diff --git a/.gitignore b/.gitignore
index 9bf4fb6..fd662a9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,6 @@
 target
 build
 Cargo.lock
-*.h
 /bdk-kotlin/local.properties
 .gradle
 wallet_db
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..6d3f227
--- /dev/null
+++ b/README.md
@@ -0,0 +1,18 @@
+
+
+Adding new structs and functions
+
+1. Create C safe Rust structs and related functions using safer-ffi
+
+2. Test generated library and `bdk_ffi.h` file with c language tests in `cc/bdk_ffi_test.c`
+
+3. Use `build.sh` and `test.sh` to build c test program and verify functionality and 
+   memory de-allocation via `valgrind` 
+
+4. Update the kotlin native interface LibJna.kt in the `bdk-kotlin` `jvm` module to match `bdk_ffi.h`
+
+5. Create kotlin wrapper classes and interfaces as needed
+
+6. Add tests to `bdk-kotlin` `test-fixtures` module 
+
+7. Use `build.sh` and `test.sh` to build and test `bdk-kotlin` `jvm` and `android` modules
\ No newline at end of file
diff --git a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/FfiResult.kt b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/FfiResult.kt
new file mode 100644
index 0000000..3755617
--- /dev/null
+++ b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/FfiResult.kt
@@ -0,0 +1,15 @@
+package org.bitcoindevkit.bdk
+
+import com.sun.jna.Pointer
+import com.sun.jna.Structure
+
+abstract class FfiResult : Structure {
+    constructor() : super()
+    constructor(pointer: Pointer) : super(pointer)
+
+    @JvmField
+    var ok: Pointer? = null
+
+    @JvmField
+    var err: Pointer? = null
+}
\ No newline at end of file
diff --git a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/LibJna.kt b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/LibJna.kt
index ca50bb7..bfb5383 100644
--- a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/LibJna.kt
+++ b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/LibJna.kt
@@ -1,52 +1,48 @@
 package org.bitcoindevkit.bdk
 
-import com.sun.jna.Library
-import com.sun.jna.Pointer
-import com.sun.jna.PointerType
+import com.sun.jna.*
 
 interface LibJna : Library {
 
-    // typedef struct VoidResult VoidResult_t;
-    class VoidResult_t : PointerType {
-        constructor() : super()
-        constructor(pointer: Pointer) : super(pointer)
+    // typedef struct {
+    //
+    //    char * * ok;
+    //
+    //    char * * err;
+    //
+    // } FfiResult_char_ptr_t;
+    open class FfiResult_char_ptr_t : FfiResult() {
+        class ByValue : FfiResult_char_ptr_t(), Structure.ByValue
+        class ByReference : FfiResult_char_ptr_t(), Structure.ByReference
+
+        override fun getFieldOrder() = listOf("ok", "err")
     }
 
-    // char * get_void_err (
-    //    VoidResult_t const * void_result);
-    fun get_void_err(void_result: VoidResult_t): Pointer?
-
-    // void free_void_result (
-    //    VoidResult_t * void_result);
-    fun free_void_result(void_result: VoidResult_t)
-
-    // typedef struct StringResult StringResult_t;
-    class StringResult_t : PointerType {
-        constructor() : super()
-        constructor(pointer: Pointer) : super(pointer)
-    }
-
-    // char * get_string_ok (
-    //    StringResult_t const * string_result);
-    fun get_string_ok(string_result: StringResult_t): Pointer?
-
-    // char * get_string_err (
-    //    StringResult_t const * string_result);
-    fun get_string_err(string_result: StringResult_t): Pointer?
-
     // void free_string_result (
-    //    StringResult_t * string_result);
-    fun free_string_result(string_result: StringResult_t)
+    //    FfiResult_char_ptr_t string_result);
+    fun free_string_result(string_result: FfiResult_char_ptr_t.ByValue)
 
-    // typedef struct WalletRef WalletRef_t;
-    class WalletRef_t : PointerType {
-        constructor() : super()
-        constructor(pointer: Pointer) : super(pointer)
+    // typedef struct {
+    //
+    //    void * ok;
+    //
+    //    char * * err;
+    //
+    // } FfiResult_void_t;
+    open class FfiResult_void_t : FfiResult() {
+        class ByValue : FfiResult_void_t(), Structure.ByValue
+        class ByReference : FfiResult_void_t(), Structure.ByReference
+
+        override fun getFieldOrder() = listOf("ok", "err")
     }
 
-    // void free_wallet_ref (
-    //    WalletRef_t * wallet_ref);
-    fun free_wallet_ref(wallet_ref: WalletRef_t)
+    // void free_void_result (
+    //    FfiResult_void_t void_result);
+    fun free_void_result(void_result: FfiResult_void_t.ByValue)
+
+    // void free_string (
+    //    char * string);
+    fun free_string(string: Pointer?)
 
     // typedef struct BlockchainConfig BlockchainConfig_t;
     class BlockchainConfig_t : PointerType {
@@ -54,54 +50,6 @@ interface LibJna : Library {
         constructor(pointer: Pointer) : super(pointer)
     }
 
-    // typedef struct DatabaseConfig DatabaseConfig_t;
-    class DatabaseConfig_t : PointerType {
-        constructor() : super()
-        constructor(pointer: Pointer) : super(pointer)
-    }
-
-    // typedef struct WalletResult WalletResult_t;
-    class WalletResult_t : PointerType {
-        constructor() : super()
-        constructor(pointer: Pointer) : super(pointer)
-    }
-
-    // WalletResult_t * new_wallet_result (
-    //    char const * descriptor,
-    //    char const * change_descriptor,
-    //    BlockchainConfig_t const * blockchain_config,
-    //    DatabaseConfig_t const * database_config);
-    fun new_wallet_result(
-        descriptor: String,
-        changeDescriptor: String?,
-        blockchainConfig: BlockchainConfig_t,
-        databaseConfig: DatabaseConfig_t,
-    ): WalletResult_t
-
-    // char * get_wallet_err (
-    //    WalletResult_t const * wallet_result);
-    fun get_wallet_err(wallet_result: WalletResult_t): Pointer?
-
-    // WalletRef_t * get_wallet_ok (
-    //    WalletResult_t const * wallet_result);
-    fun get_wallet_ok(wallet_result: WalletResult_t): WalletRef_t?
-
-    // VoidResult_t * sync_wallet (
-    //    WalletRef_t const * wallet_ref);
-    fun sync_wallet(wallet_ref: Pointer): VoidResult_t
-
-    // StringResult_t * new_address (
-    //    WalletRef_t const * wallet_ref);
-    fun new_address(wallet_ref: Pointer): StringResult_t
-
-    // void free_wallet_result (
-    //    WalletResult_t * wallet_result);
-    fun free_wallet_result(wallet_result: WalletResult_t)
-
-    // void free_string (
-    //    char * string);
-    fun free_string(string: Pointer?)
-
     // BlockchainConfig_t * new_electrum_config (
     //    char const * url,
     //    char const * socks5,
@@ -118,6 +66,193 @@ interface LibJna : Library {
     //    BlockchainConfig_t * blockchain_config);
     fun free_blockchain_config(blockchain_config: BlockchainConfig_t)
 
