Espruino/src/jswrap_storage.c

/*
 * This file is part of Espruino, a JavaScript interpreter for Microcontrollers
 *
 * Copyright (C) 2018 Gordon Williams <gw@pur3.co.uk>
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * ----------------------------------------------------------------------------
 * This file is designed to be parsed during the build process
 *
 * JavaScript Filesystem-style Flash IO functions
 * ----------------------------------------------------------------------------
 */
#include "jswrap_storage.h"
#include "jswrap_flash.h"
#include "jshardware.h"
#include "jsflash.h"
#include "jsvar.h"
#include "jsvariterator.h"
#include "jsparse.h"
#include "jsinteractive.h"
#include "jswrap_json.h"

#ifdef DEBUG
#define DBG(...) jsiConsolePrintf("[Storage] "__VA_ARGS__)
#else
#define DBG(...)
#endif

const int STORAGEFILE_CHUNKSIZE =
#if FLASH_SAVED_CODE_LENGTH < 1000000
  // for normal devices
  (((FLASH_PAGE_SIZE<4096)?FLASH_PAGE_SIZE:4096) - sizeof(JsfFileHeader)); // use 32 for testing
#else
  // where we have large external flash (eg Bangle.js), choose a chunk size much bigger than the
  // page size. This allows us to have less chunks around, and to store much bigger files.
  (FLASH_PAGE_SIZE*10) - sizeof(JsfFileHeader);
#endif

/*JSON{
  "type" : "library",
  "class" : "Storage"
}

This module allows you to read and write part of the nonvolatile flash memory of
your device using a filesystem-like API.

Also see the `Flash` library, which provides a low level, more dangerous way to
access all parts of your flash memory.

The `Storage` library provides two distinct types of file:

* `require("Storage").write(...)`/`require("Storage").read(...)`/etc create
simple contiguous files of fixed length. This is the recommended file type.
* `require("Storage").open(...)` creates a `StorageFile`, which stores the file
in numbered chunks (`"filename\1"`/`"filename\2"`/etc). It allows data to be
appended and for the file to be read line by line.

You must read a file using the same method you used to write it - e.g. you can't
create a file with `require("Storage").open(...)` and then read it with
`require("Storage").read(...)`.

**Note:** In firmware 2v05 and later, the maximum length for filenames is 28
characters. However in 2v04 and earlier the max length is 8.
*/

/*JSON{
  "type" : "staticmethod",
  "class" : "Storage",
  "name" : "eraseAll",
  "generate" : "jswrap_storage_eraseAll"
}
Erase the flash storage area. This will remove all files created with
`require("Storage").write(...)` as well as any code saved with `save()` or
`E.setBootCode()`.
 */
void jswrap_storage_eraseAll() {
  jsfEraseAll();
}

/*JSON{
  "type" : "staticmethod",
  "class" : "Storage",
  "name" : "erase",
  "generate" : "jswrap_storage_erase",
  "params" : [
    ["name","JsVar","The filename - max 28 characters (case sensitive)"]
  ],
  "typescript" : "erase(name: string): void;"
}
Erase a single file from the flash storage area.

**Note:** This function should be used with normal files, and not `StorageFile`s
created with `require("Storage").open(filename, ...)`
 */
void jswrap_storage_erase(JsVar *name) {
  jsfEraseFile(jsfNameFromVar(name));
}

/*JSON{
  "type" : "staticmethod",
  "class" : "Storage",
  "name" : "read",
  "generate" : "jswrap_storage_read",
  "params" : [
    ["name","JsVar","The filename - max 28 characters (case sensitive)"],
    ["offset","int","[optional] The offset in bytes to start from"],
    ["length","int","[optional] The length to read in bytes (if <=0, the entire file is read)"]
  ],
  "return" : ["JsVar","A string of data, or `undefined` if the file is not found"],
  "typescript" : "read(name: string, offset?: number, length?: number): string | undefined;"
}
Read a file from the flash storage area that has been written with
`require("Storage").write(...)`.

This function returns a memory-mapped String that points to the actual memory
area in read-only memory, so it won't use up RAM.

As such you can check if a file exists efficiently using
`require("Storage").read(filename)!==undefined`.

If you evaluate this string with `eval`, any functions contained in the String
will keep their code stored in flash memory.

