Deno

Using unffi on Deno — permissions, pointer helpers, structs by value, async calls.

unffi on Deno wraps Deno.dlopen. Scalar calls use V8's fast API path and compile to near-native after warmup.

Permissions

Deno gates FFI access. Pass --allow-ffi (or a path to scope it):

deno run --allow-ffi main.ts
deno run --allow-ffi=./libmath.dylib main.ts

Without it, dlopen throws a descriptive error with a link to the Deno FFI docs.

Quick start

import { ,  } from 'unffi'

const  = await ('./libmath.dylib', {
  :  { : [., .], : . },
  : { : [.],        : . },
})

const sum  = ..(3, 4)     
const sum: number
const root = ..(2.0)      
const root: number

Pointer-sized integers

Use t.deno.usize / t.deno.isize for size_t / ssize_t. They always return bigint:

import { dlopen, t } from 'unffi'

const lib = await dlopen('./alloc.dylib', {
  malloc: { args: [t.deno.usize], returns: t.pointer },
})

const ptr = lib.symbols.malloc(256n)  // bigint | null

Zero-copy buffers

Pass a TypedArray where t.buffer is expected:

import { ,  } from 'unffi'

const  = await ('./fill.dylib', {
  : { : [., .], : . },
})

const  = new (1024)
..(, .)
// buf is populated in-place — no copy

For an offset pointer or long-lived pointer:

const p = t.deno.ptrOf(buf)              // Deno.PointerValue from TypedArray
t.deno.readCString(p)                    // decode NUL-terminated string
t.deno.readArrayBuffer(p, byteLen)       // read raw bytes

Structs by value

t.deno.struct(fields) takes an array of CType tokens and creates a by-value struct type. Pass/receive as a Uint8Array matching the struct's byte layout:

import { dlopen, t } from 'unffi'

// struct Point { float x; float y; }  →  8 bytes
const Point = t.deno.struct([t.f32, t.f32])

const lib = await dlopen('./geom.dylib', {
  length: { args: [Point], returns: t.f32 },
})

const point = new Uint8Array(8)
new DataView(point.buffer).setFloat32(0, 3.0, true)
new DataView(point.buffer).setFloat32(4, 4.0, true)

lib.symbols.length(point)  // → 5.0

Async / nonblocking calls

import { ,  } from 'unffi'

const  = await ('./codec.dylib', {
  : { : [., .], : ., : true },
})

const outLen = await ..(new (1024), 1024)       
const outLen: number

Callbacks

import { ,  } from 'unffi'

const  = await ('./sorter.dylib', {
  : {
    : [., ., .([., .], .)],
    : .,
  },
})

..(new (10), 10, (a, ) => {                                        
a: number
  return  - 
})

Deno callbacks must be invoked from the main thread. Cross-thread invocations require a native queue.