--- title: C + JerryScript pagination_prev: demos/bigdata/index pagination_next: solutions/input --- import current from '/version.js'; import CodeBlock from '@theme/CodeBlock'; [JerryScript](https://jerryscript.net/) is a lightweight JavaScript engine. It is designed for microcontrollers and similar environments. [SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing data from spreadsheets. This demo uses JerryScript and SheetJS to pull data from a spreadsheet and print CSV rows. We'll explore how to load SheetJS in a JerryScript realm and process spreadsheets from C programs. The ["Integration Example"](#integration-example) section includes a complete command-line tool for reading data from files. :::caution pass This demo requires a much larger heap size than is normally used in JerryScript deployments! In local testing, the following sizes were needed: - 8192 (8M) for https://sheetjs.com/pres.xlsx - 65536 (64M) for https://sheetjs.com/pres.numbers ::: :::note Tested Environments This demo was tested in the following environments: | Architecture | Commit | Date | |:-------------|:----------|:-----------| | `darwin-x64` | `cefd391` | 2024-03-15 | | `darwin-arm` | `ef4cb2b` | 2023-12-08 | | `win10-x64` | `47bd5d4` | 2024-04-14 | | `win11-arm` | `ef4cb2b` | 2023-12-08 | | `linux-x64` | `cefd391` | 2024-03-21 | | `linux-arm` | `ef4cb2b` | 2023-12-08 | The Windows tests were run in WSL. ::: ## Integration Details :::info pass The official JerryScript documentation and examples are out of date. This explanation was verified against the latest release (commit `514fa67`). ::: ### Initialize JerryScript The global engine instance can be initialized with `jerry_init` and cleaned up with `jerry_cleanup`: ```c #include "jerryscript.h" int main (int argc, char **argv) { /* Initialize engine */ /* highlight-next-line */ jerry_init(JERRY_INIT_EMPTY); // ... use engine methods ... /* cleanup before exiting */ /* highlight-next-line */ jerry_cleanup(); return 0; } ``` API methods use `jerry_value_t` values to represent JS values and miscellany. Values representing errors can be distinguished using `jerry_value_is_error`. `jerry_value_t` values can be freed with `jerry_value_free`. ### Evaluate Code Evaluating code involves two steps: - `jerry_parse` will parse the script - `jerry_run` will run the parsed script object :::note pass The return value of `jerry_parse` is a `jerry_value_t` value that can be safely freed after `jerry_run`. ::: The following `eval_str` function parses and executes scripts. If parsing fails, the function will return the parsing error. If parsing succeeds, the function will return the result of executing the code. ```c jerry_value_t eval_str(const char *code, size_t sz) { /* try to parse code */ jerry_value_t parsed = jerry_parse(code, sz, NULL); /* return the parse error if parsing failed */ if(jerry_value_is_error(parsed)) return parsed; /* run the code */ jerry_value_t out = jerry_run(parsed); /* free the parsed representation */ jerry_value_free(parsed); /* return the result */ return out; } ``` ### Load SheetJS Scripts [SheetJS Standalone scripts](/docs/getting-started/installation/standalone) can be parsed and run in JerryScript. Scripts can be read from the filesystem using standard C functions: ```c 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) - 1; fclose(f); return buf; } ``` The shim script must be evaluated before the main library. In both cases, after reading the script file, the previous `eval_str` function can run the code: ```c /* evaluate shim.min.js */ { size_t sz; const jerry_char_t *script = (jerry_char_t *)read_file("shim.min.js", &sz); jerry_value_t result = eval_str(script, sz); if(jerry_value_is_error(result)) { // failed to parse / execute fprintf(stderr, "Failed to evaluate shim.min.js"); return 1; } jerry_value_free(result); } /* evaluate xlsx.full.min.js */ { size_t sz; const jerry_char_t *script = (jerry_char_t *)read_file("xlsx.full.min.js", &sz); jerry_value_t result = eval_str(script, sz); if(jerry_value_is_error(result)) { // failed to parse / execute fprintf(stderr, "Failed to evaluate xlsx.full.min.js"); return 1; } jerry_value_free(result); } ``` ### Reading Files Binary file data can be passed from C to JerryScript with `ArrayBuffer` objects. #### Creating ArrayBuffers `jerry_arraybuffer` will generate an `ArrayBuffer` object of specified length. After creating the array, `jerry_arraybuffer_write` will copy data. The following `load_file` function reads a file from the filesystem and loads the data into an `ArrayBuffer`: ```c static jerry_value_t load_file(const char *filename) { /* read file */ size_t len; char *buf = read_file(filename, &len); if(!buf) return 0; /* create ArrayBuffer */ jerry_value_t out = jerry_arraybuffer(len); /* copy file data into ArrayBuffer */ jerry_arraybuffer_write(out, 0, (const uint8_t*)buf, len); return out; } ``` The process may fail. The result should be tested with `jerry_value_is_error`: ```c jerry_value_t ab = load_file("pres.xlsx"); if(!ab || jerry_value_is_error(ab)) { // failed to create ArrayBuffer fprintf(stderr, "Failed to read pres.xlsx"); return 1; } ``` #### Creating Global Variable The `ArrayBuffer` object must be bound to a variable before it can be used. :::note pass The goal is to bind the `ArrayBuffer` to the `buf` property in global scope. ::: 1) Get the global `this` variable (using `jerry_current_realm`): ```c /* get the global variable */ jerry_value_t this = jerry_current_realm(); if(jerry_value_is_error(this)) { // failed to get global object fprintf(stderr, "Failed to get global object"); return 1; } ``` 2) Create a JerryScript string (`"buf"`) for the property: ```c /* create a string "buf" for the property access */ jerry_value_t prop = jerry_string_sz("buf"); if(jerry_value_is_error(this)) { // failed to create "buf" fprintf(stderr, "Failed to create string"); return 1; } ``` 3) Assign the property using `jerry_object_set`: ```c /* set global["buf"] to the ArrayBuffer */ jerry_value_t set = jerry_object_set(this, prop, ab); if(jerry_value_is_error(set)) { // failed to set property fprintf(stderr, "Failed to assign ArrayBuffer"); return 1; } ``` #### Parsing Data :::note pass The goal is to run the equivalent of the following JavaScript code: ```js /* `buf` is the `ArrayBuffer` from the previous step */ var wb = XLSX.read(buf); ``` ::: The `ArrayBuffer` from the previous step is available in the `buf` variable. That `ArrayBuffer` can be passed to the SheetJS `read` method[^1], which will parse the raw data and return a SheetJS workbook object[^2]. `var wb = XLSX.read(buf)` can be stored in a byte array and evaluated directly: ```c /* run `var wb = XLSX.read(buf)` */ { const jerry_char_t code[] = "var wb = XLSX.read(buf);"; jerry_value_t result = eval_str(code, sizeof(code) - 1); if(jerry_value_is_error(result)) { fprintf(stderr, "Failed to parse file"); return 1; } jerry_value_free(result); } ``` #### Generating CSV :::note pass The goal is to run the equivalent of the following JavaScript code: ```js /* `wb` is the workbook from the previous step */ XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]]) ``` ::: A SheetJS workbook object can contain multiple sheet objects[^3]. The `Sheets` property is an object whose keys are sheet names and whose values are sheet objects. The `SheetNames` property is an array of worksheet names. The first sheet name can be found at `wb.SheetNames[0]`. The first sheet object can be found at `wb.Sheets[wb.SheetNames[0]]`. The SheetJS `sheet_to_csv` utility function[^4] accepts a sheet object and generates a JS string. Combining everything, `XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]])` generates a CSV string based on the first worksheet in the workbook `wb`: ```c const jerry_char_t code[] = "XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]])"; jerry_value_t csv = eval_str(code, sizeof(code) - 1); if(jerry_value_is_error(result)) { // CSV generation failed fprintf(stderr, "Failed to generate csv"); return 1; } ``` #### Pulling Strings JerryScript exposes encoding-aware methods to pull JS strings into C. The `JERRY_ENCODING_UTF8` encoding forces UTF8 interpretations. The `jerry_string_size` function returns the number of bytes required to store the string. After allocating memory, `jerry_string_to_buffer` will copy data. The following `pull_str` function uses `malloc`: ```js char *pull_str(jerry_value_t str, size_t *sz) { /* determine string size in bytes */ jerry_size_t str_sz = jerry_string_size(str, JERRY_ENCODING_UTF8); /* allocate memory */ jerry_char_t *buf = (jerry_char_t *)malloc(str_sz + 1); /* copy from JS string to C byte array */ jerry_string_to_buffer(str, JERRY_ENCODING_UTF8, buf, str_sz + 1); /* pass back size and return the pointer */ *sz = str_sz; return (char *)buf; } ``` This function can be used to pull the `csv` value from the previous section: ```c size_t sz; char *buf = pull_str(result, &sz); printf("%s\n", buf); ``` ## Complete Example The "Integration Example" covers a traditional integration in a C application, while the "CLI Test" demonstrates other concepts using the `jerry` CLI tool. ### Integration Example
Build Dependencies (click to show) The JerryScript build system requires `cmake`. Debian and WSL additionally require `python3` and `python-is-python3` packages.
