Question

I’ve got a perl script backing up our TeamCity server via the REST API as follows:

use strict;
use LWP::UserAgent;
use HTTP::Request::Common qw{ POST GET }

# ... code ommitted for brevity ... #

my $url = 'http://teamcity:8080/httpAuth/app/rest/server/backup';
my $req = POST( $url . '?includeConfigs=true&includeDatabase=true&includeBuildLogs=true&fileName=' . $filename);   
$req->authorization_basic($username, $password);
my $resp = $ua->request($req);    

I tried posting the content more in line with the documentation for HTTP:Request, but for some reason it fails, complaining that I haven’t specified a file name:

# This fails
my $req= POST( $url, [ 'includeConfigs'   => 'true',
                            'includeDatabase'  => 'true',
                            'includeBuildLogs' => 'true',
                            'fileName'         => $filename, 
                          ] ); 

Yet, when I look at the backend REST log for TeamCity, the full request seems to have made it intact, and is identical to the one that passes above.

Log of successful command:

[2012-12-13 15:02:38,574]  DEBUG [www-perl/5.805 ] - rver.server.rest.APIController - REST API request received: POST '/httpAuth/app/rest/server/backup?includeConfigs=true&includeDatabase=true&includeBuildLogs=true&fileName=foo', from client 10.126.31.219, authenticated as jsmith 

Log of failed command:

[2012-12-13 14:57:00,649]  DEBUG [www-perl/5.805 ] - rver.server.rest.APIController - REST API request received: POST '/httpAuth/app/rest/server/backup?includeConfigs=true&includeDatabase=true&includeBuildLogs=true&fileName=foo', from client 10.126.31.219, authenticated as jsmith

Is there any other hidden difference between the two methods of making a POST request that could be causing the failure?

UPDATE: Here is the result of each request when printed via Data::Dumper

Successful POST:

$VAR1 = bless( {
             '_content' => '',
             '_uri' => bless( do{\(my $o = 'http://teamcity:8080/httpAuth/app/rest/server/backup?includeConfigs=true&includeDatabase=true&includeBuildLogs=true&fileName=foo')}, 'URI::http' ),
             '_headers' => bless( {
                                    'content-type' => 'application/x-www-form-urlencoded',
                                    'content-length' => 0,
                                    'authorization' => 'Basic c3lzQnVpbGRTeXN0ZW1JOnBhaWQuZmFpdGg='
                                  }, 'HTTP::Headers' ),
             '_method' => 'POST'
           }, 'HTTP::Request' );

Unsuccessful POST:

$VAR1 = bless( {
             '_content' => 'includeConfigs=true&includeDatabase=true&includeBuildLogs=true&fileName=foo',
             '_uri' => bless( do{\(my $o = 'http://teamcity:8080/httpAuth/app/rest/server/backup')}, 'URI::http' ),
             '_headers' => bless( {
                                    'content-type' => 'application/x-www-form-urlencoded',
                                    'content-length' => 75,
                                    'authorization' => 'Basic c3lzQnVpbGRTeXN0ZW1JOnBhaWQuZmFpdGg='
                                  }, 'HTTP::Headers' ),
             '_method' => 'POST'
           }, 'HTTP::Request' );

Answer 1

I think your server-side script can only handle GET parameters encoded in the URL, not POST data transmitted via standard intput. Note that there are several different methods described by HTTP, these are GET, POST, HEAD, DELETE etc. And then there are two ways of passing data to an application on the server. Most often one of those ways is also called GET parameters and the other one is called POST data because the GET parameters are usually used with the HTTP GET method and POST data is usually used for the HTTP POST method. However, they don’t have to. And I think you’re mixing up the HTTP POST method with GET parameters in the successful case and with POST data in the unsuccessful case.

GET parameters are passed via the URL by, most often by appending ? to the URL followed by the actual key/value pais. Those are available via certain environment varialbes to the script running on the server. It’s up to the script to split the variables at the &, split key/value pairs on = and undo the escaping.

For POST data the environment variable CONTENT_LENGTH tells the script how many bytes to read from its standard input. The actual key/value pairs are transmitted via a different encoding, usually as multipart encoded content. Yes, POST HTTP requests (mostly from HTML <form>s) can also be sent URL-encoded like GET parameters, but there’s a length limit imposed by the HTTP standard on the URLs including all parameters. Hence the method of transferring the data via standard input, and not via the URL.

Now it looks like your server-side script can evaluate URL-encoded parameters (aka. GET parameters) parameters but not data posted to it via standard input. Even though you use the POST HTTP method/verb you don’t actually transmit the values as POST data via standard input in your successful case. You could simply swap POST(...) for GET(...) in that case and it should still work.

In your unsuccessful case you use the POST HTTP method and the POST data way of transmitting the values.

My verbiage here may be wrong in cases, but the fundamentals should still be OK.