Add MVP

Dockerfile

+FROM golang:1.21.4-alpine3.18 AS builder
+RUN apk update && apk add --no-cache git
+WORKDIR $GOPATH/src/sshway
+COPY . .
+RUN go get -d -v
+RUN go build -ldflags="-w -s" -o /go/bin/sshway
+
+FROM alpine:3.18
+COPY --from=builder /go/bin/sshway /bin/sshway
+CMD ["/bin/sshway"]
\ No newline at end of file

go.mod

+module gitlab.sauerburger.com/frank/sshway
+
+go 1.20
+
+require golang.org/x/crypto v0.15.0
+
+require golang.org/x/sys v0.14.0 // indirect

go.sum

+golang.org/x/crypto v0.15.0 h1:frVn1TEaCEaZcn3Tmd7Y2b5KKPaZ+I32Q2OA3kYp5TA=
+golang.org/x/crypto v0.15.0/go.mod h1:4ChreQoLWfG3xLDer1WdlH5NdlQ3+mwnQq1YTKY+72g=
+golang.org/x/sys v0.14.0 h1:Vz7Qs629MkJkGyHxUlRHizWJRG2j8fbQKjELVSNhy7Q=
+golang.org/x/sys v0.14.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=

main.go

+package main
+
+import (
+	"fmt"
+	"golang.org/x/crypto/ssh"
+	"io"
+	"log"
+	"net"
+	"os"
+)
+
+var user string
+var knownHostKey ssh.PublicKey
+var localAddr string
+var remoteAddr string
+var sshHost string
+var signer ssh.Signer
+
+func main() {
+	var keyBuffer []byte
+	keyBuffer = []byte(os.Getenv("SSHWAY_PRIVATE_KEY"))
+	if len(keyBuffer) == 0 {
+		log.Fatalf("SSHWAY_PRIVATE_KEY is empty")
+	}
+
+	// Create the Signer for this private key.
+	var err error
+	signer, err = ssh.ParsePrivateKey(keyBuffer)
+	if err != nil {
+		log.Fatalf("Unable to parse private key: %v", err)
+	}
+
+	user = os.Getenv("SSHWAY_USER")
+	if len(user) == 0 {
+		log.Fatalf("SSHWAY_USER is empty")
+	}
+
+	knownHostBuffer := []byte(os.Getenv("SSHWAY_KNOWN_HOST"))
+	if len(knownHostBuffer) == 0 {
+		log.Fatalf("SSHWAY_KNOWN_HOST is empty")
+	}
+
+	knownHostKey, _, _, _, err = ssh.ParseAuthorizedKey(knownHostBuffer)
+	if err != nil {
+		log.Fatalf("Unable to parse known host key %v: %v", knownHostBuffer, err)
+	}
+
+	localAddr = os.Getenv("SSHWAY_LOCAL")
+	if len(localAddr) == 0 {
+		log.Fatalf("SSHWAY_LOCAL is empty")
+	}
+
+	remoteAddr = os.Getenv("SSHWAY_REMOTE")
+	if len(remoteAddr) == 0 {
+		log.Fatalf("SSHWAY_REMOTE is empty")
+	}
+
+	sshHost = os.Getenv("SSHWAY_SSH_HOST")
+	if len(sshHost) == 0 {
+		log.Fatalf("SSHWAY_SSH_HOST is empty")
+	}
+
+	server, err := net.Listen("tcp", localAddr)
+	if err != nil {
+		log.Fatal("Error listening:", err.Error())
+	}
+	fmt.Printf("Listening on %s\n", localAddr)
+	defer server.Close()
+
+	for {
+		connection, err := server.Accept()
+		if err != nil {
+			log.Fatalf("Error accepting local client: %v\n", err)
+		}
+		fmt.Printf("client connected %s\n", connection.RemoteAddr().String())
+		go handleClient(connection)
+	}
+}
+
+func handleClient(localSock net.Conn) {
+	defer localSock.Close()
+
+	config := &ssh.ClientConfig{
+		User: user,
+		Auth: []ssh.AuthMethod{
+			// Use the PublicKeys method for remote authentication.
+			ssh.PublicKeys(signer),
+		},
+		HostKeyCallback: ssh.FixedHostKey(knownHostKey),
+		// HostKeyAlgorithms: []string{"ssh-ed25519"},
+	}
+
+	conn, err := ssh.Dial("tcp", sshHost, config)
+	if err != nil {
+		log.Printf("SSH connection failed: %v\n", err)
+		return
+	}
+	defer conn.Close()
+
+	forwardClient, err := conn.Dial("tcp", remoteAddr)
+	if err != nil {
+		log.Printf("Port forward failed: %v\n", err)
+		return
+	}
+
+	go func() {
+		io.Copy(localSock, forwardClient)
+	}()
+
+	io.Copy(forwardClient, localSock)
+	log.Printf("Disconnected: %v\n", localSock)
+}