+    // typedef struct DatabaseConfig DatabaseConfig_t;
+    class DatabaseConfig_t : PointerType {
+        constructor() : super()
+        constructor(pointer: Pointer) : super(pointer)
+    }
+
+    // typedef struct OpaqueWallet OpaqueWallet_t;
+    class OpaqueWallet_t : PointerType {
+        constructor() : super()
+        constructor(pointer: Pointer) : super(pointer)
+    }
+
+    // typedef struct {
+    //
+    //    OpaqueWallet_t * ok;
+    //
+    //    char * * err;
+    //
+    // } FfiResult_OpaqueWallet_t;
+    open class FfiResult_OpaqueWallet_t : FfiResult() {
+        class ByValue : FfiResult_OpaqueWallet_t(), Structure.ByValue
+        class ByReference : FfiResult_OpaqueWallet_t(), Structure.ByReference
+
+        override fun getFieldOrder() = listOf("ok", "err")
+    }
+
+    // FfiResult_OpaqueWallet_t new_wallet_result (
+    //    char const * descriptor,
+    //    char const * change_descriptor,
+    //    BlockchainConfig_t const * blockchain_config,
+    //    DatabaseConfig_t const * database_config);
+    fun new_wallet_result(
+        descriptor: String,
+        changeDescriptor: String?,
+        blockchainConfig: BlockchainConfig_t,
+        databaseConfig: DatabaseConfig_t,
+    ): FfiResult_OpaqueWallet_t.ByValue
+
+    // void free_wallet_result (
+    //    FfiResult_OpaqueWallet_t wallet_result);
+    fun free_wallet_result(wallet_result: FfiResult_OpaqueWallet_t.ByValue)
+
+    // typedef struct {
+    //
+    //    char * txid;
+    //
+    //    uint32_t vout;
+    //
+    // } OutPoint_t;
+    open class OutPoint_t : Structure() {
+        class ByValue : OutPoint_t(), Structure.ByValue
+
+        @JvmField
+        var txid: String? = null
+
+        @JvmField
+        var vout: Int? = null
+
+        override fun getFieldOrder() = listOf("txid", "vout")
+    }
+
+    // typedef struct {
+    //
+    //    uint64_t value;
+    //
+    //    char * script_pubkey;
+    //
+    // } TxOut_t;
+    open class TxOut_t : Structure() {
+        class ByValue : TxOut_t(), Structure.ByValue
+
+        @JvmField
+        var value: Long? = null
+
+        @JvmField
+        var script_pubkey: String? = null
+
+        override fun getFieldOrder() = listOf("value", "script_pubkey")
+    }
+
+    // typedef struct {
+    //
+    //    OutPoint_t outpoint;
+    //
+    //    TxOut_t txout;
+    //
+    //    uint16_t keychain;
+    //
+    // } LocalUtxo_t;
+    open class LocalUtxo_t : Structure {
+        constructor() : super()
+        constructor(pointer: Pointer) : super(pointer)
+
+        class ByValue : LocalUtxo_t, Structure.ByValue {
+            constructor() : super()
+            constructor(pointer: Pointer) : super(pointer)
+        }
+
+        class ByReference : LocalUtxo_t, Structure.ByReference {
+            constructor() : super()
+            constructor(pointer: Pointer) : super(pointer)
+        }
+
+        @JvmField
+        var outpoint: OutPoint_t? = null
+
+        @JvmField
+        var txout: TxOut_t? = null
+
+        @JvmField
+        var keychain: Short? = null
+
+        override fun getFieldOrder() = listOf("outpoint", "txout", "keychain")
+    }
+
+    // typedef struct {
+    //
+    //    LocalUtxo_t * ptr;
+    //
+    //    size_t len;
+    //
+    //    size_t cap;
+    //
+    // } Vec_LocalUtxo_t;
+    open class Vec_LocalUtxo_t : Structure {
+        constructor() : super()
+        constructor(pointer: Pointer) : super(pointer)
+
+        class ByReference : Vec_LocalUtxo_t, Structure.ByReference {
+            constructor() : super()
+            constructor(pointer: Pointer) : super(pointer)
+        }
+
+        class ByValue : Vec_LocalUtxo_t, Structure.ByValue {
+            constructor() : super()
+            constructor(pointer: Pointer) : super(pointer)
+        }
+        
+        @JvmField
+        var ptr: LocalUtxo_t.ByReference? = null
+
+        @JvmField
+        var len: NativeLong? = null
+
+        @JvmField
+        var cap: NativeLong? = null
+
+        override fun getFieldOrder() = listOf("ptr", "len", "cap")
+    }
+
+    // typedef struct {
+    //
+    //    Vec_LocalUtxo_t ok;
+    //
+    //    char * * err;
+    //
+    // } FfiResultVec_LocalUtxo_t;
+    open class FfiResultVec_LocalUtxo_t : Structure() {
+        
+        class ByValue : FfiResultVec_LocalUtxo_t(), Structure.ByValue
+        class ByReference : FfiResultVec_LocalUtxo_t(), Structure.ByReference
+
+        @JvmField
+        var ok: Vec_LocalUtxo_t = Vec_LocalUtxo_t()
+
+        @JvmField
+        var err: Pointer? = null
+
+        override fun getFieldOrder() = listOf("ok", "err")
+    }
+
+    // void free_unspent_result (
+    //    FfiResultVec_LocalUtxo_t unspent_result);
+    fun free_unspent_result(unspent_result: FfiResultVec_LocalUtxo_t.ByValue)
+
+    // FfiResult_void_t sync_wallet (
+    //    OpaqueWallet_t const * opaque_wallet);
+    fun sync_wallet(opaque_wallet: OpaqueWallet_t): FfiResult_void_t.ByValue
+
+    // FfiResult_char_ptr_t new_address (
+    //    OpaqueWallet_t const * opaque_wallet);
+    fun new_address(opaque_wallet: OpaqueWallet_t): FfiResult_char_ptr_t.ByValue
+
+    // FfiResult_Vec_LocalUtxo_t list_unspent (
+    //    OpaqueWallet_t const * opaque_wallet);
+    fun list_unspent(opaque_wallet: OpaqueWallet_t): FfiResultVec_LocalUtxo_t.ByValue
+
     // DatabaseConfig_t * new_memory_config (void);
     fun new_memory_config(): DatabaseConfig_t
 
