Allow configurable suffixes for handle services for TCP connection reuse

atproto/identity/base_directory.go

@@ -29,8 +29,13 @@ type BaseDirectory struct {
 	SkipDNSDomainSuffixes []string
 	// set of fallback DNS servers (eg, domain registrars) to try as a fallback. each entry should be "ip:port", eg "8.8.8.8:53"
 	FallbackDNSServers []string
+	// Map of well-known suffixes to call the same host for handle resolution, adds a host header for virtual routing
+	WellKnownSuffixMap WellKnownSuffixMap
 }
 
+// WellKnownSuffixMap is a map of well-known suffixes to call the same host for handle resolution, adds a host header for virtual routing
+type WellKnownSuffixMap map[string]string
+
 var _ Directory = (*BaseDirectory)(nil)
 
 func (d *BaseDirectory) LookupHandle(ctx context.Context, h syntax.Handle) (*Identity, error) {

atproto/identity/handle.go

@@ -127,11 +127,24 @@ func (d *BaseDirectory) ResolveHandleDNSFallback(ctx context.Context, handle syn
 }
 
 func (d *BaseDirectory) ResolveHandleWellKnown(ctx context.Context, handle syntax.Handle) (syntax.DID, error) {
-	req, err := http.NewRequestWithContext(ctx, "GET", fmt.Sprintf("https://%s/.well-known/atproto-did", handle), nil)
+	// Check for well-known suffixes to route to a specific host
+	// allowing for reuse of TCP connections for high-traffic providers
+	requestHost := handle.String()
+	for suffix, host := range d.WellKnownSuffixMap {
+		if strings.HasSuffix(handle.String(), suffix) {
+			requestHost = host
+			break
+		}
+	}
+
+	req, err := http.NewRequestWithContext(ctx, "GET", fmt.Sprintf("https://%s/.well-known/atproto-did", requestHost), nil)
 	if err != nil {
 		return "", fmt.Errorf("constructing HTTP request for handle resolution: %w", err)
 	}
 
+	// Add host header for virtual routing
+	req.Header.Set("Host", handle.String())
+
 	resp, err := d.HTTPClient.Do(req)
 	if err != nil {
 		// check for NXDOMAIN