1// Package dkim (DomainKeys Identified Mail signatures, RFC 6376) signs and
2// verifies DKIM signatures.
4// Signatures are added to email messages in DKIM-Signature headers. By signing a
5// message, a domain takes responsibility for the message. A message can have
6// signatures for multiple domains, and the domain does not necessarily have to
7// match a domain in a From header. Receiving mail servers can build a spaminess
8// reputation based on domains that signed the message, along with other
18 cryptorand "crypto/rand"
27 "github.com/prometheus/client_golang/prometheus"
28 "github.com/prometheus/client_golang/prometheus/promauto"
30 "github.com/mjl-/mox/config"
31 "github.com/mjl-/mox/dns"
32 "github.com/mjl-/mox/mlog"
33 "github.com/mjl-/mox/moxio"
34 "github.com/mjl-/mox/publicsuffix"
35 "github.com/mjl-/mox/smtp"
38var xlog = mlog.New("dkim")
41 metricDKIMSign = promauto.NewCounterVec(
42 prometheus.CounterOpts{
43 Name: "mox_dkim_sign_total",
44 Help: "DKIM messages signings, label key is the type of key, rsa or ed25519.",
50 metricDKIMVerify = promauto.NewHistogramVec(
51 prometheus.HistogramOpts{
52 Name: "mox_dkim_verify_duration_seconds",
53 Help: "DKIM verify, including lookup, duration and result.",
54 Buckets: []float64{0.001, 0.005, 0.01, 0.05, 0.100, 0.5, 1, 5, 10, 20},
63var timeNow = time.Now // Replaced during tests.
65// Status is the result of verifying a DKIM-Signature as described by RFC 8601,
66// "Message Header Field for Indicating Message Authentication Status".
72 StatusNone Status = "none" // Message was not signed.
73 StatusPass Status = "pass" // Message was signed and signature was verified.
74 StatusFail Status = "fail" // Message was signed, but signature was invalid.
75 StatusPolicy Status = "policy" // Message was signed, but signature is not accepted by policy.
76 StatusNeutral Status = "neutral" // Message was signed, but the signature contains an error or could not be processed. This status is also used for errors not covered by other statuses.
77 StatusTemperror Status = "temperror" // Message could not be verified. E.g. because of DNS resolve error. A later attempt may succeed. A missing DNS record is treated as temporary error, a new key may not have propagated through DNS shortly after it was taken into use.
78 StatusPermerror Status = "permerror" // Message cannot be verified. E.g. when a required header field is absent or for invalid (combination of) parameters. Typically set if a DNS record does not allow the signature, e.g. due to algorithm mismatch or expiry.
83 ErrNoRecord = errors.New("dkim: no dkim dns record for selector and domain")
84 ErrMultipleRecords = errors.New("dkim: multiple dkim dns record for selector and domain")
85 ErrDNS = errors.New("dkim: lookup of dkim dns record")
86 ErrSyntax = errors.New("dkim: syntax error in dkim dns record")
89// Signature verification errors.
91 ErrSigAlgMismatch = errors.New("dkim: signature algorithm mismatch with dns record")
92 ErrHashAlgNotAllowed = errors.New("dkim: hash algorithm not allowed by dns record")
93 ErrKeyNotForEmail = errors.New("dkim: dns record not allowed for use with email")
94 ErrDomainIdentityMismatch = errors.New("dkim: dns record disallows mismatch of domain (d=) and identity (i=)")
95 ErrSigExpired = errors.New("dkim: signature has expired")
96 ErrHashAlgorithmUnknown = errors.New("dkim: unknown hash algorithm")
97 ErrBodyhashMismatch = errors.New("dkim: body hash does not match")
98 ErrSigVerify = errors.New("dkim: signature verification failed")
99 ErrSigAlgorithmUnknown = errors.New("dkim: unknown signature algorithm")
100 ErrCanonicalizationUnknown = errors.New("dkim: unknown canonicalization")
101 ErrHeaderMalformed = errors.New("dkim: mail message header is malformed")
102 ErrFrom = errors.New("dkim: bad from headers")
103 ErrQueryMethod = errors.New("dkim: no recognized query method")
104 ErrKeyRevoked = errors.New("dkim: key has been revoked")
105 ErrTLD = errors.New("dkim: signed domain is top-level domain, above organizational domain")
106 ErrPolicy = errors.New("dkim: signature rejected by policy")
107 ErrWeakKey = errors.New("dkim: key is too weak, need at least 1024 bits for rsa")
110// Result is the conclusion of verifying one DKIM-Signature header. An email can
111// have multiple signatures, each with different parameters.
