refactor(dataset): rename Group to Set, accept variadic fetchers

Set handles both single-fetcher (one git repo) and multi-fetcher
(GeoLite2 City + ASN) cases uniformly. Any fetcher reporting an update
triggers a view reload. This replaces the per-caller FetcherFunc wrapper
that combined the two MaxMind cachers and the ad-hoc atomic.Pointer +
ticker goroutine in cmd/check-ip — geoip now rides on the same
Set/View/Load/Tick surface as the blocklists.

cmd/check-ip/main.go

@@ -12,7 +12,6 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
-	"sync/atomic"
 	"syscall"
 	"time"
 
@@ -44,7 +43,7 @@ type IPCheck struct {
 
 	inbound  *dataset.View[ipcohort.Cohort]
 	outbound *dataset.View[ipcohort.Cohort]
-	geo      atomic.Pointer[geoip.Databases]
+	geo      *dataset.View[geoip.Databases]
 }
 
 func main() {
@@ -114,20 +113,20 @@ func main() {
 
 	// Blocklists: git repo with inbound + outbound IP cohort files.
 	repo := gitshallow.New(cfg.RepoURL, filepath.Join(cfg.CacheDir, "bitwire-it"), 1, "")
-	group := dataset.NewGroup(repo)
-	cfg.inbound = dataset.Add(group, func() (*ipcohort.Cohort, error) {
+	blocklists := dataset.NewSet(repo)
+	cfg.inbound = dataset.Add(blocklists, func() (*ipcohort.Cohort, error) {
 		return ipcohort.LoadFiles(
 			repo.FilePath("tables/inbound/single_ips.txt"),
 			repo.FilePath("tables/inbound/networks.txt"),
 		)
 	})
-	cfg.outbound = dataset.Add(group, func() (*ipcohort.Cohort, error) {
+	cfg.outbound = dataset.Add(blocklists, func() (*ipcohort.Cohort, error) {
 		return ipcohort.LoadFiles(
 			repo.FilePath("tables/outbound/single_ips.txt"),
 			repo.FilePath("tables/outbound/networks.txt"),
 		)
 	})
-	if err := group.Load(context.Background()); err != nil {
+	if err := blocklists.Load(context.Background()); err != nil {
 		log.Fatalf("blocklists: %v", err)
 	}
 
@@ -138,45 +137,34 @@ func main() {
 	maxmindDir := filepath.Join(cfg.CacheDir, "maxmind")
 	cityTarPath := filepath.Join(maxmindDir, "GeoLite2-City.tar.gz")
 	asnTarPath := filepath.Join(maxmindDir, "GeoLite2-ASN.tar.gz")
-	var geoFetcher dataset.Fetcher
+	var geoSet *dataset.Set
 	if cfg.GeoIPBasicAuth != "" {
-		city := &httpcache.Cacher{
-			URL:        geoip.DownloadBase + "/GeoLite2-City/download?suffix=tar.gz",
-			Path:       cityTarPath,
-			MaxAge:     3 * 24 * time.Hour,
-			AuthHeader: "Authorization",
-			AuthValue:  cfg.GeoIPBasicAuth,
-		}
-		asn := &httpcache.Cacher{
-			URL:        geoip.DownloadBase + "/GeoLite2-ASN/download?suffix=tar.gz",
-			Path:       asnTarPath,
-			MaxAge:     3 * 24 * time.Hour,
-			AuthHeader: "Authorization",
-			AuthValue:  cfg.GeoIPBasicAuth,
-		}
-		geoFetcher = dataset.FetcherFunc(func() (bool, error) {
-			cityUpdated, err := city.Fetch()
-			if err != nil {
-				return false, fmt.Errorf("fetch GeoLite2-City: %w", err)
-			}
-			asnUpdated, err := asn.Fetch()
-			if err != nil {
-				return false, fmt.Errorf("fetch GeoLite2-ASN: %w", err)
-			}
-			return cityUpdated || asnUpdated, nil
-		})
+		geoSet = dataset.NewSet(
+			&httpcache.Cacher{
+				URL:        geoip.DownloadBase + "/GeoLite2-City/download?suffix=tar.gz",
+				Path:       cityTarPath,
+				MaxAge:     3 * 24 * time.Hour,
+				AuthHeader: "Authorization",
+				AuthValue:  cfg.GeoIPBasicAuth,
+			},
+			&httpcache.Cacher{
+				URL:        geoip.DownloadBase + "/GeoLite2-ASN/download?suffix=tar.gz",
+				Path:       asnTarPath,
+				MaxAge:     3 * 24 * time.Hour,
+				AuthHeader: "Authorization",
+				AuthValue:  cfg.GeoIPBasicAuth,
+			},
+		)
 	} else {
-		geoFetcher = dataset.PollFiles(cityTarPath, asnTarPath)
+		geoSet = dataset.NewSet(dataset.PollFiles(cityTarPath, asnTarPath))
 	}
-	if _, err := geoFetcher.Fetch(); err != nil {
+	cfg.geo = dataset.Add(geoSet, func() (*geoip.Databases, error) {
+		return geoip.Open(maxmindDir)
+	})
+	if err := geoSet.Load(context.Background()); err != nil {
 		log.Fatalf("geoip: %v", err)
 	}
-	geoDB, err := geoip.Open(maxmindDir)
-	if err != nil {
-		log.Fatalf("geoip: %v", err)
-	}
-	cfg.geo.Store(geoDB)
-	defer func() { _ = cfg.geo.Load().Close() }()
+	defer func() { _ = cfg.geo.Value().Close() }()
 
