Add new utility methods on Transaction type

This PR adds the txid(), is_coin_base(), is_explicitly_rbf(),
and is_lock_time_enabled() methods.
Fixes #303

api-docs/kotlin/src/main/kotlin/org/bitcoindevkit/bdk.kt

@@ -288,13 +288,15 @@ class Blockchain(
  * @param transactionBytes The transaction bytes, bitcoin consensus encoded.
  */
 class Transaction(transactionBytes: List<UByte>) {
-    /** Return the transaction bytes, bitcoin consensus encoded. */
-    fun serialize(): List<UByte> {}
+    /** Computes the txid. */
+    fun txid(): String {}
 
     /**
      * Returns the "weight" of this transaction, as defined by BIP141.
      *
-     * For transactions with an empty witness, this is simply the consensus-serialized size times four. For transactions with a witness, this is the non-witness consensus-serialized size multiplied by three plus the with-witness consensus-serialized size.
+     * For transactions with an empty witness, this is simply the consensus-serialized size times four.
+     * For transactions with a witness, this is the non-witness consensus-serialized size multiplied by three
+     * plus the with-witness consensus-serialized size.
      */
     fun weight(): ULong {}
 
@@ -304,9 +306,25 @@ class Transaction(transactionBytes: List<UByte>) {
     /**
      * Returns the "virtual size" (vsize) of this transaction.
      *
-     * Will be ceil(weight / 4.0). Note this implements the virtual size as per BIP141, which is different to what is implemented in Bitcoin Core. The computation should be the same for any remotely sane transaction.
+     * Will be ceil(weight / 4.0). Note this implements the virtual size as per BIP141, which is different to
+     * what is implemented in Bitcoin Core. The computation should be the same for any remotely sane transaction.
      */
     fun vsize(): ULong {}
+
+    /** Return the transaction bytes, bitcoin consensus encoded. */
+    fun serialize(): List<UByte> {}
+
+    /** Is this a coin base transaction? */
+    fun isCoinBase(): Boolean {}
+
+    /**
+     * Returns true if the transaction itself opted in to be BIP-125-replaceable (RBF).
+     * This does not cover the case where a transaction becomes replaceable due to ancestors being RBF.
+     */
+    fun isExplicitlyRbf(): Boolean {}
+
+    /** Returns true if this transactions nLockTime is enabled (BIP-65). */
+    fun isLockTimeEnabled(): Boolean {}
 }
 
 /**

bdk-ffi/src/bdk.udl

@@ -247,13 +247,21 @@ interface Transaction {
   [Throws=BdkError]
   constructor(sequence<u8> transaction_bytes);
 
-  sequence<u8> serialize();
+  string txid();
 
   u64 weight();
 
   u64 size();
 
   u64 vsize();
+
+  sequence<u8> serialize();
+
+  boolean is_coin_base();
+
+  boolean is_explicitly_rbf();
+
+  boolean is_lock_time_enabled();
 };
 
 interface PartiallySignedTransaction {

bdk-ffi/src/lib.rs

@@ -251,8 +251,8 @@ impl Transaction {
         Ok(Transaction { internal: tx })
     }
 
-    fn serialize(&self) -> Vec<u8> {
-        self.internal.serialize()
+    fn txid(&self) -> String {
+        self.internal.txid().to_string()
     }
 
     fn weight(&self) -> u64 {
@@ -266,6 +266,22 @@ impl Transaction {
     fn vsize(&self) -> u64 {
         self.internal.vsize() as u64
     }
+
+    fn serialize(&self) -> Vec<u8> {
+        self.internal.serialize()
+    }
+
+    fn is_coin_base(&self) -> bool {
+        self.internal.is_coin_base()
+    }
+
+    fn is_explicitly_rbf(&self) -> bool {
+        self.internal.is_explicitly_rbf()
+    }
+
+    fn is_lock_time_enabled(&self) -> bool {
+        self.internal.is_lock_time_enabled()
+    }
 }
 
 /// A Bitcoin address.