diff --git a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/Result.kt b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/Result.kt
new file mode 100644
index 0000000..6ceef7f
--- /dev/null
+++ b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/Result.kt
@@ -0,0 +1,37 @@
+package org.bitcoindevkit.bdk
+
+import com.sun.jna.Pointer
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
+
+abstract class Result<T : FfiResult, RT : Any>(private val ffiResult: T): LibBase() {
+
+    protected open val log: Logger = LoggerFactory.getLogger(Result::class.java)
+
+    protected abstract fun getOkValue(pointer: Pointer): RT
+    
+    protected abstract fun freeResult(ffiResult: T)
+
+    fun value(): RT {
+        val err = ffiResult.err
+        val ok = ffiResult.ok
+        when {
+            err != null -> {
+                val errString = err.getPointer(0).getString(0)
+                log.error("JnaError: $errString")
+                throw JnaException(JnaError.valueOf(errString))
+            }
+            ok != null -> {
+                return getOkValue(ok)
+            }
+            else -> {
+                throw JnaException(JnaError.Generic)
+            }
+        }
+    }
+
+    protected fun finalize() {
+        freeResult(ffiResult)
+        log.debug("$ffiResult freed")
+    }
+}
\ No newline at end of file
diff --git a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/StringResult.kt b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/StringResult.kt
index 6bfa121..29da3eb 100644
--- a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/StringResult.kt
+++ b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/StringResult.kt
@@ -1,26 +1,15 @@
 package org.bitcoindevkit.bdk
 
 import com.sun.jna.Pointer
-import org.slf4j.Logger
-import org.slf4j.LoggerFactory
 
-class StringResult internal constructor(stringResultT: LibJna.StringResult_t) :
-    ResultBase<LibJna.StringResult_t, String>(stringResultT) {
+class StringResult constructor(stringResultPtr: LibJna.FfiResult_char_ptr_t.ByValue) :
+    Result<LibJna.FfiResult_char_ptr_t.ByValue, String>(stringResultPtr) {
 
-    override val log: Logger = LoggerFactory.getLogger(StringResult::class.java)
-
-    override fun err(pointerT: LibJna.StringResult_t): Pointer? {
-        return libJna.get_string_err(pointerT)
+    override fun getOkValue(pointer: Pointer): String {
+        return pointer.getPointer(0).getString(0)
     }
 
-    override fun ok(pointerT: LibJna.StringResult_t): String {
-        val okPointer = libJna.get_string_ok(pointerT)
-        val ok = okPointer!!.getString(0)
-        libJna.free_string(okPointer)
-        return ok
-    }
-
-    override fun free(pointerT: LibJna.StringResult_t) {
-        libJna.free_string_result(pointerT)
+    override fun freeResult(ffiResult: LibJna.FfiResult_char_ptr_t.ByValue) {
+        libJna.free_string_result(ffiResult)
     }
 }
\ No newline at end of file
diff --git a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/VecLocalUtxoResult.kt b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/VecLocalUtxoResult.kt
new file mode 100644
index 0000000..da69a1b
--- /dev/null
+++ b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/VecLocalUtxoResult.kt
@@ -0,0 +1,31 @@
+package org.bitcoindevkit.bdk
+
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
+
+class VecLocalUtxoResult(private val ffiResult: LibJna.FfiResultVec_LocalUtxo_t.ByValue) :
+    LibBase() {
+
+    protected open val log: Logger = LoggerFactory.getLogger(VecLocalUtxoResult::class.java)
+
+    fun value(): Array<LibJna.LocalUtxo_t.ByReference> {
+        val err = ffiResult.err
+        val ok = ffiResult.ok
+        when {
+            err != null -> {
+                val errString = err.getPointer(0).getString(0)
+                log.error("JnaError: $errString")
+                throw JnaException(JnaError.valueOf(errString))
+            }
+            else -> {
+                val first = ok.ptr!!
+                return first.toArray(ok.len!!.toInt()) as Array<LibJna.LocalUtxo_t.ByReference>
+            }
+        }
+    }
+
+    protected fun finalize() {
+        libJna.free_unspent_result(ffiResult)
+        log.debug("$ffiResult freed")
+    }
+}
\ No newline at end of file
diff --git a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/VoidResult.kt b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/VoidResult.kt
index 5ed6c25..03b46be 100644
--- a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/VoidResult.kt
+++ b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/VoidResult.kt
@@ -1,23 +1,15 @@
 package org.bitcoindevkit.bdk
 
 import com.sun.jna.Pointer
-import org.slf4j.Logger
-import org.slf4j.LoggerFactory
 
-class VoidResult internal constructor(voidResultT: LibJna.VoidResult_t) :
-    ResultBase<LibJna.VoidResult_t, Unit>(voidResultT) {
+class VoidResult constructor(voidResultPtr: LibJna.FfiResult_void_t.ByValue) :
+    Result<LibJna.FfiResult_void_t.ByValue, Unit>(voidResultPtr) {
 
-    override val log: Logger = LoggerFactory.getLogger(VoidResult::class.java)
-
-    override fun err(pointerT: LibJna.VoidResult_t): Pointer? {
-        return libJna.get_void_err(pointerT)
+    override fun getOkValue(pointer: Pointer) {
+        // No value
     }
 
-    override fun ok(pointerT: LibJna.VoidResult_t) {
-        // Void
-    }
-
-    override fun free(pointerT: LibJna.VoidResult_t) {
-        libJna.free_void_result(pointerT)
+    override fun freeResult(ffiResult: LibJna.FfiResult_void_t.ByValue) {
+        libJna.free_void_result(ffiResult)
     }
 }
\ No newline at end of file
diff --git a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/Wallet.kt b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/Wallet.kt
index d438778..7abea00 100644
--- a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/Wallet.kt
+++ b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/Wallet.kt
@@ -12,29 +12,28 @@ class Wallet constructor(
 
     val log: Logger = LoggerFactory.getLogger(Wallet::class.java)
 
