mirror of
https://blitiri.com.ar/repos/chasquid
synced 2026-10-28 15:02:28 +00:00
Alberto Bertogli
b153955d5d
When verifying emails, for each entry in the h= tag, we would scan all headers, leading to quadratic behaviour. Similarly, when signing, for each instance of a signed header we would scan all headers. This could lead to unauthenticated DoS via work amplification. This patch fixes the problem by going through the headers only once, so behaviour is now linear, and also limiting the size of the h= tag for defense in depth. The limit is in line with what other implementations use, so it should not cause any interoperability problems. Thanks to John JEAN <john@wargan.com> for finding and reporting this problem. The detailed report can be found in https://johnjean.io/advisories/chasquid-unauthenticated-remote-dos/.
473 lines
10 KiB
Go
473 lines
10 KiB
Go
package dkim
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import (
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"crypto"
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"encoding/base64"
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"errors"
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"fmt"
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"strconv"
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"strings"
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"testing"
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"time"
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"github.com/google/go-cmp/cmp"
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"github.com/google/go-cmp/cmp/cmpopts"
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)
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func TestSignatureFromHeader(t *testing.T) {
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cases := []struct {
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in string
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want *dkimSignature
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err error
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}{
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{
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in: "v=1; a=rsa-sha256",
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want: nil,
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err: errMissingRequiredTag,
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},
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{
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in: "v=1; a=rsa-sha256 ; c = simple/relaxed ;" +
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" d=example.com; h= from : to: subject ; " +
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"i=agent@example.com; l=77; q=dns/txt; " +
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"s=selector; t=1600700888; x=1600700999; " +
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"z=From:lala@lele | to:lili@lolo;" +
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"b=aG9sY\r\n SBxdWUgdGFs;" +
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"bh = Y29\ttby Bhbm Rhcw==",
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want: &dkimSignature{
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v: "1",
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a: "rsa-sha256",
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cH: simpleCanonicalization,
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cB: relaxedCanonicalization,
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d: "example.com",
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h: []string{"from", "to", "subject"},
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i: "agent@example.com",
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l: new(uint64(77)),
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q: []string{"dns/txt"},
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s: "selector",
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t: time.Unix(1600700888, 0),
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x: time.Unix(1600700999, 0),
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z: "From:lala@lele|to:lili@lolo",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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KeyType: keyTypeRSA,
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Hash: crypto.SHA256,
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},
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},
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{
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// Example from RFC.
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// https://datatracker.ietf.org/doc/html/rfc6376#section-3.5
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in: "v=1; a=rsa-sha256; d=example.net; s=brisbane;\r\n" +
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" c=simple; q=dns/txt; i=@eng.example.net;\r\n" +
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" t=1117574938; x=1118006938;\r\n" +
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" h=from:to:subject:date;\r\n" +
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" z=From:foo@eng.example.net|To:joe@example.com|\r\n" +
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" Subject:demo=20run|Date:July=205,=202005=203:44:08=20PM=20-0700;\r\n" +
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"bh=MTIzNDU2Nzg5MDEyMzQ1Njc4OTAxMjM0NTY3ODkwMTI=;\r\n" +
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"b=dzdVyOfAKCdLXdJOc9G2q8LoXSlEniS" +
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"bav+yuU4zGeeruD00lszZVoG4ZHRNiYzR",
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want: &dkimSignature{
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v: "1",
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a: "rsa-sha256",
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d: "example.net",
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s: "brisbane",
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cH: simpleCanonicalization,
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cB: simpleCanonicalization,
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q: []string{"dns/txt"},
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i: "@eng.example.net",
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t: time.Unix(1117574938, 0),
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x: time.Unix(1118006938, 0),
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h: []string{"from", "to", "subject", "date"},
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z: "From:foo@eng.example.net|To:joe@example.com|" +
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"Subject:demo=20run|" +
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"Date:July=205,=202005=203:44:08=20PM=20-0700",
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bh: []byte("12345678901234567890123456789012"),
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b: []byte("w7U\xc8\xe7\xc0('K]\xd2Ns\xd1\xb6" +
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"\xab\xc2\xe8])D\x9e$\x9bj\xff\xb2\xb9N3" +
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"\x19\xe7\xab\xb8=4\x96\xcc\xd9V\x81\xb8" +
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"dtM\x89\x8c\xd1"),
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KeyType: keyTypeRSA,
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Hash: crypto.SHA256,
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},
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},
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{
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in: "",
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want: nil,
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err: errInvalidTag,
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},
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{
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in: "v=666",
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want: nil,
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err: errInvalidVersion,
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},
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{
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in: "v=1; a=something;",
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want: nil,
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err: errBadATag,
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},
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{
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// Invalid b= tag.