 	for _, ip := range ips {
 		cfg.writeText(os.Stdout, cfg.lookup(ip))
@@ -187,36 +175,12 @@ func main() {
 
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
-	go group.Tick(ctx, refreshInterval, func(err error) {
+	go blocklists.Tick(ctx, refreshInterval, func(err error) {
 		log.Printf("blocklists refresh: %v", err)
 	})
-	go func() {
-		t := time.NewTicker(refreshInterval)
-		defer t.Stop()
-		for {
-			select {
-			case <-ctx.Done():
-				return
-			case <-t.C:
-				updated, err := geoFetcher.Fetch()
-				if err != nil {
-					log.Printf("geoip refresh: %v", err)
-					continue
-				}
-				if !updated {
-					continue
-				}
-				db, err := geoip.Open(maxmindDir)
-				if err != nil {
-					log.Printf("geoip refresh: %v", err)
-					continue
-				}
-				if old := cfg.geo.Swap(db); old != nil {
-					_ = old.Close()
-				}
-			}
-		}
-	}()
+	go geoSet.Tick(ctx, refreshInterval, func(err error) {
+		log.Printf("geoip refresh: %v", err)
+	})
 	if err := cfg.serve(ctx); err != nil {
 		log.Fatalf("serve: %v", err)
 	}

cmd/check-ip/server.go

@@ -34,7 +34,7 @@ func (c *IPCheck) lookup(ip string) Result {
 		Blocked:         in || out,
 		BlockedInbound:  in,
 		BlockedOutbound: out,
-		Geo:             c.geo.Load().Lookup(ip),
+		Geo:             c.geo.Value().Lookup(ip),
 	}
 }
 

sync/dataset/dataset.go

@@ -1,17 +1,17 @@
 // Package dataset manages values that are periodically re-fetched from an
 // upstream source and hot-swapped behind atomic pointers. Consumers read via
-// View.Value (lock-free); a single Load drives any number of views off one
-// Fetcher, so shared sources (one git pull, one zip download) don't get
-// re-fetched per view.
+// View.Value (lock-free); a single Load drives any number of views off a
+// shared set of Fetchers, so upstreams (one git pull, one tar.gz download)
+// don't get re-fetched per view.
 //
 // Typical lifecycle:
 //
-//	g := dataset.NewGroup(repo) // *gitshallow.Repo satisfies Fetcher
-//	inbound  := dataset.Add(g, func() (*ipcohort.Cohort, error) { ... })
-//	outbound := dataset.Add(g, func() (*ipcohort.Cohort, error) { ... })
-//	if err := g.Load(ctx); err != nil { ... }        // initial populate
-//	go g.Tick(ctx, 47*time.Minute)                   // background refresh
-//	current := inbound.Value()                        // lock-free read
+//	s := dataset.NewSet(repo) // *gitshallow.Repo satisfies Fetcher
+//	inbound  := dataset.Add(s, func() (*ipcohort.Cohort, error) { ... })
+//	outbound := dataset.Add(s, func() (*ipcohort.Cohort, error) { ... })
+//	if err := s.Load(ctx); err != nil { ... }       // initial populate
+//	go s.Tick(ctx, 47*time.Minute, onError)         // background refresh
+//	current := inbound.Value()                      // lock-free read
 package dataset
 
 import (
@@ -34,7 +34,7 @@ type FetcherFunc func() (bool, error)
 
 func (f FetcherFunc) Fetch() (bool, error) { return f() }
 
-// NopFetcher always reports no update. Use for groups whose source never
+// NopFetcher always reports no update. Use for sets whose source never
 // changes (test fixtures, embedded data).
 type NopFetcher struct{}
 
