Mojo::UserAgent(3)

NAME
Mojo::UserAgent - Non-blocking I/O HTTP and WebSocket user agent

SYNOPSIS
  use Mojo::UserAgent;

  # Fine grained response handling (dies on connection errors)
  my $ua  = Mojo::UserAgent->new;
  my $res = $ua->get('mojolicious.org/perldoc')->result;
  if    ($res->is_success)  { say $res->body }
  elsif ($res->is_error)    { say $res->message }
  elsif ($res->code == 301) { say $res->headers->location }
  else                      { say 'Whatever...' }

  # Say hello to the Unicode snowman and include an Accept header
  say $ua->get('www.☃.net?hello=there' => {Accept => '*/*'})->result->body;

  # Extract data from HTML and XML resources with CSS selectors
  say $ua->get('www.perl.org')->result->dom->at('title')->text;

  # Scrape the latest headlines from a news site
  say $ua->get('blogs.perl.org')
    ->result->dom->find('h2 > a')->map('text')->join("\n");

  # IPv6 PUT request with Content-Type header and content
  my $tx = $ua->put('[::1]:3000' => {'Content-Type' => 'text/plain'} => 'Hi!');

  # Quick JSON API request with Basic authentication
  my $value = $ua->get('https://sri:t3st@example.com/test.json')->result->json;

  # JSON POST (application/json) with TLS certificate authentication
  my $tx = $ua->cert('tls.crt')->key('tls.key')
    ->post('https://example.com' => json => {top => 'secret'});

  # Search DuckDuckGo anonymously through Tor
  $ua->proxy->http('socks://127.0.0.1:9050');
  say $ua->get('api.3g2upl4pq6kufc4m.onion/?q=mojolicious&format=json')
    ->result->json('/Abstract');

  # GET request via UNIX domain socket "/tmp/myapp.sock" (percent encoded slash)
  say $ua->get('http+unix://%2Ftmp%2Fmyapp.sock/perldoc')->result->body;

  # Follow redirects to download Mojolicious from GitHub
  $ua->max_redirects(5)
    ->get('https://www.github.com/kraih/mojo/tarball/master')
    ->result->content->asset->move_to('/home/sri/mojo.tar.gz');

  # Form POST (application/x-www-form-urlencoded) with manual exception handling
  my $tx = $ua->post('https://metacpan.org/search' => form => {q => 'mojo'});
  if (my $res = $tx->success) { say $res->body }
  else {
    my $err = $tx->error;
    die "$err->{code} response: $err->{message}" if $err->{code};
    die "Connection error: $err->{message}";
  }

  # Non-blocking request
  $ua->get('mojolicious.org' => sub {
    my ($ua, $tx) = @_;
    say $tx->result->dom->at('title')->text;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  # Concurrent non-blocking requests (synchronized with promises)
  my $mojo = $ua->get_p('mojolicious.org');
  my $cpan = $ua->get_p('cpan.org');
  Mojo::Promise->all($mojo, $cpan)->then(sub {
    my ($mojo, $cpan) = @_;
    say $mojo->[0]->result->dom->at('title')->text;
    say $cpan->[0]->result->dom->at('title')->text;
  })->wait;

  # WebSocket connection sending and receiving JSON via UNIX domain socket
  $ua->websocket('ws+unix://%2Ftmp%2Fmyapp.sock/echo.json' => sub {
    my ($ua, $tx) = @_;
    say 'WebSocket handshake failed!' and return unless $tx->is_websocket;
    $tx->on(json => sub {
      my ($tx, $hash) = @_;
      say "WebSocket message via JSON: $hash->{msg}";
      $tx->finish;
    });
    $tx->send({json => {msg => 'Hello World!'}});
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

DESCRIPTION
Mojo::UserAgent is a full featured non-blocking I/O HTTP and WebSocket user agent, with IPv6, TLS, SNI, IDNA, HTTP/SOCKS5 proxy, UNIX domain socket, Comet (long polling), Promises/A+, keep-alive, connection pooling, timeout, cookie, multipart, gzip compression and multiple event loop support.

All connections will be reset automatically if a new process has been forked, this allows multiple processes to share the same Mojo::UserAgent object safely.