**Note:** This function should be used with normal files, and not `StorageFile`s
created with `require("Storage").open(filename, ...)`
*/
JsVar *jswrap_storage_read(JsVar *name, int offset, int length) {
  return jsfReadFile(jsfNameFromVar(name), offset, length);
}

/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "readJSON",
  "generate" : "jswrap_storage_readJSON",
  "params" : [
    ["name","JsVar","The filename - max 28 characters (case sensitive)"],
    ["noExceptions","bool","If true and the JSON is not valid, just return `undefined` - otherwise an `Exception` is thrown"]
  ],
  "return" : ["JsVar","An object containing parsed JSON from the file, or undefined"],
  "typescript" : [
    "function readJSON(name: string, noExceptions?: false | 0): unknown;",
    "function readJSON(name: string, noExceptions?: ShortBoolean): unknown | undefined;"
  ]
}
Read a file from the flash storage area that has been written with
`require("Storage").write(...)`, and parse JSON in it into a JavaScript object.

This is identical to `JSON.parse(require("Storage").read(...))`. It will throw
an exception if the data in the file is not valid JSON.

**Note:** This function should be used with normal files, and not `StorageFile`s
created with `require("Storage").open(filename, ...)`
*/
JsVar *jswrap_storage_readJSON(JsVar *name, bool noExceptions) {
  JsVar *v = jsfReadFile(jsfNameFromVar(name),0,0);
  if (!v) return 0;
  JsVar *r = jswrap_json_parse(v);
  jsvUnLock(v);
  if (noExceptions) {
    jsvUnLock(jspGetException());
    execInfo.execute &= (JsExecFlags)~EXEC_EXCEPTION;
  }
  return r;
}

/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "readArrayBuffer",
  "generate" : "jswrap_storage_readArrayBuffer",
  "params" : [
    ["name","JsVar","The filename - max 28 characters (case sensitive)"]
  ],
  "return" : ["JsVar","An ArrayBuffer containing data from the file, or undefined"],
  "typescript" : "readArrayBuffer(name: string): ArrayBuffer | undefined;"
}
Read a file from the flash storage area that has been written with
`require("Storage").write(...)`, and return the raw binary data as an
ArrayBuffer.

This can be used:

* In a `DataView` with `new DataView(require("Storage").readArrayBuffer("x"))`
* In a `Uint8Array/Float32Array/etc` with `new
  Uint8Array(require("Storage").readArrayBuffer("x"))`

**Note:** This function should be used with normal files, and not `StorageFile`s
created with `require("Storage").open(filename, ...)`
*/
JsVar *jswrap_storage_readArrayBuffer(JsVar *name) {
  JsVar *v = jsfReadFile(jsfNameFromVar(name),0,0);
  if (!v) return 0;
  JsVar *r = jsvNewArrayBufferFromString(v, 0);
  jsvUnLock(v);
  return r;
}

/*JSON{
  "type" : "staticmethod",
  "class" : "Storage",
  "name" : "write",
  "generate" : "jswrap_storage_write",
  "params" : [
    ["name","JsVar","The filename - max 28 characters (case sensitive)"],
    ["data","JsVar","The data to write"],
    ["offset","int","[optional] The offset within the file to write"],
    ["size","int","[optional] The size of the file (if a file is to be created that is bigger than the data)"]
  ],
  "return" : ["bool","True on success, false on failure"],
  "typescript" : "write(name: string | ArrayBuffer | ArrayBufferView | number[] | object, data: any, offset?: number, size?: number): boolean;"
}
Write/create a file in the flash storage area. This is nonvolatile and will not
disappear when the device resets or power is lost.

Simply write `require("Storage").write("MyFile", "Some data")` to write a new
file, and `require("Storage").read("MyFile")` to read it.

If you supply:

* A String, it will be written as-is
* An array, will be written as a byte array (but read back as a String)
* An object, it will automatically be converted to a JSON string before being
written.

**Note:** If an array is supplied it will not be converted to JSON. To be
explicit about the conversion you can use `Storage.writeJSON`

You may also create a file and then populate data later **as long as you don't
try and overwrite data that already exists**. For instance:

```
var f = require("Storage");
f.write("a","Hello",0,14);
f.write("a"," ",5);
f.write("a","World!!!",6);
print(f.read("a")); // "Hello World!!!"
f.write("a"," ",0); // Writing to location 0 again will cause the file to be re-written
print(f.read("a")); // " "
```

This can be useful if you've got more data to write than you have RAM
available - for instance the Web IDE uses this method to write large files into
onboard storage.

