Look at connection.c:1032, which is the only place where this error is
generated:
if (connection->read_buffer_offset ==
connection->read_buffer_size)
{
if ((MHD_YES != try_grow_read_buffer (connection)) &&
(0 != (connection->daemon->options &
(MHD_USE_SELECT_INTERNALLY |
MHD_USE_THREAD_PER_CONNECTION))))
{
/* failed to grow the read buffer, and the
client which is supposed to handle the
received data in a *blocking* fashion
(in this mode) did not handle the data as
it was supposed to!
=> we would either have to do busy-waiting
(on the client, which would likely fail),
or if we do nothing, we would just timeout
on the connection (if a timeout is even
set!).
Solution: we kill the connection with an error */
transmit_error_response (connection,
MHD_HTTP_INTERNAL_SERVER_ERROR,
INTERNAL_ERROR);
The situation: you are called to handle upload data, but did not
(effectively, your callback failed to update *upload_data_size when
called). Additionally, the IO buffer is full. So your application
doesn't handle the data that is in the buffer, and we can't read more to
give your app a bigger chunk. That's deadly, as MHD shouldn't then go
into busy waiting, hence the 500 internal error.
You could specify a larger memory limit, but the better solution is to
properly handle the 'upload_data' *incrementally*. The
MHD_PostProcessor logic is an example for how to do this.
Happy hacking!
Christian
On 10/29/2015 03:20 PM, Ken Zangelin wrote:
On 29/10/15 14:13, Christian Grothoff wrote:
It limits the length of the URL and the headers, not the size of
uploaded POST data. -Christian
On 10/29/2015 12:08 PM, Ken Zangelin wrote:
Hi, I have a basic question regarding the
MHD_OPTION_CONNECTION_MEMORY_LIMIT option to MHD_start_daemon.
Will the size given to MHD_OPTION_CONNECTION_MEMORY_LIMIT limit the
maximum permitted size of any request?
Thank you,
/KZ
OK, in that case I have a follow-up question.
We recently started to play with this connection memory limit option
(MHD_OPTION_CONNECTION_MEMORY_LIMIT)
and we have seen that requests with larged payload stops working for low
memory limits.
To give some detail, changing MHD_OPTION_CONNECTION_MEMORY_LIMIT to 64k,
the max accepted size of payload seems to be 33509 bytes.
If a bigger payload is sent, then MHD responds with the following message:
HTTP/1.1 500 Internal Server Error
Content-Length: 132
Date: Thu, 29 Oct 2015 13:53:15 GMT
<?xml version="1.0"?>
<html>
<head>
<title>Internal server error</title>
</head>
<body>Some programmer needs to study the manual more
carefully.</body>
</html>
Our MHD_AccessHandlerCallback function is called twice with payload
(apart from the first call), and then
the MHD_OPTION_NOTIFY_COMPLETED callback is called and MHD responds by
itself.
With a bigger value for MHD_OPTION_CONNECTION_MEMORY_LIMIT this did not
happen.
The version of the MHD we use:
#define MHD_VERSION 0x00093300
So, we might be doing something the wrong way.
Please tell us what to do to be able to receive large payloads with a
"small" MHD_OPTION_CONNECTION_MEMORY_LIMIT.
Thank you again,
/KZ
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