Fix TLS from environment variables in client

A recent change accidently caused any TLS configuration in FromEnv to be
ignored. This change alters WithHost to create a new http client only if
one doesn't already exist, and otherwise applies the logic to the
transport on the existing client. This preserves the TLS configuration
that might already be on the client.

Signed-off-by: Drew Erny <[email protected]>

client/client.go

@@ -133,23 +133,15 @@ func FromEnv(c *Client) error {
 			},
 			CheckRedirect: CheckRedirect,
 		}
+		WithHTTPClient(httpClient)(c)
 	}
 
 	host := os.Getenv("DOCKER_HOST")
 	if host != "" {
-		var err error
+		// WithHost will create an API client if it doesn't exist
 		if err := WithHost(host)(c); err != nil {
 			return err
 		}
-		httpClient, err = defaultHTTPClient(host)
-		if err != nil {
-			return err
-		}
-	}
-	if httpClient != nil {
-		if err := WithHTTPClient(httpClient)(c); err != nil {
-			return err
-		}
 	}
 	version := os.Getenv("DOCKER_API_VERSION")
 	if version != "" {
@@ -167,7 +159,8 @@ func WithVersion(version string) func(*Client) error {
 	}
 }
 
-// WithHost overrides the client host with the specified one
+// WithHost overrides the client host with the specified one, creating a new
+// http client if one doesn't exist
 func WithHost(host string) func(*Client) error {
 	return func(c *Client) error {
 		hostURL, err := ParseHostURL(host)
@@ -178,11 +171,17 @@ func WithHost(host string) func(*Client) error {
 		c.proto = hostURL.Scheme
 		c.addr = hostURL.Host
 		c.basePath = hostURL.Path
-		client, err := defaultHTTPClient(host)
-		if err != nil {
-			return err
+		if c.client == nil {
+			client, err := defaultHTTPClient(host)
+			if err != nil {
+				return err
+			}
+			return WithHTTPClient(client)(c)
+		}
+		if transport, ok := c.client.Transport.(*http.Transport); ok {
+			return sockets.ConfigureTransport(transport, c.proto, c.addr)
 		}
-		return WithHTTPClient(client)(c)
+		return fmt.Errorf("cannot apply host to http transport")
 	}
 }