For better scalability (epoll, kqueue) and to provide non-blocking name resolution, SOCKS5 as well as TLS support, the optional modules EV (4.0+), Net::DNS::Native (0.15+), IO::Socket::Socks (0.64+) and IO::Socket::SSL (1.94+) will be used automatically if possible. Individual features can also be disabled with the "MOJO_NO_NNR", "MOJO_NO_SOCKS" and "MOJO_NO_TLS" environment variables.

See "USER AGENT" in Mojolicious::Guides::Cookbook for more.

EVENTS
Mojo::UserAgent inherits all events from Mojo::EventEmitter and can emit the following new ones.

  start
  $ua->on(start => sub {
    my ($ua, $tx) = @_;
    ...
  });

Emitted whenever a new transaction is about to start, this includes automatically prepared proxy "CONNECT" requests and followed redirects.

  $ua->on(start => sub {
    my ($ua, $tx) = @_;
    $tx->req->headers->header('X-Bender' => 'Bite my shiny metal ass!');
  });

ATTRIBUTES
Mojo::UserAgent implements the following attributes.

  ca
  my $ca = $ua->ca;
  $ua    = $ua->ca('/etc/tls/ca.crt');

Path to TLS certificate authority file used to verify the peer certificate, defaults to the value of the "MOJO_CA_FILE" environment variable. Also activates hostname verification.

  # Show certificate authorities for debugging
  IO::Socket::SSL::set_defaults(
    SSL_verify_callback => sub { say "Authority: $_[2]" and return $_[0] });

  cert
  my $cert = $ua->cert;
  $ua      = $ua->cert('/etc/tls/client.crt');

Path to TLS certificate file, defaults to the value of the "MOJO_CERT_FILE" environment variable.

  connect_timeout
  my $timeout = $ua->connect_timeout;
  $ua         = $ua->connect_timeout(5);

Maximum amount of time in seconds establishing a connection may take before getting canceled, defaults to the value of the "MOJO_CONNECT_TIMEOUT" environment variable or 10.

  cookie_jar
  my $cookie_jar = $ua->cookie_jar;
  $ua            = $ua->cookie_jar(Mojo::UserAgent::CookieJar->new);

Cookie jar to use for requests performed by this user agent, defaults to a Mojo::UserAgent::CookieJar object.

  # Ignore all cookies
  $ua->cookie_jar->ignore(sub { 1 });

  # Ignore cookies for public suffixes
  my $ps = IO::Socket::SSL::PublicSuffix->default;
  $ua->cookie_jar->ignore(sub {
    my $cookie = shift;
    return undef unless my $domain = $cookie->domain;
    return ($ps->public_suffix($domain))[0] eq '';
  });

  # Add custom cookie to the jar
  $ua->cookie_jar->add(
    Mojo::Cookie::Response->new(
      name   => 'foo',
      value  => 'bar',
      domain => 'mojolicious.org',
      path   => '/perldoc'
    )
  );

  inactivity_timeout
  my $timeout = $ua->inactivity_timeout;
  $ua         = $ua->inactivity_timeout(15);

Maximum amount of time in seconds a connection can be inactive before getting closed, defaults to the value of the "MOJO_INACTIVITY_TIMEOUT" environment variable or 20. Setting the value to 0 will allow connections to be inactive indefinitely.

  ioloop
  my $loop = $ua->ioloop;
  $ua      = $ua->ioloop(Mojo::IOLoop->new);

Event loop object to use for blocking I/O operations, defaults to a Mojo::IOLoop object.

  key
  my $key = $ua->key;
  $ua     = $ua->key('/etc/tls/client.crt');

Path to TLS key file, defaults to the value of the "MOJO_KEY_FILE" environment variable.

  local_address
  my $address = $ua->local_address;
  $ua         = $ua->local_address('127.0.0.1');

Local address to bind to.

  max_connections
  my $max = $ua->max_connections;
  $ua     = $ua->max_connections(5);

Maximum number of keep-alive connections that the user agent will retain before it starts closing the oldest ones, defaults to 5. Setting the value to 0 will prevent any connections from being kept alive.

  max_redirects
  my $max = $ua->max_redirects;
  $ua     = $ua->max_redirects(3);

