Update headers to only allocate names when needed

Author: mtdowling

http/http-api/src/main/java/software/amazon/smithy/java/http/api/HttpHeaders.java

@@ -10,6 +10,8 @@
 
 /**
  * Contains case-insensitive HTTP headers.
+ *
+ * <p>Implementations must always normalize header names to lowercase.
  */
 public interface HttpHeaders extends Iterable<Map.Entry<String, List<String>>> {
 
@@ -109,4 +111,64 @@ default boolean isEmpty() {
      * @return the created modifiable headers.
      */
     ModifiableHttpHeaders toModifiable();
+
+    /**
+     * Normalizes an HTTP header name by trimming whitespace and converting ASCII uppercase to lowercase.
+     *
+     * <p>Trimming behavior matches {@link String#trim()}, removing characters {@code <= 'u0020'}.
+     * Only ASCII uppercase letters (A-Z) are lowercased; non-ASCII characters pass through unchanged,
+     * which is correct per RFC 7230 (HTTP/1.1) and RFC 9110 (HTTP semantics) since header field names
+     * are defined as ASCII tokens.
+     *
+     * @param name the header name to normalize
+     * @return the normalized header name, or the original instance if already normalized
+     */
+    static String normalizeHeaderName(String name) {
+        int len = name.length();
+        int start = 0;
+        int end = len - 1;
+        boolean needsWork = false;
+
+        // Detect leading whitespace to trim if needed
+        while (start <= end && name.charAt(start) <= ' ') {
+            needsWork = true;
+            start++;
+        }
+
+        // Detect trailing whitespace to trim if needed
+        while (end >= start && name.charAt(end) <= ' ') {
+            needsWork = true;
+            end--;
+        }
+
+        // All whitespace
+        if (start > end) {
+            return "";
+        }
+
+        // Scan for ASCII uppercase
+        for (int i = start; i <= end; i++) {
+            char c = name.charAt(i);
+            if (c >= 'A' && c <= 'Z') {
+                needsWork = true;
+                break;
+            }
+        }
+
+        if (!needsWork) {
+            return name;
+        }
+
+        int outLen = end - start + 1;
+        char[] chars = new char[outLen];
+        for (int src = start, dst = 0; src <= end; src++, dst++) {
+            char c = name.charAt(src);
+            if (c >= 'A' && c <= 'Z') {
+                c = (char) (c + 32);
+            }
+            chars[dst] = c;
+        }
+
+        return new String(chars);
+    }
 }

http/http-api/src/main/java/software/amazon/smithy/java/http/api/SimpleModifiableHttpHeaders.java

@@ -36,7 +36,7 @@ public void addHeader(String name, List<String> values) {
     }
 
     private List<String> getOrCreateValues(String name) {
-        var key = formatPutKey(name);
+        var key = HttpHeaders.normalizeHeaderName(name);
         var values = headers.get(key);
         if (values == null) {
             values = new ArrayList<>();
@@ -47,8 +47,8 @@ private List<String> getOrCreateValues(String name) {
 
     @Override
     public void setHeader(String name, String value) {
-        var key = formatPutKey(name);
-        var list = headers.get(name);
+        var key = HttpHeaders.normalizeHeaderName(name);
+        var list = headers.get(key);
         if (list == null) {
             list = new ArrayList<>(1);
             headers.put(key, list);
@@ -61,8 +61,8 @@ public void setHeader(String name, String value) {
 
     @Override
     public void setHeader(String name, List<String> values) {
-        var key = formatPutKey(name);
-        var list = headers.get(name);
+        var key = HttpHeaders.normalizeHeaderName(name);
+        var list = headers.get(key);
         if (list == null) {
             list = new ArrayList<>(values.size());
             headers.put(key, list);
@@ -77,10 +77,6 @@ public void setHeader(String name, List<String> values) {
         }
     }
 
-    private static String formatPutKey(String name) {
-        return name.trim().toLowerCase(Locale.ENGLISH);
-    }
-
     @Override
     public void removeHeader(String name) {
         headers.remove(name.toLowerCase(Locale.ENGLISH));

http/http-api/src/main/java/software/amazon/smithy/java/http/api/SimpleUnmodifiableHttpHeaders.java

@@ -32,7 +32,7 @@ final class SimpleUnmodifiableHttpHeaders implements HttpHeaders {
             // Single pass to normalize, trim, and make immutable in one go
             Map<String, List<String>> result = HashMap.newHashMap(input.size());
             for (var entry : input.entrySet()) {
-                var key = normalizeKey(entry.getKey());
+                var key = HttpHeaders.normalizeHeaderName(entry.getKey());
                 var values = entry.getValue();
                 var existing = result.get(key);
                 if (existing == null) {
@@ -49,10 +49,6 @@ final class SimpleUnmodifiableHttpHeaders implements HttpHeaders {
         }
     }
 
-    private static String normalizeKey(String key) {
-        return key.trim().toLowerCase(Locale.ENGLISH);
-    }
-
     private static List<String> copyAndTrimValuesMutable(List<String> source) {
         int size = source.size();
         if (size == 0) {
@@ -145,7 +141,7 @@ static Map<String, List<String>> addHeaders(
             mutatedHeaders = copyHeaders(original.map());
         }
         for (var entry : from.entrySet()) {
-            var key = normalizeKey(entry.getKey());
+            var key = HttpHeaders.normalizeHeaderName(entry.getKey());
             var list = mutatedHeaders.get(key);
             if (list == null) {
                 list = copyAndTrimValuesMutable(entry.getValue());
@@ -166,7 +162,7 @@ static Map<String, List<String>> addHeader(
         if (mutatedHeaders == null) {
             mutatedHeaders = copyHeaders(original.map());
         }
-        field = normalizeKey(field);
+        field = HttpHeaders.normalizeHeaderName(field);
         value = value.trim();
         var list = mutatedHeaders.get(field);
         if (list == null) {
@@ -183,7 +179,7 @@ static Map<String, List<String>> copyHeaders(Map<String, List<String>> from) {
         }
         Map<String, List<String>> into = HashMap.newHashMap(from.size());
         for (var entry : from.entrySet()) {
-            into.put(normalizeKey(entry.getKey()), copyAndTrimValuesMutable(entry.getValue()));
+            into.put(HttpHeaders.normalizeHeaderName(entry.getKey()), copyAndTrimValuesMutable(entry.getValue()));
         }
         return into;
     }
@@ -197,7 +193,7 @@ static Map<String, List<String>> replaceHeaders(
             mutated = copyHeaders(original.map());
         }
         for (var entry : replace.entrySet()) {
-            mutated.put(normalizeKey(entry.getKey()), copyAndTrimValuesMutable(entry.getValue()));
+            mutated.put(HttpHeaders.normalizeHeaderName(entry.getKey()), copyAndTrimValuesMutable(entry.getValue()));
         }
         return mutated;
     }