early exit from httpclient.get

get.nim

import std/[asyncdispatch, asyncnet, sugar]
import myclient

proc showN(n: int, url: string) {.async.} =
  var client = newAsyncHttpClient()
  client.onRecv = () => client.contentProgress > n
  let response = await client.get(url)
  let body = response.body.await
  echo body.substr(0, n)

waitFor showN(200, "https://some-large-url/")

httpclient.patch

--- httpclient.nim	2022-08-04 13:52:29.194959085 -0500
+++ myclient.nim	2022-08-04 14:21:58.681593014 -0500
@@ -534,6 +534,7 @@
   ProgressChangedProc*[ReturnType] =
     proc (total, progress, speed: BiggestInt):
       ReturnType {.closure, gcsafe.}
+  OnRecvProc* = proc (): bool {.closure, gcsafe.}
 
   HttpClientBase*[SocketType] = ref object
     socket: SocketType
@@ -549,10 +550,11 @@
       onProgressChanged*: ProgressChangedProc[void]
     else:
       onProgressChanged*: ProgressChangedProc[Future[void]]
+    onRecv*: OnRecvProc
     when defined(ssl):
       sslContext: net.SslContext
     contentTotal: BiggestInt
-    contentProgress: BiggestInt
+    contentProgress*: BiggestInt
     oneSecondProgress: BiggestInt
     lastProgressReport: MonoTime
     when SocketType is AsyncSocket:
@@ -704,6 +706,9 @@
       await client.bodyStream.write(data)
 
     await reportProgress(client, data.len)
+    if not client.onRecv.isNil:
+      if client.onRecv():
+        return readLen
 
   return readLen
 
@@ -769,9 +774,10 @@
         if recvLen == 0:
           client.close()
           httpError("Got disconnected while trying to read body.")
-        if recvLen != length:
-          httpError("Received length doesn't match expected length. Wanted " &
-                    $length & " got: " & $recvLen)
+        # move errors like this into recvFull
+        #if recvLen != length:
+        #  httpError("Received length doesn't match expected length. Wanted " &
+        #            $length & " got: " & $recvLen)
     else:
       # (http://tools.ietf.org/html/rfc2616#section-4.4) NR.4 TODO