Maximum number of redirects the user agent will follow before it fails, defaults to the value of the "MOJO_MAX_REDIRECTS" environment variable or 0.

  max_response_size
  my $max = $ua->max_response_size;
  $ua     = $ua->max_response_size(16777216);

Maximum response size in bytes, defaults to the value of "max_message_size" in Mojo::Message::Response. Setting the value to 0 will allow responses of indefinite size. Note that increasing this value can also drastically increase memory usage, should you for example attempt to parse an excessively large response body with the methods "dom" in Mojo::Message or "json" in Mojo::Message.

  proxy
  my $proxy = $ua->proxy;
  $ua       = $ua->proxy(Mojo::UserAgent::Proxy->new);

Proxy manager, defaults to a Mojo::UserAgent::Proxy object.

  # Detect proxy servers from environment
  $ua->proxy->detect;

  # Manually configure HTTP proxy (using CONNECT for HTTPS/WebSockets)
  $ua->proxy->http('http://127.0.0.1:8080')->https('http://127.0.0.1:8080');

  # Manually configure Tor (SOCKS5)
  $ua->proxy->http('socks://127.0.0.1:9050')->https('socks://127.0.0.1:9050');

  # Manually configure UNIX domain socket (using CONNECT for HTTPS/WebSockets)
  $ua->proxy->http('http+unix://%2Ftmp%2Fproxy.sock')
    ->https('http+unix://%2Ftmp%2Fproxy.sock');

  request_timeout
  my $timeout = $ua->request_timeout;
  $ua         = $ua->request_timeout(5);

Maximum amount of time in seconds establishing a connection, sending the request and receiving a whole response may take before getting canceled, defaults to the value of the "MOJO_REQUEST_TIMEOUT" environment variable or 0. Setting the value to 0 will allow the user agent to wait indefinitely. The timeout will reset for every followed redirect.

  # Total limit of 5 seconds, of which 3 seconds may be spent connecting
  $ua->max_redirects(0)->connect_timeout(3)->request_timeout(5);

  server
  my $server = $ua->server;
  $ua        = $ua->server(Mojo::UserAgent::Server->new);

Application server relative URLs will be processed with, defaults to a Mojo::UserAgent::Server object.

  # Mock web service
  $ua->server->app(Mojolicious->new);
  $ua->server->app->routes->get('/time' => sub {
    my $c = shift;
    $c->render(json => {now => time});
  });
  my $time = $ua->get('/time')->result->json->{now};

  # Change log level
  $ua->server->app->log->level('fatal');

  # Port currently used for processing relative URLs blocking
  say $ua->server->url->port;

  # Port currently used for processing relative URLs non-blocking
  say $ua->server->nb_url->port;

  transactor
  my $t = $ua->transactor;
  $ua   = $ua->transactor(Mojo::UserAgent::Transactor->new);

Transaction builder, defaults to a Mojo::UserAgent::Transactor object.

  # Change name of user agent
  $ua->transactor->name('MyUA 1.0');

METHODS
Mojo::UserAgent inherits all methods from Mojo::EventEmitter and implements the following new ones.

  build_tx
  my $tx = $ua->build_tx(GET => 'example.com');
  my $tx = $ua->build_tx(
    PUT => 'http://example.com' => {Accept => '*/*'} => 'Content!');
  my $tx = $ua->build_tx(
    PUT => 'http://example.com' => {Accept => '*/*'} => form => {a => 'b'});
  my $tx = $ua->build_tx(
    PUT => 'http://example.com' => {Accept => '*/*'} => json => {a => 'b'});

Generate Mojo::Transaction::HTTP object with "tx" in Mojo::UserAgent::Transactor.

