The libhttpserver reference manual
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:
- HTTP 1.1 compatible request parser
- RESTful oriented interface
- Flexible handler API
- Cross-platform compatible
- Implementation is HTTP 1.1 compliant
- Multiple threading models
- Support for IPv6
- Support for SHOUTcast
- Support for incremental processing of POST data (optional)
- Support for basic and digest authentication (optional)
- Support for TLS (requires libgnutls, optional)
Table of Contents
- Introduction
- Requirements
- Building
- Getting Started
- Structures and classes type definition
- Create and work with a webserver
- The resource object
- Registering resources
- Parsing requests
- Building responses to requests
- IP Blacklisting and Whitelisting
- Authentication
- HTTP Utils
- Other Examples
Community
Appendices
- Copying statement
- GNU-LGPL: The GNU Lesser General Public License says how you can copy and share almost all of libhttpserver.
- GNU-FDL: The GNU Free Documentation License says how you can copy and share the documentation of libhttpserver.
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 format a 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.
Requirements
libhttpserver can be used without any dependencies aside from libmicrohttpd.
The minimum versions required are:
- g++ >= 5.5.0 or clang-3.6
- libmicrohttpd >= 0.9.64
- [Optionally]: for TLS (HTTPS) support, you'll need libgnutls.
- [Optionally]: to compile the code-reference, you'll need doxygen.
Additionally, for MinGW on windows you will need:
- libwinpthread (For MinGW-w64, if you use thread model posix then you have this)
For versions before 0.18.0, on MinGW, you will need:
- libgnurx >= 2.5.1
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.
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)
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).
- --enable-same-directory-build: enable to compile in the same directory. This is heavily discouraged. (def=no)
- --enable-debug: enable debug data generation. (def=no)
- --disable-doxygen-doc: don't generate any doxygen documentation. Doxygen is automatically invoked if present on the system. Automatically disabled otherwise.
- --enable-fastopen: enable use of TCP_FASTOPEN (def=yes)
- --enable-static: enable use static linking (def=yes)
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:
const 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.
Structures and classes type definition
- webserver: Represents the daemon listening on a socket for HTTP traffic.
- create_webserver: Builder class to support the creation of a webserver.
- http_resource: Represents the resource associated with a specific http endpoint.
- http_request: Represents the request received by the resource that process it.
- http_response: Represents the response sent by the server once the resource finished its work.
- string_response: A simple string response.
- file_response: A response getting content from a file.
- basic_auth_fail_response: A failure in basic authentication.
- digest_auth_fail_response: A failure in digest authentication.
- deferred_response: A response getting content from a callback.
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.
- .port(int port): The port at which the server will listen. This can also be passed to the consturctor of
create_webserver
. E.g.create_webserver(8080)
. - .max_connections(int max_conns): Maximum number of concurrent connections to accept. The default is
FD_SETSIZE - 4
(the maximum number of file descriptors supported byselect
minus four forstdin
,stdout
,stderr
and the server socket). In other words, the default is as large as possible. Note that if you set a low connection limit, you can easily get into trouble with browsers doing request pipelining. For example, if your connection limit is “1”, a browser may open a first connection to access your “index.html” file, keep it open but use a second connection to retrieve CSS files, images and the like. In fact, modern browsers are typically by default configured for up to 15 parallel connections to a single server. If this happens, the library will refuse to even accept the second connection until the first connection is closed — which does not happen until timeout. As a result, the browser will fail to render the page and seem to hang. If you expect your server to operate close to the connection limit, you should first consider using a lower timeout value and also possibly add a “Connection: close” header to your response to ensure that request pipelining is not used and connections are closed immediately after the request has completed. - .content_size_limit(size_t size_limit): Sets the maximum size of the content that a client can send over in a single block. The default is
-1 = unlimited
. - .connection_timeout(int timeout): Determines after how many seconds of inactivity a connection should be timed out automatically. The default timeout is
180 seconds
. - .memory_limit(int memory_limit): Maximum memory size per connection (followed by a
size_t
). The default is 32 kB (32*1024 bytes). Values above 128k are unlikely to result in much benefit, as half of the memory will be typically used for IO, and TCP buffers are unlikely to support window sizes above 64k on most systems. - .per_IP_connection_limit(int connection_limit): Limit on the number of (concurrent) connections made to the server from the same IP address. Can be used to prevent one IP from taking over all of the allowed connections. If the same IP tries to establish more than the specified number of connections, they will be immediately rejected. The default is
0
, which means no limit on the number of connections from the same IP address. - .bind_socket(int socket_fd): Listen socket to use. Pass a listen socket for the daemon to use (systemd-style). If this option is used, the daemon will not open its own listen socket(s). The argument passed must be of type "int" and refer to an existing socket that has been bound to a port and is listening.