113// To decide what to do with a message, both the signature parameters and the DNS
114// TXT record have to be consulted.
117 Sig *Sig // Parsed form of DKIM-Signature header. Can be nil for invalid DKIM-Signature header.
118 Record *Record // Parsed form of DKIM DNS record for selector and domain in Sig. Optional.
119 Err error // If Status is not StatusPass, this error holds the details and can be checked using errors.Is.
122// todo: use some io.Writer to hash the body and the header.
124// Sign returns line(s) with DKIM-Signature headers, generated according to the configuration.
125func Sign(ctx context.Context, localpart smtp.Localpart, domain dns.Domain, c config.DKIM, smtputf8 bool, msg io.ReaderAt) (headers string, rerr error) {
126 log := xlog.WithContext(ctx)
129 log.Debugx("dkim sign result", rerr, mlog.Field("localpart", localpart), mlog.Field("domain", domain), mlog.Field("smtputf8", smtputf8), mlog.Field("duration", time.Since(start)))
132 hdrs, bodyOffset, err := parseHeaders(bufio.NewReader(&moxio.AtReader{R: msg}))
134 return "", fmt.Errorf("%w: %s", ErrHeaderMalformed, err)
137 for _, h := range hdrs {
138 if h.lkey == "from" {
143 return "", fmt.Errorf("%w: message has %d from headers, need exactly 1", ErrFrom, nfrom)
146 type hashKey struct {
147 simple bool // Canonicalization.
148 hash string // lower-case hash.
151 var bodyHashes = map[hashKey][]byte{}
153 for _, sign := range c.Sign {
154 sel := c.Selectors[sign]
155 sig := newSigWithDefaults()
157 switch sel.Key.(type) {
158 case *rsa.PrivateKey:
159 sig.AlgorithmSign = "rsa"
160 metricDKIMSign.WithLabelValues("rsa").Inc()
161 case ed25519.PrivateKey:
162 sig.AlgorithmSign = "ed25519"
163 metricDKIMSign.WithLabelValues("ed25519").Inc()
165 return "", fmt.Errorf("internal error, unknown pivate key %T", sel.Key)
167 sig.AlgorithmHash = sel.HashEffective
169 sig.Selector = sel.Domain
170 sig.Identity = &Identity{&localpart, domain}
171 sig.SignedHeaders = append([]string{}, sel.HeadersEffective...)
172 if !sel.DontSealHeaders {
174 // Each time a header name is added to the signature, the next unused value is
175 // signed (in reverse order as they occur in the message). So we can add each
176 // header name as often as it occurs. But now we'll add the header names one
177 // additional time, preventing someone from adding one more header later on.