-    private val walletResult =
-        WalletResult(
-            libJna.new_wallet_result(
-                descriptor,
-                changeDescriptor,
-                blockchainConfig.blockchainConfigT,
-                databaseConfig.databaseConfigT
-            )
+    private val walletResult = WalletResult(
+        libJna.new_wallet_result(
+            descriptor,
+            changeDescriptor,
+            blockchainConfig.blockchainConfigT,
+            databaseConfig.databaseConfigT
         )
-    private val walletRefT = walletResult.value()
+    )
+    private val wallet = walletResult.value()
 
     fun sync() {
-        val voidResult = VoidResult(libJna.sync_wallet(walletRefT.pointer))
+        val voidResult = VoidResult(libJna.sync_wallet(wallet))
         return voidResult.value()
     }
 
     fun getAddress(): String {
-        val stringResult = StringResult(libJna.new_address(walletRefT.pointer))
+        val stringResult = StringResult(libJna.new_address(wallet))
         return stringResult.value()
     }
-
-    protected fun finalize(walletRefT: LibJna.WalletRef_t) {
-        libJna.free_wallet_ref(walletRefT)
-        log.debug("$walletRefT freed")
+    
+    fun listUnspent(): Array<LibJna.LocalUtxo_t.ByReference> {
+        val vecLocalUtxoResult = VecLocalUtxoResult(libJna.list_unspent(wallet))
+        return vecLocalUtxoResult.value()
     }
 }
\ No newline at end of file
diff --git a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/WalletResult.kt b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/WalletResult.kt
index 1b77cb8..ba8f979 100644
--- a/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/WalletResult.kt
+++ b/bdk-kotlin/jvm/src/main/java/org/bitcoindevkit/bdk/WalletResult.kt
@@ -1,23 +1,15 @@
 package org.bitcoindevkit.bdk
 
 import com.sun.jna.Pointer
-import org.slf4j.Logger
-import org.slf4j.LoggerFactory
 
-class WalletResult internal constructor(walletResultT: LibJna.WalletResult_t) :
-    ResultBase<LibJna.WalletResult_t, LibJna.WalletRef_t>(walletResultT) {
+class WalletResult constructor(walletResultPtr: LibJna.FfiResult_OpaqueWallet_t.ByValue) :
+    Result<LibJna.FfiResult_OpaqueWallet_t.ByValue, LibJna.OpaqueWallet_t>(walletResultPtr) {
 
-    override val log: Logger = LoggerFactory.getLogger(WalletResult::class.java)
-
-    override fun err(pointerT: LibJna.WalletResult_t): Pointer? {
-        return libJna.get_wallet_err(pointerT)
+    override fun getOkValue(pointer: Pointer): LibJna.OpaqueWallet_t {
+        return LibJna.OpaqueWallet_t(pointer)
     }
 
-    override fun ok(pointerT: LibJna.WalletResult_t): LibJna.WalletRef_t {
-        return libJna.get_wallet_ok(pointerT)!!
-    }
-
-    override fun free(pointerT: LibJna.WalletResult_t) {
-        libJna.free_wallet_result(pointerT)
+    override fun freeResult(ffiResult: LibJna.FfiResult_OpaqueWallet_t.ByValue) {
+        libJna.free_wallet_result(ffiResult)
     }
 }
\ No newline at end of file
diff --git a/bdk-kotlin/test-fixtures/src/main/java/org/bitcoindevkit/bdk/LibTest.kt b/bdk-kotlin/test-fixtures/src/main/java/org/bitcoindevkit/bdk/LibTest.kt
index 3d0c5a0..5c84338 100644
--- a/bdk-kotlin/test-fixtures/src/main/java/org/bitcoindevkit/bdk/LibTest.kt
+++ b/bdk-kotlin/test-fixtures/src/main/java/org/bitcoindevkit/bdk/LibTest.kt
@@ -19,6 +19,9 @@ abstract class LibTest : LibBase() {
     val change =
         "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/1/*)"
 
+    val blockchainConfig = ElectrumConfig("ssl://electrum.blockstream.info:60002", null, 5, 30)
+    val databaseConfig = MemoryConfig()
+
     abstract fun getTestDataDir(): String
 
     fun cleanupTestDataDir() {
@@ -27,48 +30,69 @@ abstract class LibTest : LibBase() {
 
     @Test
     fun walletResultError() {
-        val blockchainConfig = ElectrumConfig("ssl://electrum.blockstream.info:60002", null, 5, 30)
-        val databaseConfig = MemoryConfig()
         val jnaException = assertThrows(JnaException::class.java) {
             Wallet("bad", "bad", blockchainConfig, databaseConfig)
         }
         assertEquals(jnaException.err, JnaError.Descriptor)
     }
 
-    @Test
-    fun walletResultFinalize() {
-        val blockchainConfig = ElectrumConfig("ssl://electrum.blockstream.info:60002", null, 5, 30)
-        val databaseConfig = MemoryConfig()
-        val names = listOf("one", "two", "three")
-        names.map {
-            val wallet = Wallet(desc, change, blockchainConfig, databaseConfig)
-            assertNotNull(wallet)
-        }
-        System.gc()
-        // The only way to verify wallets freed is by checking the log
-    }
+//    @Test
+//    fun walletResultFinalize() {
+//        run {
+//            val desc =
+//                "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/0/*)"
+//            val change =
+//                "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/1/*)"
+//
+//            val blockchainConfig = ElectrumConfig("ssl://electrum.blockstream.info:60002", null, 5, 30)
+//            val databaseConfig = MemoryConfig()
+//            val wallet = Wallet(desc, change, blockchainConfig, databaseConfig)
+//            wallet.sync()
+//            assertNotNull(wallet.getAddress())
+//        }
+//        System.gc()
+//        Thread.sleep(2000)
+//        // The only way to verify wallets freed is by checking the log
+//    }
 
     @Test
     fun walletSync() {
         val blockchainConfig = ElectrumConfig("ssl://electrum.blockstream.info:60002", null, 5, 30)
         val testDataDir = getTestDataDir()
-        log.debug("testDataDir = $testDataDir")
+        // log.debug("testDataDir = $testDataDir")
         val databaseConfig = SledConfig(testDataDir, "steve-test")
         val wallet = Wallet(desc, change, blockchainConfig, databaseConfig)
-        assertNotNull(wallet)
         wallet.sync()
         cleanupTestDataDir()
     }
 
