add string type enums and retry config

pkg/client/client.go

@@ -25,8 +25,18 @@ import (
 	"time"
 )
 
-// TODO: Implement client retry configuration
-// Also support exponential backoff
+// RetryConfig controls how transient request failures (transport errors and 5xx
+// responses) are retried. The zero value disables retries.
+type RetryConfig struct {
+	// MaxRetries is the number of additional attempts made after the initial
+	// request. Zero means no retries.
+	MaxRetries int
+	// BaseDelay is the wait before the first retry. It doubles on each
+	// subsequent retry (exponential backoff). Zero means retry immediately.
+	BaseDelay time.Duration
+	// MaxDelay caps the per-retry backoff delay. Zero means no cap.
+	MaxDelay time.Duration
+}
 
 // Default ports exposed by an MGW310 station.
 const (
@@ -92,6 +102,7 @@ type Client struct {
 	tar1090   *Endpoint
 	http      *http.Client
 	userAgent string
+	retry     RetryConfig
 }
 
 // Option customizes a Client.
@@ -125,6 +136,11 @@ func WithUserAgent(ua string) Option {
 	return func(c *Client) { c.userAgent = ua }
 }
 
+// WithRetry enables retries with exponential backoff for transient failures.
+func WithRetry(cfg RetryConfig) Option {
+	return func(c *Client) { c.retry = cfg }
+}
+
 // New constructs a Client from options. A Wingbits endpoint with a non-empty
 // Host must be supplied via WithWingbitsEndpoint.
 func New(opts ...Option) (*Client, error) {

pkg/client/client_test.go

@@ -144,6 +144,61 @@ func TestClientWingbitsEndpoints(t *testing.T) {
 	}
 }
 
+func TestClientRetry(t *testing.T) {
+	// Fail with 503 for the first two attempts, then succeed; the client must
+	// retry past the failures and return the eventual body.
+	var hits int
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		if hits++; hits <= 2 {
+			http.Error(w, "warming up", http.StatusServiceUnavailable)
+			return
+		}
+		w.Write([]byte(`{}`))
+	}))
+	t.Cleanup(srv.Close)
+
+	host, port := splitHostPort(t, strings.TrimPrefix(srv.URL, "http://"))
+	c, err := New(
+		WithWingbitsEndpoint(Endpoint{Host: host, Port: port}),
+		WithRetry(RetryConfig{MaxRetries: 3, BaseDelay: time.Millisecond, MaxDelay: 5 * time.Millisecond}),
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := c.Status(context.Background()); err != nil {
+		t.Fatalf("status after retries: %v", err)
+	}
+	if hits != 3 {
+		t.Fatalf("expected 3 attempts, got %d", hits)
+	}
+}
+
+func TestClientRetryGivesUp(t *testing.T) {
+	// A 404 is not retryable: the client must fail after a single attempt even
+	// with retries configured.
+	var hits int
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		hits++
+		http.Error(w, "nope", http.StatusNotFound)
+	}))
+	t.Cleanup(srv.Close)
+
+	host, port := splitHostPort(t, strings.TrimPrefix(srv.URL, "http://"))
+	c, err := New(
+		WithWingbitsEndpoint(Endpoint{Host: host, Port: port}),
+		WithRetry(RetryConfig{MaxRetries: 3, BaseDelay: time.Millisecond}),
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := c.Status(context.Background()); err == nil {
+		t.Fatal("expected error on 404")
+	}
+	if hits != 1 {
+		t.Fatalf("expected 1 attempt for non-retryable status, got %d", hits)
+	}
+}
+
 func TestPollAircraft(t *testing.T) {
 	c := newTestClient(t)
 	ctx := t.Context()

pkg/client/query.go

@@ -3,9 +3,11 @@ package client
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
+	"time"
 
 	"gitea.libretechconsulting.com/rmcguire/wingbits/pkg/types/readsb"
 	"gitea.libretechconsulting.com/rmcguire/wingbits/pkg/types/wingbits"
@@ -79,8 +81,33 @@ func getJSON[T any](ctx context.Context, c *Client, url string) (*T, error) {
 	return out, nil
 }
 
+// statusError reports a non-200 HTTP status returned by a station.
+type statusError struct {
+	url    string
+	status string
+	code   int
+}
+
+func (e *statusError) Error() string {
+	return fmt.Sprintf("wingbits: GET %s: unexpected status %s", e.url, e.status)
+}
+
 // get performs a GET and returns the response body, which the caller must close.
+// Transient failures are retried per the client's RetryConfig.
 func (c *Client) get(ctx context.Context, url string) (io.ReadCloser, error) {
+	for attempt := 0; ; attempt++ {
+		body, err := c.doGet(ctx, url)
+		if err == nil || attempt >= c.retry.MaxRetries || !retryable(err) {
+			return body, err
+		}
+		if werr := c.waitBackoff(ctx, attempt); werr != nil {
+			return nil, werr
+		}
+	}
+}
+
+// doGet performs a single GET attempt.
+func (c *Client) doGet(ctx context.Context, url string) (io.ReadCloser, error) {
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
 	if err != nil {
 		return nil, fmt.Errorf("wingbits: building request: %w", err)
@@ -92,7 +119,47 @@ func (c *Client) get(ctx context.Context, url string) (io.ReadCloser, error) {
 	}
 	if resp.StatusCode != http.StatusOK {
 		resp.Body.Close()
-		return nil, fmt.Errorf("wingbits: GET %s: unexpected status %s", url, resp.Status)
+		return nil, &statusError{url: url, status: resp.Status, code: resp.StatusCode}
 	}
 	return resp.Body, nil
 }
+
+// retryable reports whether err is a transient failure worth retrying: any
+// transport error, or a 5xx response. Context cancellation is never retried.
+func retryable(err error) bool {
+	if err == nil || errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+		return false
+	}
+	if se, ok := errors.AsType[*statusError](err); ok {
+		return se.code >= 500
+	}
+	return true
+}
+
+// waitBackoff sleeps for the attempt's backoff delay or until ctx is done.
+func (c *Client) waitBackoff(ctx context.Context, attempt int) error {
+	t := time.NewTimer(c.backoff(attempt))
+	defer t.Stop()
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-t.C:
+		return nil
+	}
+}
+
+// backoff returns the delay before the given retry attempt (0-indexed),
+// doubling BaseDelay each attempt and capping at MaxDelay.
+func (c *Client) backoff(attempt int) time.Duration {
+	d := c.retry.BaseDelay
+	for range attempt {
+		d *= 2
+		if c.retry.MaxDelay > 0 && d >= c.retry.MaxDelay {
+			return c.retry.MaxDelay
+		}
+	}
+	if c.retry.MaxDelay > 0 && d > c.retry.MaxDelay {
+		return c.retry.MaxDelay
+	}
+	return d
+}