From b93e89dcbfa36499e435b43647ccec060e2b3214 Mon Sep 17 00:00:00 2001
From: Sebastiaan van Stijn <github@gone.nl>
Date: Fri, 28 Aug 2020 17:55:23 +0200
Subject: [PATCH] socket: try removing if socket-location is a directory on
 Linux

Due to race-conditions between containers starting and the Docker
remote API being up, containers bind-mounting the docker-socket may
cause the socket-path to be created as a directory.

This patch will attempt to remove the directory in such situations.
Removing will fail if the directory is not empty.

MacOS does not allow us to detect that the path is a directory, and we'll
return immediately instead of retrying.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
---
 sockets/unix_socket.go      | 12 +++++++++-
 sockets/unix_socket_test.go | 48 +++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/sockets/unix_socket.go b/sockets/unix_socket.go
index e7591e6e..d8f28ee5 100644
--- a/sockets/unix_socket.go
+++ b/sockets/unix_socket.go
@@ -86,8 +86,18 @@ func WithChmod(mask os.FileMode) SockOption {
 // this should only be for a short duration, it may affect other processes that
 // create files/directories during that period.
 func NewUnixSocketWithOpts(path string, opts ...SockOption) (net.Listener, error) {
+	// Using syscall.Unlink(), not os.Remove() to prevent deleting the socket if it's in use
 	if err := syscall.Unlink(path); err != nil && !os.IsNotExist(err) {
-		return nil, err
+		if err != syscall.EISDIR {
+			// On Linux, attempting to remove a directory returns syscall.EISDIR,
+			// in which case we try to remove the directory. MacOS does not return
+			// this error, so we'll return immediately, see:
+			// https://github.com/golang/go/blob/6b420169d798c7ebe733487b56ea5c3fa4aab5ce/src/os/file_unix.go#L300-L311
+			return nil, err
+		}
+		if err := syscall.Rmdir(path); err != nil {
+			return nil, err
+		}
 	}
 
 	// net.Listen does not allow for permissions to be set. As a result, when
diff --git a/sockets/unix_socket_test.go b/sockets/unix_socket_test.go
index 8957efd3..8d589559 100644
--- a/sockets/unix_socket_test.go
+++ b/sockets/unix_socket_test.go
@@ -4,8 +4,11 @@ package sockets
 
 import (
 	"fmt"
+	"io/ioutil"
 	"net"
 	"os"
+	"path"
+	"runtime"
 	"syscall"
 	"testing"
 )
@@ -75,3 +78,48 @@ func TestUnixSocketWithOpts(t *testing.T) {
 	}
 	runTest(t, path, l, echoStr)
 }
+
+func TestUnixSocketConflictDirectory(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", t.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	t.Run("conflicting directory", func(t *testing.T) {
+		if runtime.GOOS == "darwin" {
+			t.Skip("not supported on macOS")
+		}
+		path := path.Join(tmpDir, "test.sock")
+
+		// Create a conflicting directory at the socket location
+		err = os.MkdirAll(path, 0700)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		l, err := NewUnixSocketWithOpts(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer l.Close()
+		runTest(t, path, l, "hello")
+	})
+
+	t.Run("conflicting file", func(t *testing.T) {
+		// Create a conflicting file at the socket location
+		path := path.Join(tmpDir, "test2.sock")
+		f, err := os.Create(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		f.Close()
+
+		l, err := NewUnixSocketWithOpts(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer l.Close()
+		runTest(t, path, l, "hello")
+	})
+}