**Note:** This function should be used with normal files, and not `StorageFile`s
created with `require("Storage").open(filename, ...)`
*/
bool jswrap_storage_write(JsVar *name, JsVar *data, JsVarInt offset, JsVarInt _size) {
  JsVar *d;
  if (jsvIsObject(data)) {
    d = jswrap_json_stringify(data,0,0);
    offset = 0;
    _size = 0;
  } else
    d = jsvLockAgainSafe(data);
  bool success = jsfWriteFile(jsfNameFromVar(name), d, JSFF_NONE, offset, _size);
  jsvUnLock(d);
  return success;
}


/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "writeJSON",
  "generate" : "jswrap_storage_writeJSON",
  "params" : [
    ["name","JsVar","The filename - max 28 characters (case sensitive)"],
    ["data","JsVar","The JSON data to write"]
  ],
  "return" : ["bool","True on success, false on failure"],
  "typescript" : "writeJSON(name: string, data: any): boolean;"
}
Write/create a file in the flash storage area. This is nonvolatile and will not
disappear when the device resets or power is lost.

Simply write `require("Storage").writeJSON("MyFile", [1,2,3])` to write a new
file, and `require("Storage").readJSON("MyFile")` to read it.

This is equivalent to: `require("Storage").write(name, JSON.stringify(data))`

**Note:** This function should be used with normal files, and not `StorageFile`s
created with `require("Storage").open(filename, ...)`
*/
bool jswrap_storage_writeJSON(JsVar *name, JsVar *data) {
  JsVar *d = jswrap_json_stringify(data,0,0);
  bool r = jsfWriteFile(jsfNameFromVar(name), d, JSFF_NONE, 0, 0);
  jsvUnLock(d);
  return r;
}

/*JSON{
  "type" : "staticmethod",
  "class" : "Storage",
  "name" : "list",
  "generate" : "jswrap_storage_list",
  "params" : [
    ["regex","JsVar","[optional] If supplied, filenames are checked against this regular expression (with `String.match(regexp)`) to see if they match before being returned"],
    ["filter","JsVar","[optional] If supplied, File Types are filtered based on this: `{sf:true}` or `{sf:false}` for whether to show StorageFile"]
  ],
  "return" : ["JsVar","An array of filenames"],
  "typescript" : "list(regex?: RegExp, filter?: { sf: boolean }): string[];"
}
List all files in the flash storage area. An array of Strings is returned.

By default this lists files created by `StorageFile` (`require("Storage").open`)
which have a file number (`"\1"`/`"\2"`/etc) appended to them.

```
// All files
require("Storage").list()
// Files ending in '.js'
require("Storage").list(/\.js$/)
// All Storage Files
require("Storage").list(undefined, {sf:true})
// All normal files (e.g. created with Storage.write)
require("Storage").list(undefined, {sf:false})
```

**Note:** This will output system files (e.g. saved code) as well as files that
you may have written.
 */
JsVar *jswrap_storage_list(JsVar *regex, JsVar *filter) {
  JsfFileFlags containing = 0;
  JsfFileFlags notContaining = 0;
  if (jsvIsObject(filter)) {
    JsVar *v = jsvObjectGetChildIfExists(filter, "sf");
    if (v) {
      if (jsvGetBoolAndUnLock(v))
        containing |= JSFF_STORAGEFILE;
      else
        notContaining |= JSFF_STORAGEFILE;
    }
  }
  return jsfListFiles(regex, containing, notContaining);
}

/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "hash",
  "generate" : "jswrap_storage_hash",
  "params" : [
    ["regex","JsVar","[optional] If supplied, filenames are checked against this regular expression (with `String.match(regexp)`) to see if they match before being hashed"]
  ],
  "return" : ["int","A hash of the files matching"],
  "typescript" : "hash(regex: RegExp): number;"
}
List all files in the flash storage area matching the specified regex (ignores
StorageFiles), and then hash their filenames *and* file locations.

Identical files may have different hashes (e.g. if Storage is compacted and the
file moves) but the chances of different files having the same hash are
extremely small.

```
// Hash files
require("Storage").hash()
// Files ending in '.boot.js'
require("Storage").hash(/\.boot\.js$/)
```

**Note:** This function is used by Bangle.js as a way to cache files. For
instance the bootloader will add all `.boot.js` files together into a single
`.boot0` file, but it needs to know quickly whether anything has changed.
 */
JsVarInt jswrap_storage_hash(JsVar *regex) {
  return (JsVarInt)jsfHashFiles(regex, 0, JSFF_STORAGEFILE);
}

/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "compact",
  "params" : [
    ["showMessage","bool","[optional] If true, an overlay message will be displayed on the screen while compaction is happening. Default is false."]
  ],
  "generate" : "jswrap_storage_compact"
}
The Flash Storage system is journaling. To make the most of the limited write
cycles of Flash memory, Espruino marks deleted/replaced files as garbage/trash files and
moves on to a fresh part of flash memory. Espruino only fully erases those files
when it is running low on flash, or when `compact` is called.

