Allow calling initialize() only once

WasmThemis initialization fills in the "context.libthemis" singleton
that is actually used by all WasmThemis functions. That is, calling
initialize() multiple times is technically permitted, but it might not
have an effect that you expect. WasmThemis will always use WebAssembly
context from the last initialization.

While reinitialization might be useful, it does not seem to be now.
Let's allow calling initialize() only once. (This includes calling it
indirectly via the "initialized" promise.) We can always allow it later,
once the semantics of this are clarified.

src/wrappers/themis/wasm/src/index.ts

@@ -14,6 +14,7 @@
 
 import context from "./context";
 import libthemisFn from "./libthemis.js";
+import { ThemisError, ThemisErrorCode } from "./themis_error";
 
 export { SecureCellSeal } from "./secure_cell_seal";
 export { SecureCellTokenProtect } from "./secure_cell_token_protect";
@@ -41,6 +42,8 @@ let onRuntimeInitialized: () => void
 // is expected to call, then await the result to resolve before using
 // other WasmThemis functions.
 
+let libthemisInitialized = false;
+
 /**
  * Initialize WasmThemis.
  *
@@ -54,15 +57,26 @@ let onRuntimeInitialized: () => void
  *
  * @param wasmPath URL of `libthemis.wasm` to download.
  *
+ * @throws {ThemisError} is thrown if this function is called more than once,
+ * or if WasmThemis has been already initialized via `initialized`.
+ *
  * @since WasmThemis 0.14.0
  */
 export const initialize = async (wasmPath?: string) => {
+  if (libthemisInitialized) {
+    throw new ThemisError(
+      'initialize',
+      ThemisErrorCode.FAIL,
+      'WasmThemis can only be initalized once',
+    );
+  }
   context.libthemis = await libthemisFn({
     onRuntimeInitialized: () => onRuntimeInitialized(),
     locateFile: wasmPath ? function () {
       return wasmPath;
     } : undefined,
   });
+  libthemisInitialized = true;
 
   return context.libthemis;
 };
@@ -144,6 +158,9 @@ class InitializedPromise {
  * in the same directory as the executing script.
  * If you need to use a custom location, call `initialize()`.
  *
+ * Note that you cannot use `initialize()` after WasmThemis has been initialized
+ * using this promise.
+ *
  * @see initialize
  */
 export const initialized = new InitializedPromise((resolve) => {

src/wrappers/themis/wasm/test/initialization/initialize-path.js

@@ -1,4 +1,5 @@
 const themis = require('../../src/index.ts')
+const ThemisErrorCode = themis.ThemisErrorCode
 const assert = require('assert')
 
 describe('wasm-themis', function() {
@@ -16,5 +17,11 @@ describe('wasm-themis', function() {
                 done()
             })
         })
+        it('can only be initialized once', function(done) {
+            themis.initialize('src/libthemis.wasm').catch(function(e) {
+                assert.strictEqual(e.errorCode, ThemisErrorCode.FAIL)
+                done()
+            })
+        })
     })
 })

src/wrappers/themis/wasm/test/initialization/initialize.js

@@ -1,4 +1,5 @@
 const themis = require('../../src/index.ts')
+const ThemisErrorCode = themis.ThemisErrorCode
 const assert = require('assert')
 
 describe('wasm-themis', function() {
@@ -10,5 +11,11 @@ describe('wasm-themis', function() {
                 done()
             })
         })
+        it('can only be initialized once', function(done) {
+            themis.initialize().catch(function(e) {
+                assert.strictEqual(e.errorCode, ThemisErrorCode.FAIL)
+                done()
+            })
+        })
     })
 })

src/wrappers/themis/wasm/test/initialization/initialized.js

@@ -1,4 +1,5 @@
 const themis = require('../../src/index.ts')
+const ThemisErrorCode = themis.ThemisErrorCode
 const assert = require('assert')
 
 describe('wasm-themis', function() {
@@ -10,5 +11,12 @@ describe('wasm-themis', function() {
                 done()
             })
         })
+        // "themis.initialized" stays resolved but you cannot initialize again.
+        it('can only be initialized once', function(done) {
+            themis.initialize().catch(function(e) {
+                assert.strictEqual(e.errorCode, ThemisErrorCode.FAIL)
+                done()
+            })
+        })
     })
 })