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The libhttpserver reference manual

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Tl;dr

libhttpserver is a C++ library for building high performance RESTful web servers. libhttpserver is built upon libmicrohttpd to provide a simple API for developers to create HTTP services in C++.

Features:

Table of Contents

Community

Appendices

Introduction

libhttpserver is meant to constitute an easy system to build HTTP servers with REST fashion. libhttpserver is based on libmicrohttpd and, like this, it is a daemon library (parts of this documentation are, in fact, matching those of the wrapped library). The mission of this library is to support all possible HTTP features directly and with a simple semantic allowing then the user to concentrate only on his application and not on HTTP request handling details.

The library is supposed to work transparently for the client Implementing the business logic and using the library itself to realize an interface. If the user wants it must be able to change every behavior of the library itself through the registration of callbacks.

libhttpserver is able to decode certain body formats and automatically format them in object oriented fashion. This is true for query arguments and for POST and PUT requests bodies if application/x-www-form-urlencoded or multipart/form-data header are passed.

All functions are guaranteed to be completely reentrant and thread-safe (unless differently specified). Additionally, clients can specify resource limits on the overall number of connections, number of connections per IP address and memory used per connection to avoid resource exhaustion.

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Requirements

libhttpserver can be used without any dependencies aside from libmicrohttpd.

The minimum versions required are:

Additionally, for MinGW on windows you will need:

For versions before 0.18.0, on MinGW, you will need:

Furthermore, the testcases use libcurl but you don't need it to compile the library.

Please refer to the readme file for your particular distribution if there is one for important notes.

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Building

libhttpserver uses the standard system where the usual build process involves running

./bootstrap
mkdir build
cd build
../configure
make
make install # (optionally to install on the system)

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Optional parameters to configure script

A complete list of parameters can be obtained running 'configure --help'. Here are listed the libhttpserver specific options (the canonical configure options are also supported).

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Getting Started

The most basic example of creating a server and handling a requests for the path /hello:

    #include <httpserver.hpp>

    using namespace httpserver;

    class hello_world_resource : public http_resource {
    public:
        std::shared_ptr<http_response> render(const http_request&) {
            return std::shared_ptr<http_response>(new string_response("Hello, World!"));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);

        hello_world_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);
        
        return 0;
    }

To test the above example, you could run the following command from a terminal:

curl -XGET -v http://localhost:8080/hello

You can also check this example on github.

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Structures and classes type definition

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Create and work with a webserver

As you can see from the example above, creating a webserver with standard configuration is quite simple:

    webserver ws = create_webserver(8080);

The create_webserver class is a supporting builder class that eases the building of a webserver through chained syntax.

Basic Startup Options

In this section we will explore other basic options that you can use when configuring your server. More advanced options (custom callbacks, https support, etc...) will be discussed separately.

Threading Models

Custom defaulted error messages

libhttpserver allows to override internal error retrieving functions to provide custom messages to the HTTP client. There are only 3 cases in which implementing logic (an http_resource) cannot be invoked: (1) a not found resource, where the library is not being able to match the URL requested by the client to any implementing http_resource object; (2) a not allowed method, when the HTTP client is requesting a method explicitly marked as not allowed (more info here) by the implementation; (3) an exception being thrown. In all these 3 cases libhttpserver would provide a standard HTTP response to the client with the correct error code; respectively a 404, a 405 and a 500. The library allows its user to specify custom callbacks that will be called to replace the default behavior.

Example of custom errors:

      #include <httpserver.hpp>

      using namespace httpserver;

      std::shared_ptr<http_response> not_found_custom(const http_request& req) {
          return std::shared_ptr<string_response>(new string_response("Not found custom", 404, "text/plain"));
      }

      std::shared_ptr<http_response> not_allowed_custom(const http_request& req) {
          return std::shared_ptr<string_response>(new string_response("Not allowed custom", 405, "text/plain"));
      }

      class hello_world_resource : public http_resource {
      public:
          std::shared_ptr<http_response> render(const http_request&) {
              return std::shared_ptr<http_response>(new string_response("Hello, World!"));
          }
      };

      int main(int argc, char** argv) {
          webserver ws = create_webserver(8080)
              .not_found_resource(not_found_custom)
              .method_not_allowed_resource(not_allowed_custom);

          hello_world_resource hwr;
          hwr.disallow_all();
          hwr.set_allowing("GET", true);
          ws.register_resource("/hello", &hwr);
          ws.start(true);

          return 0;
      }

To test the above example, you can run the following command from a terminal:

curl -XGET -v http://localhost:8080/hello

If you try to run either of the two following commands, you'll see your custom errors:

You can also check this example on github.

