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package submit
import (
"crypto/ed25519"
"crypto/sha1"
"crypto/sha256"
"encoding/base64"
"encoding/hex"
"fmt"
"net/mail"
"net/url"
"regexp"
"strconv"
"strings"
"time"
"n2usenet/internal/config"
)
var newsgroupRE = regexp.MustCompile(`(?i)^[a-z0-9][a-z0-9.-]*[a-z0-9]$`)
type Submission struct {
From string
FromAddress string
Newsgroups []string
Subject string
References string
Hashcash string
Message string
SignedText string
PublicKeyB64 string
SignatureB64 string
TokenHash string
}
func ParseAndValidate(form url.Values, cfg config.SecurityConfig) (Submission, error) {
sub := Submission{
From: strings.TrimSpace(form.Get("from")),
Subject: cleanHeader(form.Get("subject")),
References: cleanHeader(form.Get("references")),
Hashcash: normalizeHashcash(form.Get("xhashcash")),
Message: strings.TrimSpace(form.Get("message")),
PublicKeyB64: strings.TrimSpace(form.Get("x-ed25519-pub")),
SignatureB64: strings.TrimSpace(form.Get("x-ed25519-sig")),
}
if sub.From == "" || sub.Subject == "" || sub.Hashcash == "" || sub.Message == "" {
return Submission{}, fmt.Errorf("missing required field")
}
if len(sub.Subject) > 200 {
return Submission{}, fmt.Errorf("subject too long")
}
if len([]byte(sub.Message)) < cfg.MinMessageBytes || len([]byte(sub.Message)) > cfg.MaxMessageBytes {
return Submission{}, fmt.Errorf("invalid message size")
}
addr, err := mail.ParseAddress(sub.From)
if err != nil || addr.Address == "" || addr.Name == "" {
return Submission{}, fmt.Errorf("invalid from")
}
sub.FromAddress = addr.Address
groups := splitNewsgroups(form.Get("newsgroups"))
if len(groups) == 0 || len(groups) > cfg.MaxNewsgroups {
return Submission{}, fmt.Errorf("invalid newsgroup count")
}
for _, group := range groups {
if !newsgroupRE.MatchString(group) {
return Submission{}, fmt.Errorf("invalid newsgroup")
}
}
sub.Newsgroups = groups
if err := VerifyHashcash(sub.Hashcash, sub.FromAddress, cfg.MinHashcashBits, 48*time.Hour, 2*time.Hour); err != nil {
return Submission{}, err
}
h := sha256.Sum256([]byte(sub.Hashcash))
sub.TokenHash = hex.EncodeToString(h[:])
if sub.PublicKeyB64 == "" || sub.SignatureB64 == "" {
return Submission{}, fmt.Errorf("missing signature")
}
signedText := SignedPayload(sub.Message, sub.SignatureB64)
if err := VerifySignature(signedText, sub.PublicKeyB64, sub.SignatureB64); err != nil {
return Submission{}, err
}
sub.SignedText = signedText
return sub, nil
}
func splitNewsgroups(raw string) []string {
var out []string
for _, part := range strings.Split(raw, ",") {
part = strings.ToLower(strings.TrimSpace(part))
if part != "" {
out = append(out, part)
}
}
return out
}
func cleanHeader(v string) string {
v = strings.TrimSpace(v)
v = strings.ReplaceAll(v, "\r", "")
v = strings.ReplaceAll(v, "\n", "")
return v
}
func normalizeHashcash(token string) string {
return strings.Join(strings.Fields(strings.TrimSpace(token)), "")
}
func VerifyHashcash(token, resource string, minBits int, maxAge, maxFuture time.Duration) error {
parts := strings.Split(token, ":")
if len(parts) != 7 {
return fmt.Errorf("invalid hashcash format")
}
if parts[0] != "1" {
return fmt.Errorf("unsupported hashcash version")
}
bits, err := strconv.Atoi(parts[1])
if err != nil || bits < minBits {
return fmt.Errorf("insufficient hashcash bits")
}
if !strings.EqualFold(strings.TrimSpace(parts[3]), strings.TrimSpace(resource)) {
return fmt.Errorf("hashcash resource mismatch")
}
ts, err := parseHashcashTime(parts[2])
if err != nil {
return fmt.Errorf("invalid hashcash date")
}
now := time.Now().UTC()
if now.Sub(ts) > maxAge || ts.Sub(now) > maxFuture {
return fmt.Errorf("hashcash date outside allowed window")
}
sum := sha1.Sum([]byte(token))
if leadingZeroBits(sum[:]) < bits {
return fmt.Errorf("hashcash proof invalid")
}
return nil
}
func parseHashcashTime(v string) (time.Time, error) {
layouts := []string{"060102150405", "0601021504", "06010215", "060102"}
for _, layout := range layouts {
if len(v) != len(layout) {
continue
}
if t, err := time.ParseInLocation(layout, v, time.UTC); err == nil {
return t, nil
}
}
return time.Time{}, fmt.Errorf("unsupported date")
}
func leadingZeroBits(b []byte) int {
total := 0
for _, x := range b {
if x == 0 {
total += 8
continue
}
for i := 7; i >= 0; i-- {
if x&(1<<uint(i)) == 0 {
total++
continue
}
return total
}
}
return total
}
func SignedPayload(message, sigB64 string) string {
message = strings.TrimSpace(message)
marker := "\n\n--- Digital Signature ---\n" + strings.TrimSpace(sigB64)
if strings.HasSuffix(message, marker) {
return strings.TrimSpace(strings.TrimSuffix(message, marker))
}
return message
}
func VerifySignature(message, pubB64, sigB64 string) error {
pub, err := base64.StdEncoding.DecodeString(pubB64)
if err != nil || len(pub) != ed25519.PublicKeySize {
return fmt.Errorf("invalid public key")
}
sig, err := base64.StdEncoding.DecodeString(sigB64)
if err != nil || len(sig) != ed25519.SignatureSize {
return fmt.Errorf("invalid signature")
}
if !ed25519.Verify(ed25519.PublicKey(pub), []byte(message), sig) {
return fmt.Errorf("signature verification failed")
}
return nil
}
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