refactor(#130): move IsBlockedIP to internal/netutil to remove gitea import in validateurl.go

validateurl.go is VCS-generic but imported gitea.IsBlockedIP, creating an
unexpected generic→Gitea-specific dependency. Extract IsBlockedIP and its
CIDR list to internal/netutil/ipcheck.go (a neutral shared package).

- gitea/ipcheck.go becomes a thin forwarding wrapper (preserves API compat
  for callers within the gitea package)
- gitea/ipcheck_test.go replaced with a forwarding smoke test; full coverage
  moves to internal/netutil/ipcheck_test.go
- validateurl.go now imports internal/netutil directly

gitea/ipcheck.go

@@ -1,91 +1,22 @@
 // Package gitea provides a client for the Gitea API.
-// ipcheck.go implements IP-level SSRF protection by checking resolved addresses
-// against known blocked CIDR ranges (RFC1918, loopback, link-local, etc.).
+// ipcheck.go re-exports the IsBlockedIP function from internal/netutil for use
+// by this package's safe dialer (client.go) and for backward compatibility with
+// any callers that previously imported it from here.
+//
+// The implementation has moved to internal/netutil so it can be shared with the
+// validate-url subcommand (cmd/review-bot/validateurl.go) without creating a
+// dependency from VCS-generic code on the Gitea-specific package.
 package gitea
 
 import (
-	"fmt"
 	"net"
+
+	"gitea.weiker.me/rodin/review-bot/internal/netutil"
 )
 
-// blockedCIDRStrings is the canonical list of CIDR strings that should never
-// be contacted by review-bot. See IsBlockedIP for the full list of covered
-// address families.
-//
-// These are hard-coded literals: any parse failure is a programming error.
-// Validity is verified by TestBlockedCIDRsValid in ipcheck_test.go.
-var blockedCIDRStrings = []string{
-	// IPv4 loopback
-	"127.0.0.0/8",
-	// IPv4 unspecified / "this network"
-	"0.0.0.0/8",
-	// RFC1918 private ranges
-	"10.0.0.0/8",
-	"172.16.0.0/12",
-	"192.168.0.0/16",
-	// IPv4 link-local (APIPA, also used by AWS instance metadata 169.254.169.254)
-	"169.254.0.0/16",
-	// IPv4 shared address space (RFC6598, carrier-grade NAT)
-	"100.64.0.0/10",
-	// IPv4 multicast
-	"224.0.0.0/4",
-	// IPv4 reserved / broadcast
-	"240.0.0.0/4",
-	// IPv6 loopback
-	"::1/128",
-	// IPv6 unspecified
-	"::/128",
-	// IPv6 link-local
-	"fe80::/10",
-	// IPv6 unique local (ULA) — RFC4193
-	"fc00::/7",
-	// IPv6 multicast
-	"ff00::/8",
-}
-
-// blockedCIDRs is the parsed form of blockedCIDRStrings.
-// Any entry that fails to parse is recorded in blockedCIDRParseErrors instead
-// of panicking; tests verify this slice is always empty via TestBlockedCIDRsValid.
-var (
-	blockedCIDRs           []*net.IPNet
-	blockedCIDRParseErrors []string
-)
-
-func init() {
-	blockedCIDRs = make([]*net.IPNet, 0, len(blockedCIDRStrings))
-	for _, r := range blockedCIDRStrings {
-		_, cidr, err := net.ParseCIDR(r)
-		if err != nil {
-			// Record the error rather than panicking; TestBlockedCIDRsValid
-			// will catch this during tests, and the CI build will fail.
-			blockedCIDRParseErrors = append(blockedCIDRParseErrors,
-				fmt.Sprintf("ipcheck: invalid built-in CIDR %q: %v", r, err))
-			continue
-		}
-		blockedCIDRs = append(blockedCIDRs, cidr)
-	}
-}
-
 // IsBlockedIP reports whether ip is in a blocked address range.
-// It is exported for use by the validate-url subcommand and tests outside
-// this package.
-//
-// IPv6-mapped IPv4 addresses (e.g. ::ffff:192.168.1.1) are normalized to their
-// IPv4 form before checking so that IPv4 CIDRs catch them.
-//
-// Based on:
-//   - RFC1918 private ranges
-//   - RFC5735 / RFC4193 special-use IPv4/IPv6 ranges
-//   - RFC4291 IPv6 link-local / loopback
+// It delegates to internal/netutil.IsBlockedIP; see that function for the full
+// list of blocked ranges and IPv6-mapped IPv4 normalization behavior.
 func IsBlockedIP(ip net.IP) bool {
-	// Normalize IPv6-mapped IPv4 addresses (::ffff:x.x.x.x) to plain IPv4.
-	if v4 := ip.To4(); v4 != nil {
-		ip = v4
-	}
-	for _, cidr := range blockedCIDRs {
-		if cidr.Contains(ip) {
-			return true
-		}
-	}
-	return false
+	return netutil.IsBlockedIP(ip)
 }