2 files changed, 136 insertions, 0 deletions
diff --git a/provider/dummy.go b/provider/dummy.go
new file mode 100644
index 0000000..bec5907
--- /dev/null
+++ b/provider/dummy.go
@@ -0,0 +1,32 @@
+package provider
+
+import (
+	"log/slog"
+	"net/netip"
+)
+
+// a stand-in for a real provider.
+// once asked to ensure a record is set,
+// it will tell you what was requested,
+// and not take any action.
+// very useful for debugging!
+type dummy struct {
+	log *slog.Logger
+}
+
+var _ Provider = (*dummy)(nil)
+
+func newDummy(log *slog.Logger) (*dummy, error) {
+	return &dummy{log: log.With(slog.String("provider", "dummy"))}, nil
+}
+
+func (d *dummy) Ensure(zone, name string, rtype RecordType, addr netip.Addr) (string, bool, error) {
+	d.log.Info(
+		"asked to ensure record, but nothing happened",
+		slog.String("zone", zone),
+		slog.String("name", name),
+		slog.String("record", string(rtype)),
+		slog.String("addr", addr.String()),
+	)
+	return "", true, nil
+}
diff --git a/provider/provider.go b/provider/provider.go
new file mode 100644
index 0000000..ee31ba8
--- /dev/null
+++ b/provider/provider.go
@@ -0,0 +1,104 @@
+package provider
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/netip"
+	"os"
+	"strings"
+	"time"
+)
+
+type Kind string
+
+const (
+	// only the generic dummy testing provider for now
+	KindDummy Kind = "dummy"
+)
+
+type RecordType string
+
+const (
+	TypeA    RecordType = "A"
+	TypeAAAA RecordType = "AAAA"
+)
+
+type Config struct {
+	Kind Kind `json:"kind"`
+
+	// exactly one of these supplies the api key.
+	// both expand any $environment variables!
+	Key     string `json:"key,omitempty"`
+	KeyFile string `json:"keyFile,omitempty"`
+}
+
+func (c Config) key() (string, error) {
+	if (c.Key == "") == (c.KeyFile == "") {
+		return "", errors.New("exactly one of key or keyFile must be set")
+	}
+
+	if c.Key != "" {
+		key := os.ExpandEnv(c.Key)
+		if key == "" {
+			return "", fmt.Errorf("key %q expanded to nothing", c.Key)
+		}
+		return key, nil
+	}
+
+	// expand those environment variables
+	raw, err := os.ReadFile(os.ExpandEnv(c.KeyFile))
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(raw)), nil
+}
+
+type Provider interface {
+	// Ensure makes name.zone of the given type point at addr,
+	// creating the record when it doesn't exist yet.
+	// Returns the previous value (if any) and whether anything was changed.
+	Ensure(zone, name string, rtype RecordType, addr netip.Addr) (string, bool, error)
+}
+
+func New(log *slog.Logger, cfg Config) (Provider, error) {
+	switch cfg.Kind {
+	case KindDummy:
+		return newDummy(log)
+	default:
+		return nil, fmt.Errorf("unknown provider kind %q", cfg.Kind)
+	}
+}
+
+var client = http.Client{Timeout: 30 * time.Second}
+
+// generic request sending helper, since most providers will need it.
+func request(method, url string, headers map[string]string, body io.Reader) ([]byte, error) {
+	req, err := http.NewRequest(method, url, body)
+	if err != nil {
+		return nil, err
+	}
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+	if body != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	raw, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode < 200 || resp.StatusCode > 299 {
+		return nil, fmt.Errorf("%s %s: %s: %.200s", method, url, resp.Status, raw)
+	}
+	return raw, nil
+}