  # Request with custom cookie
  my $tx = $ua->build_tx(GET => 'https://example.com/account');
  $tx->req->cookies({name => 'user', value => 'sri'});
  $tx = $ua->start($tx);

  # Deactivate gzip compression
  my $tx = $ua->build_tx(GET => 'example.com');
  $tx->req->headers->remove('Accept-Encoding');
  $tx = $ua->start($tx);

  # Interrupt response by raising an error
  my $tx = $ua->build_tx(GET => 'http://example.com');
  $tx->res->on(progress => sub {
    my $res = shift;
    return unless my $server = $res->headers->server;
    $res->error({message => 'Oh noes, it is IIS!'}) if $server =~ /IIS/;
  });
  $tx = $ua->start($tx);

  build_websocket_tx
  my $tx = $ua->build_websocket_tx('ws://example.com');
  my $tx = $ua->build_websocket_tx(
    'ws://example.com' => {DNT => 1} => ['v1.proto']);

Generate Mojo::Transaction::HTTP object with "websocket" in Mojo::UserAgent::Transactor.

  # Custom WebSocket handshake with cookie
  my $tx = $ua->build_websocket_tx('wss://example.com/echo');
  $tx->req->cookies({name => 'user', value => 'sri'});
  $ua->start($tx => sub {
    my ($ua, $tx) = @_;
    say 'WebSocket handshake failed!' and return unless $tx->is_websocket;
    $tx->on(message => sub {
      my ($tx, $msg) = @_;
      say "WebSocket message: $msg";
      $tx->finish;
    });
    $tx->send('Hi!');
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  delete
  my $tx = $ua->delete('example.com');
  my $tx = $ua->delete('http://example.com' => {Accept => '*/*'} => 'Content!');
  my $tx = $ua->delete(
    'http://example.com' => {Accept => '*/*'} => form => {a => 'b'});
  my $tx = $ua->delete(
    'http://example.com' => {Accept => '*/*'} => json => {a => 'b'});

Perform blocking "DELETE" request and return resulting Mojo::Transaction::HTTP object, takes the same arguments as "tx" in Mojo::UserAgent::Transactor (except for the "DELETE" method, which is implied). You can also append a callback to perform requests non-blocking.

  $ua->delete('http://example.com' => json => {a => 'b'} => sub {
    my ($ua, $tx) = @_;
    say $tx->result->body;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  delete_p
  my $promise = $ua->delete_p('http://example.com');

Same as "delete", but performs all requests non-blocking and returns a Mojo::Promise object instead of accepting a callback.

  $ua->delete_p('http://example.com' => json => {a => 'b'})->then(sub {
    my $tx = shift;
    say $tx->result->body;
  })->catch(sub {
    my $err = shift;
    warn "Connection error: $err";
  })->wait;

  get
  my $tx = $ua->get('example.com');
  my $tx = $ua->get('http://example.com' => {Accept => '*/*'} => 'Content!');
  my $tx = $ua->get(
    'http://example.com' => {Accept => '*/*'} => form => {a => 'b'});
  my $tx = $ua->get(
    'http://example.com' => {Accept => '*/*'} => json => {a => 'b'});

Perform blocking "GET" request and return resulting Mojo::Transaction::HTTP object, takes the same arguments as "tx" in Mojo::UserAgent::Transactor (except for the "GET" method, which is implied). You can also append a callback to perform requests non-blocking.

  $ua->get('http://example.com' => json => {a => 'b'} => sub {
    my ($ua, $tx) = @_;
    say $tx->result->body;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  get_p
  my $promise = $ua->get_p('http://example.com');

Same as "get", but performs all requests non-blocking and returns a Mojo::Promise object instead of accepting a callback.

  $ua->get_p('http://example.com' => json => {a => 'b'})->then(sub {
    my $tx = shift;
    say $tx->result->body;
  })->catch(sub {
    my $err = shift;
    warn "Connection error: $err";
  })->wait;

  head
  my $tx = $ua->head('example.com');
  my $tx = $ua->head('http://example.com' => {Accept => '*/*'} => 'Content!');
  my $tx = $ua->head(
    'http://example.com' => {Accept => '*/*'} => form => {a => 'b'});
  my $tx = $ua->head(
    'http://example.com' => {Accept => '*/*'} => json => {a => 'b'});

Perform blocking "HEAD" request and return resulting Mojo::Transaction::HTTP object, takes the same arguments as "tx" in Mojo::UserAgent::Transactor (except for the "HEAD" method, which is implied). You can also append a callback to perform requests non-blocking.

