descriptor: allow fetching child paths from iterated keys

Author: jgriffiths

include/wally.hpp

@@ -510,6 +510,18 @@ inline int descriptor_get_key(const DESCRIPTOR& descriptor, size_t index, char**
     return ret;
 }
 
+template <class DESCRIPTOR>
+inline int descriptor_get_key_child_path_str(const DESCRIPTOR& descriptor, size_t index, char** output) {
+    int ret = ::wally_descriptor_get_key_child_path_str(detail::get_p(descriptor), index, output);
+    return ret;
+}
+
+template <class DESCRIPTOR>
+inline int descriptor_get_key_child_path_str_len(const DESCRIPTOR& descriptor, size_t index, size_t* written) {
+    int ret = ::wally_descriptor_get_key_child_path_str_len(detail::get_p(descriptor), index, written);
+    return ret;
+}
+
 template <class DESCRIPTOR>
 inline int descriptor_get_network(const DESCRIPTOR& descriptor, uint32_t* value_out) {
     int ret = ::wally_descriptor_get_network(detail::get_p(descriptor), value_out);

include/wally_descriptor.h

@@ -211,6 +211,33 @@ WALLY_CORE_API int wally_descriptor_get_key(
     size_t index,
     char **output);
 
+/**
+ * Get the length of a keys child path string in a parsed output descriptor or miniscript expression.
+ *
+ * :param descriptor: Parsed output descriptor or miniscript expression.
+ * :param index: The zero-based index of the key whose child path to get.
+ * :param written: Destination for the length of the keys child path string,
+ *|    excluding the NUL terminator.
+ */
+WALLY_CORE_API int wally_descriptor_get_key_child_path_str_len(
+    const struct wally_descriptor *descriptor,
+    size_t index,
+    size_t *written);
+
+/**
+ * Get the keys child path string in a parsed output descriptor or miniscript expression.
+ *
+ * :param descriptor: Parsed output descriptor or miniscript expression.
+ * :param index: The zero-based index of the key whose child path to get.
+ * :param output: Destination for the resulting path string (may be empty).
+ *|    The string returned should be freed using `wally_free_string`.
+ */
+WALLY_CORE_API int wally_descriptor_get_key_child_path_str(
+    const struct wally_descriptor *descriptor,
+    size_t index,
+    char **output);
+
+
 /**
  * Get the maximum length of a script corresponding to an output descriptor.
  *

src/descriptor.c

@@ -2893,18 +2893,24 @@ int wally_descriptor_get_num_keys(const struct wally_descriptor *descriptor,
 #if defined(__clang__)
 #pragma clang diagnostic ignored "-Wcast-align"
 #endif
+static const ms_node *descriptor_get_key(const struct wally_descriptor *descriptor,
+                                         size_t index)
+{
+    if (!descriptor || index >= descriptor->keys.num_items)
+        return NULL;
+    return (ms_node *)descriptor->keys.items[index].value;
+}
 
 int wally_descriptor_get_key(const struct wally_descriptor *descriptor,
                              size_t index, char **output)
 {
-    const ms_node *node;
+    const ms_node *node = descriptor_get_key(descriptor, index);
 
     if (output)
         *output = 0;
-    if (!descriptor || index >= descriptor->keys.num_items || !output)
+    if (!node || !output)
         return WALLY_EINVAL;
 
