From eaccb83a7bcc215f70fc10a0a565f742925cf7b5 Mon Sep 17 00:00:00 2001
From: Brian Picciano <me@mediocregopher.com>
Date: Sat, 30 Dec 2023 12:41:08 +0100
Subject: [PATCH] Fix concurrent client usage, now each worker gets its own
 Client

---
 deadlinks.go | 38 +++++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/deadlinks.go b/deadlinks.go
index 6ff4a28..ba51eb6 100644
--- a/deadlinks.go
+++ b/deadlinks.go
@@ -33,13 +33,13 @@ import (
 // Opts are optional fields which can be provided to New. A nil Opts is
 // equivalent to an empty one.
 type Opts struct {
-	Client Client // Defaults to `NewClient(nil)`
-	Parser Parser // Defaults to `NewParser()`
+	NewClient func() Client // Defaults to `func () Client { return NewClient(nil) }`
+	Parser    Parser        // Defaults to `NewParser()`
 
 	// Concurrency determines the maximum number of URLs which can be checked
 	// simultaneously.
 	//
-	// Default: `runtime.NumCPU()`
+	// Default: `runtime.NumCPU() / 2`
 	Concurrency int
 
 	// OnError, if set, will be called whenever DeadLinks encounters an error
@@ -58,8 +58,8 @@ func (o *Opts) withDefaults() *Opts {
 		o = new(Opts)
 	}
 
-	if o.Client == nil {
-		o.Client = NewClient(nil)
+	if o.NewClient == nil {
+		o.NewClient = func() Client { return NewClient(nil) }
 	}
 
 	if o.Parser == nil {
@@ -67,7 +67,7 @@ func (o *Opts) withDefaults() *Opts {
 	}
 
 	if o.Concurrency == 0 {
-		o.Concurrency = runtime.NumCPU()
+		o.Concurrency = runtime.NumCPU() / 2
 	}
 
 	if o.RequestTimeout == 0 {
@@ -87,6 +87,7 @@ type DeadLinks struct {
 	opts     Opts
 	store    Store
 	patterns []*regexp.Regexp
+	clients  []Client
 }
 
 // New initializes and returns a DeadLinks instance which will track the
@@ -129,6 +130,11 @@ func New(
 		patterns: patterns,
 	}
 
+	d.clients = make([]Client, d.opts.Concurrency)
+	for i := range d.clients {
+		d.clients[i] = d.opts.NewClient()
+	}
+
 	if err := d.store.SetPinned(ctx, pinnedURLs); err != nil {
 		return nil, fmt.Errorf("pinning URLs: %w", err)
 	}
@@ -155,11 +161,15 @@ func (d *DeadLinks) shouldFollowURL(url URL) bool {
 	return false
 }
 
-func (d *DeadLinks) getURL(ctx context.Context, url URL) ([]URL, error) {
+func (d *DeadLinks) getURL(
+	ctx context.Context, client Client, url URL,
+) (
+	[]URL, error,
+) {
 	ctx, cancel := context.WithTimeout(ctx, d.opts.RequestTimeout)
 	defer cancel()
 
-	mimeType, body, err := d.opts.Client.Get(ctx, url)
+	mimeType, body, err := client.Get(ctx, url)
 	if err != nil {
 		return nil, err
 	}
@@ -178,14 +188,16 @@ func (d *DeadLinks) getURL(ctx context.Context, url URL) ([]URL, error) {
 }
 
 // checkURL only returns an error if storing the results of the check fails.
-func (d *DeadLinks) checkURL(ctx context.Context, url URL) error {
+func (d *DeadLinks) checkURL(
+	ctx context.Context, client Client, url URL,
+) error {
 	var (
 		now      = time.Now()
 		status   = ResourceStatusOK
 		errorStr string
 	)
 
-	outgoingURLs, err := d.getURL(ctx, url)
+	outgoingURLs, err := d.getURL(ctx, client, url)
 	if err != nil {
 		status = ResourceStatusError
 		errorStr = err.Error()
@@ -219,14 +231,14 @@ func (d *DeadLinks) update(
 
 	wg.Add(d.opts.Concurrency)
 	for i := 0; i < d.opts.Concurrency; i++ {
-		go func() {
+		go func(client Client) {
 			defer wg.Done()
 			for url := range ch {
-				if err := d.checkURL(ctx, url); err != nil {
+				if err := d.checkURL(ctx, client, url); err != nil {
 					d.onError(ctx, fmt.Errorf("checking url %q: %w", url, err))
 				}
 			}
-		}()
+		}(d.clients[i])
 	}
 
 	var (