Expose module schema string allocation.

src/examples/ArrayAsyncModule.js

@@ -8,7 +8,7 @@ export class ArrayAsyncModule extends ArrayModule {
    * @param {*} appData Application data passed to `SQLiteAPI.create_module`.
    * @param {Array<string>} argv 
    * @param {number} pVTab 
-   * @param {{ set: function(string): void}} pzString 
+   * @param {{ allocate: function(number): number, set: function(string): void }} pzString 
    * @returns {number|Promise<number>}
    */
   xCreate(db, appData, argv, pVTab, pzString) {
@@ -20,9 +20,16 @@ export class ArrayAsyncModule extends ArrayModule {
    * @param {*} appData Application data passed to `SQLiteAPI.create_module`.
    * @param {Array<string>} argv 
    * @param {number} pVTab 
-   * @param {{ set: function(string): void}} pzString 
+   * @param {{ allocate: function(number): number, set: function(string): void }} pzString 
    */
   xConnect(db, appData, argv, pVTab, pzString) {
+    // Allocate space for CREATE TABLE string. SQLite functions cannot be
+    // called within handleAsync, so this allocation must be outside the
+    // asynchronous call. It must be larger than the UTF8 representation
+    // of the string passed to pzString.set() or undefined behavior will
+    // result.
+    pzString.allocate(1024);
+
     return this.handleAsync(async () => {
       return super.xConnect(db, appData, argv, pVTab, pzString);
     });

src/libmodule.js

@@ -12,35 +12,32 @@ const mod_methods = {
     const closedVTabs = hasAsyncify ? new Set() : null;
     const closedCursors = hasAsyncify ? new Set() : null;
 
-    // Ideally this would be a static constant of the Value class, but
-    // the Emscripten optimizer doesn't like that.
-    const MAX_VALUE_STRING_BYTES = 2 ** 17;
-
     class Value {
       constructor(ptr, type) {
         this.ptr = ptr;
         this.type = type;
-
-        if (type === 's' && getValue(ptr, 'i32') === 0) {
-          // Preallocate string buffer for virtual table declaration.
-          // This preallocation is necessary for asynchronous xCreate/xConnect.
-          const p = ccall('sqlite3_malloc', 'number', ['number'], [MAX_VALUE_STRING_BYTES]);
-          setValue(this.ptr, p, 'i32');
-        }
       }
-
-      set(v) {
-        switch (this.type) {
-          case 's':
-            const length = lengthBytesUTF8(v);
-            if (length + 1 > MAX_VALUE_STRING_BYTES) throw new Error('string overflow');
-            const p = getValue(this.ptr, 'i32');
-            stringToUTF8(v, p, MAX_VALUE_STRING_BYTES);
-            break;
-          default:
-            setValue(this.ptr, v, this.type);
-            break;
-        }
+    }
+    Value.prototype['allocate'] = function(size) {
+      // Preallocate string buffer for virtual table declaration.
+      // This preallocation is necessary for asynchronous xCreate/xConnect.
+      let p = getValue(this.ptr, 'i32');
+      if (!p) {
+        p = ccall('sqlite3_malloc', 'number', ['number'], [size]);
+        setValue(this.ptr, p, 'i32');
+      }
+      return p;
+    }
+    Value.prototype['set'] = function(v) {
+      switch (this.type) {
+        case 's':
+          const length = lengthBytesUTF8(v);
+          const p = this['allocate'](length + 1);
+          stringToUTF8(v, p, length + 1);
+          break;
+        default:
+          setValue(this.ptr, v, this.type);
+          break;
       }
     }