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in: "v=1; a=rsa-sha256; b=invalid",
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want: nil,
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err: base64.CorruptInputError(4),
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},
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{
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// Invalid bh= tag.
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in: "v=1; a=rsa-sha256; bh=invalid",
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want: nil,
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err: base64.CorruptInputError(4),
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},
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{
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// Invalid c= tag.
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in: "v=1; a=rsa-sha256; c=caca",
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want: nil,
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err: errUnknownCanonicalization,
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},
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{
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// Invalid l= tag.
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in: "v=1; a=rsa-sha256; l=a1234b",
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want: nil,
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err: strconv.ErrSyntax,
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},
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{
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// q= tag without dns/txt.
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in: "v=1; a=rsa-sha256; q=other/method",
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want: nil,
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err: errInvalidSignature,
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},
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{
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// Invalid t= tag.
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in: "v=1; a=rsa-sha256; t=a1234b",
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want: nil,
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err: strconv.ErrSyntax,
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},
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{
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// Invalid x= tag.
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in: "v=1; a=rsa-sha256; x=a1234b",
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want: nil,
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err: strconv.ErrSyntax,
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},
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{
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// Invalid t= tag.
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in: "v=1; a=rsa-sha256; t=-12345",
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want: nil,
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err: errNegativeTimestamp,
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},
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{
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// Invalid x= tag.
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in: "v=1; a=rsa-sha256; x=-1234",
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want: nil,
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err: errNegativeTimestamp,
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},
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{
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// Unknown hash algorithm.
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in: "v=1; a=rsa-sxa666",
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want: nil,
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err: errUnsupportedHash,
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},
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{
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// Unknown key type.
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in: "v=1; a=rxa-sha256",
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want: nil,
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err: errUnsupportedKeyType,
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},
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}
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for _, c := range cases {
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sig, err := dkimSignatureFromHeader(c.in)
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diff := cmp.Diff(c.want, sig,
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cmp.AllowUnexported(dkimSignature{}),
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cmpopts.EquateEmpty(),
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)
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if diff != "" {
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t.Errorf("dkimSignatureFromHeader(%q) mismatch (-want +got):\n%s",
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c.in, diff)
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}
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if !errors.Is(err, c.err) {
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t.Errorf("dkimSignatureFromHeader(%q) error: got %v, want %v",
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c.in, err, c.err)
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}
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}
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}
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func TestSignatureFromHeaderHTagLimit(t *testing.T) {
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sigWithH := func(n int) string {
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return "v=1; a=rsa-sha256; d=example.com; s=selector;" +
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" b=aG9sYQ==; bh=aG9sYQ==;" +
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" h=" + strings.Repeat("x:", n-1) + "from"
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}
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// At the limit is fine.
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sig, err := dkimSignatureFromHeader(sigWithH(maxHTagEntries))
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if err != nil {
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t.Fatalf("h= with %d entries: unexpected error: %v",
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maxHTagEntries, err)
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}
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if len(sig.h) != maxHTagEntries {
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t.Errorf("h= with %d entries: got %d entries",
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maxHTagEntries, len(sig.h))
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}
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// Over the limit is not.