     @Test
     fun walletNewAddress() {
-        val blockchainConfig = ElectrumConfig("ssl://electrum.blockstream.info:60002", null, 5, 30)
-        val databaseConfig = MemoryConfig()
         val wallet = Wallet(desc, change, blockchainConfig, databaseConfig)
-        assertNotNull(wallet)
         val address = wallet.getAddress()
         assertNotNull(address)
-        log.debug("address created from kotlin: $address")
+        // log.debug("address created from kotlin: $address")
         assertEquals(address, "tb1qzg4mckdh50nwdm9hkzq06528rsu73hjxxzem3e")
     }
+
+    @Test
+    fun walletUnspent() {
+        val wallet = Wallet(desc, change, blockchainConfig, databaseConfig)
+        wallet.sync()
+        val unspent = wallet.listUnspent()
+        assertTrue(unspent.isNotEmpty())
+        
+        unspent.iterator().forEach {
+            //log.debug("unspent.outpoint.txid: ${it.outpoint!!.txid}")
+            assertNotNull(it.outpoint?.txid)
+            //log.debug("unspent.outpoint.vout: ${it.outpoint?.vout}")
+            assertTrue(it.outpoint?.vout!! >= 0)
+            //log.debug("unspent.txout.value: ${it.txout?.value}")
+            assertTrue(it.txout?.value!! > 0)
+            //log.debug("unspent.txout.script_pubkey: ${it.txout?.script_pubkey}")
+            assertNotNull(it.txout?.script_pubkey)
+            //log.debug("unspent.keychain: ${it.keychain}")
+            assertTrue(it.keychain!! >= 0)
+        }
+    }
 }
diff --git a/build.sh b/build.sh
index bbcc9bf..6b5a530 100755
--- a/build.sh
+++ b/build.sh
@@ -2,6 +2,7 @@
 set -eo pipefail -o xtrace
 
 # rust
+cargo fmt
 cargo build
 cargo test --features c-headers -- generate_headers
 
diff --git a/cc/bdk_ffi.h b/cc/bdk_ffi.h
new file mode 100644
index 0000000..eba536a
--- /dev/null
+++ b/cc/bdk_ffi.h
@@ -0,0 +1,154 @@
+/*! \file */
+/*******************************************
+ *                                         *
+ *  File auto-generated by `::safer_ffi`.  *
+ *                                         *
+ *  Do not manually edit this file.        *
+ *                                         *
+ *******************************************/
+
+#ifndef __RUST_BDK_FFI__
+#define __RUST_BDK_FFI__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct BlockchainConfig BlockchainConfig_t;
+
+BlockchainConfig_t * new_electrum_config (
+    char const * url,
+    char const * socks5,
+    int16_t retry,
+    int16_t timeout);
+
+void free_blockchain_config (
+    BlockchainConfig_t * blockchain_config);
+
+typedef struct DatabaseConfig DatabaseConfig_t;
+
+typedef struct OpaqueWallet OpaqueWallet_t;
+
+typedef struct {
+
+    OpaqueWallet_t * ok;
+
+    char * * err;
+
+} FfiResult_OpaqueWallet_t;
+
+FfiResult_OpaqueWallet_t new_wallet_result (
+    char const * descriptor,
+    char const * change_descriptor,
+    BlockchainConfig_t const * blockchain_config,
+    DatabaseConfig_t const * database_config);
+
+void free_wallet_result (
+    FfiResult_OpaqueWallet_t wallet_result);
+
+typedef struct {
+
+    char * txid;
+
+    uint32_t vout;
+
+} OutPoint_t;
+
+typedef struct {
+
+    uint64_t value;
+
+    char * script_pubkey;
+
+} TxOut_t;
+
+typedef struct {
+
+    OutPoint_t outpoint;
+
+    TxOut_t txout;
+
+    uint16_t keychain;
+
+} LocalUtxo_t;
+
+/** \brief
+ *  Same as [`Vec<T>`][`rust::Vec`], but with guaranteed `#[repr(C)]` layout
+ */
+typedef struct {
+
+    LocalUtxo_t * ptr;
+
+    size_t len;
+
+    size_t cap;
+
+} Vec_LocalUtxo_t;
+
+typedef struct {
+
+    Vec_LocalUtxo_t ok;
+
+    char * * err;
+
+} FfiResultVec_LocalUtxo_t;
+
+void free_unspent_result (
+    FfiResultVec_LocalUtxo_t unspent_result);
+
+typedef struct {
+
+    void * ok;
+
+    char * * err;
+
+} FfiResult_void_t;
+
+FfiResult_void_t sync_wallet (
+    OpaqueWallet_t const * opaque_wallet);
+
+typedef struct {
+
+    char * * ok;
+
+    char * * err;
+
+} FfiResult_char_ptr_t;
+
+FfiResult_char_ptr_t new_address (
+    OpaqueWallet_t const * opaque_wallet);
+
+FfiResultVec_LocalUtxo_t list_unspent (
+    OpaqueWallet_t const * opaque_wallet);
+
+DatabaseConfig_t * new_memory_config (void);
+
+DatabaseConfig_t * new_sled_config (
+    char const * path,
+    char const * tree_name);
+
+void free_database_config (
+    DatabaseConfig_t * database_config);
+
+void free_string_result (
+    FfiResult_char_ptr_t string_result);
+
+void free_void_result (
+    FfiResult_void_t void_result);
+
+/** \brief
+ *  Frees a Rust-allocated string
+ */
+void free_string (
+    char * string);
+
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* __RUST_BDK_FFI__ */
diff --git a/cc/bdk_ffi_test.c b/cc/bdk_ffi_test.c
index 487b20f..8ea5590 100644
--- a/cc/bdk_ffi_test.c
+++ b/cc/bdk_ffi_test.c
@@ -12,19 +12,20 @@ int main (int argc, char const * const argv[])
         //DatabaseConfig_t *db_config = new_sled_config("/home/steve/.bdk", "test_wallet");
         DatabaseConfig_t *db_config = new_memory_config();
         