`compact` may fail if there isn't enough RAM free on the stack to use as swap
space, however in this case it will not lose data.

**Note:** `compact` rearranges the contents of memory. If code is referencing
that memory (e.g. functions that have their code stored in flash) then they may
become garbled when compaction happens. To avoid this, call `eraseFiles` before
uploading data that you intend to reference to ensure that uploaded files are
right at the start of flash and cannot be compacted further.
 */
void jswrap_storage_compact(bool showMessage) {
  jsfCompact(showMessage);
}

/*JSON{
  "type" : "staticmethod",
  "ifdef" : "DEBUG",
  "class" : "Storage",
  "name" : "debug",
  "generate" : "jswrap_storage_debug"
}
This writes information about all blocks in flash memory to the console - and is
only useful for debugging flash storage.
 */
void jswrap_storage_debug() {
  jsfDebugFiles();
}

/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "getFree",
  "params" : [
    ["checkInternalFlash","bool","Check the internal flash (rather than external SPI flash).  Default false, so will check external storage"]
  ],  
  "generate" : "jswrap_storage_getFree",
  "return" : ["int","The amount of free bytes"]
}
Return the amount of free bytes available in Storage. Due to fragmentation there
may be more bytes available, but this represents the maximum size of file that
can be written.

**NOTE:** `checkInternalFlash` is only useful on DICKENS devices - other devices don't use two different flash banks
 */
int jswrap_storage_getFree(bool checkInternalFlash) {
  uint32_t addr = 0;
#ifdef FLASH_SAVED_CODE2_START
  addr = checkInternalFlash ? FLASH_SAVED_CODE_START : FLASH_SAVED_CODE2_START;
#endif
  return (int)jsfGetStorageStats(addr,true).free;
}

/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "getStats",
  "params" : [
    ["checkInternalFlash","bool","Check the internal flash (rather than external SPI flash).  Default false, so will check external storage"]
  ],  
  "generate" : "jswrap_storage_getStats",
  "return" : ["JsVar","An object containing info about the current Storage system"]
}
Returns:

```
{
  totalBytes // Amount of bytes in filesystem
  freeBytes // How many bytes are left at the end of storage?
  fileBytes // How many bytes of allocated files do we have?
  fileCount // How many allocated files do we have?
  trashBytes // How many bytes of trash files do we have?
  trashCount // How many trash files do we have? (can be cleared with .compact)
}
```

**NOTE:** `checkInternalFlash` is only useful on DICKENS devices - other devices don't use two different flash banks
 */
JsVar *jswrap_storage_getStats(bool checkInternalFlash) {
  JsVar *o = jsvNewObject();
  if (!o) return NULL;
  uint32_t addr = 0;
#ifdef FLASH_SAVED_CODE2_START
  addr = checkInternalFlash ? FLASH_SAVED_CODE_START : FLASH_SAVED_CODE2_START;
  
#endif  
  JsfStorageStats stats = jsfGetStorageStats(addr, true);
  jsvObjectSetChildAndUnLock(o, "totalBytes", jsvNewFromInteger((JsVarInt)stats.total));
  jsvObjectSetChildAndUnLock(o, "freeBytes", jsvNewFromInteger((JsVarInt)stats.free));
  jsvObjectSetChildAndUnLock(o, "fileBytes", jsvNewFromInteger((JsVarInt)stats.fileBytes));
  jsvObjectSetChildAndUnLock(o, "fileCount", jsvNewFromInteger((JsVarInt)stats.fileCount));
  jsvObjectSetChildAndUnLock(o, "trashBytes", jsvNewFromInteger((JsVarInt)stats.trashBytes));
  jsvObjectSetChildAndUnLock(o, "trashCount", jsvNewFromInteger((JsVarInt)stats.trashCount));
  return o;
}

/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "optimise",
  "generate" : "jswrap_storage_optimise"
}
Writes a lookup table for files into Bangle.js's storage. This allows any file
stored up to that point to be accessed quickly.
 */
void jswrap_storage_optimise() {
#ifdef ESPR_STORAGE_FILENAME_TABLE
  jsfCreateFileTable();
#endif
}