178 counts := map[string]int{}
179 for _, h := range hdrs {
182 for _, h := range sel.HeadersEffective {
183 for j := counts[strings.ToLower(h)]; j > 0; j-- {
184 sig.SignedHeaders = append(sig.SignedHeaders, h)
188 sig.SignTime = timeNow().Unix()
189 if sel.ExpirationSeconds > 0 {
190 sig.ExpireTime = sig.SignTime + int64(sel.ExpirationSeconds)
193 sig.Canonicalization = "simple"
194 if sel.Canonicalization.HeaderRelaxed {
195 sig.Canonicalization = "relaxed"
197 sig.Canonicalization += "/"
198 if sel.Canonicalization.BodyRelaxed {
199 sig.Canonicalization += "relaxed"
201 sig.Canonicalization += "simple"
204 h, hok := algHash(sig.AlgorithmHash)
206 return "", fmt.Errorf("unrecognized hash algorithm %q", sig.AlgorithmHash)
209 // We must now first calculate the hash over the body. Then include that hash in a
210 // new DKIM-Signature header. Then hash that and the signed headers into a data
211 // hash. Then that hash is finally signed and the signature included in the new
212 // DKIM-Signature header.
215 hk := hashKey{!sel.Canonicalization.BodyRelaxed, strings.ToLower(sig.AlgorithmHash)}
216 if bh, ok := bodyHashes[hk]; ok {
219 br := bufio.NewReader(&moxio.AtReader{R: msg, Offset: int64(bodyOffset)})
220 bh, err = bodyHash(h.New(), !sel.Canonicalization.BodyRelaxed, br)
228 sigh, err := sig.Header()
232 verifySig := []byte(strings.TrimSuffix(sigh, "\r\n"))
234 dh, err := dataHash(h.New(), !sel.Canonicalization.HeaderRelaxed, sig, hdrs, verifySig)
239 switch key := sel.Key.(type) {
240 case *rsa.PrivateKey:
241 sig.Signature, err = key.Sign(cryptorand.Reader, dh, h)
243 return "", fmt.Errorf("signing data: %v", err)
245 case ed25519.PrivateKey:
246 // crypto.Hash(0) indicates data isn't prehashed (ed25519ph). We are using
248 sig.Signature, err = key.Sign(cryptorand.Reader, dh, crypto.Hash(0))
250 return "", fmt.Errorf("signing data: %v", err)
253 return "", fmt.Errorf("unsupported private key type: %s", err)
256 sigh, err = sig.Header()
266// Lookup looks up the DKIM TXT record and parses it.
268// A requested record is <selector>._domainkey.<domain>. Exactly one valid DKIM
269// record should be present.
270func Lookup(ctx context.Context, resolver dns.Resolver, selector, domain dns.Domain) (rstatus Status, rrecord *Record, rtxt string, rerr error) {
271 log := xlog.WithContext(ctx)
274 log.Debugx("dkim lookup result", rerr, mlog.Field("selector", selector), mlog.Field("domain", domain), mlog.Field("status", rstatus), mlog.Field("record", rrecord), mlog.Field("duration", time.Since(start)))
277 name := selector.ASCII + "._domainkey." + domain.ASCII + "."
278 records, err := dns.WithPackage(resolver, "dkim").LookupTXT(ctx, name)
279 if dns.IsNotFound(err) {
281 // We must return StatusPermerror. We may want to return StatusTemperror because in
282 // practice someone will start using a new key before DNS changes have propagated.
283 return StatusPermerror, nil, "", fmt.Errorf("%w: dns name %q", ErrNoRecord, name)
284 } else if err != nil {
285 return StatusTemperror, nil, "", fmt.Errorf("%w: dns name %q: %s", ErrDNS, name, err)
289 var status = StatusTemperror
293 for _, s := range records {
295 // but isn't actually valid, results in a StatusPermFail. But a record that isn't
296 // claiming to be DKIM1 is ignored.
299 r, isdkim, err = ParseRecord(s)
300 if err != nil && isdkim {
301 return StatusPermerror, nil, txt, fmt.Errorf("%w: %s", ErrSyntax, err)
302 } else if err != nil {
303 // Hopefully the remote MTA admin discovers the configuration error and fix it for
304 // an upcoming delivery attempt, in case we rejected with temporary status.
305 status = StatusTemperror
306 err = fmt.Errorf("%w: not a dkim record: %s", ErrSyntax, err)
309 // If there are multiple valid records, return a temporary error. Perhaps the error is fixed soon.
