Preserve default Http2Settings when Http2SettingsBuilder is used (#…

…3092)

Motivation:

By default we set values for `MAX_HEADER_LIST_SIZE` and
`INITIAL_WINDOW_SIZE` settings at `H2ProtocolConfigBuilder` level.
However, if users want to change only one setting (for example,
`MAX_CONCURRENT_STREAMS`), they lose our defaults when they use
`Http2SettingsBuilder`.

Modifications:

- Move defaults initialization from `H2ProtocolConfigBuilder` to
`Http2SettingsBuilder`.

Result:

Users always start with consistent default `Http2Settings` and can use
builder methods to override what they want.

servicetalk-http-api/src/main/java/io/servicetalk/http/api/Http2SettingsBuilder.java

@@ -30,6 +30,7 @@ public final class Http2SettingsBuilder {
     private static final long MAX_UNSIGNED_INT = 0xffffffffL;
     private static final int MAX_FRAME_SIZE_LOWER_BOUND = 0x4000;
     private static final int MAX_FRAME_SIZE_UPPER_BOUND = 0xffffff;
+
     /**
      * Identifier <a href="https://datatracker.ietf.org/doc/html/rfc7540#section-6.5.2">SETTINGS_HEADER_TABLE_SIZE</a>.
      */
@@ -57,13 +58,27 @@ public final class Http2SettingsBuilder {
      *     SETTINGS_MAX_HEADER_LIST_SIZE</a>.
      */
     private static final char MAX_HEADER_LIST_SIZE = 0x6;
+
+    /**
+     * 1mb default {@link #INITIAL_WINDOW_SIZE}.
+     */
+    private static final int DEFAULT_INITIAL_WINDOW_SIZE = 1_048_576;
+    /**
+     * The initial value of {@link #MAX_HEADER_LIST_SIZE} is
+     * <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">unlimited</a>.
+     * However, in practice we don't want to allow our peers to use unlimited memory by default.
+     */
+    private static final long DEFAULT_MAX_HEADER_LIST_SIZE = 8192;
+
     private final Map<Character, Long> settings;
 
     /**
      * Create a new instance.
      */
     public Http2SettingsBuilder() {
         settings = new HashMap<>(6);
+        initialWindowSize(DEFAULT_INITIAL_WINDOW_SIZE);
+        maxHeaderListSize(DEFAULT_MAX_HEADER_LIST_SIZE);
     }
 
     /**

servicetalk-http-netty/src/main/java/io/servicetalk/http/netty/H2ProtocolConfigBuilder.java

@@ -28,7 +28,6 @@
 import java.util.function.BooleanSupplier;
 import javax.annotation.Nullable;
 
-import static io.netty.handler.codec.http2.Http2CodecUtil.DEFAULT_HEADER_LIST_SIZE;
 import static io.servicetalk.http.netty.H2KeepAlivePolicies.disabled;
 import static io.servicetalk.http.netty.H2KeepAlivePolicies.validateKeepAlivePolicy;
 import static io.servicetalk.utils.internal.NumberUtils.ensurePositive;
@@ -41,10 +40,6 @@
  */
 public final class H2ProtocolConfigBuilder {
     private static final BiPredicate<CharSequence, CharSequence> DEFAULT_SENSITIVITY_DETECTOR = (name, value) -> false;
-    /**
-     * 1mb default window size.
-     */
-    private static final int INITIAL_FLOW_CONTROL_WINDOW = 1_048_576;
     /**
      * Netty currently doubles the connection window by default so a single stream doesn't exhaust all flow control
      * bytes.
@@ -54,10 +49,7 @@ public final class H2ProtocolConfigBuilder {
      * Default allocation quantum to use for the remote flow controller.
      */
     private static final int DEFAULT_FLOW_CONTROL_QUANTUM = 1024 * 16;
-    private Http2Settings h2Settings = new Http2SettingsBuilder()
-            .initialWindowSize(INITIAL_FLOW_CONTROL_WINDOW)
-            .maxHeaderListSize(DEFAULT_HEADER_LIST_SIZE)
-            .build();
+    private Http2Settings h2Settings = new Http2SettingsBuilder().build();
     private HttpHeadersFactory headersFactory = H2HeadersFactory.INSTANCE;
     private BiPredicate<CharSequence, CharSequence> headersSensitivityDetector = DEFAULT_SENSITIVITY_DETECTOR;
     @Nullable