/*JSON{
  "type" : "staticmethod",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "Storage",
  "name" : "open",
  "generate" : "jswrap_storage_open",
  "params" : [
    ["name","JsVar","The filename - max **27** characters (case sensitive)"],
    ["mode","JsVar","The open mode - must be either `'r'` for read,`'w'` for write , or `'a'` for append"]
  ],
  "return" : ["JsVar","An object containing {read,write,erase}"],
  "return_object" : "StorageFile",
  "typescript" : "open(name: string, mode: \"r\" | \"w\" | \"a\"): StorageFile;"
}
Open a file in the Storage area. This can be used for appending data
(normal read/write operations only write the entire file).

Please see `StorageFile` for more information (and examples).

**Note:** These files write through immediately - they do not need closing.

*/
JsVar *jswrap_storage_open(JsVar *name, JsVar *modeVar) {
  char mode = 0;
  if (jsvIsStringEqual(modeVar,"r")) mode='r';
  else if (jsvIsStringEqual(modeVar,"w")) mode='w';
  else if (jsvIsStringEqual(modeVar,"a")) mode='a';
  else {
    jsExceptionHere(JSET_ERROR, "Invalid mode %j", modeVar);
    return 0;
  }

  JsVar *f = jspNewObject(0, "StorageFile");
  if (!f) return 0;

  int chunk = 1;

  JsVar *n = jsvNewFromStringVar(name,0,sizeof(JsfFileName));
  JsfFileName fname = jsfNameFromVar(n);
  int fnamei = sizeof(fname)-1;
  while (fnamei && fname.c[fnamei-1]==0) fnamei--;
  fname.c[fnamei]=(char)chunk;
  jsvObjectSetChildAndUnLock(f,"name",n);

  int offset = 0; // offset in file
  JsfFileHeader header;
  uint32_t addr = jsfFindFile(fname, &header);
  if (mode=='w') { // write,
    if (addr) { // we had a file - erase it
      jswrap_storagefile_erase(f);
      addr = 0;
    }
  }
  int fileLen = addr ? (int)jsfGetFileSize(&header) : 0;
  if (mode=='a') { // append
    // Find the last free page (eg it has 0xFF at the end)
    unsigned char lastCh = 255;
    if (addr) jshFlashRead(&lastCh, addr+jsfGetFileSize(&header)-1, 1);
    while (addr && lastCh!=255 && chunk<255) {
      chunk++;
      fname.c[fnamei]=(char)chunk;
      addr = jsfFindFile(fname, &header);
      if (addr) {
        fileLen = (int)jsfGetFileSize(&header);
        jshFlashRead(&lastCh, addr+fileLen-1, 1);
      } else {
        fileLen = 0;
      }
    }
    if (addr) {
      // if we have a page, try and find the end of it
      char buf[64];
      bool foundEnd = false;
      while (!foundEnd) {
        int l = (int)fileLen - offset;
        if (l<=0) {
          foundEnd = true;
          break;
        }
        if (l>(int)sizeof(buf)) l=(int)sizeof(buf);
        jshFlashRead(buf, addr+(uint32_t)offset, (uint32_t)l);
        for (int i=0;i<l;i++) {
          if (buf[i]==(char)255) {
            l = i;
            foundEnd = true;
            break;
          }
        }
        offset += l;
      }
    }
    // Now 'chunk' and offset points to the last (or a free) page
  }
  if (mode=='r') {
    // read - do nothing, we're good.
  }

  DBG("Open %j Chunk %d Offset %d addr 0x%08x len %d\n",name,chunk,offset,addr,fileLen);
  jsvObjectSetChildAndUnLock(f,"chunk",jsvNewFromInteger(chunk));
  jsvObjectSetChildAndUnLock(f,"offset",jsvNewFromInteger(offset));
  jsvObjectSetChildAndUnLock(f,"mode",jsvNewFromInteger(mode));

  return f;
}

/*JSON{
  "type" : "class",
  "class" : "StorageFile",
  "ifndef" : "SAVE_ON_FLASH"
}

These objects are created from `require("Storage").open` and allow Storage items
to be read/written.

The `Storage` library writes into Flash memory (which can only be erased in
chunks), and unlike a normal filesystem it allocates files in one long
contiguous area to allow them to be accessed easily from Espruino.