-        WalletResult_t *wallet_result = new_wallet_result("bad", "bad", bc_config, db_config);
-        assert(wallet_result != NULL);
+        // new wallet with bad descriptor 
+        FfiResult_OpaqueWallet_t wallet_result = new_wallet_result("bad","bad",bc_config,db_config);
+        assert(wallet_result.err != NULL);    
+        assert(wallet_result.ok == NULL);
+        
         free_blockchain_config(bc_config);
         free_database_config(db_config);
-        char *wallet_err = get_wallet_err(wallet_result);
+        
+        char *wallet_err = *wallet_result.err;
         assert(wallet_err != NULL);
         assert( 0 == strcmp(wallet_err,"Descriptor") );
-        //printf("wallet err: %s\n", wallet_err);   
-        WalletRef_t *wallet_ref = get_wallet_ok(wallet_result);
-        assert(wallet_ref == NULL);
-        free_string(wallet_err);
+        // printf("wallet err: %s\n", wallet_err);   
+        
         free_wallet_result(wallet_result);
-
     }
     
     // test new wallet
@@ -33,51 +34,94 @@ int main (int argc, char const * const argv[])
         char const *change = "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/1/*)";
     
         BlockchainConfig_t *bc_config = new_electrum_config("ssl://electrum.blockstream.info:60002", NULL, 5, 30);
-        //DatabaseConfig_t *db_config = new_sled_config("/home/steve/.bdk", "test_wallet");
         DatabaseConfig_t *db_config = new_memory_config();
     
-        WalletResult_t *wallet_result = new_wallet_result(desc, change, bc_config, db_config);
-        assert(wallet_result != NULL);
+        // new wallet
+        FfiResult_OpaqueWallet_t wallet_result = new_wallet_result(desc,change,bc_config,db_config);
+        assert(wallet_result.err == NULL);    
+        assert(wallet_result.ok != NULL);
+        
         free_blockchain_config(bc_config);
         free_database_config(db_config);
-        char *wallet_err = get_wallet_err(wallet_result);
-        assert(wallet_err == NULL);
-        WalletRef_t *wallet_ref = get_wallet_ok(wallet_result);
-        assert(wallet_ref != NULL);
         
-        // test sync_wallet
-        VoidResult_t *sync_result = sync_wallet(wallet_ref);    
-        free_void_result(sync_result);    
+        OpaqueWallet_t *wallet = wallet_result.ok;
         
-        // test new_address
-        StringResult_t *address_result1 = new_address(wallet_ref);
-        char *address1 = get_string_ok(address_result1);
-        //printf("address1: %s\n", address1);       
-        assert( 0 == strcmp(address1,"tb1qgkhp034fyxeta00h0nne9tzfm0vsxq4prduzxp"));
-        free_string(address1);
+        // test sync wallet
+        FfiResult_void_t sync_result = sync_wallet(wallet);   
+        assert(sync_result.ok != NULL);
+        assert(sync_result.err == NULL);    
+        free_void_result(sync_result);
+        
+        // test new address
+        FfiResult_char_ptr_t address_result1 = new_address(wallet);
+        assert(address_result1.ok != NULL);
+        assert(address_result1.err == NULL);
+        // printf("address1 = %s\n", *address_result1.ok);
+        assert( 0 == strcmp(*address_result1.ok,"tb1qgkhp034fyxeta00h0nne9tzfm0vsxq4prduzxp"));
         free_string_result(address_result1);
         
-        StringResult_t *address_result2 = new_address(wallet_ref);
-        char *address2 = get_string_ok(address_result2);
-        //printf("address2: %s\n", address2);
-        assert(0 == strcmp(address2,"tb1qd6u9q327sru2ljvwzdtfrdg36sapax7udz97wf"));
-        free_string(address2);
+        FfiResult_char_ptr_t address_result2 = new_address(wallet);
+        assert(address_result2.ok != NULL);
+        assert(address_result2.err == NULL);
+        // printf("address2 = %s\n", *address_result2.ok);
+        assert( 0 == strcmp(*address_result2.ok,"tb1qd6u9q327sru2ljvwzdtfrdg36sapax7udz97wf"));
         free_string_result(address_result2);
         
-        free_wallet_ref(wallet_ref);
-        
         // test free_wallet
         free_wallet_result(wallet_result);
         
-        // test free_wallet NULL doesn't crash
-        free_wallet_result(NULL);
-        
         // verify free_wallet after free_wallet fails (core dumped)
-        ////free_wallet_result(wallet_result);
+        //// free_wallet_result(wallet_result);
         
         // verify sync_wallet after free_wallet fails (core dumped)
-        ////VoidResult_t sync_result2 = sync_wallet(wallet_result);   
-
+        //// FfiResult_void_t sync_result2 = sync_wallet(wallet);    
+    }
+    
+    // test get unspent utxos
+    {
+        char const *desc = "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/0/*)";
+        char const *change = "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/1/*)";
+    
+        BlockchainConfig_t *bc_config = new_electrum_config("ssl://electrum.blockstream.info:60002", NULL, 5, 30);
+        DatabaseConfig_t *db_config = new_memory_config();
+    
+        // new wallet
+        FfiResult_OpaqueWallet_t wallet_result = new_wallet_result(desc,change,bc_config,db_config);
+        assert(wallet_result.err == NULL);    
+        assert(wallet_result.ok != NULL);
+        
+        free_blockchain_config(bc_config);
+        free_database_config(db_config);
+        
+        OpaqueWallet_t *wallet = wallet_result.ok;
+        
+        // test sync wallet
+        FfiResult_void_t sync_result = sync_wallet(wallet);   
+        assert(sync_result.ok != NULL);
+        assert(sync_result.err == NULL);    
+        free_void_result(sync_result);
+        
+        // list unspent
+        FfiResultVec_LocalUtxo_t unspent_result = list_unspent(wallet);
+        assert(unspent_result.ok.len == 7);
+        assert(unspent_result.err == NULL);
+        
+        LocalUtxo_t * unspent_ptr = unspent_result.ok.ptr;                       
+        for (int i = 0; i < unspent_result.ok.len; i++) {            
+            // printf("%d: outpoint.txid: %s\n", i, unspent_ptr[i].outpoint.txid);
+            assert(unspent_ptr[i].outpoint.txid != NULL);
+            // printf("%d: outpoint.vout: %d\n", i, unspent_ptr[i].outpoint.vout);
+            assert(unspent_ptr[i].outpoint.vout >= 0);
+            // printf("%d: txout.value: %ld\n", i, unspent_ptr[i].txout.value);
+            assert(unspent_ptr[i].txout.value > 0);
+            // printf("%d: txout.script_pubkey: %s\n", i, unspent_ptr[i].txout.script_pubkey);
+            assert(unspent_ptr[i].txout.script_pubkey != NULL);
+            // printf("%d: keychain: %d\n", i, unspent_ptr[i].keychain);
+            assert(unspent_ptr[i].keychain >= 0);
+        }
+        
+        free_unspent_result(unspent_result);          
+        free_wallet_result(wallet_result);
     }
         
     return EXIT_SUCCESS;
diff --git a/src/lib.rs b/src/lib.rs
index 72e9910..e1a9c00 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,6 +3,7 @@
 mod blockchain;
 mod database;
 mod error;
+mod types;
 mod wallet;
 