@@ -44,8 +44,8 @@ func (NopFetcher) Fetch() (bool, error) { return false, nil }
 // "updated" whenever any file's size or modtime has changed since the last
 // call. The first call always reports updated=true.
 //
-// Use for Group's whose source is local files that may be edited out of band
-// (e.g. a user-provided --inbound list) — pair with Group.Tick to pick up
+// Use for Sets whose source is local files that may be edited out of band
+// (e.g. a user-provided --inbound list) — pair with Set.Tick to pick up
 // changes automatically.
 func PollFiles(paths ...string) Fetcher {
 	return &filePoller{paths: paths, stats: make(map[string]fileStat, len(paths))}
@@ -80,13 +80,16 @@ func (p *filePoller) Fetch() (bool, error) {
 	return changed, nil
 }
 
-// Group ties one Fetcher to one or more views. A Load call fetches once and,
-// on the first call or when the source reports a change, reloads every view
-// and atomically swaps its current value.
-type Group struct {
-	fetcher Fetcher
-	views   []reloader
-	loaded  atomic.Bool
+// Set ties one or more Fetchers to one or more views. A Load call fetches
+// each source and, on the first call or when any source reports a change,
+// reloads every view and atomically swaps its current value. Use multiple
+// fetchers when a single logical dataset is spread across several archives
+// (e.g. GeoLite2 City + ASN); a single fetcher is the common case (one git
+// repo, one tar.gz).
+type Set struct {
+	fetchers []Fetcher
+	views    []reloader
+	loaded   atomic.Bool
 }
 
 // reloader is a type-erased handle to a View's reload function.
@@ -94,22 +97,29 @@ type reloader interface {
 	reload() error
 }
 
-// NewGroup creates a Group backed by fetcher.
-func NewGroup(fetcher Fetcher) *Group {
-	return &Group{fetcher: fetcher}
+// NewSet creates a Set backed by fetchers. All fetchers are called on every
+// Load; the set reloads its views whenever any one of them reports a change.
+func NewSet(fetchers ...Fetcher) *Set {
+	return &Set{fetchers: fetchers}
 }
 
-// Load fetches upstream and, on the first call or whenever the fetcher reports
-// a change, reloads every view and atomically installs the new values.
-func (g *Group) Load(ctx context.Context) error {
-	updated, err := g.fetcher.Fetch()
-	if err != nil {
-		return err
+// Load fetches upstream and, on the first call or whenever any fetcher
+// reports a change, reloads every view and atomically installs the new values.
+func (s *Set) Load(ctx context.Context) error {
+	updated := false
+	for _, f := range s.fetchers {
+		u, err := f.Fetch()
+		if err != nil {
+			return err
+		}
+		if u {
+			updated = true
+		}
 	}
-	if g.loaded.Load() && !updated {
+	if s.loaded.Load() && !updated {
 		return nil
 	}
-	for _, v := range g.views {
+	for _, v := range s.views {
 		if err := ctx.Err(); err != nil {
 			return err
 		}
@@ -117,14 +127,14 @@ func (g *Group) Load(ctx context.Context) error {
 			return err
 		}
 	}
-	g.loaded.Store(true)
+	s.loaded.Store(true)
 	return nil
 }
 
 // Tick calls Load every interval until ctx is done. Load errors are passed to
 // onError (if non-nil) and do not stop the loop; callers choose whether to log,
-// count, page, or ignore. Run in a goroutine: `go g.Tick(ctx, d, onError)`.
-func (g *Group) Tick(ctx context.Context, interval time.Duration, onError func(error)) {
+// count, page, or ignore. Run in a goroutine: `go s.Tick(ctx, d, onError)`.
+func (s *Set) Tick(ctx context.Context, interval time.Duration, onError func(error)) {
 	t := time.NewTicker(interval)
 	defer t.Stop()
 	for {
@@ -132,20 +142,20 @@ func (g *Group) Tick(ctx context.Context, interval time.Duration, onError func(e
 		case <-ctx.Done():
 			return
 		case <-t.C:
-			if err := g.Load(ctx); err != nil && onError != nil {
+			if err := s.Load(ctx); err != nil && onError != nil {
 				onError(err)
 			}
 		}
 	}
 }
 