This presents a challenge for `StorageFile` which allows you to append to a
file, so instead `StorageFile` stores files in chunks. It uses the last
character of the filename to denote the chunk number (e.g. `"foobar\1"`,
`"foobar\2"`, etc).

This means that while `StorageFile` files exist in the same area as those from
`Storage`, they should be read using `Storage.open` (and not `Storage.read`).

```
f = require("Storage").open("foobar","w");
f.write("Hell");
f.write("o World\n");
f.write("Hello\n");
f.write("World 2\n");
f.write("Hello World 3\n");
// there's no need to call 'close'
// then
f = require("Storage").open("foobar","r");
f.read(13) // "Hello World\nH"
f.read(13) // "ello\nWorld 2\n"
f.read(13) // "Hello World 3"
f.read(13) // "\n"
f.read(13) // undefined
// or
f = require("Storage").open("foobar","r");
f.readLine() // "Hello World\n"
f.readLine() // "Hello\n"
f.readLine() // "World 2\n"
f.readLine() // "Hello World 3\n"
f.readLine() // undefined
// now get rid of file
f.erase();
```

**Note:** `StorageFile` uses the fact that all bits of erased flash memory are 1
to detect the end of a file. As such you should not write character code 255
(`"\xFF"`) to these files.
*/

JsVar *jswrap_storagefile_read_internal(JsVar *f, int len) {
  bool isReadLine = len<0;
  char mode = (char)jsvGetIntegerAndUnLock(jsvObjectGetChildIfExists(f,"mode"));
  if (mode!='r') {
    jsExceptionHere(JSET_ERROR, "Can't read in this mode");
    return 0;
  }

  int chunk = jsvGetIntegerAndUnLock(jsvObjectGetChildIfExists(f,"chunk"));
  JsfFileName fname = jsfNameFromVarAndUnLock(jsvObjectGetChildIfExists(f,"name"));
  int fnamei = sizeof(fname)-1;
  while (fnamei && fname.c[fnamei-1]==0) fnamei--;
  fname.c[fnamei]=(char)chunk;
  JsfFileHeader header;
  uint32_t addr = jsfFindFile(fname, &header);
  if (!addr) return 0; // end of file/no file chunk found
  int fileLen = (int)jsfGetFileSize(&header);
  int offset = jsvGetIntegerAndUnLock(jsvObjectGetChildIfExists(f,"offset"));

  JsVar *result = 0;
  char buf[32];
  if (isReadLine) len = sizeof(buf);
  while (len) {
    int remaining = fileLen - offset;
    if (remaining<=0) { // next page
      offset = 0;
      if (chunk==255) {
        addr=0; // end of file!
      } else {
        chunk++;
        fname.c[fnamei]=(char)chunk;
        addr = jsfFindFile(fname, &header);
        fileLen = (int)jsfGetFileSize(&header);
      }
      jsvObjectSetChildAndUnLock(f,"offset",jsvNewFromInteger(offset));
      jsvObjectSetChildAndUnLock(f,"chunk",jsvNewFromInteger(chunk));
      remaining = fileLen;
      if (!addr) {
        // end of file!
        return result;
      }
    }
    int l = len;
    if (l>(int)sizeof(buf)) l=(int)sizeof(buf);
    if (l>remaining) l=remaining;
    jshFlashRead(buf, addr+(uint32_t)offset, (uint32_t)l);
    for (int i=0;i<l;i++) {
      if (buf[i]==(char)255) {
        // end of file!
        l = i;
        len = l;
        break;
      }
      if (isReadLine && buf[i]=='\n') {
        l = i+1;
        len = l;
        isReadLine = false; // done
        break;
      }
    }

    if (!l) break;
    if (!result)
      result = jsvNewFromEmptyString();
    if (result)
      jsvAppendStringBuf(result,buf,(size_t)l);

    len -= l;
    offset += l;
    // if we're still reading lines, set the length to buffer size
    if (isReadLine)
      len = sizeof(buf);
  }
  jsvObjectSetChildAndUnLock(f,"offset",jsvNewFromInteger(offset));
  return result;
}
/*JSON{
  "type" : "method",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "StorageFile",
  "name" : "read",
  "generate" : "jswrap_storagefile_read",
  "params" : [
    ["len","int","How many bytes to read"]
  ],
  "return" : ["JsVar","A String, or undefined "],
  "return_object" : "String"
}
Read 'len' bytes of data from the file, and return a String containing those
bytes.

