Support custom SSH config file for SSH connection

cli/connhelper/ssh/ssh.go

@@ -34,23 +34,25 @@ func ParseURL(daemonURL string) (*Spec, error) {
 	if u.RawQuery != "" {
 		return nil, errors.Errorf("extra query after the host: %q", u.RawQuery)
 	}
-	if u.Fragment != "" {
-		return nil, errors.Errorf("extra fragment after the host: %q", u.Fragment)
-	}
+	sp.SSHConfig = u.Fragment
 	return &sp, err
 }
 
 // Spec of SSH URL
 type Spec struct {
-	User string
-	Host string
-	Port string
-	Path string
+	User      string
+	Host      string
+	Port      string
+	Path      string
+	SSHConfig string
 }
 
 // Args returns args except "ssh" itself combined with optional additional command args
 func (sp *Spec) Args(add ...string) []string {
 	var args []string
+	if sp.SSHConfig != "" {
+		args = append(args, "-F", sp.SSHConfig)
+	}
 	if sp.User != "" {
 		args = append(args, "-l", sp.User)
 	}

cli/connhelper/ssh/ssh_test.go

@@ -27,6 +27,13 @@ func TestParseURL(t *testing.T) {
 				"--", "foo",
 			},
 		},
+		{
+			url: "ssh://foo#/path/to/ssh_config",
+			expectedArgs: []string{
+				"-F", "/path/to/ssh_config",
+				"--", "foo",
+			},
+		},
 		{
 			url:           "ssh://me:passw0rd@foo",
 			expectedError: "plain-text password is not supported",
@@ -41,10 +48,6 @@ func TestParseURL(t *testing.T) {
 			url:           "ssh://foo?bar",
 			expectedError: `extra query after the host: "bar"`,
 		},
-		{
-			url:           "ssh://foo#bar",
-			expectedError: `extra fragment after the host: "bar"`,
-		},
 		{
 			url:           "ssh://",
 			expectedError: "no host specified",

docs/reference/commandline/cli.md

@@ -336,6 +336,14 @@ component to the end of the SSH address.
 $ docker -H ssh://user@192.168.64.5/var/run/docker.sock ps
 ```
 
+In addition, you can optionally specify an SSH config file by appending a
+fragment component to the end of the SSH address (that is, behind a hash `#`).
+The given file path is passed to SSH using the `ssh -F` option.
+
+```console
+$ docker -H ssh://user@192.168.64.5#/path/to/ssh_config ps
+```
+
 ### Display help text
 
 To list the help on any command just execute the command, followed by the

docs/reference/dockerd.md

@@ -247,6 +247,7 @@ precedence over `HTTP_PROXY`.
 The Docker client supports connecting to a remote daemon via SSH:
 
 ```console
+$ docker -H ssh://me@example.com:22/var/run/docker.sock#/path/to/ssh_config ps
 $ docker -H ssh://me@example.com:22/var/run/docker.sock ps
 $ docker -H ssh://me@example.com:22 ps
 $ docker -H ssh://me@example.com ps