feat(checker): port other checkers over

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/checker/headermatches/factory.go

@@ -0,0 +1,66 @@
+package headermatches
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"regexp"
+
+	"github.com/TecharoHQ/anubis/internal"
+	"github.com/TecharoHQ/anubis/lib/checker"
+)
+
+func init() {
+	checker.Register("header_matches", Factory{})
+	checker.Register("user_agent", Factory{defaultHeader: "User-Agent"})
+}
+
+type Factory struct {
+	defaultHeader string
+}
+
+func (f Factory) Build(ctx context.Context, data json.RawMessage) (checker.Interface, error) {
+	var fc fileConfig
+
+	if f.defaultHeader != "" {
+		fc.Header = f.defaultHeader
+	}
+
+	if err := json.Unmarshal([]byte(data), &fc); err != nil {
+		return nil, errors.Join(checker.ErrUnparseableConfig, err)
+	}
+
+	if err := fc.Valid(); err != nil {
+		return nil, errors.Join(checker.ErrInvalidConfig, err)
+	}
+
+	valueRex, err := regexp.Compile(fc.ValueRegex)
+	if err != nil {
+		return nil, errors.Join(ErrInvalidRegex, err)
+	}
+
+	return &Checker{
+		header: http.CanonicalHeaderKey(fc.Header),
+		regexp: valueRex,
+		hash:   internal.FastHash(fc.String()),
+	}, nil
+}
+
+func (f Factory) Valid(ctx context.Context, data json.RawMessage) error {
+	var fc fileConfig
+
+	if f.defaultHeader != "" {
+		fc.Header = f.defaultHeader
+	}
+
+	if err := json.Unmarshal([]byte(data), &fc); err != nil {
+		return err
+	}
+
+	if err := fc.Valid(); err != nil {
+		return err
+	}
+
+	return nil
+}