use Options pattern for creating Client instance

README.md

@@ -19,8 +19,8 @@ go get github.com/tantalor93/doh-go
 
 ## Examples
 ```
-// create client with default http.Client
-c := doh.NewClient(nil)
+// create client with default settings
+c := doh.NewClient()
 
 // prepare payload
 msg := dns.Msg{}

doh/client.go

@@ -12,18 +12,21 @@ import (
 
 // Client encapsulates and provides logic for querying DNS servers over DoH.
 type Client struct {
-	c *http.Client
+	client *http.Client
 }
 
-// NewClient creates new Client instance with standard net/http client. If nil, default http.Client is used.
-func NewClient(c *http.Client) *Client {
-	if c == nil {
-		c = &http.Client{}
+// NewClient creates new Client instance with standard net/http client.
+func NewClient(opts ...Option) *Client {
+	client := &Client{
+		client: &http.Client{},
 	}
-	return &Client{c}
+	for _, opt := range opts {
+		opt.apply(client)
+	}
+	return client
 }
 
-// SendViaPost sends DNS message to the given DNS server over DoH using POST, see https://datatracker.ietf.org/doc/html/rfc8484#section-4.1
+// SendViaPost sends DNS message to the given DNS server over DoH using POST method, see https://datatracker.ietf.org/doc/html/rfc8484#section-4.1
 func (dc *Client) SendViaPost(ctx context.Context, server string, msg *dns.Msg) (*dns.Msg, error) {
 	pack, err := msg.Pack()
 	if err != nil {
@@ -41,7 +44,7 @@ func (dc *Client) SendViaPost(ctx context.Context, server string, msg *dns.Msg)
 	return dc.send(request)
 }
 
-// SendViaGet sends DNS message to the given DNS server over DoH using GET, see https://datatracker.ietf.org/doc/html/rfc8484#section-4.1
+// SendViaGet sends DNS message to the given DNS server over DoH using GET method, see https://datatracker.ietf.org/doc/html/rfc8484#section-4.1
 func (dc *Client) SendViaGet(ctx context.Context, server string, msg *dns.Msg) (*dns.Msg, error) {
 	pack, err := msg.Pack()
 	if err != nil {
@@ -60,7 +63,7 @@ func (dc *Client) SendViaGet(ctx context.Context, server string, msg *dns.Msg) (
 }
 
 func (dc *Client) send(r *http.Request) (*dns.Msg, error) {
-	resp, err := dc.c.Do(r)
+	resp, err := dc.client.Do(r)
 	if err != nil {
 		return nil, err
 	}

doh/client_test.go

@@ -58,37 +58,33 @@ func Test_SendViaPost(t *testing.T) {
 	}))
 	defer ts.Close()
 
-	type args struct {
-		server string
-		msg    *dns.Msg
-	}
 	tests := []struct {
 		name      string
-		args      args
+		msg       *dns.Msg
 		wantRcode int
 		wantErr   error
 	}{
 		{
 			name:      "NOERROR DNS resolution",
-			args:      args{server: ts.URL, msg: question(existingDomain)},
+			msg:       question(existingDomain),
 			wantRcode: dns.RcodeSuccess,
 		},
 		{
 			name:      "NXDOMAIN DNS resolution",
-			args:      args{server: ts.URL, msg: question(notExistingDomain)},
+			msg:       question(notExistingDomain),
 			wantRcode: dns.RcodeNameError,
 		},
 		{
 			name:    "bad upstream HTTP response",
-			args:    args{server: ts.URL, msg: question(badStatusDomain)},
+			msg:     question(badStatusDomain),
 			wantErr: &doh.UnexpectedServerHTTPStatusError{},
 		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			client := doh.NewClient(nil)
+			client := doh.NewClient()
 
-			got, err := client.SendViaPost(context.Background(), tt.args.server, tt.args.msg)
+			got, err := client.SendViaPost(context.Background(), ts.URL, tt.msg)
 
 			if tt.wantErr != nil {
 				require.ErrorAs(t, err, tt.wantErr, "SendViaPost() error")
@@ -142,37 +138,33 @@ func Test_SendViaGet(t *testing.T) {
 	}))
 	defer ts.Close()
 
-	type args struct {
-		server string
-		msg    *dns.Msg
-	}
 	tests := []struct {
 		name      string
-		args      args
+		msg       *dns.Msg
 		wantRcode int
 		wantErr   error
 	}{
 		{
 			name:      "NOERROR DNS resolution",
-			args:      args{server: ts.URL, msg: question(existingDomain)},
+			msg:       question(existingDomain),
 			wantRcode: dns.RcodeSuccess,
 		},
 		{
 			name:      "NXDOMAIN DNS resolution",
-			args:      args{server: ts.URL, msg: question(notExistingDomain)},
+			msg:       question(existingDomain),
 			wantRcode: dns.RcodeNameError,
 		},
 		{
 			name:    "bad upstream HTTP response",
-			args:    args{server: ts.URL, msg: question(badStatusDomain)},
+			msg:     question(badStatusDomain),
 			wantErr: &doh.UnexpectedServerHTTPStatusError{},
 		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			client := doh.NewClient(nil)
+			client := doh.NewClient()
 
-			got, err := client.SendViaGet(context.Background(), tt.args.server, tt.args.msg)
+			got, err := client.SendViaGet(context.Background(), ts.URL, tt.msg)
 
 			if tt.wantErr != nil {
 				require.ErrorAs(t, err, tt.wantErr, "SendViaPost() error")

doh/opts.go

@@ -0,0 +1,23 @@
+package doh
+
+import "net/http"
+
+// Option represents configuration options for doh.Client.
+type Option interface {
+	apply(c *Client)
+}
+
+type httpClientOption struct {
+	client *http.Client
+}
+
+func (o *httpClientOption) apply(c *Client) {
+	c.client = o.client
+}
+
+// WithHTTPClient is a configuration option that overrides default http.Client instance used by the doh.Client.
+func WithHTTPClient(c *http.Client) Option {
+	return &httpClientOption{
+		client: c,
+	}
+}