abi: add set and get error calls to the operations struct

Future error handling will support extended error codes via these
functions which are user-overridable in order to support thread safety.
Make the structure changes now without using them so we can avoid an ABI
version bump once implemented.

include/wally_core.h

@@ -350,6 +350,13 @@ typedef int (*wally_ec_nonce_t)(
 typedef struct secp256k1_context_struct *(*secp_context_t)(
     void);
 
+/** The type of an overridable function to get the last extended error code */
+typedef int (*wally_get_error_t)(void);
+
+/** The type of an overridable function to set the last extended error code */
+typedef int (*wally_set_error_t)(
+    int error_code);
+
 /** Structure holding function pointers for overridable wally operations */
 struct wally_operations {
     uintptr_t struct_size; /* Must be initialised to sizeof(wally_operations) */
@@ -358,9 +365,9 @@ struct wally_operations {
     wally_bzero_t bzero_fn;
     wally_ec_nonce_t ec_nonce_fn;
     secp_context_t secp_context_fn;
-    void *reserved_1; /* reserved_ pointers are reserved for future use */
-    void *reserved_2;
-    void *reserved_3;
+    wally_get_error_t get_error_fn;
+    wally_set_error_t set_error_fn;
+    void *reserved_3; /* reserved_ pointers are reserved for future use */
     void *reserved_4;
 };
 

src/internal.c

@@ -17,6 +17,8 @@
 
 /* Caller is responsible for thread safety */
 static secp256k1_context *global_ctx = NULL;
+/* Global extended error code. Not thread-safe unless caller-overridden */
+static int global_error = WALLY_OK;
 
 int wally_get_build_version(uint32_t *value)
 {
@@ -378,15 +380,25 @@ struct secp256k1_context_struct *wally_internal_secp_context(void)
     return global_ctx;
 }
 
+int wally_internal_get_error(void) {
+    return global_error;
+}
+
+int wally_internal_set_error(int error_code)
+{
+    global_error = error_code;
+    return error_code;
+}
+
 static struct wally_operations _ops = {
     sizeof(struct wally_operations),
     wally_internal_malloc,
     wally_internal_free,
     wally_internal_bzero,
     wally_internal_ec_nonce_fn,
     wally_internal_secp_context,
-    NULL,
-    NULL,
+    wally_internal_get_error,
+    wally_internal_set_error,
     NULL,
     NULL
 };
@@ -428,6 +440,15 @@ char *wally_strdup(const char *str)
     return wally_strdup_n(str, strlen(str));
 }
 
+int wally_get_error(void) {
+    return _ops.get_error_fn();
+}
+
+int wally_set_error(int error_code)
+{
+    return _ops.set_error_fn(error_code);
+}
+
 const struct wally_operations *wally_ops(void)
 {
     return &_ops;
@@ -447,7 +468,7 @@ int wally_set_operations(const struct wally_operations *ops)
         return WALLY_EINVAL; /* Null or invalid version of ops */
     /* Reserved pointers must be null so they can be enabled in the
      * future without breaking back compatibility */
-    if (ops->reserved_1 || ops->reserved_2 || ops->reserved_3 || ops->reserved_4)
+    if (ops->reserved_3 || ops->reserved_4)
         return WALLY_EINVAL;
 
 #define COPY_FN_PTR(name) if (ops->name) _ops.name = ops->name
@@ -456,6 +477,8 @@ int wally_set_operations(const struct wally_operations *ops)
     COPY_FN_PTR (bzero_fn);
     COPY_FN_PTR (ec_nonce_fn);
     COPY_FN_PTR (secp_context_fn);
+    COPY_FN_PTR (get_error_fn);
+    COPY_FN_PTR (set_error_fn);
 #undef COPY_FN_PTR
     return WALLY_OK;
 }