add string type enums and retry config

Reviewed-on: #1

pkg/client/client.go

@@ -25,6 +25,19 @@ import (
 	"time"
 )
 
+// 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 (
 	DefaultWingbitsPort = 8088
@@ -89,6 +102,7 @@ type Client struct {
 	tar1090   *Endpoint
 	http      *http.Client
 	userAgent string
+	retry     RetryConfig
 }
 
 // Option customizes a Client.
@@ -122,6 +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
+}

pkg/types/readsb/aircraft.go

@@ -32,7 +32,7 @@ type Aircraft struct {
 	// indicates a non-ICAO address (TIS-B).
 	Hex string `json:"hex"`
 	// Type is the message source/type, e.g. "adsb_icao", "mode_s", "mlat".
-	Type string `json:"type"`
+	Type MessageType `json:"type"`
 	// Flight is the callsign. readsb space-pads it; use Callsign for a trimmed value.
 	Flight string `json:"flight,omitempty"`
 	// Registration (r) and aircraft type (t) come from an optional database.
@@ -61,9 +61,9 @@ type Aircraft struct {
 	// Squawk is the Mode A code as 4 octal digits.
 	Squawk string `json:"squawk,omitempty"`
 	// Emergency is the emergency/priority status; "none" when not declared.
-	Emergency string `json:"emergency,omitempty"`
+	Emergency EmergencyStatus `json:"emergency,omitempty"`
 	// Category is the emitter category, e.g. "A0".."A7", "B0".. (see README-json).
-	Category string `json:"category,omitempty"`
+	Category EmitterCategory `json:"category,omitempty"`
 
 	// Lat/Lon are the last known position in decimal degrees.
 	Lat float64 `json:"lat,omitempty"`
@@ -94,7 +94,7 @@ type Aircraft struct {
 	NACP    int     `json:"nac_p,omitempty"`
 	NACV    int     `json:"nac_v,omitempty"`
 	SIL     int     `json:"sil,omitempty"`
-	SILType string `json:"sil_type,omitempty"`
+	SILType SILType `json:"sil_type,omitempty"`
 	GVA     int     `json:"gva,omitempty"`
 	SDA     int     `json:"sda,omitempty"`
 
@@ -133,7 +133,7 @@ func (a Aircraft) HasPosition() bool { return a.Lat != 0 || a.Lon != 0 }
 
 // InEmergency reports whether a non-routine emergency/priority code is set.
 func (a Aircraft) InEmergency() bool {
-	return a.Emergency != "" && a.Emergency != "none"
+	return a.Emergency != "" && a.Emergency != EmergencyNone
 }
 
 // SeenFor returns the time since the last message was received.

pkg/types/readsb/enums.go

@@ -0,0 +1,96 @@
+package readsb
+
+// MessageType is the source/type of an aircraft's data (the "type" field). It is
+// a named string so callers can compare against typed constants; it decodes from
+// and encodes to JSON exactly like a plain string. readsb lists these values in
+// descending order of trustworthiness in README-json.md.
+type MessageType string
+
+const (
+	TypeADSBICAO      MessageType = "adsb_icao"      // Mode S/ADS-B transponder, ICAO address
+	TypeADSBICAONT    MessageType = "adsb_icao_nt"   // ADS-B non-transponder emitter, ICAO address
+	TypeADSRICAO      MessageType = "adsr_icao"      // ADS-B rebroadcast (e.g. UAT), ICAO address
+	TypeTISBICAO      MessageType = "tisb_icao"      // TIS-B about a non-ADS-B target, ICAO address
+	TypeADSC          MessageType = "adsc"           // ADS-C via satellite downlink
+	TypeMLAT          MessageType = "mlat"           // position from multilateration
+	TypeOther         MessageType = "other"          // miscellaneous Basestation/SBS data
+	TypeModeS         MessageType = "mode_s"         // Mode S only, no position
+	TypeADSBOther     MessageType = "adsb_other"     // ADS-B transponder, non-ICAO address
+	TypeADSROther     MessageType = "adsr_other"     // ADS-B rebroadcast, non-ICAO address
+	TypeTISBOther     MessageType = "tisb_other"     // TIS-B about a non-ADS-B target, non-ICAO address
+	TypeTISBTrackfile MessageType = "tisb_trackfile" // TIS-B keyed by track/file id (radar)
+)
+
+// EmitterCategory is the ADS-B emitter category (the "category" field): a class
+// letter A-D and a digit 0-7. The A0/B0/C0/D0 codes mean "no category info"; the
+// remaining D codes and a few others are reserved. Decodes/encodes as a string.
+type EmitterCategory string
+
+const (
+	CatNoInfo EmitterCategory = "A0" // also B0/C0/D0: no category information
+
+	CatLight      EmitterCategory = "A1" // < 15,500 lb
+	CatSmall      EmitterCategory = "A2" // 15,500-75,000 lb
+	CatLarge      EmitterCategory = "A3" // 75,000-300,000 lb
+	CatHighVortex EmitterCategory = "A4" // high-vortex large, e.g. B757
+	CatHeavy      EmitterCategory = "A5" // > 300,000 lb
+	CatHighPerf   EmitterCategory = "A6" // > 5g and > 400 kt
+	CatRotorcraft EmitterCategory = "A7"
+
+	CatGlider         EmitterCategory = "B1" // glider / sailplane
+	CatLighterThanAir EmitterCategory = "B2"
+	CatParachutist    EmitterCategory = "B3" // parachutist / skydiver
+	CatUltralight     EmitterCategory = "B4" // ultralight / hang-glider / paraglider
+	CatUAV            EmitterCategory = "B6" // unmanned aerial vehicle
+	CatSpace          EmitterCategory = "B7" // space / transatmospheric vehicle
+
+	CatSurfaceEmergency EmitterCategory = "C1" // surface vehicle, emergency
+	CatSurfaceService   EmitterCategory = "C2" // surface vehicle, service
+	CatPointObstacle    EmitterCategory = "C3" // point obstacle (incl. tethered balloons)
+	CatClusterObstacle  EmitterCategory = "C4"
+	CatLineObstacle     EmitterCategory = "C5"
+)
+
+// catDescriptions maps every defined emitter code (including reserved ones) to a
+// human label. Codes absent from the map are undefined.
+var catDescriptions = map[EmitterCategory]string{
+	"A0": "no information", "A1": "light", "A2": "small", "A3": "large",
+	"A4": "high-vortex large", "A5": "heavy", "A6": "high performance", "A7": "rotorcraft",
+	"B0": "no information", "B1": "glider/sailplane", "B2": "lighter-than-air",
+	"B3": "parachutist", "B4": "ultralight", "B5": "reserved",
+	"B6": "unmanned aerial vehicle", "B7": "space/transatmospheric",
+	"C0": "no information", "C1": "surface emergency vehicle", "C2": "surface service vehicle",
+	"C3": "point obstacle", "C4": "cluster obstacle", "C5": "line obstacle",
+	"C6": "reserved", "C7": "reserved",
+	"D0": "no information", "D1": "reserved", "D2": "reserved", "D3": "reserved",
+	"D4": "reserved", "D5": "reserved", "D6": "reserved", "D7": "reserved",
+}
+
+// Description returns the human-readable label for the emitter category, or ""
+// if the code is not a defined A0-D7 value.
+func (c EmitterCategory) Description() string { return catDescriptions[c] }
+
+// EmergencyStatus is the emergency/priority status (the "emergency" field).
+// EmergencyNone means no emergency is declared. Decodes/encodes as a string.
+type EmergencyStatus string
+
+const (
+	EmergencyNone      EmergencyStatus = "none"
+	EmergencyGeneral   EmergencyStatus = "general"
+	EmergencyLifeguard EmergencyStatus = "lifeguard" // medical/lifeguard flight
+	EmergencyMinFuel   EmergencyStatus = "minfuel"   // minimum fuel
+	EmergencyNoRadio   EmergencyStatus = "nordo"     // no radio communication
+	EmergencyUnlawful  EmergencyStatus = "unlawful"  // unlawful interference
+	EmergencyDowned    EmergencyStatus = "downed"    // downed aircraft
+	EmergencyReserved  EmergencyStatus = "reserved"
+)
+
+// SILType describes how the SIL (source integrity level) probability is scaled
+// (the "sil_type" field): per flight hour or per sample. Decodes/encodes as a string.
+type SILType string
+
+const (
+	SILUnknown   SILType = "unknown"
+	SILPerHour   SILType = "perhour"
+	SILPerSample SILType = "persample"
+)

pkg/types/readsb/filter.go

@@ -66,16 +66,16 @@ func WithSquawk(codes ...string) AircraftFilter {
 	return func(a *Aircraft) bool { return set[strings.ToLower(a.Squawk)] }
 }
 
-// WithCategory keeps aircraft of any of the given emitter categories (e.g. "A3").
-func WithCategory(cats ...string) AircraftFilter {
-	set := lowerSet(nil, cats, "")
-	return func(a *Aircraft) bool { return set[strings.ToLower(a.Category)] }
+// WithCategory keeps aircraft of any of the given emitter categories (e.g. CatLarge).
+func WithCategory(cats ...EmitterCategory) AircraftFilter {
+	set := lowerSet(nil, strs(cats), "")
+	return func(a *Aircraft) bool { return set[strings.ToLower(string(a.Category))] }
 }
 
-// WithType keeps aircraft of any of the given source types (e.g. "adsb_icao", "mlat").
-func WithType(types ...string) AircraftFilter {
-	set := lowerSet(nil, types, "")
-	return func(a *Aircraft) bool { return set[strings.ToLower(a.Type)] }
+// WithType keeps aircraft of any of the given source types (e.g. TypeADSBICAO, TypeMLAT).
+func WithType(types ...MessageType) AircraftFilter {
+	set := lowerSet(nil, strs(types), "")
+	return func(a *Aircraft) bool { return set[strings.ToLower(string(a.Type))] }
 }
 
 // InEmergency keeps only aircraft squawking a non-routine emergency/priority code.
@@ -138,6 +138,15 @@ func Any(filters ...AircraftFilter) AircraftFilter {
 
 // lowerSet builds a lowercased lookup set, optionally pre-processing each value
 // with trim(value, cut) when trim is non-nil.
+// strs widens a slice of any string-kind type to []string for the set helpers.
+func strs[T ~string](in []T) []string {
+	out := make([]string, len(in))
+	for i, v := range in {
+		out[i] = string(v)
+	}
+	return out
+}
+
 func lowerSet(trim func(string, string) string, values []string, cut string) map[string]bool {
 	set := make(map[string]bool, len(values))
 	for _, v := range values {