- .max_thread_stack_size(int stack_size): Maximum stack size for threads created by the library. Not specifying this option or using a value of zero means using the system default (which is likely to differ based on your platform). Default is
0 (system default)
. - .use_ipv6() and .no_ipv6(): Enable or disable the IPv6 protocol support (by default, libhttpserver will just support IPv4). If you specify this and the local platform does not support it, starting up the server will throw an exception.
off
by default. - .use_dual_stack() and .no_dual_stack(): Enable or disable the support for both IPv6 and IPv4 protocols at the same time (by default, libhttpserver will just support IPv4). If you specify this and the local platform does not support it, starting up the server will throw an exception. Note that this will mean that IPv4 addresses are returned in the IPv6-mapped format (the ’structsockaddrin6’ format will be used for IPv4 and IPv6).
off
by default. - .pedantic() and .no_pedantic(): Enables pedantic checks about the protocol (as opposed to as tolerant as possible). Specifically, at the moment, this flag causes the library to reject HTTP 1.1 connections without a
Host
header. This is required by the standard, but of course in violation of the “be as liberal as possible in what you accept” norm. It is recommended to turn this off if you are testing clients against the library, and on in production.off
by default. - .debug() and .no_debug(): Enables debug messages from the library.
off
by default. - .regex_checking() and .no_regex_checking(): Enables pattern matching for endpoints. Read more here.
on
by default. - .post_process() and .no_post_process(): Enables/Disables the library to automatically parse the body of the http request as arguments if in querystring format. Read more here.
on
by default. - .put_processed_data_to_content() and .no_put_processed_data_to_content(): Enables/Disables the library to copy parsed body data to the content or to only store it in the arguments map.
on
by default. - .file_upload_target(file_upload_target_T file_upload_target): Controls, how the library stores uploaded files. Default value is
FILE_UPLOAD_MEMORY_ONLY
.FILE_UPLOAD_MEMORY_ONLY
: The content of the file is only stored in memory. Depending onput_processed_data_to_content
only as part of the arguments map or additionally in the content.FILE_UPLOAD_DISK_ONLY
: The content of the file is stored only in the file system. The path is created fromfile_upload_dir
and either a random name (ifgenerate_random_filename_on_upload
is true) or the actually uploaded file name.FILE_UPLOAD_MEMORY_AND_DISK
: The content of the file is stored in memory and on the file system.
- .file_upload_dir(const std::string& file_upload_dir): Specifies the directory to store all uploaded files. Default value is
/tmp
. - .generate_random_filename_on_upload() and .no_generate_random_filename_on_upload(): Enables/Disables the library to generate a unique and unused filename to store the uploaded file to. Otherwise the actually uploaded file name is used.
off
by default. - .deferred() and .no_deferred(): Enables/Disables the ability for the server to suspend and resume connections. Simply put, it enables/disables the ability to use
deferred_response
. Read more here.on
by default. - .single_resource() and .no_single_resource: Sets or unsets the server in single resource mode. This limits all endpoints to be served from a single resource. The resultant is that the webserver will process the request matching to the endpoint skipping any complex semantic. Because of this, the option is incompatible with
regex_checking
and requires the resource to be registered against an empty endpoint or the root endpoint ("/"
). The resource will also have to be registered as family. (For more information on resource registration, read more here).off
by default.
Threading Models
- .start_method(const http::http_utils::start_method_T& start_method): libhttpserver can operate with two different threading models that can be selected through this method. Default value is
INTERNAL_SELECT
.http::http_utils::INTERNAL_SELECT
: In this mode, libhttpserver uses only a single thread to handle listening on the port and processing of requests. This mode is preferable if spawning a thread for each connection would be costly. If the HTTP server is able to quickly produce responses without much computational overhead for each connection, this mode can be a great choice. Note that libhttpserver will still start a single thread for itself -- this way, the main program can continue with its operations after calling the start method. Naturally, if the HTTP server needs to interact with shared state in the main application, synchronization will be required. If such synchronization in code providing a response results in blocking, all HTTP server operations on all connections will stall. This mode is a bad choice if response data cannot always be provided instantly. The reason is that the code generating responses should not block (since that would block all other connections) and on the other hand, if response data is not available immediately, libhttpserver will start to busy wait on it. If you need to scale along the number of concurrent connection and scale on multiple thread you can specify a value formax_threads
(see below) thus enabling a thread pool - this is different fromTHREAD_PER_CONNECTION
below where a new thread is spawned for each connection.http::http_utils::THREAD_PER_CONNECTION
: In this mode, libhttpserver starts one thread to listen on the port for new connections and then spawns a new thread to handle each connection. This mode is great if the HTTP server has hardly any state that is shared between connections (no synchronization issues!) and may need to perform blocking operations (such as extensive IO or running of code) to handle an individual connection.
