From 860a487ac82daa419d21ba150bafebfd912c7fde Mon Sep 17 00:00:00 2001
From: Percy Wegmann <percy@tailscale.com>
Date: Tue, 23 Jan 2024 14:30:17 -0600
Subject: [PATCH] POC of gomobile

---
 .gitignore                   |   5 +-
 libtailscale/Makefile        |   4 ++
 libtailscale/go.mod          |   5 ++
 libtailscale/go.sum          |   2 +
 libtailscale/libtailscale.go | 130 +++++++++++++++++++++++++++++++++++
 5 files changed, 145 insertions(+), 1 deletion(-)
 create mode 100644 libtailscale/Makefile
 create mode 100644 libtailscale/go.mod
 create mode 100644 libtailscale/go.sum
 create mode 100644 libtailscale/libtailscale.go

diff --git a/.gitignore b/.gitignore
index fef2cbf..15213a1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,4 +26,7 @@ tailscale.jks
 *.hprof
 
 #IDE
-.vscode
\ No newline at end of file
+.vscode
+
+libtailscale-sources.jar
+libtailscale.aar
\ No newline at end of file
diff --git a/libtailscale/Makefile b/libtailscale/Makefile
new file mode 100644
index 0000000..98e59a3
--- /dev/null
+++ b/libtailscale/Makefile
@@ -0,0 +1,4 @@
+# Replace JAVA_HOME with the right path for your environment
+
+libtailscale.aar: *.go go.mod go.sum
+	JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk-21.jdk/Contents/Home gomobile bind -target android -androidapi 21 libtailscale
\ No newline at end of file
diff --git a/libtailscale/go.mod b/libtailscale/go.mod
new file mode 100644
index 0000000..eb7b71e
--- /dev/null
+++ b/libtailscale/go.mod
@@ -0,0 +1,5 @@
+module libtailscale
+
+go 1.21.5
+
+require golang.org/x/mobile v0.0.0-20240112133503-c713f31d574b // indirect
diff --git a/libtailscale/go.sum b/libtailscale/go.sum
new file mode 100644
index 0000000..6ede63f
--- /dev/null
+++ b/libtailscale/go.sum
@@ -0,0 +1,2 @@
+golang.org/x/mobile v0.0.0-20240112133503-c713f31d574b h1:kfWLZgb8iUBHdE9WydD5V5dHIS/F6HjlBZNyJfn2bs4=
+golang.org/x/mobile v0.0.0-20240112133503-c713f31d574b/go.mod h1:4efzQnuA1nICq6h4kmZRMGzbPiP06lZvgADUu1VpJCE=
diff --git a/libtailscale/libtailscale.go b/libtailscale/libtailscale.go
new file mode 100644
index 0000000..dc6031b
--- /dev/null
+++ b/libtailscale/libtailscale.go
@@ -0,0 +1,130 @@
+package libtailscale
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+
+	"tailscale.com/ipn/ipnlocal"
+	"tailscale.com/ipn/localapi"
+	"tailscale.com/net/dns"
+	"tailscale.com/net/netmon"
+	"tailscale.com/net/tsdial"
+	"tailscale.com/tsd"
+	"tailscale.com/types/logid"
+	"tailscale.com/wgengine"
+	"tailscale.com/wgengine/router"
+)
+
+type Request struct {
+	Method  string
+	Path    string
+	Headers map[string][]string
+	Body    []byte
+}
+
+type Response struct {
+	StatusCode int
+	Headers    map[string][]string
+	bodyWriter *bytes.Buffer
+}
+
+func (resp *Response) Body() []byte {
+	return resp.bodyWriter.Bytes()
+}
+
+type Tailscale interface {
+	ProcessRequest(req *Request) *Response
+}
+
+type tailscale struct {
+	backend  *ipnlocal.LocalBackend
+	localapi *localapi.Handler
+}
+
+func NewTailscale() (Tailscale, error) {
+	logf := log.Printf
+	var sys tsd.System
+	var logID logid.PrivateID
+	logID.UnmarshalText([]byte("dead0000dead0000dead0000dead0000dead0000dead0000dead0000dead0000"))
+	netMon, err := netmon.New(logf)
+	if err != nil {
+		log.Printf("netmon.New: %w", err)
+	}
+	dialer := new(tsdial.Dialer)
+	cb := &router.CallbackRouter{
+		SetBoth:           func(rcfg *router.Config, dcfg *dns.OSConfig) error { return nil },
+		SplitDNS:          false,
+		GetBaseConfigFunc: nil,
+	}
+	engine, err := wgengine.NewUserspaceEngine(logf, wgengine.Config{
+		Tun:          nil,
+		Router:       cb,
+		DNS:          cb,
+		Dialer:       dialer,
+		SetSubsystem: sys.Set,
+		NetMon:       netMon,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("runBackend: NewUserspaceEngine: %v", err)
+	}
+	sys.Set(engine)
+	backend, err := ipnlocal.NewLocalBackend(logf, logID.Public(), &sys, 0)
+	if err != nil {
+		return nil, err
+	}
+	api := localapi.NewHandler(backend, logf, netMon, logID.Public())
+	return &tailscale{
+		backend:  backend,
+		localapi: api,
+	}, nil
+}
+
+func (t *tailscale) ProcessRequest(req *Request) (resp *Response) {
+	defer func() {
+		if p := recover(); p != nil {
+			resp = &Response{
+				StatusCode: http.StatusInternalServerError,
+			}
+			fmt.Fprintf(resp, "%s", p)
+		}
+	}()
+
+	resp = &Response{
+		StatusCode: http.StatusOK,
+		Headers:    make(map[string][]string),
+		bodyWriter: &bytes.Buffer{},
+	}
+	t.localapi.ServeHTTP(resp, req.AsHTTPRequest())
+
+	return
+}
+
+func (req *Request) AsHTTPRequest() *http.Request {
+	result, _ := http.NewRequest(req.Method, fmt.Sprintf("http://server/%v", req.Path), nil)
+	if req.Body != nil {
+		result.Body = io.NopCloser(bytes.NewReader(req.Body))
+	}
+	if req.Headers != nil {
+		for name, values := range req.Headers {
+			for _, value := range values {
+				result.Header.Add(name, value)
+			}
+		}
+	}
+	return result
+}
+
+func (resp *Response) Header() http.Header {
+	return http.Header(resp.Headers)
+}
+
+func (resp *Response) WriteHeader(statusCode int) {
+	resp.StatusCode = statusCode
+}
+
+func (resp *Response) Write(p []byte) (int, error) {
+	return resp.bodyWriter.Write(p)
+}