313 return StatusTemperror, nil, "", fmt.Errorf("%w: dns name %q", ErrMultipleRecords, name)
321 return status, nil, "", err
323 return StatusNeutral, record, txt, nil
326// Verify parses the DKIM-Signature headers in a message and verifies each of them.
328// If the headers of the message cannot be found, an error is returned.
329// Otherwise, each DKIM-Signature header is reflected in the returned results.
331// NOTE: Verify does not check if the domain (d=) that signed the message is
332// the domain of the sender. The caller, e.g. through DMARC, should do this.
334// If ignoreTestMode is true and the DKIM record is in test mode (t=y), a
335// verification failure is treated as actual failure. With ignoreTestMode
336// false, such verification failures are treated as if there is no signature by
337// returning StatusNone.
338func Verify(ctx context.Context, resolver dns.Resolver, smtputf8 bool, policy func(*Sig) error, r io.ReaderAt, ignoreTestMode bool) (results []Result, rerr error) {
339 log := xlog.WithContext(ctx)
342 duration := float64(time.Since(start)) / float64(time.Second)
343 for _, r := range results {
346 alg = r.Sig.Algorithm()
348 status := string(r.Status)
349 metricDKIMVerify.WithLabelValues(alg, status).Observe(duration)
352 if len(results) == 0 {
353 log.Debugx("dkim verify result", rerr, mlog.Field("smtputf8", smtputf8), mlog.Field("duration", time.Since(start)))
355 for _, result := range results {
356 log.Debugx("dkim verify result", result.Err, mlog.Field("smtputf8", smtputf8), mlog.Field("status", result.Status), mlog.Field("sig", result.Sig), mlog.Field("record", result.Record), mlog.Field("duration", time.Since(start)))
360 hdrs, bodyOffset, err := parseHeaders(bufio.NewReader(&moxio.AtReader{R: r}))
362 return nil, fmt.Errorf("%w: %s", ErrHeaderMalformed, err)
365 // todo: reuse body hashes and possibly verify signatures in parallel. and start the dns lookup immediately.
../rfc/6376:2697
367 for _, h := range hdrs {
368 if h.lkey != "dkim-signature" {
372 sig, verifySig, err := parseSignature(h.raw, smtputf8)
375 err := fmt.Errorf("parsing DKIM-Signature header: %w", err)
376 results = append(results, Result{StatusPermerror, nil, nil, err})
380 h, canonHeaderSimple, canonDataSimple, err := checkSignatureParams(ctx, sig)
382 results = append(results, Result{StatusPermerror, nil, nil, err})
387 if err := policy(sig); err != nil {
388 err := fmt.Errorf("%w: %s", ErrPolicy, err)
389 results = append(results, Result{StatusPolicy, nil, nil, err})
393 br := bufio.NewReader(&moxio.AtReader{R: r, Offset: int64(bodyOffset)})
394 status, txt, err := verifySignature(ctx, resolver, sig, h, canonHeaderSimple, canonDataSimple, hdrs, verifySig, br, ignoreTestMode)
395 results = append(results, Result{status, sig, txt, err})
400// check if signature is acceptable.
401// Only looks at the signature parameters, not at the DNS record.
402func checkSignatureParams(ctx context.Context, sig *Sig) (hash crypto.Hash, canonHeaderSimple, canonBodySimple bool, rerr error) {
405 for _, h := range sig.SignedHeaders {
406 if strings.EqualFold(h, "from") {
412 return 0, false, false, fmt.Errorf(`%w: required "from" header not signed`, ErrFrom)
416 if sig.ExpireTime >= 0 && sig.ExpireTime < timeNow().Unix() {
417 return 0, false, false, fmt.Errorf("%w: expiration time %q", ErrSigExpired, time.Unix(sig.ExpireTime, 0).Format(time.RFC3339))
422 // Refuse signatures that reach beyond declared scope. We use the existing
423 // publicsuffix.Lookup to lookup a fake subdomain of the signing domain. If this
424 // supposed subdomain is actually an organizational domain, the signing domain
425 // shouldn't be signing for its organizational domain.
