Add filesystem limit. (#55)

- Limit approximately matches the device and prevents running out of
  space.
- Allow flash to exceed limit to avoid new error scenario. This would be
  good to revisit in future.
- Fix broken listdir due to missing Module prefix.
- Align flash and reset behaviour.

Closes microbit-foundation/python-editor-v3#950

Author: microbit-matt-hillsdon

src/board/fs.ts

@@ -1,7 +1,11 @@
+// Size as per C implementation.
+const maxSize = 31.5 * 1024;
+
 export class FileSystem {
   // Each entry is an FsFile object. The indexes are used as identifiers.
   // When a file is deleted the entry becomes ['', null] and can be reused.
   private _content: Array<FsFile | null> = [];
+  private _size = 0;
 
   create(name: string) {
     let free_idx = -1;
@@ -49,21 +53,29 @@ export class FileSystem {
   }
 
   remove(idx: number) {
-    this._content[idx] = null;
+    const file = this._content[idx];
+    if (file) {
+      this._size -= file.size();
+      this._content[idx] = null;
+    }
   }
 
   readbyte(idx: number, offset: number) {
     const file = this._content[idx];
     return file ? file.readbyte(offset) : -1;
   }
 
-  write(idx: number, data: Uint8Array) {
+  write(idx: number, data: Uint8Array, force: boolean = false): boolean {
     const file = this._content[idx];
     if (!file) {
       throw new Error("File must exist");
     }
+    if (!force && this._size + data.length > maxSize) {
+      return false;
+    }
+    this._size += data.length;
     file.append(data);
-    return data.length;
+    return true;
   }
 
   clear() {

src/board/index.ts

@@ -82,9 +82,10 @@ export class Board {
    */
   private modulePromise: Promise<ModuleWrapper> | undefined;
   /**
-   * Flag to trigger a reset after start finishes.
+   * If undefined, then when main finishes we stay stopped.
+   * Otherwise we perform the action then clear this field.
    */
-  private resetWhenDone: boolean = false;
+  private afterStopped: (() => void) | undefined;
 
   constructor(
     private notifications: Notifications,
@@ -339,17 +340,20 @@ export class Board {
     if (panicCode !== undefined) {
       this.displayPanic(panicCode);
     } else {
-      if (this.resetWhenDone) {
-        this.resetWhenDone = false;
+      if (this.afterStopped) {
+        this.afterStopped();
+        this.afterStopped = undefined;
         setTimeout(() => this.start(), 0);
       } else {
         this.displayStoppedState();
       }
     }
   }
 
-  async stop(reset: boolean = false): Promise<void> {
-    this.resetWhenDone = reset;
+  async stop(
+    afterStopped: (() => void) | undefined = undefined
+  ): Promise<void> {
+    this.afterStopped = afterStopped;
     if (this.panicTimeout) {
       clearTimeout(this.panicTimeout);
       this.panicTimeout = null;
@@ -366,17 +370,24 @@ export class Board {
   }
 
   async reset(): Promise<void> {
-    this.stop(true);
+    const noChangeRestart = () => {};
+    this.stop(noChangeRestart);
   }
 
   async flash(filesystem: Record<string, Uint8Array>): Promise<void> {
-    await this.stop();
-    this.fs.clear();
-    Object.entries(filesystem).forEach(([name, value]) => {
-      const idx = this.fs.create(name);
-      this.fs.write(idx, value);
-    });
-    this.dataLogging.delete();
+    const flashFileSystem = () => {
+      this.fs.clear();
+      Object.entries(filesystem).forEach(([name, value]) => {
+        const idx = this.fs.create(name);
+        this.fs.write(idx, value, true);
+      });
+      this.dataLogging.delete();
+    };
+    if (this.modulePromise) {
+      // If it's running then we need to stop before flash.
+      return this.stop(flashFileSystem);
+    }
+    flashFileSystem();
     return this.start();
   }
 

src/demo.html

@@ -197,6 +197,14 @@ <h1>MicroPython-micro:bit simulator example embedding</h1>
               );
               break;
             }
+            case "internal_error": {
+              console.error("Simulator internal error:");
+              console.error(e.data.error);
+              break;
+            }
+            default: {
+              // Ignore unknown message
+            }
           }
         }
       });

src/jshal.h

@@ -37,7 +37,7 @@ int mp_js_hal_filesystem_name(int idx, char *buf);
 int mp_js_hal_filesystem_size(int idx);
 void mp_js_hal_filesystem_remove(int idx);
 int mp_js_hal_filesystem_readbyte(int idx, size_t offset);
-int mp_js_hal_filesystem_write(int idx, const char *buf, size_t len);
+bool mp_js_hal_filesystem_write(int idx, const char *buf, size_t len);
 
 void mp_js_hal_panic(int code);
 void mp_js_hal_reset(void);

src/jshal.js

@@ -56,7 +56,7 @@ mergeInto(LibraryManager.library, {
   },
 
   mp_js_hal_filesystem_name: function (idx, buf) {
-    const name = fs.name(idx);
+    const name = Module.fs.name(idx);
     if (name === undefined) {
       return -1;
     }

src/microbitfs.c

@@ -209,7 +209,12 @@ STATIC mp_uint_t microbit_file_write(mp_obj_t self_in, const void *buf, mp_uint_
         *errcode = MP_EBADF;
         return MP_STREAM_ERROR;
     }
-    return mp_js_hal_filesystem_write(self->idx, buf, size);
+    bool success = mp_js_hal_filesystem_write(self->idx, buf, size);
+    if (!success) {
+        *errcode = MP_ENOSPC;
+        return MP_STREAM_ERROR;
+    }
+    return size;
 }
 
 STATIC mp_uint_t microbit_file_ioctl(mp_obj_t self_in, mp_uint_t request, uintptr_t arg, int *errcode) {