Custom logging callbacks

Example of custom logging callback

    #include <httpserver.hpp>
    #include <iostream>

    using namespace httpserver;

    void custom_access_log(const std::string& url) {
        std::cout << "ACCESSING: " << url << std::endl;
    }

    class hello_world_resource : public http_resource {
    public:
        std::shared_ptr<http_response> render(const http_request&) {
            return std::shared_ptr<http_response>(new string_response("Hello, World!"));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080)
            .log_access(custom_access_log);

        hello_world_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you can run the following command from a terminal:

curl -XGET -v http://localhost:8080/hello

You'll notice how, on the terminal runing your server, the logs will now be printed in output for each request received.

You can also check this example on github.

TLS/HTTPS

Minimal example using HTTPS

    #include <httpserver.hpp>

    using namespace httpserver;

    class hello_world_resource : public http_resource {
    public:
        std::shared_ptr<http_response> render(const http_request&) {
            return std::shared_ptr<http_response>(new string_response("Hello, World!"));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080)
            .use_ssl()
            .https_mem_key("key.pem")
            .https_mem_cert("cert.pem");

        hello_world_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you can run the following command from a terminal:

curl -XGET -v -k 'https://localhost:8080/hello'

You can also check this example on github.

IP Blacklisting/Whitelisting

libhttpserver supports IP blacklisting and whitelisting as an internal feature. This section explains the startup options related with IP blacklisting/whitelisting. See the specific section to read more about the topic.

Authentication Parameters

Examples of chaining syntax to create a webserver

    webserver ws = create_webserver(8080)
        .no_ssl()
        .no_ipv6()
        .no_debug()
        .no_pedantic()
        .no_basic_auth()
        .no_digest_auth()
        .no_comet()
        .no_regex_checking()
        .no_ban_system()
        .no_post_process();


    webserver ws = create_webserver(8080)
        .use_ssl()
        .https_mem_key("key.pem")
        .https_mem_cert("cert.pem");

Starting and stopping a webserver

Once a webserver is created, you can manage its execution through the following methods on the webserver class:

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The Resource Object

The http_resource class represents a logical collection of HTTP methods that will be associated to a URL when registered on the webserver. The class is designed for extension and it is where most of your code should ideally live. When the webserver matches a request against a resource (see: resource registration), the method correspondent to the one in the request (GET, POST, etc..) (see below) is called on the resource.

Given this, the http_resource class contains the following extensible methods (also called handlers or render methods):

Example of implementation of render methods

    #include <httpserver.hpp>

    using namespace httpserver;

    class hello_world_resource : public http_resource {
    public:
        std::shared_ptr<http_response> render_GET(const http_request&) {
            return std::shared_ptr<http_response>(new string_response("GET: Hello, World!"));
        }

        std::shared_ptr<http_response> render(const http_request&) {
            return std::shared_ptr<http_response>(new string_response("OTHER: Hello, World!"));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);

        hello_world_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you can run the following commands from a terminal:

You can also check this example on github.

Allowing and disallowing methods on a resource

By default, all methods an a resource are allowed, meaning that an HTTP request with that method will be invoked. It is possible to mark methods as not allowed on a resource. When a method not allowed is requested on a resource, the default method_not_allowed method is invoked - the default can be overriden as explain in the section Custom defaulted error messages. The base http_resource class has a set of methods that can be used to allow and disallow HTTP methods.

