Add fork of Go 1.15-dev's crypto/x509

Snapshotted from Go commit 619c7a48a38b28b521591b490fd14ccb7ea5e821
(https://go-review.googlesource.com/c/go/+/229762,
"crypto/x509: add x509omitbundledroots build tag to not embed roots")

With 975c01342a25899962969833d8b2873dc8856a4f
(https://go-review.googlesource.com/c/go/+/220721) removed, because it
depends on other stuff in Go std that doesn't yet exist in a Go
release.

Also, add a subset fork of Go's internal/testenv, for use by x509's tests.

tempfork/x509/cert_pool.go

@@ -0,0 +1,159 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package x509
+
+import (
+	"encoding/pem"
+	"errors"
+	"runtime"
+)
+
+// CertPool is a set of certificates.
+type CertPool struct {
+	bySubjectKeyId map[string][]int
+	byName         map[string][]int
+	certs          []*Certificate
+}
+
+// NewCertPool returns a new, empty CertPool.
+func NewCertPool() *CertPool {
+	return &CertPool{
+		bySubjectKeyId: make(map[string][]int),
+		byName:         make(map[string][]int),
+	}
+}
+
+func (s *CertPool) copy() *CertPool {
+	p := &CertPool{
+		bySubjectKeyId: make(map[string][]int, len(s.bySubjectKeyId)),
+		byName:         make(map[string][]int, len(s.byName)),
+		certs:          make([]*Certificate, len(s.certs)),
+	}
+	for k, v := range s.bySubjectKeyId {
+		indexes := make([]int, len(v))
+		copy(indexes, v)
+		p.bySubjectKeyId[k] = indexes
+	}
+	for k, v := range s.byName {
+		indexes := make([]int, len(v))
+		copy(indexes, v)
+		p.byName[k] = indexes
+	}
+	copy(p.certs, s.certs)
+	return p
+}
+
+// SystemCertPool returns a copy of the system cert pool.
+//
+// Any mutations to the returned pool are not written to disk and do
+// not affect any other pool returned by SystemCertPool.
+//
+// New changes in the system cert pool might not be reflected
+// in subsequent calls.
+func SystemCertPool() (*CertPool, error) {
+	if runtime.GOOS == "windows" {
+		// Issue 16736, 18609:
+		return nil, errors.New("crypto/x509: system root pool is not available on Windows")
+	}
+
+	if sysRoots := systemRootsPool(); sysRoots != nil {
+		return sysRoots.copy(), nil
+	}
+
+	return loadSystemRoots()
+}
+
+// findPotentialParents returns the indexes of certificates in s which might
+// have signed cert. The caller must not modify the returned slice.
+func (s *CertPool) findPotentialParents(cert *Certificate) []int {
+	if s == nil {
+		return nil
+	}
+
+	var candidates []int
+	if len(cert.AuthorityKeyId) > 0 {
+		candidates = s.bySubjectKeyId[string(cert.AuthorityKeyId)]
+	}
+	if len(candidates) == 0 {
+		candidates = s.byName[string(cert.RawIssuer)]
+	}
+	return candidates
+}
+
+func (s *CertPool) contains(cert *Certificate) bool {
+	if s == nil {
+		return false
+	}
+
+	candidates := s.byName[string(cert.RawSubject)]
+	for _, c := range candidates {
+		if s.certs[c].Equal(cert) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// AddCert adds a certificate to a pool.
+func (s *CertPool) AddCert(cert *Certificate) {
+	if cert == nil {
+		panic("adding nil Certificate to CertPool")
+	}
+
+	// Check that the certificate isn't being added twice.
+	if s.contains(cert) {
+		return
+	}
+
+	n := len(s.certs)
+	s.certs = append(s.certs, cert)
+
+	if len(cert.SubjectKeyId) > 0 {
+		keyId := string(cert.SubjectKeyId)
+		s.bySubjectKeyId[keyId] = append(s.bySubjectKeyId[keyId], n)
+	}
+	name := string(cert.RawSubject)
+	s.byName[name] = append(s.byName[name], n)
+}
+
+// AppendCertsFromPEM attempts to parse a series of PEM encoded certificates.
+// It appends any certificates found to s and reports whether any certificates
+// were successfully parsed.
+//
+// On many Linux systems, /etc/ssl/cert.pem will contain the system wide set
+// of root CAs in a format suitable for this function.
+func (s *CertPool) AppendCertsFromPEM(pemCerts []byte) (ok bool) {
+	for len(pemCerts) > 0 {
+		var block *pem.Block
+		block, pemCerts = pem.Decode(pemCerts)
+		if block == nil {
+			break
+		}
+		if block.Type != "CERTIFICATE" || len(block.Headers) != 0 {
+			continue
+		}
+
+		cert, err := ParseCertificate(block.Bytes)
+		if err != nil {
+			continue
+		}
+
+		s.AddCert(cert)
+		ok = true
+	}
+
+	return
+}
+
+// Subjects returns a list of the DER-encoded subjects of
+// all of the certificates in the pool.
+func (s *CertPool) Subjects() [][]byte {
+	res := make([][]byte, len(s.certs))
+	for i, c := range s.certs {
+		res[i] = c.RawSubject
+	}
+	return res
+}