sandbox: support vsock connection to task api

Signed-off-by: Abel Feng <fshb1988@gmail.com>

vendor/github.com/mdlayher/vsock/conn_linux.go

@@ -0,0 +1,62 @@
+//go:build linux
+// +build linux
+
+package vsock
+
+import (
+	"context"
+
+	"github.com/mdlayher/socket"
+	"golang.org/x/sys/unix"
+)
+
+// A conn is the net.Conn implementation for connection-oriented VM sockets.
+// We can use socket.Conn directly on Linux to implement all of the necessary
+// methods.
+type conn = socket.Conn
+
+// dial is the entry point for Dial on Linux.
+func dial(cid, port uint32, _ *Config) (*Conn, error) {
+	// TODO(mdlayher): Config default nil check and initialize. Pass options to
+	// socket.Config where necessary.
+
+	c, err := socket.Socket(unix.AF_VSOCK, unix.SOCK_STREAM, 0, "vsock", nil)
+	if err != nil {
+		return nil, err
+	}
+
+	sa := &unix.SockaddrVM{CID: cid, Port: port}
+	rsa, err := c.Connect(context.Background(), sa)
+	if err != nil {
+		_ = c.Close()
+		return nil, err
+	}
+
+	// TODO(mdlayher): getpeername(2) appears to return nil in the GitHub CI
+	// environment, so in the event of a nil sockaddr, fall back to the previous
+	// method of synthesizing the remote address.
+	if rsa == nil {
+		rsa = sa
+	}
+
+	lsa, err := c.Getsockname()
+	if err != nil {
+		_ = c.Close()
+		return nil, err
+	}
+
+	lsavm := lsa.(*unix.SockaddrVM)
+	rsavm := rsa.(*unix.SockaddrVM)
+
+	return &Conn{
+		c: c,
+		local: &Addr{
+			ContextID: lsavm.CID,
+			Port:      lsavm.Port,
+		},
+		remote: &Addr{
+			ContextID: rsavm.CID,
+			Port:      rsavm.Port,
+		},
+	}, nil
+}