2 files changed, 71 insertions, 5 deletions

diff --git a/ext/wasm/api/sqlite3-api-prologue.js b/ext/wasm/api/sqlite3-api-prologue.js
index 60ed61477..08e3ebf6e 100644
--- a/ext/wasm/api/sqlite3-api-prologue.js
+++ b/ext/wasm/api/sqlite3-api-prologue.js
@@ -576,6 +576,55 @@ self.sqlite3ApiBootstrap = function(config){
       ["sqlite3_total_changes64", "i64", ["sqlite3*"]]
   ];
 
+  /** State for sqlite3_web_persistent_dir(). */
+  let __persistentDir;
+  /**
+     An experiment. Do not use.
+
+     If the wasm environment has a persistent storage directory,
+     its path is returned by this function. If it does not then
+     it returns one of:
+
+     - `undefined` if initIfNeeded is false and this function has
+       never been called before.
+
+     - `""` if no persistent storage is available.
+
+     Note that in both cases the return value is falsy.
+  */
+  capi.sqlite3_web_persistent_dir = function(initIfNeeded=true){
+    if(undefined !== __persistentDir) return __persistentDir;
+    else if(!initIfNeeded) return;
+    // If we have no OPFS, there is no persistent dir
+    if(!self.FileSystemHandle || !self.FileSystemDirectoryHandle
+       || !self.FileSystemFileHandle){
+      return __persistentDir = "";
+    }
+    try{
+      if(0===this.wasm.xCall('sqlite3_wasm_init_opfs')){
+        /** OPFS does not support locking and will trigger errors if
+            we try to lock. We don't _really_ want to
+            _unconditionally_ install a non-locking sqlite3 VFS as the
+            default, but we do so here for simplicy's sake for the
+            time being. That said: locking is a no-op on all of the
+            current WASM storage, so this isn't (currently) as bad as
+            it may initially seem. */
+        const pVfs = this.sqlite3_vfs_find("unix-none");
+        if(pVfs){
+          this.sqlite3_vfs_register(pVfs,1);
+          //warn("Installed 'unix-none' as the default sqlite3 VFS.");
+        }
+        return __persistentDir =
+          "/persistent" /* name is hard-coded in sqlite3_wasm_init_opfs()!*/;
+      }else{
+        return __persistentDir = "";
+      }
+    }catch(e){
+      // sqlite3_wasm_init_opfs() is not available
+      return __persistentDir = "";
+    }
+  }.bind(capi);
+
   /* The remainder of the API will be set up in later steps. */
   return {
     capi,
diff --git a/ext/wasm/api/sqlite3-wasm.c b/ext/wasm/api/sqlite3-wasm.c
index 30a9dafeb..487baecf1 100644
--- a/ext/wasm/api/sqlite3-wasm.c
+++ b/ext/wasm/api/sqlite3-wasm.c
@@ -430,7 +430,7 @@ int sqlite3_wasm_vfs_unlink(const char * zName){
   return rc;
 }
 
-#ifdef __EMSCRIPTEN__
+#if defined(__EMSCRIPTEN__) && defined(SQLITE_WASM_OPFS)
 #include <emscripten/wasmfs.h>
 #include <emscripten/console.h>
 /*
@@ -443,17 +443,34 @@ int sqlite3_wasm_vfs_unlink(const char * zName){
 ** WASMFS backend impl for OPFS. On success, subsequent calls are
 ** no-ops.
 **
-** Returns 0 on success, SQLITE_NOMEM if intantiation of the backend
-** object fails.
+** Returns 0 on success, SQLITE_NOMEM if instantiation of the backend
+** object fails, SQLITE_IOERR if mkdir() of the "/persistent" dir in
+** the virtual FS fails. In builds compiled without SQLITE_WASM_OPFS
+** defined, SQLITE_NOTFOUND is returned without side effects.
 */
 int sqlite3_wasm_init_opfs(void){
   static backend_t pOpfs = 0;
+  static const char * zDir = "/persistent";
   if( !pOpfs ){
     pOpfs = wasmfs_create_opfs_backend();
     if( pOpfs ){
-      emscripten_console_log("Created OPFS WASMFS backend.");
+      emscripten_console_log("Created WASMFS OPFS backend.");
     }
   }
+  /** It's not enough to instantiate the backend. We have to create a
+      mountpoint in the VFS and attach the backend to it. */
+  if( pOpfs && 0!=access(zDir, F_OK) ){
+    /* mkdir() simply hangs when called from fiddle app. Cause is
+       not yet determined but the hypothesis is an init-order
+       issue. */
+    const int rc = wasmfs_create_directory(zDir, 0777, pOpfs);
+    emscripten_console_log(rc ? "OPFS mkdir failed." : "OPFS mkdir ok.");
+    if(rc) return SQLITE_IOERR;
+  }
   return pOpfs ? 0 : SQLITE_NOMEM;
 }
-#endif /* __EMSCRIPTEN__ */
+#else
+int sqlite3_wasm_init_opfs(void){
+  return SQLITE_NOTFOUND;
+}
+#endif /* __EMSCRIPTEN__ && SQLITE_WASM_OPFS */