forked from sheetjs/docs.sheetjs.com
v8
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.gitignore
vendored
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.gitignore
vendored
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*.bak
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package-lock.json
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pnpm-lock.yaml
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docs
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/docs
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2
Makefile
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Makefile
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.PHONY: dev
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dev:
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cd docz; npm run start; cd ..
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cd docz; npm run start -- --host=0.0.0.0; cd ..
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.PHONY: serve
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serve:
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261
docz/docs/03-demos/12-engines/02_v8.md
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docz/docs/03-demos/12-engines/02_v8.md
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---
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title: C++ + V8
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pagination_prev: demos/bigdata/index
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pagination_next: solutions/input
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---
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import current from '/version.js';
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import CodeBlock from '@theme/CodeBlock';
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V8 is an embeddable JS engine written in C++. It powers Chromium and Chrome,
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NodeJS and Deno, Adobe UXP and other platforms.
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The [Standalone scripts](/docs/getting-started/installation/standalone) can be
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parsed and evaluated in a V8 context.
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## Integration Details
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_Initialize V8_
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The official V8 `hello-world` example covers initialization and cleanup. For the
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purposes of this demo, the key variables are noted below:
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```cpp
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v8::Isolate* isolate = v8::Isolate::New(create_params);
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v8::Local<v8::Context> context = v8::Context::New(isolate);
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```
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The following helper function evaluates C strings as JS code:
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```cpp
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v8::Local<v8::Value> eval_code(v8::Isolate *i, v8::Local<v8::Context> c, char* code) {
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v8::Local<v8::String> source = v8::String::NewFromUtf8(i, code).ToLocalChecked();
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v8::Local<v8::Script> script = v8::Script::Compile(i, source).ToLocalChecked();
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return script->Run(c).ToLocalChecked();
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}
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```
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_Load SheetJS Scripts_
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The main library can be loaded by reading the scripts from the file system and
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evaluating in the V8 context:
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```cpp
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/* simple wrapper to read the entire script file */
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static char *read_file(const char *filename, size_t *sz) {
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FILE *f = fopen(filename, "rb");
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if(!f) return NULL;
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long fsize; { fseek(f, 0, SEEK_END); fsize = ftell(f); fseek(f, 0, SEEK_SET); }
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char *buf = (char *)malloc(fsize * sizeof(char));
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*sz = fread((void *) buf, 1, fsize, f);
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fclose(f);
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return buf;
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}
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// ...
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size_t sz; char *file = read_file("xlsx.full.min.js", &sz);
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v8::Local<v8::Value> result = eval_code(isolate, context, file);
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```
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To confirm the library is loaded, `XLSX.version` can be inspected:
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```cpp
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/* get version string */
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v8::Local<v8::Value> result = eval_code(isolate, context, "XLSX.version");
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v8::String::Utf8Value vers(isolate, result);
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printf("SheetJS library version %s\n", *vers);
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```
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### Reading Files
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V8 supports `ArrayBuffer` natively. Assuming `buf` is a C byte array, with
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length `len`, this snippet stores the data as an `ArrayBuffer` in global scope:
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```cpp
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/* load C char array and save to an ArrayBuffer */
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std::unique_ptr<v8::BackingStore> back = v8::ArrayBuffer::NewBackingStore(isolate, len);
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memcpy(back->Data(), buf, len);
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v8::Local<v8::ArrayBuffer> ab = v8::ArrayBuffer::New(isolate, std::move(back));
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v8::Maybe<bool> res = context->Global()->Set(context, v8::String::NewFromUtf8Literal(isolate, "buf"), ab);
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/* parse with SheetJS */
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v8::Local<v8::Value> result = eval_code(isolate, context, "globalThis.wb = XLSX.read(buf)");
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```
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`wb` will be a variable in the JS environment that can be inspected using the
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various SheetJS API functions.
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### Writing Files
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The underlying memory from an `ArrayBuffer` can be recovered:
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```c
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/* write with SheetJS using type: "array" */
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v8::Local<v8::Value> result = eval_code(isolate, context, "XLSX.write(wb, {type:'array', bookType:'xlsb'})");
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/* pull result back to C++ */
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v8::Local<v8::ArrayBuffer> ab = v8::Local<v8::ArrayBuffer>::Cast(result);
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size_t sz = ab->ByteLength();
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char *buf = ab->Data();
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```
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The resulting `buf` can be written to file with `fwrite`.
