smarthttp: optionally follow info/refs redirects into Endpoint

Adds Conn.FollowInfoRefsRedirect (off by default). When set,
RequestInfoRefs rewrites Endpoint.Scheme + Endpoint.Host to the final
URL after HTTP redirects, so subsequent PostRPC* calls target the
redirected node instead of the originally-configured entry point.

Matches vanilla git's smart-HTTP behaviour for discovery-aware servers
that 307 /info/refs to a hosting replica (the entiredb info/refs
discovery design). Endpoint.Path is never modified — it still holds
the repo path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Entire-Checkpoint: 359b871b7cfb

Author: nodo

internal/gitproto/smarthttp.go

@@ -45,6 +45,16 @@ type Conn struct {
 	Transport transport.Transport
 	HTTP      *http.Client
 	Auth      transport.AuthMethod
+
+	// FollowInfoRefsRedirect, when true, rewrites Endpoint.Scheme and
+	// Endpoint.Host to the final URL returned by RequestInfoRefs after
+	// HTTP redirects. Subsequent PostRPC* calls then target the
+	// redirected host directly, matching vanilla git's smart-HTTP
+	// behaviour for discovery-aware servers that 307 /info/refs to a
+	// hosting replica. Endpoint.Path is never modified — it still
+	// contains the repo path. Off by default to preserve behaviour for
+	// callers that rely on Endpoint being stable.
+	FollowInfoRefsRedirect bool
 }
 
 // NewConn creates a new connection to the given endpoint.
@@ -109,6 +119,13 @@ func RequestInfoRefs(ctx context.Context, conn *Conn, service transport.Service,
 	if err := httpError(res); err != nil {
 		return nil, err
 	}
+	if conn.FollowInfoRefsRedirect && res.Request != nil && res.Request.URL != nil {
+		final := res.Request.URL
+		if final.Host != conn.Endpoint.Host || final.Scheme != conn.Endpoint.Scheme {
+			conn.Endpoint.Scheme = final.Scheme
+			conn.Endpoint.Host = final.Host
+		}
+	}
 	// Bound the read to prevent unbounded memory allocation (issue #9).
 	const maxInfoRefsSize = 64 * 1024 * 1024 // 64 MiB
 	lr := io.LimitReader(res.Body, maxInfoRefsSize+1)

internal/gitproto/smarthttp_test.go

@@ -5,6 +5,8 @@ import (
 	"errors"
 	"io"
 	"net/http"
+	"net/http/httptest"
+	"strings"
 	"testing"
 	"time"
 
@@ -170,6 +172,71 @@ func TestPostRPCStreamContextCanceled(t *testing.T) {
 	}
 }
 
+// TestRequestInfoRefs_FollowInfoRefsRedirect verifies that when the flag is
+// set, a 307 on /info/refs rewrites Conn.Endpoint.Host so subsequent PostRPC
+// calls target the redirected node. Matches vanilla git's smart-HTTP
+// behaviour and lets clients use a cluster entry domain for info/refs while
+// packs land on the hosting replica.
+func TestRequestInfoRefs_FollowInfoRefsRedirect(t *testing.T) {
+	node := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/x-git-upload-pack-advertisement")
+		_, _ = w.Write([]byte("001e# service=git-upload-pack\n0000"))
+	}))
+	defer node.Close()
+
+	entry := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, node.URL+r.URL.Path+"?"+r.URL.RawQuery, http.StatusTemporaryRedirect)
+	}))
+	defer entry.Close()
+
+	ep, err := transport.NewEndpoint(entry.URL + "/repo.git")
+	if err != nil {
+		t.Fatalf("parse endpoint: %v", err)
+	}
+	conn := NewConn(ep, "test", nil, http.DefaultTransport)
+	conn.FollowInfoRefsRedirect = true
+
+	if _, err := RequestInfoRefs(t.Context(), conn, transport.UploadPackService, ""); err != nil {
+		t.Fatalf("RequestInfoRefs: %v", err)
+	}
+
+	nodeURL := strings.TrimPrefix(node.URL, "http://")
+	if conn.Endpoint.Host != nodeURL {
+		t.Errorf("Endpoint.Host = %q, want %q (endpoint should follow the 307)", conn.Endpoint.Host, nodeURL)
+	}
+}
+
+// TestRequestInfoRefs_DoesNotFollowByDefault confirms the default behaviour
+// is unchanged: Endpoint is stable even if the server 307s.
+func TestRequestInfoRefs_DoesNotFollowByDefault(t *testing.T) {
+	node := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/x-git-upload-pack-advertisement")
+		_, _ = w.Write([]byte("001e# service=git-upload-pack\n0000"))
+	}))
+	defer node.Close()
+
+	entry := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, node.URL+r.URL.Path+"?"+r.URL.RawQuery, http.StatusTemporaryRedirect)
+	}))
+	defer entry.Close()
+
+	ep, err := transport.NewEndpoint(entry.URL + "/repo.git")
+	if err != nil {
+		t.Fatalf("parse endpoint: %v", err)
+	}
+	entryHost := ep.Host
+	conn := NewConn(ep, "test", nil, http.DefaultTransport)
+	// FollowInfoRefsRedirect intentionally not set.
+
+	if _, err := RequestInfoRefs(t.Context(), conn, transport.UploadPackService, ""); err != nil {
+		t.Fatalf("RequestInfoRefs: %v", err)
+	}
+
+	if conn.Endpoint.Host != entryHost {
+		t.Errorf("Endpoint.Host = %q, want %q (endpoint should be unchanged by default)", conn.Endpoint.Host, entryHost)
+	}
+}
+
 func TestHTTPErrorBoundsBodyRead(t *testing.T) {
 	req, err := http.NewRequestWithContext(t.Context(), http.MethodGet, "https://example.com/repo.git", nil)
 	if err != nil {