From 01af0739c6a24d80edaa4000fa9509e6e90f0566 Mon Sep 17 00:00:00 2001
From: Franck Cuny <franck@fcuny.net>
Date: Sun, 24 Aug 2025 11:09:08 -0700
Subject: add Go vanity URL service for custom import paths

Go vanity URLs allow developers to use custom domain names for Go module
imports instead of being tied to specific hosting platforms like GitHub.

This service implements the go-import meta tag protocol, allowing Go tools
to automatically discover the actual Git repository location while
presenting a clean, branded import path to users.
---
 cmd/goget/main.go | 165 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 165 insertions(+)
 create mode 100644 cmd/goget/main.go

(limited to 'cmd')

diff --git a/cmd/goget/main.go b/cmd/goget/main.go
new file mode 100644
index 0000000..ae8b3a6
--- /dev/null
+++ b/cmd/goget/main.go
@@ -0,0 +1,165 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net/http"
+	"net/url"
+	"os"
+	"os/signal"
+	"slices"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"golang.org/x/mod/semver"
+)
+
+const (
+	forgeDomain = "code.fcuny.net"
+	forgeUser   = "fcuny"
+	goPkgDomain = "go.fcuny.net"
+)
+
+var (
+	goGetReqs = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "goget_requests_total",
+		Help: "go get requests processed, by repository name.",
+	}, []string{"name"})
+
+	modules = []string{"x"}
+)
+
+func main() {
+	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer cancel()
+
+	metricsMux := http.NewServeMux()
+	metricsMux.Handle("/metrics", promhttp.Handler())
+	metricsServer := &http.Server{
+		Addr: ":9091", Handler: metricsMux,
+		ReadTimeout: 10 * time.Second, WriteTimeout: 10 * time.Second,
+	}
+
+	go func() {
+		log.Println("Starting metrics server on :9091")
+		if err := metricsServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+			log.Printf("Metrics server error: %v", err)
+		}
+	}()
+
+	s := &http.Server{
+		Addr:         ":8080",
+		Handler:      handler(),
+		ReadTimeout:  10 * time.Second,
+		WriteTimeout: 10 * time.Second,
+		IdleTimeout:  1 * time.Minute,
+	}
+
+	go func() {
+		log.Println("Starting main server on :8080")
+		if err := s.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+			log.Printf("Main server error: %v", err)
+		}
+	}()
+
+	<-ctx.Done()
+	log.Println("Shutdown signal received, starting graceful shutdown...")
+
+	shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer shutdownCancel()
+
+	var shutdownErr error
+
+	log.Println("Shutting down main server...")
+	if err := s.Shutdown(shutdownCtx); err != nil {
+		log.Printf("Main server shutdown error: %v", err)
+		shutdownErr = err
+	}
+
+	log.Println("Shutting down metrics server...")
+	if err := metricsServer.Shutdown(shutdownCtx); err != nil {
+		log.Printf("Metrics server shutdown error: %v", err)
+		if shutdownErr == nil {
+			shutdownErr = err
+		}
+	}
+
+	if shutdownErr != nil {
+		log.Printf("Shutdown completed with errors")
+		os.Exit(1)
+	}
+
+	log.Println("Shutdown completed successfully")
+}
+
+func handler() http.Handler {
+	mux := http.NewServeMux()
+
+	mux.Handle(goPkgDomain+"/{name}", siteHandler(modules))
+	mux.Handle(goPkgDomain+"/{name}/", siteHandler(modules))
+
+	goGetMux := http.NewServeMux()
+	for _, name := range modules {
+		module := goPkgDomain + "/" + name
+		goGetMux.Handle(
+			module+"/",
+			goImportHandler(module, "https://"+forgeDomain+"/"+forgeUser+"/"+name),
+		)
+	}
+
+	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			status := http.StatusMethodNotAllowed
+			http.Error(rw, http.StatusText(status), status)
+			return
+		}
+
+		if r.URL.Query().Get("go-get") == "1" {
+			goGetMux.ServeHTTP(rw, r)
+			return
+		}
+		mux.ServeHTTP(rw, r)
+	})
+}
+
+func goImportHandler(module, repo string) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		goGetReqs.WithLabelValues(module).Inc()
+		w.Header().Set("Content-Type", "text/html; charset=UTF-8")
+		if _, err := fmt.Fprintf(w, `<head><meta name="go-import" content="%s git %s">`, module, repo); err != nil {
+			log.Printf("Error writing response: %v", err)
+		}
+	})
+}
+
+func siteHandler(names []string) http.Handler {
+	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		name := r.PathValue("name")
+		name, version, hasV := strings.Cut(name, "@")
+		if !hasV {
+			name, _, _ = strings.Cut(name, ".")
+		}
+		if hasV && !semver.IsValid(version) || !slices.Contains(names, name) {
+			http.NotFound(rw, r)
+			return
+		}
+		u := &url.URL{
+			Scheme: "https",
+			Host:   forgeDomain,
+			Path:   forgeUser + r.URL.Path,
+		}
+		if !hasV {
+			path, symbol, hasSymbol := strings.Cut(r.URL.Path, ".")
+			if hasSymbol {
+				u.Path = forgeUser + "/" + path
+				u.Fragment = symbol
+			}
+		}
+		http.Redirect(rw, r, u.String(), http.StatusFound)
+	})
+}
-- 
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