feat: add HTTP link checker and GitHub GraphQL repo checker

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/checker/http.go

@@ -0,0 +1,111 @@
+package checker
+
+import (
+	"context"
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/veggiemonk/awesome-docker/internal/cache"
+)
+
+const (
+	defaultTimeout     = 30 * time.Second
+	defaultConcurrency = 10
+	userAgent          = "awesome-docker-checker/1.0"
+)
+
+// LinkResult holds the result of checking a single URL.
+type LinkResult struct {
+	URL         string
+	OK          bool
+	StatusCode  int
+	Redirected  bool
+	RedirectURL string
+	Error       string
+}
+
+// CheckLink checks a single URL. Uses HEAD first, falls back to GET.
+func CheckLink(url string, client *http.Client) LinkResult {
+	result := LinkResult{URL: url}
+
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTimeout)
+	defer cancel()
+
+	// Try HEAD first
+	req, err := http.NewRequestWithContext(ctx, http.MethodHead, url, nil)
+	if err != nil {
+		result.Error = err.Error()
+		return result
+	}
+	req.Header.Set("User-Agent", userAgent)
+
+	// Track redirects
+	var finalURL string
+	origCheckRedirect := client.CheckRedirect
+	client.CheckRedirect = func(req *http.Request, via []*http.Request) error {
+		finalURL = req.URL.String()
+		if len(via) >= 10 {
+			return http.ErrUseLastResponse
+		}
+		return nil
+	}
+	defer func() { client.CheckRedirect = origCheckRedirect }()
+
+	resp, err := client.Do(req)
+	if err != nil {
+		// Fallback to GET
+		req, err2 := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+		if err2 != nil {
+			result.Error = err.Error()
+			return result
+		}
+		req.Header.Set("User-Agent", userAgent)
+		resp, err = client.Do(req)
+		if err != nil {
+			result.Error = err.Error()
+			return result
+		}
+	}
+	defer resp.Body.Close()
+
+	result.StatusCode = resp.StatusCode
+	result.OK = resp.StatusCode >= 200 && resp.StatusCode < 400
+
+	if finalURL != "" && finalURL != url {
+		result.Redirected = true
+		result.RedirectURL = finalURL
+	}
+
+	return result
+}
+
+// CheckLinks checks multiple URLs concurrently.
+func CheckLinks(urls []string, concurrency int, exclude *cache.ExcludeList) []LinkResult {
+	if concurrency <= 0 {
+		concurrency = defaultConcurrency
+	}
+
+	results := make([]LinkResult, len(urls))
+	sem := make(chan struct{}, concurrency)
+	var wg sync.WaitGroup
+
+	for i, url := range urls {
+		if exclude != nil && exclude.IsExcluded(url) {
+			results[i] = LinkResult{URL: url, OK: true}
+			continue
+		}
+
+		wg.Add(1)
+		go func(idx int, u string) {
+			defer wg.Done()
+			sem <- struct{}{}
+			defer func() { <-sem }()
+			client := &http.Client{Timeout: defaultTimeout}
+			results[idx] = CheckLink(u, client)
+		}(i, url)
+	}
+
+	wg.Wait()
+	return results
+}