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## Complete Example
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:::note
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This demo was tested in the following deployments:
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| V8 Version | Platform | OS Version | Compiler | Date |
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|:--------------|:-------------|:-----------|:---------------|:-----------|
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| `11.3.244.11` | `darwin-x64` | macOS 13.2 | `clang 14.0.3` | 2023-05-20 |
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:::
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This program parses a file and prints CSV data from the first worksheet. It also
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generates an XLSB file and writes to the filesystem.
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:::caution
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At the time of writing, there were errors in the official V8 embed guide for the
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macOS platform. The correct instructions are included below.
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:::
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:::caution
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The build process is long and will test your patience.
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:::
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### Preparation
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1) Download and install `depot_tools`:
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```bash
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mkdir -p /usr/local/lib
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cd /usr/local/lib
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git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
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```
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2) Add the path to the `PATH` environment variable:
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```bash
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export PATH="/usr/local/lib/depot_tools:$PATH"
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```
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At this point, it is strongly recommended to add the line to a shell startup
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script such as `.bashrc` or `.zshrc`
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3) Run `gclient` once to update `depot_tools`:
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```bash
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gclient
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```
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### Clone V8
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4) Create a base directory:
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```bash
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mkdir -p ~/dev/v8
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cd ~/dev/v8
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fetch v8
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cd v8
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```
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Note that the actual repo will be placed in `~/dev/v8/v8`.
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5) Checkout the desired version. The following command pulls `11.3.244.11`:
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```bash
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git checkout refs/tags/11.3.244.11 -b sample -t
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```
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### Build V8
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6) Build the static library.
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```bash
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tools/dev/v8gen.py x64.release.sample
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ninja -C out.gn/x64.release.sample v8_monolith
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```
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7) Ensure the sample `hello-world` compiles and runs:
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```bash
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g++ -I. -Iinclude samples/hello-world.cc -o hello_world -fno-rtti -lv8_monolith \
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-lv8_libbase -lv8_libplatform -ldl -Lout.gn/x64.release.sample/obj/ -pthread \
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-std=c++17 -DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
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./hello_world
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```
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### Prepare Project
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8) Make a new project folder:
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```bash
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cd ~/dev
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mkdir sheetjs-v8
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cd sheetjs-v8
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```
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9) Copy the sample source:
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```bash
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cp ~/dev/v8/v8/samples/hello-world.cc .
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```
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10) Create symbolic links to the `include` headers and `obj` library folders:
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```bash
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ln -s ~/dev/v8/v8/include
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ln -s ~/dev/v8/v8/out.gn/x64.release.sample/obj
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```
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11) Build and run the `hello-world` example from this folder:
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```bash
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g++ -I. -Iinclude hello-world.cc -o hello_world -fno-rtti -lv8_monolith \
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-lv8_libbase -lv8_libplatform -ldl -Lobj/ -pthread -std=c++17 \
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-DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
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./hello_world
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```
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### Add SheetJS
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12) Download the standalone script and test file:
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<ul>
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<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}>xlsx.full.min.js</a></li>
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<li><a href="https://sheetjs.com/pres.numbers">pres.numbers</a></li>
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</ul>
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<CodeBlock language="bash">{`\
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curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js
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curl -LO https://sheetjs.com/pres.numbers`}
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</CodeBlock>
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13) Download [`sheetjs.v8.cc`](pathname:///v8/sheetjs.v8.cc):
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```bash
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curl -LO https://docs.sheetjs.com/v8/sheetjs.v8.cc
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```
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14) Compile standalone `sheetjs.v8` binary
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```bash
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g++ -I. -Iinclude sheetjs.v8.cc -o sheetjs.v8 -fno-rtti -lv8_monolith \
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-lv8_libbase -lv8_libplatform -ldl -Lobj/ -pthread -std=c++17 \
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-DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
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```
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15) Run the demo:
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```bash
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./sheetjs.v8 pres.numbers
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```
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If the program succeeded, the CSV contents will be printed to console and the
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file `sheetjsw.xlsb` will be created. That file can be opened with Excel.
