goipgrep: refactor into module; pure-Go ping/resolve; cache+CI; drop binary

projects/go-tools/go/goipgrep/internal/resolve/reverse.go

@@ -0,0 +1,74 @@
+package resolve
+
+import (
+	"context"
+	"net"
+	"runtime"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+)
+
+type ReverseResult struct {
+	IP       string `json:"ip"`
+	Hostname string `json:"hostname,omitempty"`
+}
+
+func ReverseLookupAll(ctx context.Context, ips []string, timeout time.Duration, jobs int) []ReverseResult {
+	if jobs <= 0 {
+		jobs = runtime.GOMAXPROCS(0)
+	}
+
+	in := make(chan string)
+	out := make(chan ReverseResult)
+	var wg sync.WaitGroup
+
+	worker := func() {
+		defer wg.Done()
+		for ip := range in {
+			r := ReverseResult{IP: ip}
+			cctx, cancel := context.WithTimeout(ctx, timeout)
+			names, err := net.DefaultResolver.LookupAddr(cctx, ip)
+			cancel()
+			if err == nil && len(names) > 0 {
+				// trim trailing dot for readability
+				r.Hostname = strings.TrimSuffix(names[0], ".")
+			}
+			select {
+			case out <- r:
+			case <-ctx.Done():
+				return
+			}
+		}
+	}
+
+	wg.Add(jobs)
+	for i := 0; i < jobs; i++ {
+		go worker()
+	}
+
+	go func() {
+		defer close(in)
+		for _, ip := range ips {
+			select {
+			case in <- ip:
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+
+	go func() {
+		wg.Wait()
+		close(out)
+	}()
+
+	var res []ReverseResult
+	for r := range out {
+		res = append(res, r)
+	}
+
+	sort.Slice(res, func(i, j int) bool { return res[i].IP < res[j].IP })
+	return res
+}