 /// The following test function is necessary for the header generation.
diff --git a/src/types.rs b/src/types.rs
new file mode 100644
index 0000000..25a1f2a
--- /dev/null
+++ b/src/types.rs
@@ -0,0 +1,34 @@
+use ::safer_ffi::prelude::*;
+use safer_ffi::char_p::char_p_boxed;
+
+#[derive_ReprC]
+#[repr(C)]
+#[derive(Debug)]
+pub struct FfiResult<T> {
+    pub ok: Option<repr_c::Box<T>>,
+    pub err: Option<repr_c::Box<char_p_boxed>>,
+}
+
+#[derive_ReprC]
+#[repr(C)]
+pub struct FfiResultVec<T> {
+    pub ok: repr_c::Vec<T>,
+    pub err: Option<repr_c::Box<char_p_boxed>>,
+}
+
+#[ffi_export]
+fn free_string_result(string_result: FfiResult<char_p_boxed>) {
+    drop(string_result)
+}
+
+#[ffi_export]
+fn free_void_result(void_result: FfiResult<()>) {
+    drop(void_result)
+}
+
+// TODO do we need this? remove?
+/// Frees a Rust-allocated string
+#[ffi_export]
+fn free_string(string: Option<char_p_boxed>) {
+    drop(string)
+}
diff --git a/src/wallet.rs b/src/wallet.rs
index 454f547..b7996dc 100644
--- a/src/wallet.rs
+++ b/src/wallet.rs
@@ -1,82 +1,23 @@
-use crate::blockchain::BlockchainConfig;
-use crate::database::DatabaseConfig;
-use crate::error::get_name;
+use std::convert::TryFrom;
+
 use ::safer_ffi::prelude::*;
 use bdk::bitcoin::network::constants::Network::Testnet;
-use bdk::blockchain::{
-    log_progress, AnyBlockchain, AnyBlockchainConfig, ConfigurableBlockchain,
-    ElectrumBlockchainConfig,
-};
+use bdk::blockchain::{log_progress, AnyBlockchain, AnyBlockchainConfig, ConfigurableBlockchain};
 use bdk::database::{AnyDatabase, AnyDatabaseConfig, ConfigurableDatabase};
 use bdk::wallet::AddressIndex::New;
 use bdk::{Error, Wallet};
 use safer_ffi::boxed::Box;
 use safer_ffi::char_p::{char_p_boxed, char_p_ref};
 
-#[derive_ReprC]
-#[ReprC::opaque]
-pub struct VoidResult {
-    raw: Result<(), Error>,
-}
-
-#[ffi_export]
-fn get_void_err(void_result: &VoidResult) -> Option<char_p_boxed> {
-    void_result
-        .raw
-        .as_ref()
-        .err()
-        .map(|e| char_p_boxed::try_from(get_name(e)).unwrap())
-}
-
-#[ffi_export]
-fn free_void_result(void_result: Option<Box<VoidResult>>) {
-    drop(void_result)
-}
+use crate::blockchain::BlockchainConfig;
+use crate::database::DatabaseConfig;
+use crate::error::get_name;
+use crate::types::{FfiResult, FfiResultVec};
 
 #[derive_ReprC]
 #[ReprC::opaque]
-pub struct StringResult {
-    raw: Result<String, Error>,
-}
-
-#[ffi_export]
-fn get_string_ok(string_result: &StringResult) -> Option<char_p_boxed> {
-    string_result
-        .raw
-        .as_ref()
-        .ok()
-        .map(|s| char_p_boxed::try_from(s.clone()).unwrap())
-}
-
-#[ffi_export]
-fn get_string_err(string_result: &StringResult) -> Option<char_p_boxed> {
-    string_result
-        .raw
-        .as_ref()
-        .err()
-        .map(|e| char_p_boxed::try_from(get_name(e)).unwrap())
-}
-
-#[ffi_export]
-fn free_string_result(string_result: Option<Box<StringResult>>) {
-    drop(string_result)
-}
-
-#[derive_ReprC]
-#[ReprC::opaque]
-pub struct WalletRef<'lt> {
-    raw: &'lt Wallet<AnyBlockchain, AnyDatabase>,
-}
-
-#[ffi_export]
-fn free_wallet_ref(wallet_ref: Option<Box<WalletRef>>) {
-    drop(wallet_ref)
-}
-
-#[derive_ReprC]
-#[ReprC::opaque]
-pub struct WalletResult {
-    raw: Result<Wallet<AnyBlockchain, AnyDatabase>, Error>,
+pub struct OpaqueWallet {
+    raw: Wallet<AnyBlockchain, AnyDatabase>,
 }
 