Example of methods allowed/disallowed

      #include <httpserver.hpp>

      using namespace httpserver;

      class hello_world_resource : public http_resource {
      public:
          std::shared_ptr<http_response> render(const http_request&) {
              return std::shared_ptr<http_response>(new string_response("Hello, World!"));
          }
      };

      int main(int argc, char** argv) {
          webserver ws = create_webserver(8080);

          hello_world_resource hwr;
          hwr.disallow_all();
          hwr.set_allowing("GET", true);
          ws.register_resource("/hello", &hwr);
          ws.start(true);

          return 0;
      }

To test the above example, you can run the following command from a terminal:

curl -XGET -v http://localhost:8080/hello

If you try to run the following command, you'll see a method_not_allowed error:

You can also check this example on github.

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Registering resources

Once you have created your resource and extended its methods, you'll have to register the resource on the webserver. Registering a resource will associate it with an endpoint and allows the webserver to route it. The webserver class offers a method to register a resource:

Specifying endpoints

There are essentially four ways to specify an endpoint string:

      #include <httpserver.hpp>

      using namespace httpserver;

      class hello_world_resource : public http_resource {
      public:
          std::shared_ptr<http_response> render(const http_request&) {
              return std::shared_ptr<http_response>(new string_response("Hello, World!"));
          }
      };

      class handling_multiple_resource : public http_resource {
      public:
          std::shared_ptr<http_response> render(const http_request& req) {
              return std::shared_ptr<http_response>(new string_response("Your URL: " + req.get_path()));
          }
      };

      class url_args_resource : public http_resource {
      public:
          std::shared_ptr<http_response> render(const http_request& req) {
              std::string arg1(req.get_arg("arg1"));
              std::string arg2(req.get_arg("arg2"));
              return std::shared_ptr<http_response>(new string_response("ARGS: " + arg1 + " and " + arg2));
          }
      };

      int main(int argc, char** argv) {
          webserver ws = create_webserver(8080);

          hello_world_resource hwr;
          ws.register_resource("/hello", &hwr);

          handling_multiple_resource hmr;
          ws.register_resource("/family", &hmr, true);
          ws.register_resource("/with_regex_[0-9]+", &hmr);

          url_args_resource uar;
          ws.register_resource("/url/with/{arg1}/and/{arg2}", &uar);
          ws.register_resource("/url/with/parametric/args/{arg1|[0-9]+}/and/{arg2|[A-Z]+}", &uar);

          ws.start(true);

          return 0;
      }

To test the above example, you can run the following commands from a terminal:

Conversely, you can observe how these URL will not be matched (al the following will give you a not found message):

You can also check this example on github.

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Parsing requests

As seen in the documentation of http_resource, every extensible method takes in input a http_request object. The webserver takes the responsibility to extract the data from the HTTP request on the network and does all the heavy lifting to build the instance of http_request.

The http_request class has a set of methods you will have access to when implementing your handlers:

Details on the http::file_info structure.

Details on the http_arg_value structure.

Example of handler reading arguments from a request

    #include <httpserver.hpp>

    using namespace httpserver;

    class hello_world_resource : public http_resource {
    public:
        std::shared_ptr<http_response> render(const http_request& req) {
            return std::shared_ptr<http_response>(new string_response("Hello: " + std::string(req.get_arg("name"))));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);

        hello_world_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you can run the following command from a terminal:

curl -XGET -v "http://localhost:8080/hello?name=John"

You will receive the message Hello: John in reply. Given that the body post processing is enabled, you can also run curl -d "name=John" -X POST http://localhost:8080/hello to obtain the same result.

You can also check this example on github.

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Building responses to requests

As seen in the documentation of http_resource, every extensible method returns in output a http_response object. The webserver takes the responsibility to convert the http_response object you create into a response on the network.

There are 5 types of response that you can create - we will describe them here through their constructors:

Setting additional properties of the response

The http_response class offers an additional set of methods to "decorate" your responses. This set of methods is:

Example of response setting headers

    #include <httpserver.hpp>

    using namespace httpserver;

    class hello_world_resource : public http_resource {
    public:
        std::shared_ptr<http_response> render(const http_request&) {
            std::shared_ptr<http_response> response = std::shared_ptr<http_response>(new string_response("Hello, World!"));
            response->with_header("MyHeader", "MyValue");
            return response;
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);

        hello_world_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you could run the following command from a terminal:

curl -XGET -v "http://localhost:8080/hello"

You will receive the message custom header in reply.