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docz/static/v8/sheetjs.v8.cc
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docz/static/v8/sheetjs.v8.cc
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/* sheetjs.v8 (C) SheetJS -- https://sheetjs.com */
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/* based on the official V8 samples ("BSD-3-Clause") */
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include "include/libplatform/libplatform.h"
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#include "include/v8.h"
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static char *read_file(const char *filename, size_t *sz) {
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FILE *f = fopen(filename, "rb");
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if(!f) return NULL;
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long fsize; { fseek(f, 0, SEEK_END); fsize = ftell(f); fseek(f, 0, SEEK_SET); }
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char *buf = (char *)malloc(fsize * sizeof(char));
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*sz = fread((void *) buf, 1, fsize, f);
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fclose(f);
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return buf;
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}
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v8::Local<v8::Value> eval_code(v8::Isolate *isolate, v8::Local<v8::Context> context, char* code) {
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v8::Local<v8::String> source = v8::String::NewFromUtf8(isolate, code).ToLocalChecked();
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v8::Local<v8::Script> script = v8::Script::Compile(context, source).ToLocalChecked();
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return script->Run(context).ToLocalChecked();
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}
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#define EVAL_CODE(x) eval_code(isolate, context, (char *)x)
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int main(int argc, char* argv[]) {
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/* initialize -- this part is from the hello world example */
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v8::V8::InitializeICUDefaultLocation(argv[0]);
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v8::V8::InitializeExternalStartupData(argv[0]);
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std::unique_ptr<v8::Platform> platform = v8::platform::NewDefaultPlatform();
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v8::V8::InitializePlatform(platform.get());
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v8::V8::Initialize();
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v8::Isolate::CreateParams create_params;
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create_params.array_buffer_allocator = v8::ArrayBuffer::Allocator::NewDefaultAllocator();
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v8::Isolate* isolate = v8::Isolate::New(create_params);
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{
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v8::Isolate::Scope isolate_scope(isolate);
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v8::HandleScope handle_scope(isolate);
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v8::Local<v8::Context> context = v8::Context::New(isolate);
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v8::Context::Scope context_scope(context);
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/* load library */
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{
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/* read file */
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size_t sz; char *file = read_file("xlsx.full.min.js", &sz);
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if(!file) { perror("Error reading xlsx.full.min.js"); return 1; }
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/* evaluate */
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v8::Local<v8::Value> result = EVAL_CODE(file);
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/* free */
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free(file);
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}
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/* get version string */
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{
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v8::Local<v8::Value> result = EVAL_CODE("XLSX.version");
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v8::String::Utf8Value vers(isolate, result);
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printf("SheetJS library version %s\n", *vers);
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}
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/* read file */
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{
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/* read bytes */
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size_t sz; char *file = read_file(argv[1], &sz);
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if(!file) { perror("Error reading file"); return 1; }
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/* copy into array buffer and assign to `buf` in the global scope */
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{
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std::unique_ptr<v8::BackingStore> back = v8::ArrayBuffer::NewBackingStore(isolate, sz);
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memcpy(back->Data(), file, sz);
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v8::Local<v8::ArrayBuffer> ab = v8::ArrayBuffer::New(isolate, std::move(back));
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v8::Maybe<bool> res = context->Global()->Set(context, v8::String::NewFromUtf8Literal(isolate, "buf"), ab);
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}
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printf("Loaded file %s\n", argv[1]);
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}
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/* parse workbook and assign to global `wb` property */
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{
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v8::Local<v8::Value> result = EVAL_CODE("globalThis.wb = XLSX.read(buf)");
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}
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/* print CSV of first worksheet */
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{
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v8::Local<v8::Value> result = EVAL_CODE("XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]])");
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v8::String::Utf8Value csv(isolate, result);
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printf("%s\n", *csv);
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}
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// write sheetjsw.xlsb
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{
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v8::Local<v8::Value> result = EVAL_CODE("XLSX.write(wb, {type:'array', bookType:'xlsb'})");
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v8::Local<v8::ArrayBuffer> ab = v8::Local<v8::ArrayBuffer>::Cast(result);
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FILE *f = fopen("sheetjsw.xlsb", "wb"); fwrite((char *)ab->Data(), 1, ab->ByteLength(), f); fclose(f);
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}
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}
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/* cleanup -- this part is from the hello world example */
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isolate->Dispose();
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v8::V8::Dispose();
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v8::V8::DisposePlatform();
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delete create_params.array_buffer_allocator;
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return 0;
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}
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