- .max_threads(int max_threads): A thread pool can be combined with the
INTERNAL_SELECT
mode to benefit implementations that require scalability. As said before, by default this mode only uses a single thread. When combined with the thread pool option, it is possible to handle multiple connections with multiple threads. Any value greater than one for this option will activate the use of the thread pool. In contrast to theTHREAD_PER_CONNECTION
mode (where each thread handles one and only one connection), threads in the pool can handle a large number of concurrent connections. UsingINTERNAL_SELECT
in combination with a thread pool is typically the most scalable (but also hardest to debug) mode of operation for libhttpserver. Default value is1
. This option is incompatible withTHREAD_PER_CONNECTION
.
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.
- .not_found_resource(const shared_ptr<http_response>(*render_ptr)(const http_request&) resource): Specifies a function to handle a request when no matching registered endpoint exist for the URL requested by the client.
- .method_not_allowed_resource(const shared_ptr<http_response>(*render_ptr)(const http_request&) resource): Specifies a function to handle a request that is asking for a method marked as not allowed on the matching http_resource.
- .internal_error_resource(const shared_ptr<http_response>(*render_ptr)(const http_request&) resource): Specifies a function to handle a request that is causing an uncaught exception during its execution. REMEMBER: is this callback is causing an exception itself, the standard default response from libhttpserver will be reported to the HTTP client.
Example of custom errors:
#include <httpserver.hpp>
using namespace httpserver;
const 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"));
}
const 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:
const 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:
curl -XGET -v http://localhost:8080/morning
: will return your customnot found
error.curl -XPOST -v http://localhost:8080/hello
: will return your customnot allowed
error.
You can also check this example on github.
Custom logging callbacks
- .log_access(void(*log_access_ptr)(const std::string&) functor): Specifies a function used to log accesses (requests) to the server.
- .log_error(void(*log_error_ptr)(const std::string&) functor): Specifies a function used to log errors generating from the server.
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:
const 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
- .use_ssl() and .no_ssl(): Determines whether to run in HTTPS-mode or not. If you set this as on and libhttpserver was compiled without SSL support, the library will throw an exception at start of the server.
off
by default. - .cred_type(const http::http_utils::cred_type_T& cred_type): Daemon credentials type. Either certificate or anonymous. Acceptable values are:
NONE
: No credentials.CERTIFICATE
: Certificate credential.ANON
: Anonymous credential.SRP
: SRP credential.PSK
: PSK credential.IA
: IA credential.
- .https_mem_key(const std::string& filename): String representing the path to a file containing the private key to be used by the HTTPS daemon. This must be used in conjunction with
https_mem_cert
. - .https_mem_cert(const std::string& filename): String representing the path to a file containing the certificate to be used by the HTTPS daemon. This must be used in conjunction with
https_mem_key
. - .https_mem_trust(const std::string& filename): String representing the path to a file containing the CA certificate to be used by the HTTPS daemon to authenticate and trust clients certificates. The presence of this option activates the request of certificate to the client. The request to the client is marked optional, and it is the responsibility of the server to check the presence of the certificate if needed. Note that most browsers will only present a client certificate only if they have one matching the specified CA, not sending any certificate otherwise.
- .https_priorities(const std::string& priority_string): SSL/TLS protocol version and ciphers. Must be followed by a string specifying the SSL/TLS protocol versions and ciphers that are acceptable for the application. The string is passed unchanged to gnutls_priority_init. If this option is not specified,
"NORMAL"
is used.
Minimal example using HTTPS
#include <httpserver.hpp>
using namespace httpserver;
class hello_world_resource : public http_resource {
public:
const 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.
- .ban_system() and .no_ban_system: Can be used to enable/disable the ban system.
on
by default. - .default_policy(const http::http_utils::policy_T& default_policy): Specifies what should be the default behavior when receiving a request. Possible values are
ACCEPT
andREJECT
. Default isACCEPT
.
