docs: document script handler and signer

ckb/src/main/java/org/nervos/ckb/transaction/AbstractTransactionBuilder.java

@@ -19,6 +19,12 @@ public abstract class AbstractTransactionBuilder {
  protected List<TransactionInput> inputsDetail = new ArrayList<>();
  protected Transaction tx = new Transaction();
 
+ /**
+ * Initialites the transaction builder.
+ *
+ * @param configuration This is the bundle of configuration for builder,
+ * such as fee rate and registerred {@link org.nervos.ckb.transaction.handler.ScriptHandler}.
+ */
  public AbstractTransactionBuilder(TransactionBuilderConfiguration configuration, Iterator<TransactionInput> availableInputs) {
  this.configuration = configuration;
  this.availableInputs = availableInputs;
@@ -94,9 +100,24 @@ protected static long calculateTxFee(Transaction transaction, long feeRate) {
  return Calculator.calculateTransactionFee(transaction, feeRate);
  }
 
+ /**
+ * Builds the transaction with a default context for script handlers.
+ *
+ * This function will call script handlers in {@code TransactionConfiguration} with a
+ * default context null. Use {@link #build(Object...)} to pass custom contexts.
+ *
+ * @see org.nervos.ckb.transaction.handler.ScriptHandler#buildTransaction(AbstractTransactionBuilder, ScriptGroup, Object)
+ */
  public TransactionWithScriptGroups build() {
  return build((Object) null);
  }
 
+ /**
+ * Builds the transaction with custom contexts for script handlers.
+ *
+ * The contexts will be passed to the registered script handlers in the same order.
+ *
+ * @see org.nervos.ckb.transaction.handler.ScriptHandler#buildTransaction(AbstractTransactionBuilder, ScriptGroup, Object)
+ */
  abstract TransactionWithScriptGroups build(Object... contexts);
 }

ckb/src/main/java/org/nervos/ckb/transaction/handler/ScriptHandler.java

@@ -4,7 +4,58 @@
 import org.nervos.ckb.sign.ScriptGroup;
 import org.nervos.ckb.transaction.AbstractTransactionBuilder;
 
+/**
+ * ScriptHandler implements the building logic for various scripts.
+ *
+ * These handlers should be registered in the transaction builder via {@link
+ * org.nervos.ckb.transaction.TransactionBuilderConfiguration}.
+ */
 public interface ScriptHandler {
+ /**
+ * Build the transaction for the script.
+ *
+ * This function is called by transaction builder for each script group and each context.
+ *
+ * Generally this function should:
+ *
+ * <ol>
+ * <li>Check the scriptGroup to determine whether to proceed with the next steps or skip them.</li>
+ * <li>Add cell deps for the script.</li>
+ * <li>
+ * Prefill the witness for the script so the transaction size will not
+ * increase after signing, which may invalidate the fee calculation.
+ * </li>
+ * </ol>
+ *
+ * <p>For example:</p>
+ *
+ * <pre>{@code
+ * @Override
+ * boolean buildTransaction(AbstractTransactionBuilder txBuilder, ScriptGroup scriptGroup, Object context) {
+ * // Only change the transaction when the script is used.
+ * if (scriptGroup == null || !isMatched(scriptGroup.getScript())) {
+ * return false;
+ * }
+ * // Add celldeps
+ * txBuilder.addCellDeps(cellDeps);
+ *
+ * // Prefill witness placeholder
+ * int witnessIndex = scriptGroup.getInputIndices().get(0);
+ * byte[] dummyWitness = new byte[8];
+ * txBuilder.setWitness(witnessIndex, WitnessArgs.Type.LOCK, dummyWitness);
+ *
+ * return true;
+ * }
+ * }</pre>
+ *
+ * @param txBuilder The transaction in building.
+ * @param scriptGroup Transaction builder calls this callback for each script group found in the transaction.
+ * The script handler is responsoble for determining whether it should handle the given script group.
+ * @param context This is null passed from {@link org.nervos.ckb.transaction.AbstractTransactionBuilder#build()},
+ * or provided contexts in {@link org.nervos.ckb.transaction.AbstractTransactionBuilder#build(Object...)}.
+ * @return {@code true} when the script handler has modified the transaction.
+ *
+ */
  boolean buildTransaction(AbstractTransactionBuilder txBuilder, ScriptGroup scriptGroup, Object context);
 
  void init(Network network);

core/src/main/java/org/nervos/ckb/sign/ScriptSigner.java

@@ -2,6 +2,27 @@
 
 import org.nervos.ckb.type.Transaction;
 
+/**
+ * ScriptSigner implements the signing logic for various scripts.
+ *
+ * These signers should be registered in {@link TransactionSigner}.
+ */
 public interface ScriptSigner {
+ /**
+ * Sign the transaction for the script.
+ *
+ * This function is called by {@link TransactionSigner}
+ * for each context and each matched script group.
+ *
+ * @param transaction The transaction to be signed.
+ * @param scriptGroup TransactionSigner selects the corresponding ScriptSigner for each script group.
+ * This selection is based on the registered ScriptSigner's provided script type and hash.
+ * @param context This is passed from {@code TransactionSigner.signTransaction}
+ * @return {@code true} when the script handler has modified the transaction.
+ *
+ * @see TransactionSigner#signTransaction(TransactionWithScriptGroups, Context...)
+ * @see TransactionSigner#signTransaction(TransactionWithScriptGroups, Set<Context>)
+ * @see TransactionSigner#signTransaction(TransactionWithScriptGroups, String...)
+ */
  boolean signTransaction(Transaction transaction, ScriptGroup scriptGroup, Context context);
 }

core/src/main/java/org/nervos/ckb/sign/TransactionSigner.java

@@ -87,12 +87,25 @@ public TransactionSigner registerLockScriptSigner(String codeHash, ScriptSigner
  return registerLockScriptSigner(Numeric.hexStringToByteArray(codeHash), scriptSigner);
  }
 
-
+ /**
+ * signTransaction signs the transaction using registered ScriptSigners.
+ *
+ * @param transaction Transaction to be signed.
+ * @param contexts Contexts for {@link org.nervos.ckb.sign.ScriptSigner}.
+ * @return signed groups indices.
+ */
  public Set<Integer> signTransaction(
  TransactionWithScriptGroups transaction, Context... contexts) {
  return signTransaction(transaction, new HashSet<>(Arrays.asList(contexts)));
  }
 
+ /**
+ * signTransaction signs the transaction using registered ScriptSigners.
+ *
+ * @param transaction Transaction to be signed.
+ * @param contexts Contexts for {@link org.nervos.ckb.sign.ScriptSigner}.
+ * @return signed groups indices.
+ */
  public Set<Integer> signTransaction(
  TransactionWithScriptGroups transaction, Set<Context> contexts) {
  Set<Integer> signedGroupsIndices = new HashSet<>();
@@ -122,6 +135,13 @@ public Set<Integer> signTransaction(
  return signedGroupsIndices;
  }
 
+ /**
+ * signTransaction signs the transaction using registered ScriptSigners.
+ *
+ * @param transaction Transaction to be signed.
+ * @param privateKeys Each private key is wrapped in one {@link Context}. These contexts will be passed to ScriptSigners.
+ * @return signed groups indices.
+ */
  public Set<Integer> signTransaction(
  TransactionWithScriptGroups transaction, String... privateKeys) {
  Contexts contexts = new Contexts();