1) Create a project folder: ```bash mkdir SheetJSJerry cd SheetJSJerry ``` 2) Clone the repository and build the library with required options: ```bash git clone --depth=1 https://github.com/jerryscript-project/jerryscript.git cd jerryscript python3 tools/build.py --error-messages=ON --logging=ON --mem-heap=8192 --cpointer-32bit=ON cd .. ``` 3) Download the SheetJS Standalone script, shim script and test file. Move all three files to the `SheetJSJerry` directory: {`\ curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js curl -LO https://sheetjs.com/pres.xlsx`} 4) Download [`sheetjs.jerry.c`](pathname:///jerryscript/sheetjs.jerry.c) into the same folder: ```bash curl -LO https://docs.sheetjs.com/jerryscript/sheetjs.jerry.c ``` 5) Build the sample application: ```bash gcc -o sheetjs.jerry -Ijerryscript/jerry-ext/include -Ijerryscript/jerry-math/include -Ijerryscript/jerry-core/include sheetjs.jerry.c -ljerry-core -ljerry-ext -ljerry-port -lm -Ljerryscript/build/lib -Wno-pointer-sign ``` 6) Run the test program: ```bash ./sheetjs.jerry pres.xlsx ``` If successful, the program will print contents of the first sheet as CSV rows. ### CLI Test :::note pass Due to limitations of the standalone binary, this demo will encode a test file as a Base64 string and directly add it to an amalgamated script. ::: 0) Build the library and command line tool with required options. :::info pass The "Integration Example" builds JerryScript. The CLI test must be run from the repo folder. ```bash cd jerryscript ``` ::: If the "Integration Example" was not tested, run the following commands: ```bash git clone --depth=1 https://github.com/jerryscript-project/jerryscript.git cd jerryscript python3 tools/build.py --error-messages=ON --logging=ON --mem-heap=8192 --cpointer-32bit=ON ``` 1) Download the SheetJS Standalone script, shim script and test file. Move all three files to the `jerryscript` cloned repo directory: {`\ curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js curl -LO https://sheetjs.com/pres.xlsx`} 2) Bundle the test file and create `payload.js`: ```bash node -e "fs.writeFileSync('payload.js', 'var payload = \"' + fs.readFileSync('pres.xlsx').toString('base64') + '\";')" ``` 3) Create support scripts: - `global.js` creates a `global` variable and defines a fake `console`: ```js title="global.js" var global = (function(){ return this; }).call(null); var console = { log: function(x) { print(x); } }; ``` - `jerry.js` will call `XLSX.read` and `XLSX.utils.sheet_to_csv`: ```js title="jerry.js" var wb = XLSX.read(payload, {type:'base64'}); console.log(XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]])); ``` 4) Create the amalgamation `xlsx.jerry.js`: ```bash cat global.js xlsx.full.min.js payload.js jerry.js > xlsx.jerry.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 `jerry` standalone binary: ```bash build/bin/jerry xlsx.jerry.js; echo $? ``` If successful, the contents of the test file will be displayed in CSV rows. The status code `0` will be printed after the rows. [^1]: See [`read` in "Reading Files"](/docs/api/parse-options) [^2]: See ["Workbook Object" in "SheetJS Data Model"](/docs/csf/book) [^3]: See ["Sheet Objects"](/docs/csf/sheet) [^4]: See [`sheet_to_csv` in "CSV and Text"](/docs/api/utilities/csv#delimiter-separated-output)