 #[ffi_export]
@@ -85,13 +26,83 @@ fn new_wallet_result(
     change_descriptor: Option<char_p_ref>,
     blockchain_config: &BlockchainConfig,
     database_config: &DatabaseConfig,
-) -> Box<WalletResult> {
+) -> FfiResult<OpaqueWallet> {
     let descriptor = descriptor.to_string();
     let change_descriptor = change_descriptor.map(|s| s.to_string());
     let bc_config = &blockchain_config.raw;
     let db_config = &database_config.raw;
     let wallet_result = new_wallet(descriptor, change_descriptor, bc_config, db_config);
-    Box::new(WalletResult { raw: wallet_result })
+
+    match wallet_result {
+        Ok(w) => FfiResult {
+            ok: Some(Box::new(OpaqueWallet { raw: w })),
+            err: None,
+        },
+        Err(e) => FfiResult {
+            ok: None,
+            err: Some(Box::new(char_p_boxed::try_from(get_name(&e)).unwrap())),
+        },
+    }
+}
+
+#[ffi_export]
+fn free_wallet_result(wallet_result: FfiResult<OpaqueWallet>) {
+    drop(wallet_result);
+}
+
+#[ffi_export]
+fn free_unspent_result(unspent_result: FfiResultVec<LocalUtxo>) {
+    drop(unspent_result)
+}
+
+#[ffi_export]
+fn sync_wallet(opaque_wallet: &OpaqueWallet) -> FfiResult<()> {
+    let void_result = opaque_wallet.raw.sync(log_progress(), Some(100));
+    match void_result {
+        Ok(v) => FfiResult {
+            ok: Some(Box::new(v)),
+            err: None,
+        },
+        Err(e) => FfiResult {
+            ok: None,
+            err: Some(Box::new(char_p_boxed::try_from(get_name(&e)).unwrap())),
+        },
+    }
+}
+
+#[ffi_export]
+fn new_address(opaque_wallet: &OpaqueWallet) -> FfiResult<char_p_boxed> {
+    let new_address = opaque_wallet.raw.get_address(New);
+    let string_result = new_address.map(|a| a.to_string());
+    match string_result {
+        Ok(a) => FfiResult {
+            ok: Some(Box::new(char_p_boxed::try_from(a).unwrap())),
+            err: None,
+        },
+        Err(e) => FfiResult {
+            ok: None,
+            err: Some(Box::new(char_p_boxed::try_from(get_name(&e)).unwrap())),
+        },
+    }
+}
+
+#[ffi_export]
+fn list_unspent(opaque_wallet: &OpaqueWallet) -> FfiResultVec<LocalUtxo> {
+    let unspent_result = opaque_wallet.raw.list_unspent();
+
+    match unspent_result {
+        Ok(v) => FfiResultVec {
+            ok: {
+                let ve: Vec<LocalUtxo> = v.iter().map(|lu| LocalUtxo::from(lu)).collect();
+                repr_c::Vec::from(ve)
+            },
+            err: None,
+        },
+        Err(e) => FfiResultVec {
+            ok: repr_c::Vec::EMPTY,
+            err: Some(Box::new(char_p_boxed::try_from(get_name(&e)).unwrap())),
+        },
+    }
 }
 
 fn new_wallet(
@@ -111,44 +122,64 @@ fn new_wallet(
     Wallet::new(descriptor, change_descriptor, network, database, client)
 }
 
-#[ffi_export]
-fn get_wallet_err(wallet_result: &WalletResult) -> Option<char_p_boxed> {
-    wallet_result
-        .raw
-        .as_ref()
-        .err()
-        .map(|e| char_p_boxed::try_from(get_name(&e)).unwrap())
+// Non-opaque returned structs
+
+#[derive_ReprC]
+#[repr(C)]
+#[derive(Debug, Clone)]
+pub struct OutPoint {
+    /// The referenced transaction's txid, as hex string
+    pub txid: char_p_boxed,
+    /// The index of the referenced output in its transaction's vout
+    pub vout: u32,
 }
 
-#[ffi_export]
-fn get_wallet_ok<'lt>(wallet_result: &'lt WalletResult) -> Option<Box<WalletRef<'lt>>> {
-    wallet_result
-        .raw
-        .as_ref()
-        .ok()
-        .map(|w| Box::new(WalletRef { raw: w }))
+impl From<&bdk::bitcoin::OutPoint> for OutPoint {
+    fn from(op: &bdk::bitcoin::OutPoint) -> Self {
+        OutPoint {
+            txid: char_p_boxed::try_from(op.txid.to_string()).unwrap(),
+            vout: op.vout,
+        }
+    }
 }
 
-#[ffi_export]
-fn sync_wallet<'lt>(wallet_ref: &'lt WalletRef<'lt>) -> Box<VoidResult> {
-    let void_result = wallet_ref.raw.sync(log_progress(), Some(100));
-    Box::new(VoidResult { raw: void_result })
+#[derive_ReprC]
+#[repr(C)]
+#[derive(Debug, Clone)]
+pub struct TxOut {
+    /// The value of the output, in satoshis
+    pub value: u64,
+    /// The script which must satisfy for the output to be spent, as hex string
+    pub script_pubkey: char_p_boxed,
 }
 
-#[ffi_export]
-fn new_address<'lt>(wallet_ref: &'lt WalletRef<'lt>) -> Box<StringResult> {
-    let new_address = wallet_ref.raw.get_address(New);
-    let string_result = new_address.map(|a| a.to_string());
-    Box::new(StringResult { raw: string_result })
+impl From<&bdk::bitcoin::TxOut> for TxOut {
+    fn from(to: &bdk::bitcoin::TxOut) -> Self {
+        TxOut {
+            value: to.value,
+            script_pubkey: char_p_boxed::try_from(to.script_pubkey.to_string()).unwrap(),
+        }
+    }
 }
 
-#[ffi_export]
-fn free_wallet_result(wallet_result: Option<Box<WalletResult>>) {
-    drop(wallet_result)
+#[derive_ReprC]
+#[repr(C)]
+#[derive(Debug, Clone)]
+pub struct LocalUtxo {
+    /// Reference to a transaction output
+    pub outpoint: OutPoint,
+    /// Transaction output
+    pub txout: TxOut,
+    /// Type of keychain, as short 0 for "external" or 1 for "internal"
+    pub keychain: u16,
 }
 
-/// Frees a Rust-allocated string
-#[ffi_export]
-fn free_string(string: Option<char_p_boxed>) {
-    drop(string)
+impl From<&bdk::LocalUtxo> for LocalUtxo {
+    fn from(lu: &bdk::LocalUtxo) -> Self {
+        LocalUtxo {
+            outpoint: OutPoint::from(&lu.outpoint),
+            txout: TxOut::from(&lu.txout),
+            keychain: lu.keychain as u16,
+        }
+    }
 }
diff --git a/test.sh b/test.sh
index 03855c5..99a3ac8 100755
--- a/test.sh
+++ b/test.sh
@@ -6,9 +6,9 @@ cargo test --features c-headers -- generate_headers
 
 # cc
 export LD_LIBRARY_PATH=`pwd`/target/debug
-#valgrind --leak-check=full --show-leak-kinds=all cc/bdk_ffi_test
-cc/bdk_ffi_test
+valgrind --leak-check=full --show-leak-kinds=all cc/bdk_ffi_test
+#cc/bdk_ffi_test
 
-## bdk-kotlin
+# bdk-kotlin
 (cd bdk-kotlin && gradle test)
 (cd bdk-kotlin && gradle :android:connectedDebugAndroidTest)