Add support for Transfer-Encoding: chunked (#16636)

* Add support for Transfer-Encoding: chunked

* Minor whitespace fixes

* Use recv instead of recvLineInto

* Undo changes to httpcore, inline changes

lib/pure/asynchttpserver.nim

@@ -142,6 +142,17 @@ proc parseProtocol(protocol: string): tuple[orig: string, major, minor: int] =
 proc sendStatus(client: AsyncSocket, status: string): Future[void] =
   client.send("HTTP/1.1 " & status & "\c\L\c\L")
 
+func hasChunkedEncoding(request: Request): bool = 
+  ## Searches for a chunked transfer encoding
+  const transferEncoding = "Transfer-Encoding"
+
+  if request.headers.hasKey(transferEncoding):
+    for encoding in seq[string](request.headers[transferEncoding]):
+      if "chunked" == encoding.strip:
+        # Returns true if it is both an HttpPost and has chunked encoding
+        return request.reqMethod == HttpPost
+  return false
+
 proc processRequest(
   server: AsyncHttpServer,
   req: FutureVar[Request],
@@ -261,6 +272,39 @@ proc processRequest(
       if request.body.len != contentLength:
         await request.respond(Http400, "Bad Request. Content-Length does not match actual.")
         return true
+  elif hasChunkedEncoding(request):
+    # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Transfer-Encoding
+    var sizeOrData = 0
+    var bytesToRead = 0
+    request.body = ""
+
+    while true:
+      lineFut.mget.setLen(0)
+      lineFut.clean()
+      
+      # The encoding format alternates between specifying a number of bytes to read
+      # and the data to be read, of the previously specified size
+      if sizeOrData mod 2 == 0:
+        # Expect a number of chars to read
+        await client.recvLineInto(lineFut, maxLength = maxLine)
+        try:
+          bytesToRead = lineFut.mget.parseHexInt
+        except ValueError:
+          # Malformed request
+          await request.respond(Http411, ("Invalid chunked transfer encoding - " &
+                                          "chunk data size must be hex encoded"))
+          return true
+      else:
+        if bytesToRead == 0:
+          # Done reading chunked data
+          break
+
+        # Read bytesToRead and add to body
+        # Note we add +2 because the line must be terminated by \r\n
+        let chunk = await client.recv(bytesToRead + 2)
+        request.body = request.body & chunk
+
+      inc sizeOrData
   elif request.reqMethod == HttpPost:
     await request.respond(Http411, "Content-Length required.")
     return true