net/http: give the HTTPS client trust roots on darwin

http/client.go

@@ -293,7 +293,9 @@ func roundTrip(req *Request) (*Response, error) {
 		if missingPort {
 			host = host + ":443"
 		}
-		conn, err = tls.Dial("tcp", host, nil)
+		// TINYGO: defaultTLSConfig is nil everywhere but darwin, where it
+		// TINYGO: carries the trust roots crypto/x509 cannot find for itself.
+		conn, err = tls.Dial("tcp", host, defaultTLSConfig())
 	}
 	if err != nil {
 		req.closeBody()

http/tlsconfig_darwin.go

@@ -0,0 +1,58 @@
+//go:build darwin
+
+// TINYGO: darwin trust roots for the HTTPS client.
+
+package http
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"os"
+	"sync"
+)
+
+// certFileEnv is the environment variable that crypto/x509 reads on unix for
+// an alternative root bundle.
+const certFileEnv = "SSL_CERT_FILE"
+
+// darwinCertFile is the PEM bundle of macOS. crypto/x509 does not read it on
+// darwin, because it uses the system verifier, so the client must read it.
+const darwinCertFile = "/etc/ssl/cert.pem"
+
+var darwinRoots struct {
+	once sync.Once
+	pool *x509.CertPool
+}
+
+// defaultTLSConfig returns the config that the client dials HTTPS with.
+//
+// On darwin crypto/x509 verifies a certificate with the platform verifier and
+// not with a root pool, and crypto/x509/internal/macos in TinyGo is a stub, so
+// a nil RootCAs makes every verification fail. A non-nil pool sends x509 to its
+// pure Go path, which works. The roots come from $SSL_CERT_FILE, or from
+// /etc/ssl/cert.pem.
+//
+// If no file can be read, the config has no RootCAs, so the result is an
+// ordinary verification error and not a check that is silently skipped.
+func defaultTLSConfig() *tls.Config {
+	darwinRoots.once.Do(loadDarwinRoots)
+	if darwinRoots.pool == nil {
+		return nil
+	}
+	return &tls.Config{RootCAs: darwinRoots.pool}
+}
+
+func loadDarwinRoots() {
+	path := os.Getenv(certFileEnv)
+	if path == "" {
+		path = darwinCertFile
+	}
+	pem, err := os.ReadFile(path)
+	if err != nil {
+		return
+	}
+	pool := x509.NewCertPool()
+	if pool.AppendCertsFromPEM(pem) {
+		darwinRoots.pool = pool
+	}
+}

http/tlsconfig_other.go

@@ -0,0 +1,14 @@
+//go:build !darwin
+
+// TINYGO: trust roots for the HTTPS client, everywhere but darwin.
+
+package http
+
+import "crypto/tls"
+
+// defaultTLSConfig returns the config that the client dials HTTPS with. Off
+// darwin crypto/x509 reads the system roots from the usual certificate files,
+// so a nil config is correct.
+func defaultTLSConfig() *tls.Config {
+	return nil
+}