Multi-args instead of comma-separated

This seems to fix the issues with concurrency.

README.md

@@ -19,11 +19,11 @@ The command-line utility can be installed using `go install`:
 go install code.betamike.com/mediocregopher/deadlinks/cmd/deadlinks
 ```
 
-The `-urls` parameter is required. Given one or more URLs it will check each one
-for any dead links:
+The `-url` parameter is required. Given a URL it will check it for
+any dead links. Can be specified more than once:
 
 ```
-deadlinks -urls 'https://mediocregopher.com,gemini://mediocregopher.com'
+deadlinks -url='https://mediocregopher.com' -url='gemini://mediocregopher.com'
 ```
 
 Any links which are dead will be output to stdout as YAML objects, each
@@ -36,8 +36,8 @@ so on):
 
 ```
 deadlinks \
-    -urls 'https://mediocregopher.com,gemini://mediocregopher.com' \
-    -patterns '://mediocregopher.com'
+    -url='https://mediocregopher.com' -url='gemini://mediocregopher.com' \
+    -pattern='://mediocregopher.com'
 ```
 
 There are further options available which affect the utility's behavior, see

client.go

@@ -36,6 +36,11 @@ type ClientOpts struct {
 		Do(*http.Request) (*http.Response, error)
 	}
 
+	// HTTPUserAgent overwrites the user agent used by the HTTPClient.
+	//
+	// Defaults to whatever http.Client uses by default.
+	HTTPUserAgent string
+
 	// MaxRedirects indicates the maximum number of redirects which will be
 	// allowed when resolving a resource. A negative value indicates no
 	// redirects are allowed.
@@ -54,7 +59,9 @@ func (o *ClientOpts) withDefaults() *ClientOpts {
 	}
 
 	if o.HTTPClient == nil {
-		o.HTTPClient = new(http.Client)
+		o.HTTPClient = &http.Client{
+			Transport: http.DefaultTransport.(*http.Transport).Clone(),
+		}
 	}
 
 	if o.MaxRedirects == 0 {
@@ -188,6 +195,10 @@ func (c *client) getHTTP(
 		return "", nil, fmt.Errorf("building request: %w", err)
 	}
 
+	if c.opts.HTTPUserAgent != "" {
+		req.Header.Set("User-Agent", c.opts.HTTPUserAgent)
+	}
+
 	res, err := c.opts.HTTPClient.Do(req)
 	if err != nil {
 		return "", nil, fmt.Errorf("performing request: %w", err)

cmd/deadlinks/flag.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"flag"
+	"strings"
+)
+
+// Created so that multiple inputs can be accecpted
+type arrayFlags struct {
+	strs *[]string
+}
+
+func flagStrings(name, usage string) arrayFlags {
+	f := arrayFlags{new([]string)}
+	flag.Var(&f, name, usage)
+	return f
+}
+
+func (i arrayFlags) String() string {
+	if i.strs == nil {
+		return ""
+	}
+	return strings.Join(*i.strs, ", ")
+}
+
+func (i arrayFlags) Set(value string) error {
+	*i.strs = append(*i.strs, strings.TrimSpace(value))
+	return nil
+}

cmd/deadlinks/main.go

@@ -8,7 +8,6 @@ import (
 	"os"
 	"os/signal"
 	"runtime"
-	"strings"
 	"time"
 
 	"code.betamike.com/mediocregopher/deadlinks"
@@ -31,22 +30,18 @@ func (c loggingClient) Get(
 
 func main() {
 	var (
-		storePath   = flag.String("store-path", "", "Path to sqlite storage file. If not given then a temporary in-memory storage is used")
-		maxAge      = flag.Duration("max-age", 0, "Maximum duration since last check of a resource, before it must be checked again. Must be used with -store-path")
-		urls        = flag.String("urls", "", `Comma-separated list of URLs which are always checked. At least one is required`)
-		patternsStr = flag.String("patterns", "", "Comma-separated list of regexps. All URLs which match one of these will have their links checked as well")
-		concurrency = flag.Int("concurrency", runtime.NumCPU()/2, "Number simultaneous requests to make at a time")
+		storePath     = flag.String("store-path", "", "Path to sqlite storage file. If not given then a temporary in-memory storage is used")
+		maxAge        = flag.Duration("max-age", 0, "Maximum duration since last check of a resource, before it must be checked again. Must be used with -store-path")
+		urls          = flagStrings("url", "URL which is always checked. Must be given at least once")
+		patterns      = flagStrings("pattern", "URLs matching this regex will have their links checked as well. Can be specified multiple times")
+		concurrency   = flag.Int("concurrency", runtime.NumCPU()/2, "Number simultaneous requests to make at a time")
+		httpUserAgent = flag.String("http-user-agent", "", "User-agent to use for http requests")
 	)
 
 	flag.Parse()
 
-	if *urls == "" {
-		log.Fatal("-urls is required")
-	}
-
-	var patterns []string
-	if *patternsStr != "" {
-		patterns = strings.Split(*patternsStr, ",")
+	if len(*urls.strs) == 0 {
+		log.Fatal("at least one -url is required")
 	}
 
 	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
@@ -60,11 +55,13 @@ func main() {
 	dl, err := deadlinks.New(
 		ctx,
 		store,
-		strings.Split(*urls, ","),
-		patterns,
+		*urls.strs,
+		*patterns.strs,
 		&deadlinks.Opts{
 			NewClient: func() deadlinks.Client {
-				return loggingClient{deadlinks.NewClient(nil)}
+				return loggingClient{deadlinks.NewClient(&deadlinks.ClientOpts{
+					HTTPUserAgent: *httpUserAgent,
+				})}
 			},
 			Concurrency: *concurrency,
 			OnError: func(err error) {