proxy multipart to peers via multipart uploadID (#15926)

cmd/site-replication.go

@@ -4843,3 +4843,27 @@ func isUserInfoEqual(u1, u2 madmin.UserInfo) bool {
 func isPolicyMappingEqual(p1, p2 srPolicyMapping) bool {
 	return p1.Policy == p2.Policy && p1.IsGroup == p2.IsGroup && p1.UserOrGroup == p2.UserOrGroup
 }
+
+type srPeerInfo struct {
+	madmin.PeerInfo
+	EndpointURL *url.URL
+}
+
+// getPeerForUpload returns the site replication peer handling this upload. Defaults to local cluster otherwise
+func (c *SiteReplicationSys) getPeerForUpload(deplID string) (pi srPeerInfo, local bool) {
+	ci, _ := c.GetClusterInfo(GlobalContext)
+	if !ci.Enabled {
+		return pi, true
+	}
+	for _, site := range ci.Sites {
+		if deplID == site.DeploymentID {
+			ep, _ := url.Parse(site.Endpoint)
+			pi = srPeerInfo{
+				PeerInfo:    site,
+				EndpointURL: ep,
+			}
+			return pi, site.DeploymentID == globalDeploymentID
+		}
+	}
+	return pi, true
+}