You can also check this example on github.

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IP Blacklisting and Whitelisting

libhttpserver provides natively a system to blacklist and whitelist IP addresses. To enable/disable the system, it is possible to use the ban_system and no_ban_system methods on the create_webserver class. In the same way, you can specify what you want to be your "default behavior" (allow by default or disallow by default) by using the default_policy method (see here).

The system supports both IPV4 and IPV6 and manages them transparently. The only requirement is for ipv6 to be enabled on your server - you'll have to enable this by using the use_ipv6 method on create_webserver.

You can explicitly ban or allow an IP address using the following methods on the webserver class:

IP String Format

The IP string format can represent both IPV4 and IPV6. Addresses will be normalized by the webserver to operate in the same sapce. Any valid IPV4 or IPV6 textual representation works. It is also possible to specify ranges of IPs. To do so, omit the octect you want to express as a range and specify a '*' in its place. Examples of valid IPs include:

Example of IP Whitelisting/Blacklisting

    #include <httpserver.hpp>

    using namespace httpserver;

    class hello_world_resource : public http_resource {
    public:
        std::shared_ptr<http_response> render(const http_request&) {
            return std::shared_ptr<http_response>(new string_response("Hello, World!"));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080)
            .default_policy(http::http_utils::REJECT);

        ws.allow_ip("127.0.0.1");

        hello_world_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you could run the following command from a terminal:

curl -XGET -v "http://localhost:8080/hello"

You can also check this example on github.

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Authentication

libhttpserver support three types of client authentication.

Basic authentication uses a simple authentication method based on BASE64 algorithm. Username and password are exchanged in clear between the client and the server, so this method must only be used for non-sensitive content or when the session is protected with https. When using basic authentication libhttpserver will have access to the clear password, possibly allowing to create a chained authentication toward an external authentication server. You can enable/disable support for Basic authentication through the basic_auth and no_basic_auth methods of the create_webserver class.

Digest authentication uses a one-way authentication method based on MD5 hash algorithm. Only the hash will transit over the network, hence protecting the user password. The nonce will prevent replay attacks. This method is appropriate for general use, especially when https is not used to encrypt the session. You can enable/disable support for Digest authentication through the digest_auth and no_digest_auth methods of the create_webserver class.

Client certificate authentication uses a X.509 certificate from the client. This is the strongest authentication mechanism but it requires the use of HTTPS. Client certificate authentication can be used simultaneously with Basic or Digest Authentication in order to provide a two levels authentication (like for instance separate machine and user authentication). You can enable/disable support for Certificate authentication through the use_ssl and no_ssl methods of the create_webserver class.

Using Basic Authentication

    #include <httpserver.hpp>

    using namespace httpserver;

    class user_pass_resource : public httpserver::http_resource {
    public:
        std::shared_ptr<http_response> render_GET(const http_request& req) {
            if (req.get_user() != "myuser" || req.get_pass() != "mypass") {
                return std::shared_ptr<basic_auth_fail_response>(new basic_auth_fail_response("FAIL", "test@example.com"));
            }
            return std::shared_ptr<string_response>(new string_response(req.get_user() + " " + req.get_pass(), 200, "text/plain"));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);

        user_pass_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you can run the following command from a terminal:

curl -XGET -v -u myuser:mypass "http://localhost:8080/hello"

You will receive back the user and password you passed in input. Try to pass the wrong credentials to see the failure.

You can also check this example on github.

