client: Extract clientConfig for opt applying

Change functional options for the client so that they operate on an
intermediate struct instead of the public `Client` instance directly.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

client/client.go

@@ -114,35 +114,7 @@ var _ APIClient = &Client{}
 // Client is the API client that performs all operations
 // against a docker server.
 type Client struct {
-	// scheme sets the scheme for the client
-	scheme string
-	// host holds the server address to connect to
-	host string
-	// proto holds the client protocol i.e. unix.
-	proto string
-	// addr holds the client address.
-	addr string
-	// basePath holds the path to prepend to the requests.
-	basePath string
-	// client used to send and receive http requests.
-	client *http.Client
-	// version of the server to talk to.
-	version string
-	// userAgent is the User-Agent header to use for HTTP requests. It takes
-	// precedence over User-Agent headers set in customHTTPHeaders, and other
-	// header variables. When set to an empty string, the User-Agent header
-	// is removed, and no header is sent.
-	userAgent *string
-	// custom HTTP headers configured by users.
-	customHTTPHeaders map[string]string
-	// manualOverride is set to true when the version was set by users.
-	manualOverride bool
-
-	// negotiateVersion indicates if the client should automatically negotiate
-	// the API version to use when making requests. API version negotiation is
-	// performed on the first request, after which negotiated is set to "true"
-	// so that subsequent requests do not re-negotiate.
-	negotiateVersion bool
+	clientConfig
 
 	// negotiated indicates that API version negotiation took place
 	negotiated atomic.Bool
@@ -150,8 +122,6 @@ type Client struct {
 	// negotiateLock is used to single-flight the version negotiation process
 	negotiateLock sync.Mutex
 
-	traceOpts []otelhttp.Option
-
 	// When the client transport is an *http.Transport (default) we need to do some extra things (like closing idle connections).
 	// Store the original transport as the http.Client transport will be wrapped with tracing libs.
 	baseTransport *http.Transport
@@ -207,21 +177,23 @@ func NewClientWithOpts(ops ...Opt) (*Client, error) {
 		return nil, err
 	}
 	c := &Client{
-		host:    DefaultDockerHost,
-		version: DefaultAPIVersion,
-		client:  client,
-		proto:   hostURL.Scheme,
-		addr:    hostURL.Host,
-
-		traceOpts: []otelhttp.Option{
-			otelhttp.WithSpanNameFormatter(func(_ string, req *http.Request) string {
-				return req.Method + " " + req.URL.Path
-			}),
+		clientConfig: clientConfig{
+			host:    DefaultDockerHost,
+			version: DefaultAPIVersion,
+			client:  client,
+			proto:   hostURL.Scheme,
+			addr:    hostURL.Host,
+			traceOpts: []otelhttp.Option{
+				otelhttp.WithSpanNameFormatter(func(_ string, req *http.Request) string {
+					return req.Method + " " + req.URL.Path
+				}),
+			},
 		},
 	}
+	cfg := &c.clientConfig
 
 	for _, op := range ops {
-		if err := op(c); err != nil {
+		if err := op(cfg); err != nil {
 			return nil, err
 		}
 	}

client/client_mock_test.go

@@ -29,7 +29,7 @@ func transportEnsureBody(f transportFunc) transportFunc {
 
 // WithMockClient is a test helper that allows you to inject a mock client for testing.
 func WithMockClient(doer func(*http.Request) (*http.Response, error)) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		c.client = &http.Client{
 			Transport: transportEnsureBody(transportFunc(doer)),
 		}

client/options.go

@@ -16,8 +16,43 @@ import (
 	"go.opentelemetry.io/otel/trace"
 )
 
+type clientConfig struct {
+	// scheme sets the scheme for the client
+	scheme string
+	// host holds the server address to connect to
+	host string
+	// proto holds the client protocol i.e. unix.
+	proto string
+	// addr holds the client address.
+	addr string
+	// basePath holds the path to prepend to the requests.
+	basePath string
+	// client used to send and receive http requests.
+	client *http.Client
+	// version of the server to talk to.
+	version string
+	// userAgent is the User-Agent header to use for HTTP requests. It takes
+	// precedence over User-Agent headers set in customHTTPHeaders, and other
+	// header variables. When set to an empty string, the User-Agent header
+	// is removed, and no header is sent.
+	userAgent *string
+	// custom HTTP headers configured by users.
+	customHTTPHeaders map[string]string
+	// manualOverride is set to true when the version was set by users.
+	manualOverride bool
+
+	// negotiateVersion indicates if the client should automatically negotiate
+	// the API version to use when making requests. API version negotiation is
+	// performed on the first request, after which negotiated is set to "true"
+	// so that subsequent requests do not re-negotiate.
+	negotiateVersion bool
+
+	// traceOpts is a list of options to configure the tracing span.
+	traceOpts []otelhttp.Option
+}
+
 // Opt is a configuration option to initialize a [Client].
-type Opt func(*Client) error
+type Opt func(*clientConfig) error
 
