docs.sheetjs.com/docz/docs/03-demos/12-engines/20_chakra.md

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ChakraCore is an embeddable JS engine written in C++.

The Standalone scripts can be parsed and evaluated in a ChakraCore context.

Integration Details

Initialize ChakraCore

ChakraCore provides a global object through JsGetGlobalObject:

/* initialize */
JsRuntimeHandle runtime;
JsContextRef context;
size_t cookie = 0;
JsCreateRuntime(JsRuntimeAttributeNone, nullptr, &runtime);
JsCreateContext(runtime, &context);
JsSetCurrentContext(context);

/* obtain reference to global object */
JsValueRef global;
JsGetGlobalObject(&global);

/* DO WORK HERE */

/* cleanup */
JsSetCurrentContext(JS_INVALID_REFERENCE);
JsDisposeRuntime(runtime);

:::note

Cleanup and validation code is omitted from the discussion. The integration example shows structured validation and controlled memory usage.

:::

Load SheetJS Scripts

The main library can be loaded by reading the script from the file system and evaluating in the ChakraCore context:

static char *read_file(const char *filename, size_t *sz) {
  FILE *f = fopen(filename, "rb");
  if(!f) return NULL;
  long fsize; { fseek(f, 0, SEEK_END); fsize = ftell(f); fseek(f, 0, SEEK_SET); }
  char *buf = (char *)malloc(fsize * sizeof(char));
  *sz = fread((void *) buf, 1, fsize, f);
  fclose(f);
  return buf;
}

#define EVAL_FILE(path) {\
  JsValueRef filename; \
  JsValueRef result; \
  JsCreateString(path, strlen(path), &filename); \
  size_t len; const char* script = read_file(path, &len);\
  JsValueRef src;\
  JsCreateExternalArrayBuffer((void*)script, len, nullptr, nullptr, &src);\
  JsRun(src, cookie++, filename, JsParseScriptAttributeNone, &result); \
}

// ...
  /* load library */
  EVAL_FILE("shim.min.js")
  EVAL_FILE("xlsx.full.min.js")

Reading Files

JsCreateExternalArrayBuffer can generate an ArrayBuffer from a C byte array:

/* read file */
size_t len; char *buf = read_file(argv[1], &len);

/* load data into array buffer */
JsValueRef ab;
JsCreateExternalArrayBuffer((void*)buf, len, nullptr, nullptr, &ab);

After pushing the data, it is easiest to store properties on globalThis:

/* assign to the `buf` global variable */
JsValueRef buf_str; JsCreateString("buf", strlen("buf"), &buf_str);
JsObjectSetProperty(global, buf_str, ab, true);

/* call globalThis.wb = XLSX.read(ab) */
const char* script_str ="globalThis.wb = XLSX.read(buf);"

JsValueRef script;
JsCreateExternalArrayBuffer((void*)script_str, (size_t)strlen(script_str), nullptr, nullptr, &script);
JsRun(script, cookie++, fname, JsParseScriptAttributeNone, &result);

Complete Example

The "Integration Example" covers a traditional integration in a C application, while the "CLI Test" demonstrates other concepts using the ch CLI tool.

Integration Example

:::note

This demo was tested in the following deployments:

Architecture	Git Commit	Date
darwin-x64	c3ead3f	2023-07-05
darwin-arm	c3ead3f	2023-07-05
linux-x64	c3ead3f	2023-07-05

:::

0. Install icu and cmake dependencies.

brew install icu4c cmake

brew install icu4c cmake

On Arch Linux / HoloOS:

sudo pacman -S cmake clang

1. Download ChakraCore:

git clone https://github.com/Microsoft/ChakraCore
cd ChakraCore
git checkout c3ead3f
cd ..

2. Build ChakraCore:

cd ChakraCore
./build.sh --static --icu=/usr/local/opt/icu4c/include --test-build -j=8
cd ..

:::caution

When this demo was last tested, the build failed with the message:

!!! couldn't find ICU ...

This was fixed with a local symlink to the icu4c folder before the build step:

cd ChakraCore
mkdir -p usr/local/opt
ln -s /opt/homebrew/opt/icu4c usr/local/opt/icu4c
cd ..

:::

:::info

When the demo was last tested, ChakraCore JIT was not supported.

:::

cd ChakraCore
./build.sh --static --icu=/usr/local/opt/icu4c/include --test-build -j=8 --no-jit
cd ..

:::caution

When this demo was last tested, the build failed with the message:

!!! couldn't find ICU ...

This was fixed with a local symlink to the icu4c folder before the build step:

cd ChakraCore
mkdir -p usr/local/opt
ln -s /opt/homebrew/opt/icu4c usr/local/opt/icu4c
cd ..

:::

:::caution

When the demo was last tested, ChakraCore JIT was not supported.

:::

cd ChakraCore
./build.sh --static --embed-icu --test-build -j=8 --no-jit
cd ..

3. Download the source file and Makefile:

• sheetjs.ch.cpp
• Makefile

curl -LO https://docs.sheetjs.com/chakra/sheetjs.ch.cpp
curl -LO https://docs.sheetjs.com/chakra/Makefile

4. Build the sample application:

make

This program tries to parse the file specified by the first argument

:::caution

When this demo was last tested on macOS, the build failed with the message:

clang: error: no such file or directory: '/usr/local/opt/icu4c/lib/libicudata.a'

This was fixed by creating a symbolic link:

cd /usr/local
sudo mkdir -p opt
cd opt
sudo ln -s /opt/homebrew/opt/icu4c

:::

5. Download the standalone script, shim script, and test file:

• xlsx.full.min.js
• shim.min.js
• pres.numbers

{\ curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js curl -LO https://sheetjs.com/pres.numbers}

6. Run the test program:

./sheetjs.ch pres.numbers

If successful, the program will print the contents of the first sheet as CSV.

CLI Test

:::note

This demo was last tested on 2023 April 09 against ch 1.13.0.0-beta. The command line tool was built against commit c3ead3f.

:::

Due to limitations of the ch standalone binary, this demo will encode a test file as a Base64 string and directly add it to an amalgamated script.

0. Download and extract the ChakraCore release ZIP. Copy the binary (bin/ch) to your project folder.

1. Download the standalone script, shim, and test file:

• xlsx.full.min.js
• shim.min.js
• pres.numbers

2. Bundle the test file and create payload.js:

node -e "fs.writeFileSync('payload.js', 'var payload = \"' + fs.readFileSync('pres.numbers').toString('base64') + '\";')"

3. Create support scripts:

• global.js creates a global variable:

var global = (function(){ return this; }).call(null);

• chakra.js will call XLSX.read and XLSX.utils.sheet_to_csv:

var wb = XLSX.read(payload, {type:'base64'});
console.log(XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]]));

4. Create the amalgamation xlsx.chakra.js:

cat global.js xlsx.full.min.js payload.js chakra.js > xlsx.chakra.js

The final script defines global before loading the standalone library. Once ready, it will read the bundled test data and print the contents as CSV.

5. Run the script using the ChakraCore standalone binary:

./ch xlsx.chakra.js