feat(geoip-update): CLI for downloading GeoLite2 databases via conditional HTTP GET

- Downloads all editions listed in a GeoIP.conf
  - Flags: -config, -dir, -fresh-days, -base-url (override
    DownloadBase for custom mirror/proxy), -V/--version, -help
  - Version output shows name, version, commit, date, copyright and
    license (populated via ldflags at build time)
  - Uses Basic auth with split credential encoding for readability
  - ETag/Last-Modified caching via httpcache

net/geoip/cmd/geoip-update/main.go

@@ -0,0 +1,136 @@
+// geoip-update downloads GeoLite2 edition tarballs listed in GeoIP.conf
+// via conditional HTTP GETs, writing them to the configured directory.
+package main
+
+import (
+	"context"
+	"encoding/base64"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/therootcompany/golib/net/geoip"
+	"github.com/therootcompany/golib/net/httpcache"
+)
+
+// Replaced by goreleaser / ldflags at build time.
+var (
+	name         = "geoip-update"
+	version      = "0.0.0-dev"
+	commit       = "0000000"
+	date         = "0001-01-01"
+	licenseYear  = "2026"
+	licenseOwner = "AJ ONeal"
+	licenseType  = "MPL-2.0"
+)
+
+func printVersion(w io.Writer) {
+	_, _ = fmt.Fprintf(w, "%s v%s %s (%s)\n", name, version, commit[:7], date)
+	_, _ = fmt.Fprintf(w, "Copyright (C) %s %s\n", licenseYear, licenseOwner)
+	_, _ = fmt.Fprintf(w, "Licensed under %s\n", licenseType)
+}
+
+type Config struct {
+	ConfPath string
+	Dir      string
+	BaseURL  string
+	FreshDays int
+}
+
+func main() {
+	cfg := Config{}
+	fs := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
+	fs.StringVar(&cfg.ConfPath, "config", "GeoIP.conf", "path to GeoIP.conf")
+	fs.StringVar(&cfg.Dir, "dir", "", "directory to store .tar.gz files (overrides DatabaseDirectory in config)")
+	fs.StringVar(&cfg.BaseURL, "base-url", "", "base URL for database downloads (overrides DownloadBase in geoip package)")
+	fs.IntVar(&cfg.FreshDays, "fresh-days", 3, "skip download if file is younger than N days")
+
+	if len(os.Args) > 1 {
+		switch os.Args[1] {
+		case "-V", "-version", "--version", "version":
+			printVersion(os.Stdout)
+			os.Exit(0)
+		case "help", "-help", "--help":
+			printVersion(os.Stdout)
+			fmt.Fprintln(os.Stdout, "")
+			fs.SetOutput(os.Stdout)
+			fs.Usage()
+			os.Exit(0)
+		}
+	}
+	if err := fs.Parse(os.Args[1:]); err != nil {
+		if errors.Is(err, flag.ErrHelp) {
+			os.Exit(0)
+		}
+		os.Exit(1)
+	}
+
+	data, err := os.ReadFile(cfg.ConfPath)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+	conf, err := geoip.ParseConf(string(data))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+
+	outDir := cfg.Dir
+	if outDir == "" {
+		outDir = conf.DatabaseDirectory
+	}
+	if outDir == "" {
+		outDir = "."
+	}
+	if err := os.MkdirAll(outDir, 0o755); err != nil {
+		fmt.Fprintf(os.Stderr, "error: mkdir %s: %v\n", outDir, err)
+		os.Exit(1)
+	}
+
+	if len(conf.EditionIDs) == 0 {
+		fmt.Fprintf(os.Stderr, "error: no EditionIDs found in %s\n", cfg.ConfPath)
+		os.Exit(1)
+	}
+
+	creds := base64.StdEncoding.EncodeToString([]byte(conf.AccountID + ":" + conf.LicenseKey))
+	authHeader := http.Header{"Authorization": []string{"Basic " + creds}}
+	maxAge := time.Duration(cfg.FreshDays) * 24 * time.Hour
+
+	exitCode := 0
+	for _, edition := range conf.EditionIDs {
+		path := filepath.Join(outDir, geoip.TarGzName(edition))
+		base := geoip.DownloadBase
+		if cfg.BaseURL != "" {
+			base = cfg.BaseURL
+		}
+		cacher := httpcache.New(
+			base+"/"+edition+"/download?suffix=tar.gz",
+			path,
+		)
+		cacher.MaxAge = maxAge
+		cacher.Header = authHeader
+		fmt.Fprintf(os.Stderr, "Fetching %s... ", edition)
+		t := time.Now()
+		updated, err := cacher.Fetch(context.Background())
+		if err != nil {
+			fmt.Fprintln(os.Stderr)
+			fmt.Fprintf(os.Stderr, "error: %s: %v\n", edition, err)
+			exitCode = 1
+			continue
+		}
+		state := "fresh"
+		if updated {
+			state = "updated"
+		}
+		fmt.Fprintf(os.Stderr, "%s (%s)\n", time.Since(t).Round(time.Millisecond), state)
+		info, _ := os.Stat(path)
+		fmt.Printf("%-10s %s -> %s (%s)\n", state+":", edition, path, info.ModTime().Format("2006-01-02"))
+	}
+	os.Exit(exitCode)
+}