docs.sheetjs.com/docz/static/jsc/sheetjs-jsc.c

#include <stdio.h>
#include <stdlib.h>
#include <JavaScriptCore/JavaScript.h>

/* simple wrapper to read the entire script file */
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(buf, 1, fsize, f);
  fclose(f);
  return buf;
}

#define JS_STR_TO_C \
  JSStringRef str = JSValueToStringCopy(ctx, result, NULL); \
  size_t sz = JSStringGetMaximumUTF8CStringSize(str); \
  char *buf = (char *)malloc(sz); \
  JSStringGetUTF8CString(str, buf, sz); \

#define DOIT(cmd) \
  JSStringRef script = JSStringCreateWithUTF8CString(cmd); \
  JSValueRef result = JSEvaluateScript(ctx, script, NULL, NULL, 0, NULL); \
  JSStringRelease(script);

int main(int argc, char **argv) {
  int res = 0;
  size_t sz = 0;
  char *file = NULL;

  /* initialize */
  JSGlobalContextRef ctx = JSGlobalContextCreate(NULL);
  /* JSC does not expose a standard "global" by default */
  { DOIT("var global = (function(){ return this; }).call(null);") }

  /* load library */
  {
    file = read_file("xlsx.full.min.js", &sz);
    DOIT(file);
    free(file);
  }

  /* get version string */
  {
    DOIT("XLSX.version")

    if(!JSValueIsString(ctx, result)) {
      printf("Could not get SheetJS version.\n");
      res = 1; goto cleanup;
    }

    JS_STR_TO_C

    printf("SheetJS library version %s\n", buf);
    free(buf);
    JSStringRelease(str);
  }

  /* read file */
  file = read_file(argv[1], &sz);
  {
    /* push data to JSC */
    JSValueRef u8 = JSObjectMakeTypedArrayWithBytesNoCopy(ctx, kJSTypedArrayTypeUint8Array, file, sz, NULL, NULL, NULL);

    /* assign to `global.buf` */
    JSObjectRef global = JSContextGetGlobalObject(ctx);
    JSStringRef key = JSStringCreateWithUTF8CString("buf");
    JSObjectSetProperty(ctx, global, key, u8, 0, NULL);
    JSStringRelease(key);
  }

  /* parse workbook and print CSV */
  {
    DOIT(
      "var wb = XLSX.read(global.buf);"
      "var ws = wb.Sheets[wb.SheetNames[0]];"
      "XLSX.utils.sheet_to_csv(ws)"
    )

    if(!JSValueIsString(ctx, result)) {
      printf("Could not generate CSV.\n");
      res = 2; goto cleanup;
    }

    JS_STR_TO_C

    printf("%s\n", buf);
    free(buf);
    JSStringRelease(str);
  }

  /* write file */
  {
    DOIT("XLSX.write(wb, {type:'buffer', bookType:'xlsb'});")

    /* pull Uint8Array data back to C */
    JSObjectRef u8 = JSValueToObject(ctx, result, NULL);
    size_t sz = JSObjectGetTypedArrayLength(ctx, u8, NULL);
    char *buf = (char *)JSObjectGetTypedArrayBytesPtr(ctx, u8, NULL);

    /* save file */
    FILE *f = fopen("sheetjsw.xlsb", "wb"); fwrite(buf, 1, sz, f); fclose(f);
  }

cleanup:
  // Release the JavaScript context
  JSGlobalContextRelease(ctx);
  if(file) free(file);

  return res;
}