feat(checker): port other checkers over

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

lib/checker/headermatches/config.go

@@ -0,0 +1,44 @@
+package headermatches
+
+import (
+	"errors"
+	"fmt"
+	"regexp"
+)
+
+var (
+	ErrNoHeader     = errors.New("headermatches: no header is configured")
+	ErrNoValueRegex = errors.New("headermatches: no value regex is configured")
+	ErrInvalidRegex = errors.New("headermatches: value regex is invalid")
+)
+
+type fileConfig struct {
+	Header     string `json:"header" yaml:"header"`
+	ValueRegex string `json:"value_regex" yaml:"value_regex"`
+}
+
+func (fc fileConfig) String() string {
+	return fmt.Sprintf("header=%q value_regex=%q", fc.Header, fc.ValueRegex)
+}
+
+func (fc fileConfig) Valid() error {
+	var errs []error
+
+	if fc.Header == "" {
+		errs = append(errs, ErrNoHeader)
+	}
+
+	if fc.ValueRegex == "" {
+		errs = append(errs, ErrNoValueRegex)
+	}
+
+	if _, err := regexp.Compile(fc.ValueRegex); err != nil {
+		errs = append(errs, ErrInvalidRegex, err)
+	}
+
+	if len(errs) != 0 {
+		return errors.Join(errs...)
+	}
+
+	return nil
+}