net/http: remove hasPort and simplify logic

Fixes #76651

Change-Id: I306e127375095bc0caedb01ac458107cfec5f085
Reviewed-on: https://go-review.googlesource.com/c/go/+/725740
Auto-Submit: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>

4 files changed, 30 insertions, 14 deletions

diff --git a/src/net/http/http.go b/src/net/http/http.go
index d3e9a2787a..100d4fe4a1 100644
--- a/src/net/http/http.go
+++ b/src/net/http/http.go
@@ -106,15 +106,15 @@ type contextKey struct {
 
 func (k *contextKey) String() string { return "net/http context value " + k.name }
 
-// Given a string of the form "host", "host:port", or "[ipv6::address]:port",
-// return true if the string includes a port.
-func hasPort(s string) bool { return strings.LastIndex(s, ":") > strings.LastIndex(s, "]") }
-
-// removeEmptyPort strips the empty port in ":port" to ""
-// as mandated by RFC 3986 Section 6.2.3.
-func removeEmptyPort(host string) string {
-	if hasPort(host) {
-		return strings.TrimSuffix(host, ":")
+// removePort strips the port while correclty handling IPv6.
+func removePort(host string) string {
+	for i := len(host) - 1; i >= 0; i-- {
+		switch host[i] {
+		case ':':
+			return host[:i]
+		case ']':
+			return host
+		}
 	}
 	return host
 }
diff --git a/src/net/http/http_test.go b/src/net/http/http_test.go
index c12bbedac9..9ac6e97032 100644
--- a/src/net/http/http_test.go
+++ b/src/net/http/http_test.go
@@ -220,3 +220,22 @@ func BenchmarkHexEscapeNonASCII(b *testing.B) {
 		hexEscapeNonASCII(redirectURL)
 	}
 }
+
+func TestRemovePort(t *testing.T) {
+	tests := []struct {
+		in, want string
+	}{
+		{"example.com:8080", "example.com"},
+		{"example.com", "example.com"},
+		{"[2001:db8::1]:443", "[2001:db8::1]"},
+		{"[2001:db8::1]", "[2001:db8::1]"},
+		{"192.0.2.1:8080", "192.0.2.1"},
+		{"192.0.2.1", "192.0.2.1"},
+	}
+	for _, tc := range tests {
+		got := removePort(tc.in)
+		if got != tc.want {
+			t.Errorf("removePort(%q) = %q; want %q", tc.in, got, tc.want)
+		}
+	}
+}
diff --git a/src/net/http/request.go b/src/net/http/request.go
index 167cff585a..f49bbeee16 100644
--- a/src/net/http/request.go
+++ b/src/net/http/request.go
@@ -908,7 +908,7 @@ func NewRequestWithContext(ctx context.Context, method, url string, body io.Read
 		rc = io.NopCloser(body)
 	}
 	// The host's colon:port should be normalized. See Issue 14836.
-	u.Host = removeEmptyPort(u.Host)
+	u.Host = strings.TrimSuffix(u.Host, ":")
 	req := &Request{
 		ctx:        ctx,
 		Method:     method,
diff --git a/src/net/http/transport.go b/src/net/http/transport.go
index 924e7cfcb0..49f9096e3f 100644
--- a/src/net/http/transport.go
+++ b/src/net/http/transport.go
@@ -2087,10 +2087,7 @@ func (cm *connectMethod) addr() string {
 // TLS certificate.
 func (cm *connectMethod) tlsHost() string {
 	h := cm.targetAddr
-	if hasPort(h) {
-		h = h[:strings.LastIndex(h, ":")]
-	}
-	return h
+	return removePort(h)
 }
 
 // connectMethodKey is the map key version of connectMethod, with a