Error handling in disambiguateHttp

Add some consistency to the error handling in the checkIfXXX methods
used in disambiguateHttp. Return IOErrors if for 401 responses. Log
403 responses and move on to the next check. Fixes
#1435

Author: lesserwhirls

cdm/core/src/main/java/ucar/nc2/dataset/DatasetUrl.java

@@ -1,27 +1,34 @@
 /*
- * Copyright (c) 1998-2018 John Caron and University Corporation for Atmospheric Research/Unidata
+ * Copyright (c) 1998-2025 John Caron and University Corporation for Atmospheric Research/Unidata
  * See LICENSE for license information.
  */
+
 package ucar.nc2.dataset;
 
 import static java.net.HttpURLConnection.HTTP_FORBIDDEN;
 import static java.net.HttpURLConnection.HTTP_NOT_ACCEPTABLE;
 import static java.net.HttpURLConnection.HTTP_OK;
 import static java.net.HttpURLConnection.HTTP_UNAUTHORIZED;
+
 import com.google.common.annotations.VisibleForTesting;
+import java.io.BufferedInputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
 import javax.annotation.Nullable;
 
-import com.google.common.collect.Multimap;
 import thredds.client.catalog.ServiceType;
-import thredds.inventory.MFile;
-import thredds.inventory.MFiles;
 import ucar.httpservices.HTTPFactory;
 import ucar.httpservices.HTTPMethod;
 import ucar.nc2.util.EscapeStrings;
 import ucar.unidata.util.StringUtil2;
 import ucar.unidata.util.Urlencoded;
-import java.io.*;
-import java.util.*;
 
 /**
  * Detection of the protocol from a location string.
@@ -31,6 +38,7 @@
  * @since 10/20/2015.
  */
 public class DatasetUrl {
+  private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(DatasetUrl.class);
   private static final String alpha = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
   private static final String slashalpha = "\\/" + alpha;
 
@@ -398,15 +406,23 @@ private static ServiceType disambiguateHttp(String location) throws IOException
     return null;
   }
 
+  private static void handleCheckIfResponse(HTTPMethod method, int statusCode, ServiceType serviceChecked)
+      throws IOException {
+    if (statusCode == HTTP_UNAUTHORIZED) {
+      throw new IOException("Unauthorized to open dataset " + method.getURI());
+    } else if (statusCode == HTTP_FORBIDDEN) {
+      logger.warn(String.format(
+          "Forbidden Request to %s - assuming remote server is not a %s server, but could also indicate incorrect credentials.",
+          method.getURI(), serviceChecked));
+    }
+  }
+
   // cdmremote
   private static ServiceType checkIfCdmr(String location) throws IOException {
     try (HTTPMethod method = HTTPFactory.Head(location + "?req=header")) {
       int statusCode = method.execute();
       if (statusCode >= 300) {
-        if (statusCode == HTTP_UNAUTHORIZED || statusCode == HTTP_FORBIDDEN)
-          throw new IOException("Unauthorized to open dataset " + location);
-        else
-          throw new IOException(location + " is not a valid URL, return status=" + statusCode);
+        handleCheckIfResponse(method, statusCode, ServiceType.CdmRemote);
       }
 
       Optional<String> value = method.getResponseHeaderValue("Content-Description");
@@ -442,8 +458,7 @@ private static ServiceType checkIfDods(String location) throws IOException {
             throw new IOException("OPeNDAP Server Error= " + method.getResponseAsString());
         }
       }
-      if (status == HTTP_UNAUTHORIZED || status == HTTP_FORBIDDEN)
-        throw new IOException("Unauthorized to open dataset " + location);
+      handleCheckIfResponse(method, status, ServiceType.OPENDAP);
 
       // not dods
       return null;
@@ -471,6 +486,7 @@ else if (location.endsWith(".html"))
             return ServiceType.DAP4;
         }
       }
+      handleCheckIfResponse(method, status, ServiceType.DAP4);
       // not dap4
       return null;
     }
@@ -497,14 +513,15 @@ private static boolean checkIfRemoteNcml(String location) throws IOException {
         method.setRequestHeader("accept-encoding", "identity");
         int statusCode = method.execute();
         if (statusCode >= 300) {
-          if (statusCode == HTTP_UNAUTHORIZED) {
-            throw new IOException("Unauthorized to open dataset " + location);
-          } else if (statusCode == HTTP_NOT_ACCEPTABLE) {
+          handleCheckIfResponse(method, statusCode, ServiceType.NCML);
+          // additional checks
+          if (statusCode == HTTP_NOT_ACCEPTABLE) {
             String msg = location + " - this server does not support returning content without any encoding.";
             msg = msg + " Please download the file locally. Return status=" + statusCode;
             throw new IOException(msg);
           } else {
-            throw new IOException(location + " is not a valid URL, return status=" + statusCode);
+            throw new IOException(String.format("Error opening %s: %s, (HTTP Status Code %d)", location,
+                method.getResponseAsString(), statusCode));
           }
         }