Using Digest Authentication

    #include <httpserver.hpp>

    #define MY_OPAQUE "11733b200778ce33060f31c9af70a870ba96ddd4"

    using namespace httpserver;

    class digest_resource : public httpserver::http_resource {
    public:
        std::shared_ptr<http_response> render_GET(const http_request& req) {
            if (req.get_digested_user() == "") {
                return std::shared_ptr<digest_auth_fail_response>(new digest_auth_fail_response("FAIL", "test@example.com", MY_OPAQUE, true));
            }
            else {
                bool reload_nonce = false;
                if(!req.check_digest_auth("test@example.com", "mypass", 300, reload_nonce)) {
                    return std::shared_ptr<digest_auth_fail_response>(new digest_auth_fail_response("FAIL", "test@example.com", MY_OPAQUE, reload_nonce));
                }
            }
            return std::shared_ptr<string_response>(new string_response("SUCCESS", 200, "text/plain"));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);

        digest_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you can run the following command from a terminal:

curl -XGET -v --digest --user myuser:mypass localhost:8080/hello

You will receive a SUCCESS in response (observe the response message from the server in detail and you'll see the full interaction). Try to pass the wrong credentials or send a request without digest active to see the failure.

You can also check this example on github.

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HTTP Utils

libhttpserver provides a set of constants to help you develop your HTTP server. It would be redundant to list them here; so, please, consult the list directly here.

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Other Examples

Example of returning a response from a file

    #include <httpserver.hpp>

    using namespace httpserver;

    class file_response_resource : public http_resource {
    public:
        std::shared_ptr<http_response> render_GET(const http_request& req) {
            return std::shared_ptr<file_response>(new file_response("test_content", 200, "text/plain"));
        }
    };

    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);

        file_response_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);

        return 0;
    }

To test the above example, you can run the following command from a terminal:

curl -XGET -v localhost:8080/hello

You can also check this example on github.

Example of a deferred response through callback

    #include <httpserver.hpp>
    
    using namespace httpserver;
    
    static int counter = 0;
    
    ssize_t test_callback (std::shared_ptr<void> closure_data, char* buf, size_t max) {
        if (counter == 2) {
            return -1;
        }
        else {
            memset(buf, 0, max);
            strcat(buf, " test ");
            counter++;
            return std::string(buf).size();
        }
    }
    
    class deferred_resource : public http_resource {
        public:
            std::shared_ptr<http_response> render_GET(const http_request& req) {
                return std::shared_ptr<deferred_response<void> >(new deferred_response<void>(test_callback, nullptr, "cycle callback response"));
            }
    };
    
    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);
    
        deferred_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);
    
        return 0;
    }

To test the above example, you can run the following command from a terminal:

curl -XGET -v localhost:8080/hello

You can also check this example on github.

Example of a deferred response through callback (passing additional data along)

    #include <atomic>
    #include <httpserver.hpp>
    
    using namespace httpserver;
    
    std::atomic<int> counter;
    
    ssize_t test_callback (std::shared_ptr<std::atomic<int> > closure_data, char* buf, size_t max) {
        int reqid;
        if (closure_data == nullptr) {
            reqid = -1;
        } else {
            reqid = *closure_data;
        }
    
        // only first 5 connections can be established
        if (reqid >= 5) {
            return -1;
        } else {
            // respond corresponding request IDs to the clients
            std::string str = "";
            str += std::to_string(reqid) + " ";
            memset(buf, 0, max);
            std::copy(str.begin(), str.end(), buf);
    
            // keep sending reqid
            sleep(1);
    
            return (ssize_t)max;
        }
    }
    
    class deferred_resource : public http_resource {
        public:
            std::shared_ptr<http_response> render_GET(const http_request& req) {
                std::shared_ptr<std::atomic<int> > closure_data(new std::atomic<int>(counter++));
                return std::shared_ptr<deferred_response<std::atomic<int> > >(new deferred_response<std::atomic<int> >(test_callback, closure_data, "cycle callback response"));
            }
    };
    
    int main(int argc, char** argv) {
        webserver ws = create_webserver(8080);
    
        deferred_resource hwr;
        ws.register_resource("/hello", &hwr);
        ws.start(true);
    
        return 0;
    }

To test the above example, you can run the following command from a terminal:

curl -XGET -v localhost:8080/hello

You can also check this example on github.

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Copying

This manual is for libhttpserver, C++ library for creating an embedded Rest HTTP server (and more).

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.