427 subdom.ASCII = "x." + subdom.ASCII
428 if subdom.Unicode != "" {
429 subdom.Unicode = "x." + subdom.Unicode
431 if orgDom := publicsuffix.Lookup(ctx, subdom); subdom.ASCII == orgDom.ASCII {
432 return 0, false, false, fmt.Errorf("%w: %s", ErrTLD, sig.Domain)
435 h, hok := algHash(sig.AlgorithmHash)
437 return 0, false, false, fmt.Errorf("%w: %q", ErrHashAlgorithmUnknown, sig.AlgorithmHash)
440 t := strings.SplitN(sig.Canonicalization, "/", 2)
442 switch strings.ToLower(t[0]) {
444 canonHeaderSimple = true
447 return 0, false, false, fmt.Errorf("%w: header canonicalization %q", ErrCanonicalizationUnknown, sig.Canonicalization)
454 switch strings.ToLower(canon) {
456 canonBodySimple = true
459 return 0, false, false, fmt.Errorf("%w: body canonicalization %q", ErrCanonicalizationUnknown, sig.Canonicalization)
463 if len(sig.QueryMethods) > 0 {
465 for _, m := range sig.QueryMethods {
466 if strings.EqualFold(m, "dns/txt") {
472 return 0, false, false, fmt.Errorf("%w: need dns/txt", ErrQueryMethod)
476 return h, canonHeaderSimple, canonBodySimple, nil
479// lookup the public key in the DNS and verify the signature.
480func verifySignature(ctx context.Context, resolver dns.Resolver, sig *Sig, hash crypto.Hash, canonHeaderSimple, canonDataSimple bool, hdrs []header, verifySig []byte, body *bufio.Reader, ignoreTestMode bool) (Status, *Record, error) {
482 status, record, _, err := Lookup(ctx, resolver, sig.Selector, sig.Domain)
484 // todo: for temporary errors, we could pass on information so caller returns a 4.7.5 ecode,
../rfc/6376:2777
485 return status, nil, err
487 status, err = verifySignatureRecord(record, sig, hash, canonHeaderSimple, canonDataSimple, hdrs, verifySig, body, ignoreTestMode)
488 return status, record, err
491// verify a DKIM signature given the record from dns and signature from the email message.
492func verifySignatureRecord(r *Record, sig *Sig, hash crypto.Hash, canonHeaderSimple, canonDataSimple bool, hdrs []header, verifySig []byte, body *bufio.Reader, ignoreTestMode bool) (rstatus Status, rerr error) {
496 for _, f := range r.Flags {
497 if strings.EqualFold(f, "y") {
504 if rstatus != StatusPass {
512 if len(r.Hashes) > 0 {
514 for _, h := range r.Hashes {
515 if strings.EqualFold(h, sig.AlgorithmHash) {
521 return StatusPermerror, fmt.Errorf("%w: dkim dns record expects one of %q, message uses %q", ErrHashAlgNotAllowed, strings.Join(r.Hashes, ","), sig.AlgorithmHash)
526 if !strings.EqualFold(r.Key, sig.AlgorithmSign) {
527 return StatusPermerror, fmt.Errorf("%w: dkim dns record requires algorithm %q, message has %q", ErrSigAlgMismatch, r.Key, sig.AlgorithmSign)
531 if r.PublicKey == nil {
532 return StatusPermerror, ErrKeyRevoked
533 } else if rsaKey, ok := r.PublicKey.(*rsa.PublicKey); ok && rsaKey.N.BitLen() < 1024 {
534 // todo: find a reference that supports this.