-// View is a read-only handle to one dataset inside a Group.
+// View is a read-only handle to one dataset inside a Set.
 type View[T any] struct {
 	loader func() (*T, error)
 	ptr    atomic.Pointer[T]
 }
 
-// Value returns the current snapshot. Nil before the Group is first loaded.
+// Value returns the current snapshot. Nil before the Set is first loaded.
 func (v *View[T]) Value() *T {
 	return v.ptr.Load()
 }
@@ -159,10 +169,10 @@ func (v *View[T]) reload() error {
 	return nil
 }
 
-// Add registers a new view in g and returns it. Call after NewGroup and
-// before the first Load.
-func Add[T any](g *Group, loader func() (*T, error)) *View[T] {
+// Add registers a new view in s and returns it. Call after NewSet and before
+// the first Load.
+func Add[T any](s *Set, loader func() (*T, error)) *View[T] {
 	v := &View[T]{loader: loader}
-	g.views = append(g.views, v)
+	s.views = append(s.views, v)
 	return v
 }

sync/dataset/dataset_test.go

@@ -21,9 +21,9 @@ func (f *countFetcher) Fetch() (bool, error) {
 	return f.updated, f.err
 }
 
-func TestGroup_LoadPopulatesAllViews(t *testing.T) {
+func TestSet_LoadPopulatesAllViews(t *testing.T) {
 	f := &countFetcher{}
-	g := dataset.NewGroup(f)
+	g := dataset.NewSet(f)
 
 	var aCalls, bCalls int
 	a := dataset.Add(g, func() (*string, error) {
@@ -54,9 +54,9 @@ func TestGroup_LoadPopulatesAllViews(t *testing.T) {
 	}
 }
 
-func TestGroup_SecondLoadSkipsUnchanged(t *testing.T) {
+func TestSet_SecondLoadSkipsUnchanged(t *testing.T) {
 	f := &countFetcher{updated: false}
-	g := dataset.NewGroup(f)
+	g := dataset.NewSet(f)
 	calls := 0
 	dataset.Add(g, func() (*string, error) {
 		calls++
@@ -77,9 +77,9 @@ func TestGroup_SecondLoadSkipsUnchanged(t *testing.T) {
 	}
 }
 
-func TestGroup_LoadOnUpdateSwaps(t *testing.T) {
+func TestSet_LoadOnUpdateSwaps(t *testing.T) {
 	f := &countFetcher{updated: true}
-	g := dataset.NewGroup(f)
+	g := dataset.NewSet(f)
 	n := 0
 	v := dataset.Add(g, func() (*int, error) {
 		n++
@@ -96,8 +96,8 @@ func TestGroup_LoadOnUpdateSwaps(t *testing.T) {
 	}
 }
 
-func TestGroup_ValueBeforeLoad(t *testing.T) {
-	g := dataset.NewGroup(dataset.NopFetcher{})
+func TestSet_ValueBeforeLoad(t *testing.T) {
+	g := dataset.NewSet(dataset.NopFetcher{})
 	v := dataset.Add(g, func() (*string, error) {
 		s := "x"
 		return &s, nil
@@ -107,9 +107,9 @@ func TestGroup_ValueBeforeLoad(t *testing.T) {
 	}
 }
 
-func TestGroup_FetchError(t *testing.T) {
+func TestSet_FetchError(t *testing.T) {
 	f := &countFetcher{err: errors.New("offline")}
-	g := dataset.NewGroup(f)
+	g := dataset.NewSet(f)
 	dataset.Add(g, func() (*string, error) {
 		s := "x"
 		return &s, nil
@@ -119,8 +119,8 @@ func TestGroup_FetchError(t *testing.T) {
 	}
 }
 
-func TestGroup_LoaderError(t *testing.T) {
-	g := dataset.NewGroup(dataset.NopFetcher{})
+func TestSet_LoaderError(t *testing.T) {
+	g := dataset.NewSet(dataset.NopFetcher{})
 	dataset.Add(g, func() (*string, error) {
 		return nil, errors.New("parse fail")
 	})