-    node = (ms_node *)descriptor->keys.items[index].value;
     if (node->kind == KIND_PUBLIC_KEY) {
         return wally_hex_from_bytes((const unsigned char *)node->data,
                                     node->data_len, output);
@@ -2923,3 +2929,30 @@ int wally_descriptor_get_key(const struct wally_descriptor *descriptor,
         return WALLY_ENOMEM;
     return WALLY_OK;
 }
+
+int wally_descriptor_get_key_child_path_str_len(
+    const struct wally_descriptor *descriptor, size_t index, size_t *written)
+{
+    const ms_node *node = descriptor_get_key(descriptor, index);
+
+    if (written)
+        *written = 0;
+    if (!node || !written)
+        return WALLY_EINVAL;
+    *written = node->child_path_len;
+    return WALLY_OK;
+}
+
+int wally_descriptor_get_key_child_path_str(
+    const struct wally_descriptor *descriptor, size_t index, char **output)
+{
+    const ms_node *node = descriptor_get_key(descriptor, index);
+
+    if (output)
+        *output = 0;
+    if (!node || !output)
+        return WALLY_EINVAL;
+    if (!(*output = wally_strdup_n(node->child_path, node->child_path_len)))
+        return WALLY_ENOMEM;
+    return WALLY_OK;
+}

src/swig_java/swig.i

@@ -562,6 +562,8 @@ static jobjectArray create_jstringArray(JNIEnv *jenv, char **p, size_t len) {
 %returns_size_t(wally_descriptor_get_features);
 %returns_size_t(wally_descriptor_get_network);
 %returns_string(wally_descriptor_get_key);
+%returns_string(wally_descriptor_get_key_child_path_str);
+%returns_size_t(wally_descriptor_get_key_child_path_str_len);
 %returns_size_t(wally_descriptor_get_num_keys);
 %returns_size_t(wally_descriptor_get_num_paths);
 %returns_size_t(wally_descriptor_get_num_variants);

src/test/test_descriptor.py

@@ -321,26 +321,41 @@ def test_key_iteration(self):
         wif = 'L1AAHuEC7XuDM7pJ7yHLEqYK1QspMo8n1kgxyZVdgvEpVC1rkUrM'
         pk = '03b428da420cd337c7208ed42c5331ebb407bb59ffbe3dc27936a227c619804284'
         pk_u = '0414fc03b8df87cd7b872996810db8458d61da8448e531569c8517b469a119d267be5645686309c6e6736dbd93940707cc9143d3cf29f1b877ff340e2cb2d259cf'
+        policy_keys = wally_map_from_dict({f'@{i}': xpub for i,xpub in enumerate([k1])})
+        P = POLICY
+
         # Valid args
-        for descriptor, expected in [
+        for flags, descriptor, expected, child_path in [
             # Bip32 xpub
-            (f'pkh({k1})', k1),
+            (0, f'pkh({k1})',         k1,   ''),
+            (0, f'pkh({k1}/*)',       k1,   '*'),
+            (0, f'pkh({k1}/0/1/2/*)', k1,   '0/1/2/*'),
+            (0, f'pkh({k1}/<0;1>/*)', k1,   '<0;1>/*'),
+            # Bip32 xpub (as policy)
+            (P, 'pkh(@0/*)',          k1,   '*'),
+            (P, 'pkh(@0/**)',         k1,   '<0;1>/*'),
+            (P, 'pkh(@0/<0;1>/*)',    k1,   '<0;1>/*'),
             # BIP32 xprv
-            (f'pkh({k2})', k2),
+            (0, f'pkh({k2})',         k2,   ''),
             # WIF
-            (f'pkh({wif})', wif),
+            (0, f'pkh({wif})',        wif,  ''),
             # Hex pubkey, compressed
-            (f'pk({pk})', pk),
+            (0, f'pk({pk})',          pk,   ''),
             # Hex pubkey, uncompressed
-            (f'pk({pk_u})', pk_u),
+            (0, f'pk({pk_u})',        pk_u, ''),
         ]:
             d = c_void_p()
-            ret = wally_descriptor_parse(descriptor, None, NETWORK_BTC_MAIN, 0, d)
+            keys = policy_keys if flags & P else None
+            ret = wally_descriptor_parse(descriptor, keys, NETWORK_BTC_MAIN, flags, d)
             self.assertEqual(ret, WALLY_OK)
             ret, num_keys = wally_descriptor_get_num_keys(d)
             self.assertEqual((ret, num_keys), (WALLY_OK, 1))
             ret, key_str = wally_descriptor_get_key(d, 0)
             self.assertEqual((ret, key_str), (WALLY_OK, expected))
+            ret, path_len = wally_descriptor_get_key_child_path_str_len(d, 0)
+            self.assertEqual((ret, path_len), (WALLY_OK, len(child_path)))
+            ret, path_str = wally_descriptor_get_key_child_path_str(d, 0)
+            self.assertEqual((ret, path_str), (WALLY_OK, child_path))
             wally_descriptor_free(d)
 