If the end of the file is reached, the String may be smaller than the amount of
bytes requested, or if the file is already at the end, `undefined` is returned.
*/
JsVar *jswrap_storagefile_read(JsVar *f, int len) {
  if (len<0) len=0;
  return jswrap_storagefile_read_internal(f,len);
}
/*JSON{
  "type" : "method",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "StorageFile",
  "name" : "readLine",
  "generate" : "jswrap_storagefile_readLine",
  "return" : ["JsVar","A line of data"],
  "return_object" : "String"
}
Read a line of data from the file (up to and including `"\n"`)
*/
JsVar *jswrap_storagefile_readLine(JsVar *f) {
  return jswrap_storagefile_read_internal(f,-1);
}
/*JSON{
  "type" : "method",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "StorageFile",
  "name" : "getLength",
  "generate" : "jswrap_storagefile_getLength",
  "return" : ["int","The current length in bytes of the file"]
}
Return the length of the current file.

This requires Espruino to read the file from scratch, which is not a fast
operation.
*/
int jswrap_storagefile_getLength(JsVar *f) {
  // Get name and position of name digit
  JsVar *n = jsvObjectGetChildIfExists(f,"name");
  JsfFileName fname = jsfNameFromVar(n);
  jsvUnLock(n);
  int fnamei = sizeof(fname)-1;
  while (fnamei && fname.c[fnamei-1]==0) fnamei--;
  int chunk = 1;
  fname.c[fnamei]=(char)chunk;

  int length = 0; // actual length
  int offset = 0; // offset in file
  JsfFileHeader header;
  uint32_t addr = jsfFindFile(fname, &header);
  // Find the last free page
  unsigned char lastCh = 255;
  if (addr) jshFlashRead(&lastCh, addr+jsfGetFileSize(&header)-1, 1);
  while (addr && lastCh!=255 && chunk<255) {
    length += (int)jsfGetFileSize(&header);
    chunk++;
    fname.c[fnamei]=(char)chunk;
    addr = jsfFindFile(fname, &header);
    if (addr) jshFlashRead(&lastCh, addr+jsfGetFileSize(&header)-1, 1);
  }
  if (addr) {
    // if we have a page, try and find the end of it
    char buf[64];
    bool foundEnd = false;
    while (!foundEnd) {
      int l = (int)jsfGetFileSize(&header) - offset;
      if (l<=0) {
        foundEnd = true;
        break;
      }
      if (l>(int)sizeof(buf)) l=(int)sizeof(buf);
      jshFlashRead(buf, addr+(uint32_t)offset, (uint32_t)l);
      for (int i=0;i<l;i++) {
        if (buf[i]==(char)255) {
          l = i;
          foundEnd = true;
          break;
        }
      }
      offset += l;
    }
  }
  length += offset;
  return length;
}



/*JSON{
  "type" : "method",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "StorageFile",
  "name" : "write",
  "generate" : "jswrap_storagefile_write",
  "params" : [
    ["data","JsVar","The data to write. This should not include `'\\xFF'` (character code 255)"]
  ],
  "typescript" : "write(data: string): void;"
}
Append the given data to a file. You should not attempt to append `"\xFF"`
(character code 255).
*/
void jswrap_storagefile_write(JsVar *f, JsVar *_data) {
  char mode = (char)jsvGetIntegerAndUnLock(jsvObjectGetChildIfExists(f,"mode"));
  if (mode!='w' && mode!='a') {
    jsExceptionHere(JSET_ERROR, "Can't write in this mode");
    return;
  }

  JsVar *data = jsvAsString(_data);
  if (!data) return;
  size_t len = jsvGetStringLength(data);
  if (len==0) {
    jsvUnLock(data);
    return;
  }
  int offset = jsvGetIntegerAndUnLock(jsvObjectGetChildIfExists(f,"offset"));
  int chunk = jsvGetIntegerAndUnLock(jsvObjectGetChildIfExists(f,"chunk"));
  JsfFileName fname = jsfNameFromVarAndUnLock(jsvObjectGetChildIfExists(f,"name"));
  int fnamei = sizeof(fname)-1;
  while (fnamei && fname.c[fnamei-1]==0) fnamei--;
  //DBG("Filename[%d]=%d\n",fnamei,chunk);
  fname.c[fnamei]=(char)chunk;

  JsfFileHeader header;
  uint32_t addr = jsfFindFile(fname, &header);
  int fileLen = addr ? (int)jsfGetFileSize(&header) : 0;

