From 85dacbe2dead9d0016ad8bb225c8e635bbe7eaca Mon Sep 17 00:00:00 2001
From: Steven Polley <himself@stevenpolley.net>
Date: Fri, 29 May 2020 21:44:20 -0600
Subject: [PATCH] add support for testing redirection

---
 test.go | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)

diff --git a/test.go b/test.go
index 1fcca18..8d2539e 100644
--- a/test.go
+++ b/test.go
@@ -1,9 +1,100 @@
 package main
 
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"sync"
+)
+
+var sem chan Empty // semaphore to limit requess in flight
+
 // test accepts a slice of type Redirect and returns an error
 // it performs actual HTTP GET requests on each source URL and validates that a redirect occurs
 // to the destination URL and that the redirect type/status code is correct
 func test(redirects []Redirect) error { //TBD: implement
 
+	wg := &sync.WaitGroup{}
+	mu := &sync.Mutex{}
+	var summaryOutput string
+
+	sem = make(Semaphore, *maxConcurrentRequests)
+
+	for _, redirect := range redirects {
+		wg.Add(1)
+		P(1)
+
+		go func(redirect Redirect) {
+			defer V(1)
+			defer wg.Done()
+			client := &http.Client{
+				CheckRedirect: func(req *http.Request, via []*http.Request) error {
+					return http.ErrUseLastResponse
+				},
+			}
+
+			// writing to std out is critical section
+			mu.Lock()
+			fmt.Printf("Checking redirect for: %s\n", redirect.sourceURL)
+			mu.Unlock()
+
+			// Make the request
+			resp, err := client.Get(redirect.sourceURL)
+			if err != nil {
+				log.Printf("HTTP GET failed for source URL '%s': %v", redirect.sourceURL, err)
+			}
+
+			// Check the status code
+			if resp.StatusCode != redirect.statusCode {
+				// Modifying output is critical section
+				mu.Lock()
+				summaryOutput += fmt.Sprintf("redirect for source URL '%s': expected status code'%d': got '%d\n", redirect.sourceURL, redirect.statusCode, resp.StatusCode)
+				mu.Unlock()
+				return
+			}
+
+			// Check that the redirect went to the correct location
+			destURL, err := resp.Location()
+			if err != nil {
+				log.Printf("failed to parse response location to URL: %v", err)
+			}
+
+			if destURL.String() != redirect.destinationURL {
+				// Modifying output is critical section
+				mu.Lock()
+				summaryOutput += fmt.Sprintf("redirect for source URL '%s': expected '%s': got '%s\n", redirect.sourceURL, redirect.destinationURL, destURL.String())
+				mu.Unlock()
+				return
+			}
+
+		}(redirect)
+	}
+
+	wg.Wait()
+	fmt.Printf("\ndone tests.\n---------------------------------------------\nSummary:\n\n%s", summaryOutput)
+
 	return nil
 }
+
+// Semaphore helper functions
+
+// Empty is an empty struct used by the semaphores
+type Empty struct{}
+
+// Semaphore is a channel which passes empty structs and acts as a resource lock
+type Semaphore chan Empty
+
+// P acquire n resources - standard semaphore design pattern to limit number of requests in flight
+func P(n int) {
+	e := Empty{}
+	for i := 0; i < n; i++ {
+		sem <- e
+	}
+}
+
+// V release n resources - standard semaphore design pattern to limit number of requests in flight
+func V(n int) {
+	for i := 0; i < n; i++ {
+		<-sem
+	}
+}