 

src/test/util.py

@@ -314,6 +314,8 @@ class wally_psbt(Structure):
     ('wally_descriptor_get_depth', c_int, [c_void_p, c_uint32_p]),
     ('wally_descriptor_get_features', c_int, [c_void_p, c_uint32_p]),
     ('wally_descriptor_get_key', c_int, [c_void_p, c_size_t, c_char_p_p]),
+    ('wally_descriptor_get_key_child_path_str', c_int, [c_void_p, c_size_t, c_char_p_p]),
+    ('wally_descriptor_get_key_child_path_str_len', c_int, [c_void_p, c_size_t, c_size_t_p]),
     ('wally_descriptor_get_network', c_int, [c_void_p, c_uint32_p]),
     ('wally_descriptor_get_num_keys', c_int, [c_void_p, c_uint32_p]),
     ('wally_descriptor_get_num_paths', c_int, [c_void_p, c_uint32_p]),

src/wasm_package/src/functions.js

@@ -124,6 +124,7 @@ export function descriptor_get_checksum(descriptor: Ref_wally_descriptor, flags:
 export function descriptor_get_depth(descriptor: Ref_wally_descriptor): number;
 export function descriptor_get_features(descriptor: Ref_wally_descriptor): number;
 export function descriptor_get_key(descriptor: Ref_wally_descriptor, index: number): string;
+export function descriptor_get_key_child_path_str_len(descriptor: Ref_wally_descriptor, index: number): number;
 export function descriptor_get_network(descriptor: Ref_wally_descriptor): number;
 export function descriptor_get_num_keys(descriptor: Ref_wally_descriptor): number;
 export function descriptor_get_num_paths(descriptor: Ref_wally_descriptor): number;
@@ -725,6 +726,7 @@ export function asset_surjectionproof(output_asset: Buffer|Uint8Array, output_ab
 export function base58_n_to_bytes(str_in: string, str_len: number, flags: number): Buffer;
 export function base58_to_bytes(str_in: string, flags: number): Buffer;
 export function base64_to_bytes(str_in: string, flags: number): Buffer;
+export function descriptor_get_key_child_path_str(descriptor: Ref_wally_descriptor, index: number): string;
 export function descriptor_to_script(descriptor: Ref_wally_descriptor, depth: number, index: number, variant: number, multi_index: number, child_num: number, flags: number): Buffer;
 export function ec_sig_from_bytes(priv_key: Buffer|Uint8Array, bytes: Buffer|Uint8Array, flags: number): Buffer;
 export function ec_sig_from_bytes_aux(priv_key: Buffer|Uint8Array, bytes: Buffer|Uint8Array, aux_rand: Buffer|Uint8Array, flags: number): Buffer;

src/wasm_package/src/index.d.ts

@@ -82,6 +82,8 @@ EXPORTED_FUNCTIONS="['_malloc','_free','_bip32_key_free' \
 ,'_wally_descriptor_get_depth' \
 ,'_wally_descriptor_get_features' \
 ,'_wally_descriptor_get_key' \
+,'_wally_descriptor_get_key_child_path_str' \
+,'_wally_descriptor_get_key_child_path_str_len' \
 ,'_wally_descriptor_get_network' \
 ,'_wally_descriptor_get_num_keys' \
 ,'_wally_descriptor_get_num_paths' \