Do not use externs directly due to inline

package.json

@@ -11,7 +11,7 @@
   },
   "scripts": {
     "preinstall": "scripts/download-libraries.sh",
-    "install": "node-gyp configure && node-gyp build && mkdir -p dist/ && cp build/Release/asherah.node dist/asherah.node && cp src/asherah.d.ts dist/asherah.d.ts",
+    "install": "scripts/build.sh",
     "test:mocha": "mocha",
     "test": "nyc npm run test:mocha",
     "posttest": "npm run lint",

scripts/build.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+node-gyp configure && node-gyp build && mkdir -p dist/ && cp build/Release/asherah.node dist/asherah.node && cp src/asherah.d.ts dist/asherah.d.ts

src/asherah.cc

@@ -45,8 +45,7 @@ void setup(const Napi::CallbackInfo &info) {
   Napi::String product_id = config_json.Get("ProductID").As<Napi::String>();
   Napi::String service_name = config_json.Get("ServiceName").As<Napi::String>();
 
-  est_intermediate_key_overhead =
-      product_id.Utf8Value().length() + service_name.Utf8Value().length();
+  set_est_intermediate_key_overhead(product_id.Utf8Value().length() + service_name.Utf8Value().length());
 
   Napi::Value verbose = config_json.Get("Verbose");
   if (likely(verbose.IsBoolean())) {
@@ -745,7 +744,7 @@ void set_safety_padding_overhead(const Napi::CallbackInfo &info) {
 
   Napi::Number safety_padding_number = info[0].ToNumber();
 
-  safety_padding_bytes = (size_t)safety_padding_number.Int32Value();
+  set_safety_padding_bytes((size_t)safety_padding_number.Int32Value());
 }
 
 Napi::Object Init(Napi::Env env, Napi::Object exports) {

src/cobhan_napi_interop.cc

@@ -1,3 +1,11 @@
 #include <stddef.h>
 size_t est_intermediate_key_overhead = 0;
 size_t safety_padding_bytes = 0;
+
+void set_est_intermediate_key_overhead(size_t est_intermediate_key_overhead) {
+  ::est_intermediate_key_overhead = est_intermediate_key_overhead;
+}
+
+void set_safety_padding_bytes(size_t safety_padding_bytes) {
+  ::safety_padding_bytes = safety_padding_bytes;
+}

src/cobhan_napi_interop.h

@@ -6,15 +6,18 @@
 #include "logging.h"
 #include "hints.h"
 
-extern "C" size_t est_intermediate_key_overhead;
-extern "C" size_t safety_padding_bytes;
+extern size_t est_intermediate_key_overhead;
+extern size_t safety_padding_bytes;
 
 const size_t est_encryption_overhead = 48;
 const size_t est_envelope_overhead = 185;
 const double base64_overhead = 1.34;
 
 const size_t cobhan_header_size_bytes = 64 / 8;
 
+void set_est_intermediate_key_overhead(size_t est_intermediate_key_overhead);
+void set_safety_padding_bytes(size_t safety_padding_bytes);
+
 std::string napi_status_to_string(napi_status status) {
   switch (status) {
   case napi_ok: