Look up HTTP headers while ignoring case

OpenStack Swift uses lower-case headers.  Fixes #664.

src/main/java/org/gaul/s3proxy/CaseInsensitiveImmutableMultimap.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2014-2021 Andrew Gaul <andrew@gaul.org>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.gaul.s3proxy;
+
+import java.util.Collection;
+import java.util.Map;
+
+import com.google.common.collect.ForwardingMultimap;
+import com.google.common.collect.ImmutableMultimap;
+import com.google.common.collect.Multimap;
+
+final class CaseInsensitiveImmutableMultimap
+        extends ForwardingMultimap<String, String> {
+    private final Multimap<String, String> inner;
+
+    CaseInsensitiveImmutableMultimap(Multimap<String, String> map) {
+        var builder = ImmutableMultimap.<String, String>builder();
+        for (Map.Entry<String, String> entry : map.entries()) {
+            builder.put(lower(entry.getKey()), entry.getValue());
+        }
+        this.inner = builder.build();
+    }
+
+    @Override
+    protected Multimap<String, String> delegate() {
+        return inner;
+    }
+
+    @Override
+    public Collection<String> get(String key) {
+        return inner.get(lower(key));
+    }
+
+    private static String lower(String key) {
+        return key == null ? null : key.toLowerCase();
+    }
+}

src/main/java/org/gaul/s3proxy/S3ProxyHandler.java

@@ -1775,9 +1775,12 @@ public class S3ProxyHandler {
         addCorsResponseHeader(request, response);
 
         addMetadataToResponse(request, response, blob.getMetadata());
+
         // TODO: handles only a single range due to jclouds limitations
+        var headers = new CaseInsensitiveImmutableMultimap(
+                blob.getAllHeaders());
         Collection<String> contentRanges =
-                blob.getAllHeaders().get(HttpHeaders.CONTENT_RANGE);
+                headers.get(HttpHeaders.CONTENT_RANGE);
         if (!contentRanges.isEmpty()) {
             response.addHeader(HttpHeaders.CONTENT_RANGE,
                     contentRanges.iterator().next());