 // FromEnv configures the client with values from environment variables. It
 // is the equivalent of using the [WithTLSClientConfigFromEnv], [WithHostFromEnv],
@@ -32,7 +67,7 @@ type Opt func(*Client) error
 //     which to load the TLS certificates ("ca.pem", "cert.pem", "key.pem').
 //   - DOCKER_TLS_VERIFY ([EnvTLSVerify]) to enable or disable TLS verification
 //     (off by default).
-func FromEnv(c *Client) error {
+func FromEnv(c *clientConfig) error {
 	ops := []Opt{
 		WithTLSClientConfigFromEnv(),
 		WithHostFromEnv(),
@@ -50,7 +85,7 @@ func FromEnv(c *Client) error {
 // used to set the Timeout and KeepAlive settings of the client. It returns
 // an error if the client does not have a [http.Transport] configured.
 func WithDialContext(dialContext func(ctx context.Context, network, addr string) (net.Conn, error)) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		if transport, ok := c.client.Transport.(*http.Transport); ok {
 			transport.DialContext = dialContext
 			return nil
@@ -61,7 +96,7 @@ func WithDialContext(dialContext func(ctx context.Context, network, addr string)
 
 // WithHost overrides the client host with the specified one.
 func WithHost(host string) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		hostURL, err := ParseHostURL(host)
 		if err != nil {
 			return err
@@ -86,7 +121,7 @@ func WithHost(host string) Opt {
 // DOCKER_HOST ([EnvOverrideHost]) environment variable. If DOCKER_HOST is not set,
 // or set to an empty value, the host is not modified.
 func WithHostFromEnv() Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		if host := os.Getenv(EnvOverrideHost); host != "" {
 			return WithHost(host)(c)
 		}
@@ -96,7 +131,7 @@ func WithHostFromEnv() Opt {
 
 // WithHTTPClient overrides the client's HTTP client with the specified one.
 func WithHTTPClient(client *http.Client) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		if client != nil {
 			c.client = client
 		}
@@ -106,7 +141,7 @@ func WithHTTPClient(client *http.Client) Opt {
 
 // WithTimeout configures the time limit for requests made by the HTTP client.
 func WithTimeout(timeout time.Duration) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		c.client.Timeout = timeout
 		return nil
 	}
@@ -116,7 +151,7 @@ func WithTimeout(timeout time.Duration) Opt {
 // It overrides any User-Agent set in headers. When set to an empty string,
 // the User-Agent header is removed, and no header is sent.
 func WithUserAgent(ua string) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		c.userAgent = &ua
 		return nil
 	}
@@ -126,7 +161,7 @@ func WithUserAgent(ua string) Opt {
 // It does not allow for built-in headers (such as "User-Agent", if set) to
 // be overridden. Also see [WithUserAgent].
 func WithHTTPHeaders(headers map[string]string) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		c.customHTTPHeaders = headers
 		return nil
 	}
@@ -134,7 +169,7 @@ func WithHTTPHeaders(headers map[string]string) Opt {
 
 // WithScheme overrides the client scheme with the specified one.
 func WithScheme(scheme string) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		c.scheme = scheme
 		return nil
 	}
@@ -142,7 +177,7 @@ func WithScheme(scheme string) Opt {
 
 // WithTLSClientConfig applies a TLS config to the client transport.
 func WithTLSClientConfig(cacertPath, certPath, keyPath string) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		transport, ok := c.client.Transport.(*http.Transport)
 		if !ok {
 			return fmt.Errorf("cannot apply tls config to transport: %T", c.client.Transport)
@@ -173,7 +208,7 @@ func WithTLSClientConfig(cacertPath, certPath, keyPath string) Opt {
 //   - DOCKER_TLS_VERIFY ([EnvTLSVerify]) to enable or disable TLS verification
 //     (off by default).
 func WithTLSClientConfigFromEnv() Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		dockerCertPath := os.Getenv(EnvOverrideCertPath)
 		if dockerCertPath == "" {
 			return nil
@@ -204,7 +239,7 @@ func WithTLSClientConfigFromEnv() Opt {
 // and callers should verify if the version is in the correct format and
 // lower than the maximum supported version as defined by [DefaultAPIVersion].
 func WithVersion(version string) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		if v := strings.TrimPrefix(version, "v"); v != "" {
 			c.version = v
 			c.manualOverride = true
@@ -222,7 +257,7 @@ func WithVersion(version string) Opt {
 // and callers should verify if the version is in the correct format and
 // lower than the maximum supported version as defined by [DefaultAPIVersion].
 func WithVersionFromEnv() Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		return WithVersion(os.Getenv(EnvOverrideAPIVersion))(c)
 	}
 }
@@ -232,7 +267,7 @@ func WithVersionFromEnv() Opt {
 // to use when making requests. API version negotiation is performed on the first
 // request; subsequent requests do not re-negotiate.
 func WithAPIVersionNegotiation() Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		c.negotiateVersion = true
 		return nil
 	}
@@ -246,7 +281,7 @@ func WithTraceProvider(provider trace.TracerProvider) Opt {
 
 // WithTraceOptions sets tracing span options for the client.
 func WithTraceOptions(opts ...otelhttp.Option) Opt {
-	return func(c *Client) error {
+	return func(c *clientConfig) error {
 		c.traceOpts = append(c.traceOpts, opts...)
 		return nil
 	}