chore: start refactor of checkers into separate packages

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

lib/policy/checker/remoteaddress/remoteaddress.go

@@ -0,0 +1,104 @@
+package remoteaddress
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/netip"
+
+	"github.com/TecharoHQ/anubis/internal"
+	"github.com/TecharoHQ/anubis/lib/policy"
+	"github.com/TecharoHQ/anubis/lib/policy/checker"
+	"github.com/TecharoHQ/anubis/lib/policy/config"
+	"github.com/gaissmai/bart"
+)
+
+var (
+	ErrNoRemoteAddresses = errors.New("remoteaddress: no remote addresses defined")
+)
+
+func init() {}
+
+type Factory struct{}
+
+func (Factory) ValidateConfig(inp json.RawMessage) error {
+	var fc fileConfig
+	if err := json.Unmarshal([]byte(inp), &fc); err != nil {
+		return fmt.Errorf("%w: %w", config.ErrUnparseableConfig, err)
+	}
+
+	if err := fc.Valid(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (Factory) Create(inp json.RawMessage) (checker.Impl, error) {
+	c := struct {
+		RemoteAddr []netip.Prefix `json:"remote_addresses,omitempty" yaml:"remote_addresses,omitempty"`
+	}{}
+
+	if err := json.Unmarshal([]byte(inp), &c); err != nil {
+		return nil, fmt.Errorf("%w: %w", config.ErrUnparseableConfig, err)
+	}
+
+	table := new(bart.Lite)
+
+	for _, cidr := range c.RemoteAddr {
+		table.Insert(cidr)
+	}
+
+	return &RemoteAddrChecker{
+		prefixTable: table,
+		hash:        internal.FastHash(string(inp)),
+	}, nil
+}
+
+type fileConfig struct {
+	RemoteAddr []string `json:"remote_addresses,omitempty" yaml:"remote_addresses,omitempty"`
+}
+
+func (fc fileConfig) Valid() error {
+	var errs []error
+
+	if len(fc.RemoteAddr) == 0 {
+		errs = append(errs, ErrNoRemoteAddresses)
+	}
+
+	for _, cidr := range fc.RemoteAddr {
+		if _, err := netip.ParsePrefix(cidr); err != nil {
+			errs = append(errs, fmt.Errorf("%w: cidr %q is invalid: %w", config.ErrInvalidCIDR, cidr, err))
+		}
+	}
+
+	if len(errs) != 0 {
+		return fmt.Errorf("%w: %w", policy.ErrMisconfiguration, errors.Join(errs...))
+	}
+
+	return nil
+}
+
+type RemoteAddrChecker struct {
+	prefixTable *bart.Lite
+	hash        string
+}
+
+func (rac *RemoteAddrChecker) Check(r *http.Request) (bool, error) {
+	host := r.Header.Get("X-Real-Ip")
+	if host == "" {
+		return false, fmt.Errorf("%w: header X-Real-Ip is not set", policy.ErrMisconfiguration)
+	}
+
+	addr, err := netip.ParseAddr(host)
+	if err != nil {
+		return false, fmt.Errorf("%w: %s is not an IP address: %w", policy.ErrMisconfiguration, host, err)
+	}
+
+	return rac.prefixTable.Contains(addr), nil
+}
+
+func (rac *RemoteAddrChecker) Hash() string {
+	return rac.hash
+}