tailcat.go:736–741
6 lines in 2 placesgo56 tokens
internal/capi/api.go:308–313 internal/capi/api.go:321–326

Largest clones over all files, tests and data included

8 lines in 6 placesgotests53 tokens

listen_test.go:19–26tailcat_test.go:360–367tailcat_test.go:418–425tailcat_test.go:512–519tailcat_test.go:1022–1029and 1 more

19func TestListen(t *testing.T) {
20    t.Parallel()
21
22    dm := integration.RunDERPAndSTUN(t, mkLogger(t, "derpstun"), "127.0.0.1")
23    reg := dm.Regions[1]
24    if reg == nil {
25        t.Fatal("no region 1 in derpmap")
26    }

25 lines in 2 placesgotests196 tokens

tailcat_test.go:711–735tailcat_test.go:857–881

711func TestUDPForward(t *testing.T) {
712    dm := integration.RunDERPAndSTUN(t, mkLogger(t, "derpstun"), "127.0.0.1")
713    reg := dm.Regions[1]
714    if reg == nil {
715        t.Fatal("no region 1 in derpmap")
716    }
717
718    backend, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1)})
719    if err != nil {
720        t.Fatal(err)

First 10 of 25 lines.

26 lines in 2 placesgotests182 tokens

cmd/tailcat/socks_test.go:226–251tailcat_test.go:712–737

226dm := integration.RunDERPAndSTUN(t, testLogger(t, "derpstun"), "127.0.0.1")
227reg := dm.Regions[1]
228if reg == nil {
229    t.Fatal("no region 1 in derpmap")
230}
231
232backend, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1)})
233if err != nil {
234    t.Fatal(err)
235}

First 10 of 26 lines.

25 lines in 2 placesgotests169 tokens
cmd/tailcat/forward_test.go:62–86 cmd/tailcat/forward_test.go:124–148
25 lines in 2 placesgotests156 tokens
web/wasm_test.go:253–277 web/wasm_test.go:485–509

By format, code only

Format	Files	Lines	Clones	Duplicated lines	Duplication
go	40	12,516	9	93	0.74%
c-header	1	407	0	0	0%
javascript	1	344	0	0	0%
bash	1	41	0	0	0%

By format, all files

Format	Files	Lines	Clones	Duplicated lines	Duplication
go	77	21,302	64	678	3.18%
yaml	6	423	1	11	2.6%
markdown	7	1,545	0	0	0%
c-header	1	407	0	0	0%
javascript	1	344	0	0	0%
bash	3	188	0	0	0%
go-module	1	113	0	0	0%
c	2	66	0	0	0%
markup	1	63	0	0	0%
nix	1	38	0	0	0%

Trending appearances

Day	Rank	Stars	Files	Lines	Clones	All files	Code	Health	Commit
Nov 14, 2026	#7	9,548 (+256)	100	24,489	65	2.81%	0.7%	C 55	`e00cdde`

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