How to use EnumProcesses in node-ffi - winapi

Question

I was trying to use EnumProcesses with node-ffi. I got code below:
import ffi from 'ffi'
export const psapi = ffi.Library('psapi', {
EnumProcesses: ['bool', ['ulong', 'ulong', 'uint16*']]
})
export class Win32ProcessManager {
public async getProcessList () {
let lpidProcess = ref.alloc('ulong*')
const cb = 1024
const lpcbNeeded = ref.alloc('uint16*')
const res = psapi.EnumProcesses(lpidProcess, cb, lpcbNeeded)
const ulongSize = (ref as any).sizeof.ulong
const totalBytesReturned = lpcbNeeded.readInt16LE()
const processCount = totalBytesReturned / ulongSize
console.log(`processCount: ${processCount}`)
// ??? How to get the value from the lpidProcess?
return lpidProcess
}
}
I tried with ref.get but I encountered errors:
let processId = ref.get(array, 0, ref.types.ulong)
console.log(processId)
const pointerSize = (ref as any).sizeof.pointer
console.log(pointerSize)
let processId2 = ref.get(array, (ref as any).sizeof.pointer, ref.types.ulong)
console.log(processId2)
Errors:
RangeError [ERR_BUFFER_OUT_OF_BOUNDS]: Attempt to write outside buffer bounds
Anyone knows how to use node-ffi read the array data from dll?

Answer 1

Thanks #DrakeWu-MSFT, I finally got my code works, here are how they looks finally:
import ffi from 'ffi';
import ref from 'ref';
import ArrayType from "ref-array";
export const psapi = ffi.Library('psapi', {
EnumProcesses: ['bool', ['ulong*', 'ulong', 'uint16*']],
});
export class Win32ProcessManager {
public getProcessIdList (): number[] {
const processIdLength = 1024;
const ulongSize = (ref as any).sizeof.ulong;
const cb = processIdLength * ulongSize;
let processIdArray = ArrayType('ulong', processIdLength);
let lpidProcess = ref.alloc(processIdArray);
const lpcbNeeded = ref.alloc('uint16*');
const res = psapi.EnumProcesses(lpidProcess, cb, lpcbNeeded);
if (res) {
const totalBytesReturned = lpcbNeeded.readInt16LE();
const processCount = totalBytesReturned / ulongSize;
const processArray = (lpidProcess as any).deref();
let resultProcessArray: number[] = [];
for (let i = 0; i < processCount; i++) {
resultProcessArray.push(processArray[i]);
}
return resultProcessArray;
} else {
console.error(`Get process list failed with result from EnumProcess: ${res}`);
return [];
}
}
}
I was struggled with getting array data from the pointer, and that was wrong, as #DrakeWu-MSFT said in the comment, because I didn't allocate enough spaces for the buffer, no data can be write into that. With ref-array and a pointer to the array, it works like a charm.