  $ua->head('http://example.com' => json => {a => 'b'} => sub {
    my ($ua, $tx) = @_;
    say $tx->result->body;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  head_p
  my $promise = $ua->head_p('http://example.com');

Same as "head", but performs all requests non-blocking and returns a Mojo::Promise object instead of accepting a callback.

  $ua->head_p('http://example.com' => json => {a => 'b'})->then(sub {
    my $tx = shift;
    say $tx->result->body;
  })->catch(sub {
    my $err = shift;
    warn "Connection error: $err";
  })->wait;

  options
  my $tx = $ua->options('example.com');
  my $tx = $ua->options('http://example.com' => {Accept => '*/*'} => 'Content!');
  my $tx = $ua->options(
    'http://example.com' => {Accept => '*/*'} => form => {a => 'b'});
  my $tx = $ua->options(
    'http://example.com' => {Accept => '*/*'} => json => {a => 'b'});

Perform blocking "OPTIONS" request and return resulting Mojo::Transaction::HTTP object, takes the same arguments as "tx" in Mojo::UserAgent::Transactor (except for the "OPTIONS" method, which is implied). You can also append a callback to perform requests non-blocking.

  $ua->options('http://example.com' => json => {a => 'b'} => sub {
    my ($ua, $tx) = @_;
    say $tx->result->body;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  options_p
  my $promise = $ua->options_p('http://example.com');

Same as "options", but performs all requests non-blocking and returns a Mojo::Promise object instead of accepting a callback.

  $ua->options_p('http://example.com' => json => {a => 'b'})->then(sub {
    my $tx = shift;
    say $tx->result->body;
  })->catch(sub {
    my $err = shift;
    warn "Connection error: $err";
  })->wait;

  patch
  my $tx = $ua->patch('example.com');
  my $tx = $ua->patch('http://example.com' => {Accept => '*/*'} => 'Content!');
  my $tx = $ua->patch(
    'http://example.com' => {Accept => '*/*'} => form => {a => 'b'});
  my $tx = $ua->patch(
    'http://example.com' => {Accept => '*/*'} => json => {a => 'b'});

Perform blocking "PATCH" request and return resulting Mojo::Transaction::HTTP object, takes the same arguments as "tx" in Mojo::UserAgent::Transactor (except for the "PATCH" method, which is implied). You can also append a callback to perform requests non-blocking.

  $ua->patch('http://example.com' => json => {a => 'b'} => sub {
    my ($ua, $tx) = @_;
    say $tx->result->body;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  patch_p
  my $promise = $ua->patch_p('http://example.com');

Same as "patch", but performs all requests non-blocking and returns a Mojo::Promise object instead of accepting a callback.

  $ua->patch_p('http://example.com' => json => {a => 'b'})->then(sub {
    my $tx = shift;
    say $tx->result->body;
  })->catch(sub {
    my $err = shift;
    warn "Connection error: $err";
  })->wait;

  post
  my $tx = $ua->post('example.com');
  my $tx = $ua->post('http://example.com' => {Accept => '*/*'} => 'Content!');
  my $tx = $ua->post(
    'http://example.com' => {Accept => '*/*'} => form => {a => 'b'});
  my $tx = $ua->post(
    'http://example.com' => {Accept => '*/*'} => json => {a => 'b'});

Perform blocking "POST" request and return resulting Mojo::Transaction::HTTP object, takes the same arguments as "tx" in Mojo::UserAgent::Transactor (except for the "POST" method, which is implied). You can also append a callback to perform requests non-blocking.

  $ua->post('http://example.com' => json => {a => 'b'} => sub {
    my ($ua, $tx) = @_;
    say $tx->result->body;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  post_p
  my $promise = $ua->post_p('http://example.com');

Same as "post", but performs all requests non-blocking and returns a Mojo::Promise object instead of accepting a callback.

