Skip redundant toLowerCase for HTTP/2 response headers

HTTP/2 header names are already lowercase per RFC 7540 §8.1.2. Add
keysAlreadyLowerCased flag to HttpHeaders to skip toLowerCase() in
set() and getHeader() for HTTP/2 responses (~25 scans saved per
response). In RxGatewayStoreModel, use toMap() instead of
toLowerCaseMap() when keys are already lowercase to avoid redundant
HashMap allocation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 2 people

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/RxGatewayStoreModel.java

@@ -230,6 +230,11 @@ public StoreResponse unwrapToStoreResponse(
         // If there is any error in the header response this throws exception
         validateOrThrow(request, HttpResponseStatus.valueOf(statusCode), headers, retainedContent);
 
+        // For HTTP/2, header keys are already lowercase per RFC 7540 §8.1.2 and were stored
+        // as-is (no toLowerCase) in HttpHeaders. Use toMap() directly to avoid redundant work.
+        Map<String, String> headerMap = HttpUtils.unescape(
+            headers.areKeysLowerCased() ? headers.toMap() : headers.toLowerCaseMap());
+
         int size;
         if ((size = retainedContent.readableBytes()) > 0) {
             if (leakDetectionDebuggingEnabled) {
@@ -240,7 +245,7 @@ public StoreResponse unwrapToStoreResponse(
             return new StoreResponse(
                 endpoint,
                 statusCode,
-                HttpUtils.unescape(headers.toLowerCaseMap()),
+                headerMap,
                 new ByteBufInputStream(retainedContent, true),
                 size);
         } else {
@@ -250,7 +255,7 @@ public StoreResponse unwrapToStoreResponse(
         return new StoreResponse(
             endpoint,
             statusCode,
-            HttpUtils.unescape(headers.toLowerCaseMap()),
+            headerMap,
             null,
             0);
     }
@@ -731,7 +736,8 @@ private void validateOrThrow(RxDocumentServiceRequest request,
                 String.format("%s, StatusCode: %s", cosmosError.getMessage(), statusCodeString),
                 cosmosError.getPartitionedQueryExecutionInfo());
 
-            CosmosException dce = BridgeInternal.createCosmosException(request.requestContext.resourcePhysicalAddress, statusCode, cosmosError, headers.toLowerCaseMap());
+            CosmosException dce = BridgeInternal.createCosmosException(request.requestContext.resourcePhysicalAddress, statusCode, cosmosError,
+                headers.areKeysLowerCased() ? headers.toMap() : headers.toLowerCaseMap());
             BridgeInternal.setRequestHeaders(dce, request.getHeaders());
             throw dce;
         }

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/http/HttpHeaders.java

@@ -19,19 +19,36 @@
  */
 public class HttpHeaders implements Iterable<HttpHeader>, JsonSerializable {
     private Map<String, HttpHeader> headers;
+    private final boolean keysAlreadyLowerCased;
 
     /**
      * Create an empty HttpHeaders instance.
      */
     public HttpHeaders() {
         this.headers = new HashMap<>();
+        this.keysAlreadyLowerCased = false;
     }
 
     /**
      * Create an HttpHeaders instance with the given size.
      */
     public HttpHeaders(int size) {
         this.headers = new HashMap<>(size);
+        this.keysAlreadyLowerCased = false;
+    }
+
+    /**
+     * Create an HttpHeaders instance with the given size.
+     * When {@code keysAlreadyLowerCased} is true, {@link #set(String, String)} skips
+     * the {@code toLowerCase()} call on header names. This is an optimization for HTTP/2
+     * responses where header names are guaranteed to be lowercase per RFC 7540 §8.1.2.
+     *
+     * @param size the initial capacity
+     * @param keysAlreadyLowerCased true if header names are guaranteed to be lowercase (e.g. HTTP/2)
+     */
+    public HttpHeaders(int size, boolean keysAlreadyLowerCased) {
+        this.headers = new HashMap<>(size);
+        this.keysAlreadyLowerCased = keysAlreadyLowerCased;
     }
 
     /**
@@ -41,6 +58,7 @@ public HttpHeaders(int size) {
      */
     public HttpHeaders(Map<String, String> headers) {
         this.headers = new HashMap<>(headers.size());
+        this.keysAlreadyLowerCased = false;
         for (final Map.Entry<String, String> header : headers.entrySet()) {
             this.set(header.getKey(), header.getValue());
         }
@@ -66,7 +84,7 @@ public int size() {
      * @return this HttpHeaders
      */
     public HttpHeaders set(String name, String value) {
-        final String headerKey = name.toLowerCase(Locale.ROOT);
+        final String headerKey = keysAlreadyLowerCased ? name : name.toLowerCase(Locale.ROOT);
         if (value == null) {
             headers.remove(headerKey);
         } else {
@@ -100,7 +118,7 @@ public String[] values(String name) {
     }
 
     private HttpHeader getHeader(String headerName) {
-        final String headerKey = headerName.toLowerCase(Locale.ROOT);
+        final String headerKey = keysAlreadyLowerCased ? headerName : headerName.toLowerCase(Locale.ROOT);
         return headers.get(headerKey);
     }
 
@@ -130,6 +148,14 @@ public Map<String, String> toLowerCaseMap() {
         return result;
     }
 
+    /**
+     * Returns true if header keys are guaranteed to be lowercase,
+     * meaning {@link #toLowerCaseMap()} and {@link #toMap()} produce equivalent keys.
+     */
+    public boolean areKeysLowerCased() {
+        return keysAlreadyLowerCased;
+    }
+
     @Override
     public Iterator<HttpHeader> iterator() {
         return headers.values().iterator();

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/http/ReactorNettyClient.java

@@ -409,7 +409,11 @@ public String headerValue(String name) {
 
         @Override
         public HttpHeaders headers() {
-            HttpHeaders headers = new HttpHeaders(reactorNettyResponse.responseHeaders().size());
+            // HTTP/2 header names are guaranteed lowercase per RFC 7540 §8.1.2.
+            // Detect directly from the response protocol version, not from the request record,
+            // to handle HTTP/1.1 fallback correctly even when H2 was requested.
+            boolean isHttp2 = reactorNettyResponse.version().majorVersion() == 2;
+            HttpHeaders headers = new HttpHeaders(reactorNettyResponse.responseHeaders().size(), isHttp2);
             reactorNettyResponse.responseHeaders().forEach(e -> headers.set(e.getKey(), e.getValue()));
             return headers;
         }