upy-fs-builder: Calculate size a file will take in the filesystem.

Replaces the naive method implemented in higher levels of
abstraction where they only counted the number of data bytes.

Note: That because chunks are not shared the file size calculation
will always be a multiple of the chunk size.

Author: microbit-carlos

src/__tests__/micropython-fs-builder.spec.ts

@@ -558,7 +558,9 @@ describe('Reading files from the filesystem.', () => {
     expect(failCase).toThrow(Error);
   });
 
-  // TODO: Create tests with a file that has chunks in non-continuous order
-  // TODO: Create test with chunks that point to each other in an infinite loop
-  // TODO: Create test with chunks that point to each other in the Marker/Tail
+  // TODO: Read tests with a file that has chunks in non-continuous order
+  // TODO: Read test with chunks that point to each other in an infinite loop
+  // TODO: Read test with chunks that don't point to each other in Marker/Tail
+  // TODO: Read test with chunks using the all the start file markers
+  // TODO: Test calculateFileSize()
 });

src/__tests__/micropython-fs-hex.spec.ts

@@ -277,14 +277,15 @@ describe('Tests exists method.', () => {
 describe('Test size method.', () => {
   it('File size is retrieved correctly.', () => {
     const micropythonFs = new MicropythonFsHex(uPyHexFile);
-    micropythonFs.write(
-      'five_bytes.txt',
-      new Uint8Array([30, 31, 32, 33, 34, 35])
-    );
+    micropythonFs.write('five_bytes.txt', new Uint8Array([30, 31, 32, 33, 34]));
+    micropythonFs.write('more_bytes.txt', new Uint8Array(128).fill(0x55));
 
-    const fileSize = micropythonFs.size('five_bytes.txt');
+    const fileSize1 = micropythonFs.size('five_bytes.txt');
+    const fileSize2 = micropythonFs.size('more_bytes.txt');
 
-    expect(fileSize).toEqual(6);
+    // Real size counts chunks, so always a multiple of 128
+    expect(fileSize1).toEqual(128);
+    expect(fileSize2).toEqual(256);
   });
 
   it('Throw error with invalid file name.', () => {

src/micropython-fs-builder.ts

@@ -270,6 +270,29 @@ class FsFile {
     }
     return fileFsBytes;
   }
+
+  /**
+   * @returns Size, in bytes, of how much space the file takes in the filesystem
+   *     flash memory.
+   */
+  getFsFileSize(): number {
+    let chunksUsed = Math.ceil(this._fsDataBytes.length / CHUNK_DATA_LEN);
+    // When MicroPython uses up to the last byte of the last chunk it will
+    // still consume the next chunk, even if it doesn't add any data to it
+    if (!(this._fsDataBytes.length % CHUNK_DATA_LEN)) {
+      chunksUsed += 1;
+    }
+    return chunksUsed * CHUNK_LEN;
+  }
+}
+
+/**
+ * @returns Size, in bytes, of how much space the file would take in the
+ *     MicroPython filesystem.
+ */
+function calculateFileSize(filename: string, data: Uint8Array): number {
+  const file = new FsFile(filename, data);
+  return file.getFsFileSize();
 }
 
 /**
@@ -457,4 +480,9 @@ function getIntelHexFiles(
   return files;
 }
 
-export { addIntelHexFile, addIntelHexFiles, getIntelHexFiles };
+export {
+  addIntelHexFile,
+  addIntelHexFiles,
+  calculateFileSize,
+  getIntelHexFiles,
+};

src/micropython-fs-hex.ts

@@ -1,6 +1,10 @@
 /** Manage files in a MicroPython hex file. */
 import { FsInterface } from './fs-interface';
-import { addIntelHexFiles, getIntelHexFiles } from './micropython-fs-builder';
+import {
+  addIntelHexFiles,
+  calculateFileSize,
+  getIntelHexFiles,
+} from './micropython-fs-builder';
 import { SimpleFile } from './simple-file';
 
 export class MicropythonFsHex implements FsInterface {
@@ -149,7 +153,10 @@ export class MicropythonFsHex implements FsInterface {
     if (!this.exists(filename)) {
       throw new Error(`File "${filename}" does not exist.`);
     }
-    return this._files[filename].getSize();
+    return calculateFileSize(
+      this._files[filename].filename,
+      this._files[filename].getBytes()
+    );
   }
 
   /**

src/simple-file.ts

@@ -37,8 +37,4 @@ export class SimpleFile {
   getBytes(): Uint8Array {
     return this._dataBytes;
   }
-
-  getSize(): number {
-    return this._dataBytes.length;
-  }
 }