abi: force users to explicitly opt-out of exporting Elements function…

…s (2)

Part 2, source changes.

README.md

@@ -80,13 +80,12 @@ $ brew install swig
    interface. After building, see `src/swig_java/src/com/blockstream/libwally/Wally.java`
    for the Java interface definition (default: no).
 - `--disable-elements`. Disables support for [Elements](https://elementsproject.org/)
-   features, including [Liquid](https://blockstream.com/liquid/) support (default: no).
-   Note that to use Elements API calls from C/C++, the caller must define `BUILD_ELEMENTS`
-   when including the wally header files.
-- `--disable-elements-abi`. Ensures that exposed library structures maintain the same ABI
-   regardless of `--disable-elements`. If disabled, elements support must be disabled and
-   the user must define `WALLY_ABI_NO_ELEMENTS` before including all wally header files.
-   This option *must be set if wally is being installed as a system/shared library*. (default: no).
+   features, including [Liquid](https://blockstream.com/liquid/) support. Elements
+   functions exported by the library will always return WALLY_ERROR (default: no).
+- `--disable-elements-abi`. Changes the exposed library ABI to completely remove Elements
+   structure members and exported functions. When configured, elements support must be
+   disabled and the user must define `WALLY_ABI_NO_ELEMENTS` before including all wally
+   header files. This option *must not be given if wally is being installed as a system/shared library*. (default: no).
 - `--enabled-standard-secp`. Excludes support for features that are unavailable in
    the standard [libsecp256k1 library](https://github.com/bitcoin-core/secp256k1).
 - `--enable-mbed-tls`. Use mbed-tls hashing functions if available. This typically
@@ -97,10 +96,10 @@ $ brew install swig
    need [lcov](http://ltp.sourceforge.net/coverage/lcov.php) installed to
    build with this option enabled and generate coverage reports.
 - `--disable-shared`. Disables building a shared library and builds a static
-  library instead.
-- `--disable-tests`. Disables building library tests.
+  library instead. (default: no)
+- `--disable-tests`. Disables building library tests. (default: no)
 - `--disable-clear-tests`. Disables just the test_clear test (required to pass
-  the test suite with some compilers).
+  the test suite with some compilers). (default: no)
 
 ### Recommended development configure options
 

include/wally_psbt.h

@@ -2419,6 +2419,7 @@ WALLY_CORE_API int wally_psbt_clone_alloc(
     uint32_t flags,
     struct wally_psbt **output);
 
+#ifndef WALLY_ABI_NO_ELEMENTS
 /**
  * Blind a PSBT.
  *
@@ -2464,6 +2465,7 @@ WALLY_CORE_API int wally_psbt_blind_alloc(
     uint32_t output_index,
     uint32_t flags,
     struct wally_map **output);
+#endif /* WALLY_ABI_NO_ELEMENTS */
 
 /**
  * Sign PSBT inputs corresponding to a given private key.

src/bip32.c

@@ -837,13 +837,16 @@ int bip32_key_from_parent_path_alloc(const struct ext_key *hdkey,
     return ret;
 }
 
-#ifdef BUILD_ELEMENTS
+#ifndef WALLY_ABI_NO_ELEMENTS
 int bip32_key_with_tweak_from_parent_path(const struct ext_key *hdkey,
                                           const uint32_t *child_path,
                                           size_t child_path_len,
                                           uint32_t flags,
                                           struct ext_key *output)
 {
+#ifndef BUILD_ELEMENTS
+    return WALLY_ERROR;
+#else
     const secp256k1_context *ctx;
     secp256k1_pubkey pub_key;
     size_t len = EC_PUBLIC_KEY_LEN;
@@ -865,13 +868,17 @@ int bip32_key_with_tweak_from_parent_path(const struct ext_key *hdkey,
         return wipe_key_fail(output);
 
     return WALLY_OK;
+#endif /* BUILD_ELEMENTS */
 }
 
 int bip32_key_with_tweak_from_parent_path_alloc(const struct ext_key *hdkey,
                                                 const uint32_t *child_path, size_t child_path_len,
                                                 uint32_t flags,
                                                 struct ext_key **output)
 {
+#ifndef BUILD_ELEMENTS
+    return WALLY_ERROR;
+#else
     int ret;
 