535 return StatusPermerror, ErrWeakKey
539 if !r.ServiceAllowed("email") {
540 return StatusPermerror, ErrKeyNotForEmail
542 for _, t := range r.Flags {
545 if strings.EqualFold(t, "s") && sig.Identity != nil {
546 if sig.Identity.Domain.ASCII != sig.Domain.ASCII {
547 return StatusPermerror, fmt.Errorf("%w: i= identity domain %q must match d= domain %q", ErrDomainIdentityMismatch, sig.Domain.ASCII, sig.Identity.Domain.ASCII)
553 // todo future: implement l= parameter in signatures. we don't currently allow this through policy check.
554 return StatusPermerror, fmt.Errorf("l= (length) parameter in signature not yet implemented")
557 // We first check the signature is with the claimed body hash is valid. Then we
558 // verify the body hash. In case of invalid signatures, we won't read the entire
563 dh, err := dataHash(hash.New(), canonHeaderSimple, sig, hdrs, verifySig)
565 // Any error is likely an invalid header field in the message, hence permanent error.
566 return StatusPermerror, fmt.Errorf("calculating data hash: %w", err)
569 switch k := r.PublicKey.(type) {
571 if err := rsa.VerifyPKCS1v15(k, hash, dh, sig.Signature); err != nil {
572 return StatusFail, fmt.Errorf("%w: rsa verification: %s", ErrSigVerify, err)
574 case ed25519.PublicKey:
575 if ok := ed25519.Verify(k, dh, sig.Signature); !ok {
576 return StatusFail, fmt.Errorf("%w: ed25519 verification", ErrSigVerify)
579 return StatusPermerror, fmt.Errorf("%w: unrecognized signature algorithm %q", ErrSigAlgorithmUnknown, r.Key)
582 bh, err := bodyHash(hash.New(), canonDataSimple, body)
584 // Any error is likely some internal error, hence temporary error.
585 return StatusTemperror, fmt.Errorf("calculating body hash: %w", err)
587 if !bytes.Equal(sig.BodyHash, bh) {
588 return StatusFail, fmt.Errorf("%w: signature bodyhash %x != calculated bodyhash %x", ErrBodyhashMismatch, sig.BodyHash, bh)
591 return StatusPass, nil
594func algHash(s string) (crypto.Hash, bool) {
595 if strings.EqualFold(s, "sha1") {
596 return crypto.SHA1, true
597 } else if strings.EqualFold(s, "sha256") {
598 return crypto.SHA256, true
603// bodyHash calculates the hash over the body.
604func bodyHash(h hash.Hash, canonSimple bool, body *bufio.Reader) ([]byte, error) {
605 // todo: take l= into account. we don't currently allow it for policy reasons.
607 var crlf = []byte("\r\n")
613 buf, err := body.ReadBytes('\n')
614 if len(buf) == 0 && err == io.EOF {
617 if err != nil && err != io.EOF {
620 hascrlf := bytes.HasSuffix(buf, crlf)
622 buf = buf[:len(buf)-2]
625 for ; ncrlf > 0; ncrlf-- {
636 hb := bufio.NewWriter(h)
638 // We go through the body line by line, replacing WSP with a single space and removing whitespace at the end of lines.
639 // We stash "empty" lines. If they turn out to be at the end of the file, we must drop them.
640 stash := &bytes.Buffer{}
641 var line bool // Whether buffer read is for continuation of line.
642 var prev byte // Previous byte read for line.
643 linesEmpty := true // Whether stash contains only empty lines and may need to be dropped.
644 var bodynonempty bool // Whether body is non-empty, for adding missing crlf.
645 var hascrlf bool // Whether current/last line ends with crlf, for adding missing crlf.
647 // todo: should not read line at a time, count empty lines. reduces max memory usage. a message with lots of empty lines can cause high memory use.
648 buf, err := body.ReadBytes('\n')
649 if len(buf) == 0 && err == io.EOF {
652 if err != nil && err != io.EOF {
657 hascrlf = bytes.HasSuffix(buf, crlf)
659 buf = buf[:len(buf)-2]
662 // todo: what is "whitespace"? it isn't WSP (space and tab), the next line mentions WSP explicitly for another rule. should we drop trailing \r, \n, \v, more?
