curl not overwriting header fields - perl

Question

I've encountering an issue where the endpoint server is returning a '417 Expectation Failed' error after 1024kb has been sent. I don't believe curl is rewriting the headers appropriately before the request is sent to the endpoint. I am using the -H flag and been reading over many different threads, to include the curl manpages, in an attempt to understand what I may be doing wrong.
I'm writing in Perl. Here is how I am setting my headers.
my $curlpath = "/usr/local/bin/curl";
my $xml = #-- yes, xml is really passed but i omitted it
push #curl_vars, "-H 'Content-Type: text/xml; Expect:'"; #-- header flag
push #curl_vars, "-v"; #-- verbose mode
push #curl_vars, "-d"; #-- data flag
push #curl_vars, $xml; #-- data
push #curl_vars, $endpoint;
eval
{
#-- command line execution
open (FILE, "-|") || exec $curlpath, #curl_vars;
$response = join '', <FILE>;
close (FILE);
};
Here is the trimmed curl response from the log.
[Fri Oct 10 16:04:36 2014] > Host: myhost.com\r
[Fri Oct 10 16:04:36 2014] > Accept: */*\r
[Fri Oct 10 16:04:36 2014] > 'Content-Type: text/xml; Expect:'\r
[Fri Oct 10 16:04:36 2014] > Content-Length: 1069\r
[Fri Oct 10 16:04:36 2014] > Content-Type: application/x-www-form-urlencoded\r
[Fri Oct 10 16:04:36 2014] > Expect: 100-continue\r
[Fri Oct 10 16:04:36 2014] > \r
[Fri Oct 10 16:04:36 2014] * HTTP 1.0, assume close after body
[Fri Oct 10 16:04:36 2014] < HTTP/1.0 417 Expectation Failed\r
[Fri Oct 10 16:04:36 2014] < Connection: close\r
[Fri Oct 10 16:04:36 2014] < Content-Length: 18\r
[Fri Oct 10 16:04:36 2014] < \r

Answer 1

You want to change one header and remove another one, so invoke curl with two -H uses:
-H 'Content-Type: text/xml' -H 'Expect:'
That is, each -H changes a single header so you need one -H for every header you want to modify.
Combined with the error ikegami pointed out, that means you'd need
push #curl_vars, '-H', 'Content-Type: text/xml';
push #curl_vars, '-H', 'Expect:';

Answer 2

When you say
curl -H 'Content-Type: text/xml; Expect:'
you call curl with two arguments.
-H
Content-Type: text/xml; Expect:
In your Perl code, however, you pass single argument.
-H 'Content-Type: text/xml; Expect:'
Perhaps you need
push #curl_vars, '-H', 'Content-Type: text/xml; Expect:';
There could be other problems.