Module http

Module http


The http module, specifically the http.client submodule, provides the functionality of an HTTP client with support for HTTPS and keepalive. It uses routines in the libcurl library.


Below is a list of all http functions.

Name Use Create an HTTP client instance
client_object:request() Perform an HTTP request
client_object:stat() Get a table with statistics[options])

Construct a new HTTP client instance.

  • options (table) – integer settings which are passed to libcurl.

The two possible options are max_connections and max_total_connections.

max_connections is the maximum number of entries in the cache. It affects libcurl CURLMOPT_MAXCONNECTS. The default is -1.

max_total_connections is the maximum number of active connections. It affects libcurl CURLMOPT_MAX_TOTAL_CONNECTIONS. It is ignored if the curl version is less than 7.30. The default is 0, which allows libcurl to scale according to easy handles count.

The default option values are usually good enough but in rare cases it might be good to set them. In that case here are two tips.

1. You may want to control the maximum number of sockets that a particular http client uses simultaneously. If a system passes many requests to distinct hosts, then libcurl cannot reuse sockets. In this case setting max_total_connections may be useful, since it causes curl to avoid creating too many sockets which would not be used anyway.

2. Do not set max_connections less than max_total_connections unless you are confident about your actions. When max_connections is less then max_total_connections, in some cases libcurl will not reuse sockets for requests that are going to the same host. If the limit is reached and a new request occurs, then libcurl will first create a new socket, send the request, wait for the first connection to be free, and close it, in order to avoid exceeding the max_connections cache size. In the worst case, libcurl will create a new socket for every request, even if all requests are going to the same host. See this Tarantool issue on github for details.

Return:a new HTTP client instance


tarantool> http_client = require('http.client').new({max_connections = 5})
object client_object
client_object:request(method, url, body, opts)

If http_client is an HTTP client instance, http_client:request() will perform an HTTP request and, if there is a successful connection, will return a table with connection information.

  • method (string) – HTTP method, for example ‘GET’ or ‘POST’ or ‘PUT’
  • url (string) – location, for example ‘
  • body (string) – optional initial message, for example ‘My text string!’
  • opts (table) –

    table of connection options, with any of these components:

    • timeout - number of seconds to wait for a curl API read request before timing out
    • ca_path - path to a directory holding one or more certificates to verify the peer with
    • ca_file - path to an SSL certificate file to verify the peer with
    • verify_host - set on/off verification of the certificate’s name (CN) against host. See also CURLOPT_SSL_VERIFYHOST
    • verify_peer - set on/off verification of the peer’s SSL certificate. See also CURLOPT_SSL_VERIFYPEER
    • ssl_key - path to a private key file for a TLS and SSL client certificate. See also CURLOPT_SSLKEY
    • ssl_cert - path to a SSL client certificate file. See also CURLOPT_SSLCERT
    • headers - table of HTTP headers
    • keepalive_idle - delay, in seconds, that the operating system will wait while the connection is idle before sending keepalive probes. See also CURLOPT_TCP_KEEPIDLE and the note below about keepalive_interval.
    • keepalive_interval - the interval, in seconds, that the operating system will wait between sending keepalive probes. See also CURLOPT_TCP_KEEPINTVL. If both keepalive_idle and keepalive_interval are set, then Tarantool will also set HTTP keepalive headers: Connection:Keep-Alive and Keep-Alive:timeout=<keepalive_idle>. Otherwise Tarantool will send Connection:close
    • low_speed_time - set the “low speed time” – the time that the transfer speed should be below the “low speed limit” for the library to consider it too slow and abort. See also CURLOPT_LOW_SPEED_TIME
    • low_speed_limit - set the “low speed limit” – the average transfer speed in bytes per second that the transfer should be below during “low speed time” seconds for the library to consider it to be too slow and abort. See also CURLOPT_LOW_SPEED_LIMIT
    • verbose - set on/off verbose mode
    • unix_socket - a socket name to use instead of an Internet address, for a local connection. The Tarantool server must be built with libcurl 7.40 or later. See the second example later in this section.
    • max_header_name_len - the maximal length of a header name. If a header name is bigger than this value, it is truncated to this length. The default value is ‘32’.

connection information, with all of these components:

  • status - HTTP response status
  • reason - HTTP response status text
  • headers - a Lua table with normalized HTTP headers
  • body - response body
  • proto - protocol version


The following “shortcuts” exist for requests:

  • http_client:get(url, options) - shortcut for http_client:request("GET", url, nil, opts)
  • http_client:post (url, body, options) - shortcut for http_client:request("POST", url, body, opts)
  • http_client:put(url, body, options) - shortcut for http_client:request("PUT", url, body, opts)
  • http_client:patch(url, body, options) - shortcut for http_client:request("PATCH", url, body, opts)
  • http_client:options(url, options) - shortcut for http_client:request("OPTIONS", url, nil, opts)
  • http_client:head(url, options) - shortcut for http_client:request("HEAD", url, nil, opts)
  • http_client:delete(url, options) - shortcut for http_client:request("DELETE", url, nil, opts)
  • http_client:trace(url, options) - shortcut for http_client:request("TRACE", url, nil, opts)
  • http_client:connect:(url, options) - shortcut for http_client:request("CONNECT", url, nil, opts)

Requests may be influenced by environment variables, for example users can set up an http proxy by setting HTTP_PROXY=proxy before initiating any requests. See the web page document Environment variables libcurl understands.


The http_client:stat() function returns a table with statistics:

  • active_requests - number of currently executing requests
  • sockets_added - total number of sockets added into an event loop
  • sockets_deleted - total number of sockets sockets from an event loop
  • total_requests - total number of requests
  • http_200_responses - total number of requests which have returned code HTTP 200
  • http_other_responses - total number of requests which have not returned code HTTP 200
  • failed_requests - total number of requests which have failed including system errors, curl errors, and HTTP errors

Example 1:

Connect to an HTTP server, look at the size of the response for a ‘GET’ request, and look at the statistics for the session.

tarantool> http_client = require('http.client').new()
tarantool> r = http_client:request('GET','')
tarantool> string.len(r.body)
- 21725
tarantool> http_client:stat()
- total_requests: 1
  sockets_deleted: 2
  failed_requests: 0
  active_requests: 0
  http_other_responses: 0
  http_200_responses: 1
  sockets_added: 2

Example 2:

Start two Tarantool instances on the same computer.

On the first Tarantool instance, listen on a Unix socket:


On the second Tarantool instance, send via http_client:

http_client = require('http.client').new({5})
http_client:put('http://localhost/','body',{unix_socket = '/tmp/unix_domain_socket.sock'})

Terminal #1 will show an error message: “Invalid MsgPack”. This is not useful but demonstrates the syntax and demonstrates that was sent was received.