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GNU Lesser General Public License

Version 2.1, February 1999

Copyright © 1991, 1999 Free Software Foundation, Inc. 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

This is the first released version of the Lesser GPL. It also counts as the successor of the GNU Library Public License, version 2, hence the version number 2.1.

Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public Licenses are intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users.

This license, the Lesser General Public License, applies to some specially designated software packages--typically libraries--of the Free Software Foundation and other authors who decide to use it. You can use it too, but we suggest you first think carefully about whether this license or the ordinary General Public License is the better strategy to use in any particular case, based on the explanations below.

When we speak of free software, we are referring to freedom of use, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish); that you receive source code or can get it if you want it; that you can change the software and use pieces of it in new free programs; and that you are informed that you can do these things.

To protect your rights, we need to make restrictions that forbid distributors to deny you these rights or to ask you to surrender these rights. These restrictions translate to certain responsibilities for you if you distribute copies of the library or if you modify it.

For example, if you distribute copies of the library, whether gratis or for a fee, you must give the recipients all the rights that we gave you. You must make sure that they, too, receive or can get the source code. If you link other code with the library, you must provide complete object files to the recipients, so that they can relink them with the library after making changes to the library and recompiling it. And you must show them these terms so they know their rights.

We protect your rights with a two-step method: (1) we copyright the library, and (2) we offer you this license, which gives you legal permission to copy, distribute and/or modify the library.

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TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

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13. The Free Software Foundation may publish revised and/or new versions of the Lesser General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number. If the Library specifies a version number of this License which applies to it and “any later version”, you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Library does not specify a license version number, you may choose any version ever published by the Free Software Foundation.

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END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Libraries

If you develop a new library, and you want it to be of the greatest possible use to the public, we recommend making it free software that everyone can redistribute and change. You can do so by permitting redistribution under these terms (or, alternatively, under the terms of the ordinary General Public License).

To apply these terms, attach the following notices to the library. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.

<one line to give the library's name and a brief idea of what it does.>
Copyright (C) <year>  <name of author>

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

Also add information on how to contact you by electronic and paper mail.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the library, if necessary. Here is a sample; alter the names:

Yoyodyne, Inc., hereby disclaims all copyright interest in the library `Frob' (a library for tweaking knobs) written by James Random Hacker.

<signature of Ty Coon>, 1 April 1990 Ty Coon, President of Vice

That's all there is to it!

Back to TOC

GNU Free Documentation License

Version 1.3, 3 November 2008

Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. <http://fsf.org/>

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other functional and useful document “free” in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

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2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

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If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements”.

6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See <http://www.gnu.org/copyleft/>.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

11. RELICENSING

“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

“Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

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Thanks

This library has been originally developed under the zencoders flags and this community has always supported me all along this work so I am happy to put the logo on this readme.

          When you see this tree, know that you've came across ZenCoders

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         format  lists:  ++:   conc   ++ "my  an   WHERE  for(   == myi         
       `sys:  myvalue(myvalue) sys.t   Console.W  try{    rais     using        
      connec  SELECT * FROM table mycnf acco desc and or selector::clas  at     
     openldap string  sys.   print "zenc der " { 'a':  `ls -l` >  appe &firs    
    import Tkinter    paste( $obh  &a or it myval  bro roll:  :: [] require a   
   case `` super. +y  <svg x="100">  expr    say " %rooms 1  --account fb- yy   
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 and    main (--) import loop $$ or  end onload  UNION WITH tab   timer 150 *2  
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cout << endl   public genera   #include "b ost   ::ac myna const cast<char*> mys
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          BNE            BLTZAL R1 1 LUI 001 NOOP MULTU           SLLV          
            MOV R1     ADD R1 R2  JUMP  10 1001 BEQ R1 R2 1      ANDI            
               1101  1010001100  111 001 01  1010 101100 1001  100              
                 110110 100   0  01 101 01100 100 100 1000100011                
                    11101001001  00   11  100   11  10100010                    
                        000101001001 10  1001   101000101                       
                             010010010010110101001010

For further information: visit our website https://zencoders.github.io

Author: Sebastiano Merlino

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