Authentication Parameters
- .basic_auth() and .no_basic_auth: Can be used to enable/disable parsing of the basic authorization header sent by the client.
on
by default. - .digest_auth() and .no_digest_auth: Can be used to enable/disable parsing of the digested authentication data sent by the client.
on
by default. - .nonce_nc_size(int nonce_size): Size of an array of nonce and nonce counter map. This option represents the size (number of elements) of a map of a nonce and a nonce-counter. If this option is not specified, a default value of 4 will be used (which might be too small for servers handling many requests). You should calculate the value of NC_SIZE based on the number of connections per second multiplied by your expected session duration plus a factor of about two for hash table collisions. For example, if you expect 100 digest-authenticated connections per second and the average user to stay on your site for 5 minutes, then you likely need a value of about 60000. On the other hand, if you can only expect only 10 digest-authenticated connections per second, tolerate browsers getting a fresh nonce for each request and expect a HTTP request latency of 250 ms, then a value of about 5 should be fine.
- .digest_auth_random(const std::string& nonce_seed): Digest Authentication nonce’s seed. For security, you SHOULD provide a fresh random nonce when actually using Digest Authentication with libhttpserver in production.
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:
- void webserver::start(bool blocking): Allows to start a server. If the
blocking
flag is passed astrue
, it will block the execution of the current thread until a call to stop on the same webserver object is performed. - void webserver::stop(): Allows to stop a server. It immediately stops it.
- bool webserver::is_running(): Checks if a server is running
- void webserver::sweet_kill(): Allows to stop a server. It doesn't guarantee an immediate halt to allow for thread termination and connection closure.
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
):
- const std::shared_ptr<http_response> http_resource::render_GET(const http_request& req): Invoked on an HTTP GET request.
- const std::shared_ptr<http_response> http_resource::render_POST(const http_request& req): Invoked on an HTTP POST request.
- const std::shared_ptr<http_response> http_resource::render_PUT(const http_request& req): Invoked on an HTTP PUT request.
- const std::shared_ptr<http_response> http_resource::render_HEAD(const http_request& req): Invoked on an HTTP HEAD request.
- const std::shared_ptr<http_response> http_resource::render_DELETE(const http_request& req): Invoked on an HTTP DELETE request.
- const std::shared_ptr<http_response> http_resource::render_TRACE(const http_request& req): Invoked on an HTTP TRACE request.
- const std::shared_ptr<http_response> http_resource::render_OPTIONS(const http_request& req): Invoked on an HTTP OPTIONS request.
- const std::shared_ptr<http_response> http_resource::render_CONNECT(const http_request& req): Invoked on an HTTP CONNECT request.
- const std::shared_ptr<http_response> http_resource::render(const http_request& req): Invoked as a backup method if the matching method is not implemented. It can be used whenever you want all the invocations on a URL to activate the same behavior regardless of the HTTP method requested. The default implementation of the
render
method returns an empty response with a404
.
Example of implementation of render methods
#include <httpserver.hpp>
using namespace httpserver;
class hello_world_resource : public http_resource {
public:
const std::shared_ptr<http_response> render_GET(const http_request&) {
return std::shared_ptr<http_response>(new string_response("GET: Hello, World!"));
}
const 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:
curl -XGET -v http://localhost:8080/hello
: will returnGET: Hello, World!
.curl -XPOST -v http://localhost:8080/hello
: will returnOTHER: Hello, World!
. You can try requesting other methods besidePOST
to verify how the same message will be returned.
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.
- void http_resource::set_allowing(const std::string& method, bool allowed): Used to allow or disallow a method. The
method
parameter is a string representing an HTTP method (GET, POST, PUT, etc...). - void http_resource::allow_all(): Marks all HTTP methods as allowed.
- void http_resource::disallow_all(): Marks all HTTP methods as not allowed.
Example of methods allowed/disallowed
#include <httpserver.hpp>
using namespace httpserver;
class hello_world_resource : public http_resource {
public:
const 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:
curl -XPOST -v http://localhost:8080/hello
.
You can also check this example on github.
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:
- bool register_resource(const std::string& endpoint, http_resource* resource, bool family =
false
): Registers theresource
to anendpoint
. The endpoint is a string representing the path on your webserver from where you want your resource to be served from (e.g."/path/to/resource"
). The optionalfamily
parameter allows to register a resource as a "family" resource that will match any path nested into the one specified. For example, if family is set totrue
and endpoint is set to"/path"
, the webserver will route to the resource not only the requests against"/path"
but also everything in its nested path"/path/on/the/previous/one"
.
