Objective 1: Identify and correct errors in the HealthCheck function

main.go

@@ -46,25 +46,35 @@ func main() {
 
 // HealthCheck report if a list of web service is up and running.
 func HealthCheck(urls []string) []Result {
-	results := make([]Result, 0, len(urls))
+	results := make([]Result, len(urls))
 
 	var wg sync.WaitGroup
 	wg.Add(len(urls))
-	for _, url := range urls {
-		go func() {
+	for i, url := range urls {
+		// Pass a copy of `i` and `url` to avoid loop variable capture issue for Go 1.21 and below.
+		// (unnecessary for Go 1.22+: https://go.dev/blog/loopvar-preview)
+		go func(i int, url string) {
 			defer wg.Done()
-			var result Result
 			start := time.Now()
 			resp, err := http.Get(url)
+
+			// Instead of append, use `i` to assign to specific index of `results` to avoid data race.
+			// Use direct index writes instead of mutex to preserve same order as the `urls` slice input.
 			if err != nil {
-				result.Err = err
+				results[i] = Result{Err: err}
 			} else {
-				result.Status = resp.StatusCode
-				result.Url = url
-				result.Latency = time.Since(start)
+				results[i] = Result{
+					Status:  resp.StatusCode,
+					Url:     url,
+					Latency: time.Since(start),
+				}
+
+				// Close the response body as recommended in the http.Get documentation.
+				defer resp.Body.Close()
+				// We don't need to read the body, so we drain up to 4KB of it to ensure connection reuse.
+				io.CopyN(io.Discard, resp.Body, 4096)
 			}
-			results = append(results, result)
-		}()
+		}(i, url)
 	}
 
 	wg.Wait()

main_test.go

@@ -1,9 +1,13 @@
 package main
 
 import (
-	"golang.org/x/exp/slices"
+	"net/http"
+	"net/http/httptest"
 	"strings"
 	"testing"
+	"time"
+
+	"golang.org/x/exp/slices"
 )
 
 var services = `https://stackoverflow.com
@@ -15,7 +19,54 @@ https://www.finconsgroup.com
 `
 
 func TestHealthCheck(t *testing.T) {
-	panic("TODO implements me")
+	var urls []string
+	statusCodes := []int{http.StatusOK, http.StatusPermanentRedirect, http.StatusNotFound, http.StatusInternalServerError}
+
+	// Create a mock server for each status code
+	for _, statusCode := range statusCodes {
+		status := statusCode
+		latency := time.Duration(status) * time.Millisecond
+
+		server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			time.Sleep(latency)
+			w.WriteHeader(status)
+		}))
+		t.Cleanup(server.Close)
+
+		// Add each mock server URL to the list of URLs
+		urls = append(urls, server.URL)
+	}
+
+	// Add an invalid URL test case
+	urls = append(urls, "http:/invalid-url")
+
+	results := HealthCheck(urls)
+
+	if len(results) != len(urls) {
+		t.Errorf("want: %d results, got %d results", len(urls), len(results))
+	}
+	for i, result := range results {
+		// Check the last invalid URL
+		if i == len(results)-1 {
+			if result.Err == nil {
+				t.Errorf("[URL index %d] want: non-nil error, got: error <nil>", i)
+			}
+			continue
+		}
+
+		// Check the other valid URLs
+		expectedStatus := statusCodes[i]
+		expectedLatency := time.Duration(expectedStatus) * time.Millisecond
+		if result.Err != nil {
+			t.Errorf("[URL index %d][err] want: <nil>, got: %v", i, result.Err)
+		}
+		if result.Status != expectedStatus {
+			t.Errorf("[URL index %d][status] want: %v, got: %v", i, expectedStatus, result.Status)
+		}
+		if result.Latency < expectedLatency {
+			t.Errorf("[URL index %d][latency] want: >= %v, got: %v", i, expectedLatency, result.Latency)
+		}
+	}
 }
 
 func TestGetServices(t *testing.T) {