feat: adds fdv2 payload parsing and protocol handling

lib/shared/internal/src/main/java/com/launchdarkly/sdk/internal/GsonHelpers.java

@@ -1,12 +1,16 @@
 package com.launchdarkly.sdk.internal;
 
 import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.launchdarkly.sdk.internal.fdv2.payloads.IntentCode;
 
 /**
  * General-purpose Gson helpers.
  */
 public abstract class GsonHelpers {
-  private static final Gson GSON_INSTANCE = new Gson();
+  private static final Gson GSON_INSTANCE = new GsonBuilder()
+      .registerTypeAdapter(IntentCode.class, new IntentCode.IntentCodeTypeAdapter())
+      .create();
 
   /**
    * A singleton instance of Gson with the default configuration.

lib/shared/internal/src/main/java/com/launchdarkly/sdk/internal/fdv2/payloads/DeleteObject.java

@@ -0,0 +1,111 @@
+package com.launchdarkly.sdk.internal.fdv2.payloads;
+
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonToken;
+import com.launchdarkly.sdk.json.SerializationException;
+
+import java.io.IOException;
+import java.util.Objects;
+
+/**
+ * Represents the delete-object event, which contains a payload object that should be deleted.
+ */
+public final class DeleteObject {
+  private final int version;
+  private final String kind;
+  private final String key;
+
+  /**
+   * Constructs a new DeleteObject.
+   *
+   * @param version the minimum payload version this change applies to
+   * @param kind the kind of object being deleted ("flag" or "segment")
+   * @param key the identifier of the object being deleted
+   */
+  public DeleteObject(int version, String kind, String key) {
+    this.version = version;
+    this.kind = Objects.requireNonNull(kind, "kind");
+    this.key = Objects.requireNonNull(key, "key");
+  }
+
+  /**
+   * Returns the minimum payload version this change applies to.
+   *
+   * @return the version
+   */
+  public int getVersion() {
+    return version;
+  }
+
+  /**
+   * Returns the kind of the object being deleted ("flag" or "segment").
+   *
+   * @return the kind
+   */
+  public String getKind() {
+    return kind;
+  }
+
+  /**
+   * Returns the identifier of the object being deleted.
+   *
+   * @return the key
+   */
+  public String getKey() {
+    return key;
+  }
+
+  /**
+   * Parses a DeleteObject from a JsonReader.
+   *
+   * @param reader the JSON reader
+   * @return the parsed DeleteObject
+   * @throws SerializationException if the JSON is invalid
+   */
+  public static DeleteObject parse(JsonReader reader) throws SerializationException {
+    Integer version = null;
+    String kind = null;
+    String key = null;
+
+    try {
+      if (reader.peek() != JsonToken.BEGIN_OBJECT) {
+        throw new SerializationException("expected object");
+      }
+      reader.beginObject();
+
+      while (reader.peek() != JsonToken.END_OBJECT) {
+        String name = reader.nextName();
+        switch (name) {
+        case "version":
+          version = reader.nextInt();
+          break;
+        case "kind":
+          kind = reader.nextString();
+          break;
+        case "key":
+          key = reader.nextString();
+          break;
+        default:
+          reader.skipValue();
+          break;
+        }
+      }
+      reader.endObject();
+
+      if (version == null) {
+        throw new SerializationException("delete object missing required property 'version'");
+      }
+      if (kind == null) {
+        throw new SerializationException("delete object missing required property 'kind'");
+      }
+      if (key == null) {
+        throw new SerializationException("delete object missing required property 'key'");
+      }
+
+      return new DeleteObject(version, kind, key);
+    } catch (IOException | RuntimeException e) {
+      throw new SerializationException(e);
+    }
+  }
+}
+

lib/shared/internal/src/main/java/com/launchdarkly/sdk/internal/fdv2/payloads/Error.java

@@ -0,0 +1,91 @@
+package com.launchdarkly.sdk.internal.fdv2.payloads;
+
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonToken;
+import com.launchdarkly.sdk.json.SerializationException;
+
+import java.io.IOException;
+import java.util.Objects;
+
+/**
+ * Represents the error event, which indicates an error encountered server-side affecting
+ * the payload transfer. SDKs must discard partially transferred data. The SDK remains
+ * connected and expects the server to recover.
+ */
+public final class Error {
+  private final String id;
+  private final String reason;
+
+  /**
+   * Constructs a new Error.
+   *
+   * @param id the unique string identifier of the entity the error relates to
+   * @param reason human-readable reason the error occurred
+   */
+  public Error(String id, String reason) {
+    this.id = id;
+    this.reason = Objects.requireNonNull(reason, "reason");
+  }
+
+  /**
+   * Returns the unique string identifier of the entity the error relates to.
+   *
+   * @return the identifier, or null if not present
+   */
+  public String getId() {
+    return id;
+  }
+
+  /**
+   * Returns the human-readable reason the error occurred.
+   *
+   * @return the reason
+   */
+  public String getReason() {
+    return reason;
+  }
+
+  /**
+   * Parses an Error from a JsonReader.
+   *
+   * @param reader the JSON reader
+   * @return the parsed Error
+   * @throws SerializationException if the JSON is invalid
+   */
+  public static Error parse(JsonReader reader) throws SerializationException {
+    String id = null;
+    String reason = null;
+
+    try {
+      if (reader.peek() != JsonToken.BEGIN_OBJECT) {
+        throw new SerializationException("expected object");
+      }
+      reader.beginObject();
+
+      while (reader.peek() != JsonToken.END_OBJECT) {
+        String name = reader.nextName();
+        switch (name) {
+        case "id":
+          id = reader.nextString();
+          break;
+        case "reason":
+          reason = reader.nextString();
+          break;
+        default:
+          reader.skipValue();
+          break;
+        }
+      }
+      reader.endObject();
+
+      if (reason == null) {
+        throw new SerializationException("error missing required property 'reason'");
+      }
+
+      return new Error(id, reason);
+    } catch (IOException | RuntimeException e) {
+      throw new SerializationException(e);
+    }
+  }
+}
+