[GitHub] [trafficcontrol] rob05c commented on a diff in pull request #7096: Add health client parent health

[GitBox <gi...@apache.org>]

rob05c commented on code in PR #7096:
URL: https://github.com/apache/trafficcontrol/pull/7096#discussion_r1003762350


##########
tc-health-client/sar/ephemeralportholder.go:
##########
@@ -0,0 +1,77 @@
+package sar
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import (
+	"errors"
+	"net"
+	"strconv"
+)
+
+// EphemeralPortHolder serves 2 purposes: it gets an ephemeral TCP port, and it holds
+// onto the port so the OS doesn't assign it to any other app.
+//
+// It listens on :0 thereby getting a socket on an ephemeral port.
+// It continues listening but never reading from the socket until Close is called.
+type EphemeralPortHolder struct {
+	listener net.Listener
+	port     int
+}
+
+// GetAndHoldEphemeralPort gets an ephemeral port, and listens on it to prevent
+// the OS assigning the port to other apps.
+// Close must be called on the returned EphemeralPortHolder to stop listening.
+func GetAndHoldEphemeralPort(addr string) (*EphemeralPortHolder, error) {
+	addr += ":0"
+	listener, err := net.Listen("tcp", addr)
+	if err != nil {
+		return nil, errors.New("listening: " + err.Error())
+	}
+
+	// get the port now, so EphemeralPortHolder.Port() doesn't need to return an error
+
+	listenAddr := listener.Addr().String()
+	ipPort := SplitLast(listenAddr, ":")
+	if len(ipPort) < 1 {
+		return nil, errors.New("malformed addr '" + listenAddr + "', should have been ip:port") // should never happen
+	}
+	portStr := ipPort[1]
+	port, err := strconv.Atoi(portStr)
+	if err != nil {
+		return nil, errors.New("malformed addr '" + listenAddr + "' port was not an integer") // should never happen
+	}
+	if port > 65535 || port < 0 {

Review Comment:
   The number is technically the same, but "the last valid port number" is semantically different than "the last number a uint16 can store." We could make a constant, but it seems a bit overkill for just a port check, I'd prefer to just keep the literal for now



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