async_exception.nim

proc get*(client: MemcacheAsyncClient, key: string): Future[string] =
  let res = newFuture[string]()
  client.sendCommand(CommandOpcode.Get, key = key.toRawData()).callback = proc(future: Future[Response]) {.closure, gcsafe.} =
    let response = future.read()
    if response.header.status == ResponseStatus.KeyNotFound:
      res.fail(newException(KeyNotFoundError, "Key " & key & " is not found"))
    else:
      res.complete(response.value)
  res

proc getAsync*(client: MemcacheAsyncClient, key: string): Future[string] {. async .} =
  let response = await client.sendCommand(CommandOpcode.Get, key = key.toRawData())
  if response.header.status == ResponseStatus.KeyNotFound:
    raise newException(KeyNotFoundError, "Key " & key & " is not found")
  else:
    result = response.value

when isMainModule:
  proc test(): Future[void] {. async .} =
    const hello = "hello"
    const world = "world"
    var memcache = newMemcache()
    await memcache.connect(host = "127.0.0.1", port = 11211.Port)
    assert(await(memcache.add(hello, world)) == Added, "Key shouldn't exist before")
    try: # works fine
      let value = await memcache.get("unknown")
      assert false
    except KeyNotFoundError:
      assert true
    try: # fail with error
      let value = await memcache.getAsync("unknown")
      assert false
    except KeyNotFoundError:
      assert true
    echo "All tests passed"
  waitFor test()

error

raceback (most recent call last)
memcacheasync.nim(157)   memcacheasync
asyncdispatch.nim(1545)  waitFor
asyncdispatch.nim(983)   poll
asyncdispatch.nim(1091)  cb
asyncdispatch.nim(186)   complete
asyncdispatch.nim(1199)  cb
asyncnet.nim(256)        recvIter
asyncdispatch.nim(186)   complete
asyncdispatch.nim(1204)  cb
asyncdispatch.nim(224)   callback=
asyncdispatch.nim(1199)  cb
memcacheasync.nim(72)    waitForResponseIter
asyncdispatch.nim(186)   complete
asyncdispatch.nim(1199)  cb
memcacheasync.nim(82)    sendCommandIter
asyncdispatch.nim(186)   complete
asyncdispatch.nim(1211)  cb
SIGSEGV: Illegal storage access. (Attempt to read from nil?)
Error: execution of an external program failed