  $ua->post_p('http://example.com' => json => {a => 'b'})->then(sub {
    my $tx = shift;
    say $tx->result->body;
  })->catch(sub {
    my $err = shift;
    warn "Connection error: $err";
  })->wait;

  put
  my $tx = $ua->put('example.com');
  my $tx = $ua->put('http://example.com' => {Accept => '*/*'} => 'Content!');
  my $tx = $ua->put(
    'http://example.com' => {Accept => '*/*'} => form => {a => 'b'});
  my $tx = $ua->put(
    'http://example.com' => {Accept => '*/*'} => json => {a => 'b'});

Perform blocking "PUT" request and return resulting Mojo::Transaction::HTTP object, takes the same arguments as "tx" in Mojo::UserAgent::Transactor (except for the "PUT" method, which is implied). You can also append a callback to perform requests non-blocking.

  $ua->put('http://example.com' => json => {a => 'b'} => sub {
    my ($ua, $tx) = @_;
    say $tx->result->body;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  put_p
  my $promise = $ua->put_p('http://example.com');

Same as "put", but performs all requests non-blocking and returns a Mojo::Promise object instead of accepting a callback.

  $ua->put_p('http://example.com' => json => {a => 'b'})->then(sub {
    my $tx = shift;
    say $tx->result->body;
  })->catch(sub {
    my $err = shift;
    warn "Connection error: $err";
  })->wait;

  start
  my $tx = $ua->start(Mojo::Transaction::HTTP->new);

Perform blocking request for a custom Mojo::Transaction::HTTP object, which can be prepared manually or with "build_tx". You can also append a callback to perform requests non-blocking.

  my $tx = $ua->build_tx(GET => 'http://example.com');
  $ua->start($tx => sub {
    my ($ua, $tx) = @_;
    say $tx->result->body;
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

  start_p
  my $promise = $ua->start_p(Mojo::Transaction::HTTP->new);

Same as "start", but performs all requests non-blocking and returns a Mojo::Promise object instead of accepting a callback.

  my $tx = $ua->build_tx(GET => 'http://example.com');
  $ua->start_p($tx)->then(sub {
    my $tx = shift;
    say $tx->result->body;
  })->catch(sub {
    my $err = shift;
    warn "Connection error: $err";
  })->wait;

  websocket
  $ua->websocket('ws://example.com' => sub {...});
  $ua->websocket(
    'ws://example.com' => {DNT => 1} => ['v1.proto'] => sub {...});

Open a non-blocking WebSocket connection with transparent handshake, takes the same arguments as "websocket" in Mojo::UserAgent::Transactor. The callback will receive either a Mojo::Transaction::WebSocket or Mojo::Transaction::HTTP object, depending on if the handshake was successful.

  $ua->websocket('wss://example.com/echo' => ['v1.proto'] => sub {
    my ($ua, $tx) = @_;
    say 'WebSocket handshake failed!' and return unless $tx->is_websocket;
    say 'Subprotocol negotiation failed!' and return unless $tx->protocol;
    $tx->on(finish => sub {
      my ($tx, $code, $reason) = @_;
      say "WebSocket closed with status $code.";
    });
    $tx->on(message => sub {
      my ($tx, $msg) = @_;
      say "WebSocket message: $msg";
      $tx->finish;
    });
    $tx->send('Hi!');
  });
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

You can activate "permessage-deflate" compression by setting the "Sec-WebSocket-Extensions" header, this can result in much better performance, but also increases memory usage by up to 300KiB per connection.

  $ua->websocket('ws://example.com/foo' => {
    'Sec-WebSocket-Extensions' => 'permessage-deflate'
  } => sub {...});

  websocket_p
  my $promise = $ua->websocket_p('ws://example.com');

Same as "websocket", but returns a Mojo::Promise object instead of accepting a callback.

  $ua->websocket_p('wss://example.com/echo')->then(sub {
    my $tx = shift;
    my $promise = Mojo::Promise->new;
    $tx->on(finish => sub { $promise->resolve });
    $tx->on(message => sub {
      my ($tx, $msg) = @_;
      say "WebSocket message: $msg";
      $tx->finish;
    });
    $tx->send('Hi!');
    return $promise;
  })->catch(sub {
    my $err = shift;
    warn "WebSocket error: $err";
  })->wait;

DEBUGGING
You can set the "MOJO_USERAGENT_DEBUG" environment variable to get some advanced diagnostics information printed to "STDERR".

  MOJO_USERAGENT_DEBUG=1

SEE ALSO
Mojolicious, Mojolicious::Guides, <http://mojolicious.org>.