Added simple subscribe sample

.vscode/launch.json

@@ -0,0 +1,25 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Launch",
+            "type": "go",
+            "request": "launch",
+            "mode": "auto",
+            "program": "${fileDirname}",
+            "env": {},
+            "args": ["127.0.0.1", "7165"]
+        },
+        {
+            "name": "Attach to Process",
+            "type": "go",
+            "request": "attach",
+            "mode": "local",
+            "processId": 0
+        }
+
+    ]
+}

examples/SimpleSubscribe/SimpleSubscribe.go

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+//******************************************************************************************************
+//  SimpleSubscribe.go - Gbtc
+//
+//  Copyright © 2021, Grid Protection Alliance.  All Rights Reserved.
+//
+//  Licensed to the Grid Protection Alliance (GPA) under one or more contributor license agreements. See
+//  the NOTICE file distributed with this work for additional information regarding copyright ownership.
+//  The GPA licenses this file to you under the MIT License (MIT), the "License"; you may not use this
+//  file except in compliance with the License. You may obtain a copy of the License at:
+//
+//      http://opensource.org/licenses/MIT
+//
+//  Unless agreed to in writing, the subject software distributed under the License is distributed on an
+//  "AS-IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. Refer to the
+//  License for the specific language governing permissions and limitations.
+//
+//  Code Modification History:
+//  ----------------------------------------------------------------------------------------------------
+//  09/17/2021 - J. Ritchie Carroll
+//       Generated original version of source code.
+//
+//******************************************************************************************************
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"math"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/sttp/goapi/sttp"
+	"github.com/sttp/goapi/sttp/transport"
+)
+
+// SimpleSubscriber is a simple STTP data subscriber implementation.
+type SimpleSubscriber struct {
+	sttp.SubscriberBase
+}
+
+// NewSimpleSubscriber creates a new SimpleSubscriber.
+func NewSimpleSubscriber() SimpleSubscriber {
+	subscriber := SimpleSubscriber{}
+	subscriber.SubscriberBase = sttp.NewSubscriberBase(&subscriber)
+	return subscriber
+}
+
+func main() {
+	hostname, port := parseCmdLineArgs()
+	subscriber := NewSimpleSubscriber()
+	subscription := subscriber.Subscription()
+
+	subscriber.Hostname = hostname
+	subscriber.Port = port
+	subscriber.CompressPayloadData = false
+
+	subscription.FilterExpression = "FILTER TOP 5 ActiveMeasurements WHERE SignalType = 'FREQ'"
+
+	subscriber.Connect()
+	defer subscriber.Dispose()
+
+	reader := bufio.NewReader(os.Stdin)
+	reader.ReadRune()
+}
+
+// ReceivedMetadata handles reception of the metadata response.
+func (ss *SimpleSubscriber) ReceivedMetadata(metadata []byte) {
+	ss.StatusMessage(fmt.Sprintf("Received %d bytes of metadata", len(metadata)))
+}
+
+// SubscriptionUpdated handles notifications that a new SignalIndexCache has been received.
+func (ss *SimpleSubscriber) SubscriptionUpdated(signalIndexCache *transport.SignalIndexCache) {
+	ss.StatusMessage(fmt.Sprintf("Received signal index cache with %d mappings", signalIndexCache.Count()))
+}
+
+var lastMessageDisplay time.Time
+
+// ReceivedNewMeasurements handles reception of new measurements.
+func (ss *SimpleSubscriber) ReceivedNewMeasurements(measurements []transport.Measurement) {
+
+	if time.Since(lastMessageDisplay).Seconds() < 5.0 {
+		return
+	}
+
+	defer func() { lastMessageDisplay = time.Now() }()
+
+	if lastMessageDisplay.IsZero() {
+		ss.StatusMessage("Receiving measurements...")
+		return
+	}
+
+	var message strings.Builder
+
+	message.WriteString(strconv.FormatUint(ss.TotalMeasurementsReceived(), 10))
+	message.WriteString(" measurements received so far...\n")
+	message.WriteString("Timestamp: ")
+	message.WriteString(measurements[0].DateTime().Format("2006-01-02 15:04:05.999999999"))
+	message.WriteRune('\n')
+	message.WriteString("\tID\tSignal ID\t\t\t\tValue\n")
+
+	for i := 0; i < len(measurements); i++ {
+		measurement := measurements[i]
+
+		message.WriteRune('\t')
+		message.WriteString(strconv.FormatUint(measurement.Metadata().ID, 10))
+		message.WriteRune('\t')
+		message.WriteString(measurement.SignalID.String())
+		message.WriteRune('\t')
+		message.WriteString(strconv.FormatFloat(measurement.Value, 'f', 6, 64))
+		message.WriteRune('\n')
+	}
+
+	ss.StatusMessage(message.String())
+}
+
+// ConnectionTerminated handles notification that a connection has been terminated.
+func (ss *SimpleSubscriber) ConnectionTerminated() {
+	// Call base class method which will display connection terminated to os.Stderr
+	ss.SubscriberBase.ConnectionTerminated()
+
+	// Reset last message display time on disconnect
+	lastMessageDisplay = time.Time{}
+}
+
+func parseCmdLineArgs() (string, uint16) {
+	args := os.Args
+
+	if len(args) < 3 {
+		fmt.Println("Usage:")
+		fmt.Println("    SimpleSubscribe HOSTNAME PORT")
+		os.Exit(1)
+	}
+
+	hostname := args[1]
+	port, err := strconv.Atoi(args[2])
+
+	if err != nil {
+		fmt.Printf("Invalid port number \"%s\": %s\n", args[1], err.Error())
+		os.Exit(2)
+	}
+
+	if port < 1 || port > math.MaxUint16 {
+		fmt.Printf("Port number \"%s\" is out of range: must be 1 to %d\n", args[1], math.MaxUint16)
+		os.Exit(2)
+	}
+
+	return hostname, uint16(port)
+}