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sig, err = dkimSignatureFromHeader(sigWithH(maxHTagEntries + 1))
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if sig != nil || !errors.Is(err, errInvalidTag) {
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t.Errorf("h= with %d entries: wanted nil / %v, got %v / %v",
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maxHTagEntries+1, errInvalidTag, sig, err)
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}
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}
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func TestCanonicalizationFromString(t *testing.T) {
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cases := []struct {
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in string
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cH, cB canonicalization
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err error
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}{
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{
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in: "",
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cH: simpleCanonicalization,
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cB: simpleCanonicalization,
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},
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{
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in: "simple",
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cH: simpleCanonicalization,
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cB: simpleCanonicalization,
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},
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{
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in: "relaxed",
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cH: relaxedCanonicalization,
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cB: simpleCanonicalization,
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},
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{
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in: "simple/simple",
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cH: simpleCanonicalization,
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cB: simpleCanonicalization,
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},
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{
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in: "relaxed/relaxed",
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cH: relaxedCanonicalization,
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cB: relaxedCanonicalization,
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},
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{
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in: "simple/relaxed",
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cH: simpleCanonicalization,
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cB: relaxedCanonicalization,
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},
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{
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in: "relaxed/bad",
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cH: relaxedCanonicalization,
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err: errUnknownCanonicalization,
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},
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{
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in: "bad/relaxed",
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err: errUnknownCanonicalization,
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},
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{
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in: "bad",
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err: errUnknownCanonicalization,
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},
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}
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for _, c := range cases {
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sig := &dkimSignature{}
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err := sig.canonicalizationFromString(c.in)
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if sig.cH != c.cH || sig.cB != c.cB || !errors.Is(err, c.err) {
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t.Errorf("canonicalizationFromString(%q) "+
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"got (%v, %v, %v), want (%v, %v, %v)",
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c.in, sig.cH, sig.cB, err, c.cH, c.cB, c.err)
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}
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}
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}
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func TestCheckRequiredTags(t *testing.T) {
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cases := []struct {
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sig *dkimSignature
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err string
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}{
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{
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sig: &dkimSignature{},
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err: "missing required tag: a=",
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},
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{
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sig: &dkimSignature{a: "rsa-sha256"},
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err: "missing required tag: b=",
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},
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{
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sig: &dkimSignature{a: "rsa-sha256", b: []byte("hola que tal")},
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err: "missing required tag: bh=",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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},
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err: "missing required tag: d=",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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d: "example.com",
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},
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err: "missing required tag: h=",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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d: "example.com",
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h: []string{"from"},
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},
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err: "missing required tag: s=",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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d: "example.com",
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h: []string{"subject"},
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s: "selector",
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},
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err: "invalid tag: h= does not contain 'from'",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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d: "example.com",
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h: []string{"from"},
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s: "selector",
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i: "@example.net",
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},
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err: "invalid tag: i= is not a subdomain of d=",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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d: "example.com",
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h: []string{"from"},
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s: "selector",
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i: "@anexample.com", // i= is a substring but not subdomain.
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},
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err: "invalid tag: i= is not a subdomain of d=",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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d: "example.com",
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h: []string{"From"}, // Capitalize to check case fold.
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s: "selector",
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i: "@example.com", // i= is the same as d=
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},
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err: "<nil>",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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d: "example.com",
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h: []string{"From"},
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s: "selector",
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i: "@sub.example.com", // i= is a subdomain of d=
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},
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err: "<nil>",
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},
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{
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sig: &dkimSignature{
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a: "rsa-sha256",
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b: []byte("hola que tal"),
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bh: []byte("como andas"),
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d: "example.com",
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h: []string{"from"},
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s: "selector",
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},
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err: "<nil>",
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},
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}
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for i, c := range cases {
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err := c.sig.checkRequiredTags()
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got := fmt.Sprintf("%v", err)
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if c.err != got {
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t.Errorf("%d: checkRequiredTags() got %v, want %v",
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i, err, c.err)
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}
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}
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}
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func TestParseTags(t *testing.T) {
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cases := []struct {
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in string
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want tags
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err error
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}{
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{
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in: "v=1; a=lalala; b = 123 ; c= 456;\t d \t= \t789\t ",
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want: tags{
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"v": "1",
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"a": "lalala",
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"b": "123",
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"c": "456",
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"d": "789",
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},
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err: nil,
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},
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{
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// Trailing semicolon.
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in: "v=1; a=lalala ; ",
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want: tags{
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"v": "1",
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"a": "lalala",
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},
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err: nil,
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},
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{
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// Missing tag value; this is okay.
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in: "v=1; b = ; c = d;",
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want: tags{
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"v": "1",
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"b": "",
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"c": "d",
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},
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err: nil,
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},
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{
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// Missing '='.
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in: "v=1; ; c = d;",
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want: nil,
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err: errInvalidTag,
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},
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{
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// Missing tag name.
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in: "v=1; = b ; c = d;",
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want: nil,
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err: errInvalidTag,
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},
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{
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// Duplicate tag.
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in: "v=1; a=b; a=c;",
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want: nil,
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err: errInvalidTag,
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},
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}
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for _, c := range cases {
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got, err := parseTags(c.in)
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if diff := cmp.Diff(c.want, got); diff != "" {
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t.Errorf("parseTags(%q) mismatch (-want +got):\n%s", c.in, diff)
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}
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if !errors.Is(err, c.err) {
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t.Errorf("parseTags(%q) error: got %v, want %v", c.in, err, c.err)
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}
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}
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}
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