  DBG("Write Chunk %d Offset %d addr 0x%08x\n",chunk,offset,addr);
  if (!addr) {
    DBG("Write Create Chunk\n");
    // What if data length > the chunk size? jsfWriteFile fails with error currently
    if (jsfWriteFile(fname, data, JSFF_STORAGEFILE, 0, STORAGEFILE_CHUNKSIZE)) {
      addr = jsfFindFile(fname, &header);
      fileLen = (int)jsfGetFileSize(&header);
      offset = (int)len;
      jsvObjectSetChildAndUnLock(f,"offset",jsvNewFromInteger(offset));
    } else {
      DBG("Write Create Chunk FAILED\n");
      // there would already have been an exception
      jsvObjectSetChildAndUnLock(f,"mode",jsvNewFromInteger(0)); // set mode to 0 so no more writing
    }
    jsvUnLock(data);
    return;
  }
  int remaining = fileLen - offset;
  if ((int)len<remaining) {
    DBG("Write Append Chunk\n");
    // Great, it all fits in
    jswrap_flash_write(data, (int)addr+offset);
    offset += (int)len;
    jsvObjectSetChildAndUnLock(f,"offset",jsvNewFromInteger(offset));
  } else {
    DBG("Write Append Chunk and create new file\n");
    // Fill up this page, do part of old page
    // End of this page
    JsVar *part = jsvNewFromStringVar(data,0,(size_t)remaining);
    jswrap_flash_write(part, (int)addr+offset);
    offset += remaining; // update offset now we've written
    jsvObjectSetChildAndUnLock(f,"offset",jsvNewFromInteger(offset));
    jsvUnLock(part);
    // Next page
    if (chunk==255) {
      jsExceptionHere(JSET_ERROR, "File too big!");
      jsvUnLock(data);
      return;
    } else {
      chunk++;
      fname.c[fnamei]=(char)chunk;
    }
    // Write Next page
    part = jsvNewFromStringVar(data,(size_t)remaining,JSVAPPENDSTRINGVAR_MAXLENGTH);
    if (jsfWriteFile(fname, part, JSFF_STORAGEFILE, 0, STORAGEFILE_CHUNKSIZE)) {
      offset = (int)jsvGetStringLength(part);
      jsvObjectSetChildAndUnLock(f,"chunk",jsvNewFromInteger(chunk));
      jsvObjectSetChildAndUnLock(f,"offset",jsvNewFromInteger(offset));
    } else {
      // there would already have been an exception - no need to return
      // we can free data up below
      jsvObjectSetChildAndUnLock(f,"mode",jsvNewFromInteger(0)); // set mode to 0 so no more writing
    }
    jsvUnLock(part);
  }
  jsvUnLock(data);
}

/*JSON{
  "type" : "method",
  "ifndef" : "SAVE_ON_FLASH",
  "class" : "StorageFile",
  "name" : "erase",
  "generate" : "jswrap_storagefile_erase"
}
Erase this file
*/
void jswrap_storagefile_erase(JsVar *f) {
  JsfFileName fname = jsfNameFromVarAndUnLock(jsvObjectGetChildIfExists(f,"name"));
  int fnamei = sizeof(fname)-1;
  while (fnamei && fname.c[fnamei-1]==0) fnamei--;
  // erase all numbered files
  int chunk = 1;
  bool ok = true;
  while (ok) {
    fname.c[fnamei]=(char)chunk;
    ok = jsfEraseFile(fname);
    chunk++;
  }
  // reset everything
  jsvObjectSetChildAndUnLock(f,"chunk",jsvNewFromInteger(1));
  jsvObjectSetChildAndUnLock(f,"offset",jsvNewFromInteger(0));
  jsvObjectSetChildAndUnLock(f,"mode",jsvNewFromInteger(0));
}


/*JSON{
  "type" : "method",
  "class" : "StorageFile",
  "name" : "pipe",
  "ifndef" : "SAVE_ON_FLASH",
  "generate" : "jswrap_pipe",
  "params" : [
    ["destination","JsVar","The destination file/stream that will receive content from the source."],
    ["options","JsVar",["[optional] An object `{ chunkSize : int=32, end : bool=true, complete : function }`","chunkSize : The amount of data to pipe from source to destination at a time","complete : a function to call when the pipe activity is complete","end : call the 'end' function on the destination when the source is finished"]]
  ],
  "typescript": "pipe(destination: any, options?: PipeOptions): void"
}
Pipe this file to a stream (an object with a 'write' method)
*/