663 buf = bytes.TrimRight(buf, " \t")
666 // Replace one or more WSP to a single SP.
667 for i, c := range buf {
668 wsp := c == ' ' || c == '\t'
669 if (i >= 0 || line) && wsp {
688 hb.Write(stash.Bytes())
694 // Only for non-empty bodies without trailing crlf do we add the missing crlf.
695 if bodynonempty && !hascrlf {
701 return h.Sum(nil), nil
704func dataHash(h hash.Hash, canonSimple bool, sig *Sig, hdrs []header, verifySig []byte) ([]byte, error) {
706 revHdrs := map[string][]header{}
707 for _, h := range hdrs {
708 revHdrs[h.lkey] = append([]header{h}, revHdrs[h.lkey]...)
711 for _, key := range sig.SignedHeaders {
712 lkey := strings.ToLower(key)
717 revHdrs[lkey] = h[1:]
718 s := string(h[0].raw)
724 ch, err := relaxedCanonicalHeaderWithoutCRLF(s)
726 return nil, fmt.Errorf("canonicalizing header: %w", err)
728 headers += ch + "\r\n"
732 h.Write([]byte(headers))
735 ch, err := relaxedCanonicalHeaderWithoutCRLF(string(verifySig))
737 return nil, fmt.Errorf("canonicalizing DKIM-Signature header: %w", err)
742 return h.Sum(nil), nil
745// a single header, can be multiline.
746func relaxedCanonicalHeaderWithoutCRLF(s string) (string, error) {
748 t := strings.SplitN(s, ":", 2)
750 return "", fmt.Errorf("%w: invalid header %q", ErrHeaderMalformed, s)
753 // Unfold, we keep the leading WSP on continuation lines and fix it up below.
754 v := strings.ReplaceAll(t[1], "\r\n", "")
756 // Replace one or more WSP to a single SP.
759 for i, c := range []byte(v) {
760 if i >= 0 && c == ' ' || c == '\t' {
772 ch := strings.ToLower(strings.TrimRight(t[0], " \t")) + ":" + strings.Trim(string(nv), " \t")
777 key string // Key in original case.
778 lkey string // Key in lower-case, for canonical case.
779 value []byte // Literal header value, possibly spanning multiple lines, not modified in any way, including crlf, excluding leading key and colon.
780 raw []byte // Like value, but including original leading key and colon. Ready for use as simple header canonicalized use.
783func parseHeaders(br *bufio.Reader) ([]header, int, error) {
790 line, err := readline(br)
795 if bytes.Equal(line, []byte("\r\n")) {
798 if line[0] == ' ' || line[0] == '\t' {
799 if len(l) == 0 && key == "" {
800 return nil, 0, fmt.Errorf("malformed message, starts with space/tab")
802 value = append(value, line...)
803 raw = append(raw, line...)
807 l = append(l, header{key, lkey, value, raw})
809 t := bytes.SplitN(line, []byte(":"), 2)
811 return nil, 0, fmt.Errorf("malformed message, header without colon")
814 key = strings.TrimRight(string(t[0]), " \t") // todo: where is this specified?
816 for _, c := range key {
817 if c <= ' ' || c >= 0x7f {
818 return nil, 0, fmt.Errorf("invalid header field name")
822 return nil, 0, fmt.Errorf("empty header key")
824 lkey = strings.ToLower(key)
825 value = append([]byte{}, t[1]...)
826 raw = append([]byte{}, line...)
829 l = append(l, header{key, lkey, value, raw})
834func readline(r *bufio.Reader) ([]byte, error) {
837 line, err := r.ReadBytes('\n')
841 if bytes.HasSuffix(line, []byte("\r\n")) {
845 return append(buf, line...), nil
847 buf = append(buf, line...)