generic: add MutexMap

ops/devcontainer/Dockerfile

@@ -7,7 +7,7 @@ RUN apk add build-base git go sqlite vim shellcheck curl jq sudo bash docker
 # Busybox `less` doesn't appear to support colors (makes git diff lose color)
 RUN apk add less
 
-RUN curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b /usr/local/bin v2.0.2
+RUN curl -sSfL https://golangci-lint.run/install.sh | sh -s -- -b /usr/local/bin v2.14.0
 RUN GOBIN=/usr/local/bin go install git.offline-twitter.com/offline-labs/gocheckout@v0.0.2
 
 COPY etc/group /etc/group

pkg/db/vsc.go

@@ -0,0 +1,51 @@
+package db
+
+import (
+	"database/sql/driver"
+	"encoding/json"
+	"errors"
+	"strings"
+)
+
+const separator = "\x1f"
+
+type VSC []string
+
+// MarshalJSON replaces `nil` with `[]` for hygiene.
+func (vs VSC) MarshalJSON() ([]byte, error) {
+	if vs == nil {
+		vs = VSC{}
+	}
+	return json.Marshal([]string(vs)) //nolint: wrapcheck // Passthrough
+}
+
+func (vs VSC) Value() (driver.Value, error) {
+	fields := make([]string, len(vs))
+	for i, v := range vs {
+		fields[i] = strings.ReplaceAll(v, separator, "")
+	}
+	return strings.Join(fields, separator), nil
+}
+
+var ErrWrongVSCType = errors.New("incompatible DB type for VSC")
+
+func (vs *VSC) Scan(src any) error {
+	var s string
+	switch v := src.(type) {
+	case string:
+		s = v
+	case []byte:
+		s = string(v)
+	case nil:
+		*vs = nil
+		return nil
+	default:
+		return ErrWrongVSCType
+	}
+	if s == "" {
+		*vs = VSC{}
+		return nil
+	}
+	*vs = strings.Split(s, separator)
+	return nil
+}

pkg/db/vsc_test.go

@@ -0,0 +1,48 @@
+package db_test
+
+import (
+	"testing"
+
+	"github.com/jmoiron/sqlx"
+	_ "github.com/mattn/go-sqlite3"
+	"github.com/stretchr/testify/require"
+
+	"git.offline-twitter.com/offline-labs/gas-stack/pkg/db"
+)
+
+func TestVSCDBRoundTrip(t *testing.T) {
+	conn, err := sqlx.Open("sqlite3", ":memory:")
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, conn.Close()) })
+
+	_, err = conn.Exec(`create table vsc_items (id integer primary key, items text not null)`)
+	require.NoError(t, err)
+
+	type vscRow struct {
+		ID    int    `db:"id"`
+		Items db.VSC `db:"items"`
+	}
+
+	for _, want := range []vscRow{
+		{ID: 1, Items: db.VSC{"email"}},
+		{ID: 2, Items: db.VSC{"email", "profile"}},
+		{ID: 3, Items: db.VSC{}},
+	} {
+		_, err = conn.NamedExec(`insert into vsc_items (id, items) values (:id, :items)`, want)
+		require.NoError(t, err)
+
+		var got vscRow
+		require.NoError(t, conn.Get(&got, `select id, items from vsc_items where id = ?`, want.ID))
+		require.Equal(t, want, got)
+	}
+	t.Run("nil gets upgrade to empty list", func(t *testing.T) {
+		want := vscRow{ID: 4, Items: nil}
+		_, err = conn.NamedExec(`insert into vsc_items (id, items) values (:id, :items)`, want)
+		require.NoError(t, err)
+
+		var got vscRow
+		require.NoError(t, conn.Get(&got, `select id, items from vsc_items where id = ?`, want.ID))
+		require.NotNil(t, got.Items)
+		require.Equal(t, db.VSC{}, got.Items)
+	})
+}

pkg/generic/mutexmap.go

@@ -0,0 +1,76 @@
+package generic
+
+import (
+	"maps"
+	"sync"
+)
+
+type MutexMap[K comparable, V any] struct {
+	mu       sync.RWMutex
+	contents map[K]V
+}
+
+func NewMutexMap[K comparable, V any]() *MutexMap[K, V] {
+	return &MutexMap[K, V]{contents: make(map[K]V)}
+}
+
+func (m *MutexMap[K, V]) Set(key K, value V) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.contents[key] = value
+}
+
+func (m *MutexMap[K, V]) Get(key K) (V, bool) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	v, ok := m.contents[key]
+	return v, ok
+}
+
+func (m *MutexMap[K, V]) Len() int {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return len(m.contents)
+}
+
+// Upd atomically updates the value for key.  `fn` is used to determine how to update an existing
+// value, if there is one.  It will be passed the existing value, and should return `(newValue V, shouldReplace bool)`.
+//
+// Returns the value that ends up associated with key after the call and whether an update occurred.
+func (m *MutexMap[K, V]) Upd(key K, fn func(prev V) (next V, shouldReplace bool)) (V, bool) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	prev := m.contents[key]
+	if next, shouldReplace := fn(prev); shouldReplace {
+		m.contents[key] = next
+		return next, true
+	}
+	return prev, false
+}
+
+// Del removes key from the map. Returns true if the key was present.
+func (m *MutexMap[K, V]) Del(key K) bool { //nolint: boolnames // Return value is incidental, not the main purpose of the function
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if _, ok := m.contents[key]; !ok {
+		return false
+	}
+	delete(m.contents, key)
+	return true
+}
+
+func (m *MutexMap[K, V]) Cpy() map[K]V {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	cp := make(map[K]V, len(m.contents))
+	maps.Copy(cp, m.contents)
+	return cp
+}
+
+func (m *MutexMap[K, V]) Pop(key K) (ret V, isOk bool) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	ret, isOk = m.contents[key]
+	delete(m.contents, key)
+	return
+}