`picow_http_client` & `picow_http_verify` examples appear to truncate files longer than about 16,000 bytes

[andygpz11]

I used the picow_http_client and picow_http_verify examples as the starting point for application which needs to download a relatively large file from a webserver - specifically about 500 kB.

But, each time, the download falls short, it halts a few hundred bytes over 16,000 (and still under 16384).

I checked and confirmed that I can replicate the same truncation behaviour with unchanged example code from the repo (with the exception of changing file to be downloaded to point to a larger one, also on the RPI server) viz:

#define URL_REQUEST "/os_list_imagingutility_v3.json"

Which is 43k in size.

I see truncation and the tests failing using both http and https transfers and and also on pico_w and pico2_w boards.

Looking at a Wireshark trace (attached) I can see that LwIP is reporting TCP Window FULL around the time things to grind to a halt.

I've commented out the payload printing and just report the cumulative lengths but that's not made any difference.

So, I'm wondering if there's a bug in the http methods provided in LwIP.

[andygpz11]

[peterharperuk]

If you want to try a fix, add the following lines to the end of internal_recv_fn

static err_t internal_recv_fn(void *arg, struct altcp_pcb *conn, struct pbuf *p, err_t err) {
    assert(arg);
    EXAMPLE_HTTP_REQUEST_T *req = (EXAMPLE_HTTP_REQUEST_T*)arg;
    int rc = ERR_OK;
    if (req->recv_fn) {
        rc = req->recv_fn(req->callback_arg, conn, p, err);
    }
    altcp_recved(conn, p->tot_len);
    pbuf_free(p);
    return rc;
}

[andygpz11]

Ah, this looks like the same thing: How to configure HTTP client for files larger than 16KB

[andygpz11]

@peterharperuk I think the above fix is good, I've tested it with a 500k file using crc32 checking on the original file and the received data.

Would you like to raise a PR or shall I?

[peterharperuk]

If it's easy for you to raise a PR that would be great.