     ALLOC_KEY();
@@ -882,8 +889,9 @@ int bip32_key_with_tweak_from_parent_path_alloc(const struct ext_key *hdkey,
         *output = NULL;
     }
     return ret;
-}
 #endif /* BUILD_ELEMENTS */
+}
+#endif /* WALLY_ABI_NO_ELEMENTS */
 
 int bip32_key_from_parent_path_str_n(const struct ext_key *hdkey,
                                      const char *str, size_t str_len,
@@ -1137,9 +1145,15 @@ GET_B(chain_code)
 GET_B(parent160)
 GET_B(hash160)
 GET_B(pub_key)
-#ifdef BUILD_ELEMENTS
+#ifndef WALLY_ABI_NO_ELEMENTS
+#ifndef BUILD_ELEMENTS
+int bip32_key_get_pub_key_tweak_sum(const struct ext_key *hdkey, unsigned char *bytes_out, size_t len) {
+    return WALLY_ERROR;
+}
+#else
 GET_B(pub_key_tweak_sum)
 #endif /* BUILD_ELEMENTS */
+#endif /* WALLY_ABI_NO_ELEMENTS */
 
 int bip32_key_get_priv_key(const struct ext_key *hdkey, unsigned char *bytes_out, size_t len) {
     return getb_impl(hdkey, hdkey->priv_key + 1, sizeof(hdkey->priv_key) - 1, bytes_out, len);

src/bip32_int.h

@@ -32,14 +32,14 @@ WALLY_CORE_API int bip32_key_get_hash160(const struct ext_key *hdkey, unsigned c
  */
 WALLY_CORE_API int bip32_key_get_pub_key(const struct ext_key *hdkey, unsigned char *bytes_out, size_t len);
 
-#ifdef BUILD_ELEMENTS
+#ifndef WALLY_ABI_NO_ELEMENTS
 
 /**
  * FIXED_SIZED_OUTPUT(len, bytes_out, WALLY_BIP32_TWEAK_SUM_LEN)
  */
 WALLY_CORE_API int bip32_key_get_pub_key_tweak_sum(const struct ext_key *hdkey, unsigned char *bytes_out, size_t len);
 
-#endif /* BUILD_ELEMENTS */
+#endif /* WALLY_ABI_NO_ELEMENTS */
 
 WALLY_CORE_API int bip32_key_get_depth(const struct ext_key *hdkey, size_t *written);
 WALLY_CORE_API int bip32_key_get_child_num(const struct ext_key *hdkey, size_t *written);

src/blech32.c

@@ -27,7 +27,6 @@
 #include "script.h"
 
 #ifdef BUILD_ELEMENTS
-
 #define CHECKSUM_BLECH32 0x1
 #define CHECKSUM_BLECH32M 0x455972a3350f7a1ull
 
@@ -208,13 +207,18 @@ static int blech32_addr_decode(uint8_t *witver, uint8_t *witdata, size_t *witdat
     wally_clear_2(data, sizeof(data), hrp_actual, sizeof(hrp_actual));
     return 0;
 }
+#endif /* BUILD_ELEMENTS */
 
+#ifndef WALLY_ABI_NO_ELEMENTS
 int wally_confidential_addr_to_addr_segwit(
     const char *address,
     const char *confidential_addr_family,
     const char *addr_family,
     char **output)
 {
+#ifndef BUILD_ELEMENTS
+    return WALLY_ERROR;
+#else
     unsigned char buf[WALLY_BLECH32_MAXLEN];
     unsigned char *hash_bytes_p = &buf[EC_PUBLIC_KEY_LEN - 2];
     size_t written = 0;
@@ -241,6 +245,7 @@ int wally_confidential_addr_to_addr_segwit(
 
     wally_clear(buf, sizeof(buf));
     return ret;
+#endif /* BUILD_ELEMENTS */
 }
 
 int wally_confidential_addr_segwit_to_ec_public_key(
@@ -249,6 +254,9 @@ int wally_confidential_addr_segwit_to_ec_public_key(
     unsigned char *bytes_out,
     size_t len)
 {
+#ifndef BUILD_ELEMENTS
+    return WALLY_ERROR;
+#else
     unsigned char buf[WALLY_BLECH32_MAXLEN];
     size_t written = 0;
     int ret = WALLY_OK;
@@ -266,6 +274,7 @@ int wally_confidential_addr_segwit_to_ec_public_key(
 
     wally_clear(buf, sizeof(buf));
     return ret;
+#endif /* BUILD_ELEMENTS */
 }
 
 int wally_confidential_addr_from_addr_segwit(
@@ -276,6 +285,9 @@ int wally_confidential_addr_from_addr_segwit(
     size_t pub_key_len,
     char **output)
 {
+#ifndef BUILD_ELEMENTS
+    return WALLY_ERROR;
+#else
     char result[WALLY_BLECH32_MAXLEN + 1];
     unsigned char buf[EC_PUBLIC_KEY_LEN + SHA256_LEN];
     unsigned char *hash_bytes_p = &buf[EC_PUBLIC_KEY_LEN - 2];
@@ -320,6 +332,6 @@ int wally_confidential_addr_from_addr_segwit(
     wally_clear(buf, sizeof(buf));
     wally_clear(result, sizeof(result));
     return ret;
-}
-
 #endif /* BUILD_ELEMENTS */
+}
+#endif /* WALLY_ABI_NO_ELEMENTS */