Specifying endpoints
There are essentially four ways to specify an endpoint string:
-
A simple path (e.g.
"/path/to/resource"
). In this case, the webserver will try to match exactly the value of the endpoint. -
A regular exception. In this case, the webserver will try to match the URL of the request with the regex passed. For example, if passing
"/path/as/decimal/[0-9]+
, requests on URLs like"/path/as/decimal/5"
or"/path/as/decimal/42"
will be matched; instead, URLs like"/path/as/decimal/three"
will not. -
A parametrized path. (e.g.
"/path/to/resource/with/{arg1}/{arg2}/in/url"
). In this case, the webserver will match the argument with any value passed. In addition to this, the arguments will be passed to the resource as part of the arguments (readable from thehttp_request::get_arg
method - see here). For example, if passing"/path/to/resource/with/{arg1}/{arg2}/in/url"
will match any request on URL with any value in place of{arg1}
and{arg2}
. -
A parametrized path with custom parameters. This is the same of a normal parametrized path, but allows to specify a regular expression for the argument (e.g.
"/path/to/resource/with/{arg1|[0-9]+}/{arg2|[a-z]+}/in/url"
. In this case, the webserver will match the arguments with any value passed that satisfies the regex. In addition to this, as above, the arguments will be passed to the resource as part of the arguments (readable from thehttp_request::get_arg
method - see here). For example, if passing"/path/to/resource/with/{arg1|[0-9]+}/{arg2|[a-z]+}/in/url"
will match requests on URLs like"/path/to/resource/with/10/AA/in/url"
but not like""/path/to/resource/with/BB/10/in/url""
-
Any of the above marked as
family
. Will match any request on URLs having path that is prefixed by the path passed. For example, if family is set totrue
and endpoint is set to"/path"
, the webserver will route to the resource not only the requests against"/path"
but also everything in its nested path"/path/on/the/previous/one"
.#include <httpserver.hpp> using namespace httpserver; class hello_world_resource : public http_resource { public: const 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: const 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: const std::shared_ptr<http_response> render(const http_request& req) { return std::shared_ptr<http_response>(new string_response("ARGS: " + req.get_arg("arg1") + " and " + req.get_arg("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:
curl -XGET -v http://localhost:8080/hello
: will return theHello, World!
message.curl -XGET -v http://localhost:8080/family
: will return theYour URL: /family
message.curl -XGET -v http://localhost:8080/family/with/suffix
: will return theYour URL: /family/with/suffix
message.curl -XGET -v http://localhost:8080/with_regex_10
: will return theYour URL: /with_regex_10
message.curl -XGET -v http://localhost:8080/url/with/AA/and/BB
: will return theARGS: AA and BB
message. You can changeAA
andBB
with any value and observe how the URL is still matched and parameters are read.curl -XGET -v http://localhost:8080/url/with/parametric/args/10/and/AA
: will return theARGS: 10 and AA
message. You can change10
andAA
with any value matching the regexes and observe how the URL is still matched and parameters are read.
Conversely, you can observe how these URL will not be matched (al the following will give you a not found
message):
curl -XGET -v http://localhost:8080/with_regex_A
curl -XGET -v http://localhost:8080/url/with/parametric/args/AA/and/BB
You can also check this example on github.
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:
- const std::string& get_path() const: Returns the path as requested from the HTTP client.
- const std::vector<std::string>& get_path_pieces() const: Returns the components of the path requested by the HTTP client (each piece of the path split by
'/'
. - const std::string& get_path_piece(int index) const: Returns one piece of the path requested by the HTTP client. The piece is selected through the
index
parameter (0-indexed). - const std::string& get_method() const: Returns the method requested by the HTTP client.
- const std::string get_header(const std::string& key) const: Returns the header with name equal to
key
if present in the HTTP request. Returns anempty string
otherwise. - const std::string get_cookie(const std::string& key) const: Returns the cookie with name equal to
key
if present in the HTTP request. Returns anempty string
otherwise. - const std::string get_footer(const std::string& key) const: Returns the footer with name equal to
key
if present in the HTTP request (only for http 1.1 chunked encodings). Returns anempty string
otherwise. - const std::string get_arg(const std::string& key) const: Returns the argument with name equal to
key
if present in the HTTP request. Arguments can be (1) querystring parameters, (2) path argument (in case of parametric endpoint, (3) parameters parsed from the HTTP request body if the body is inapplication/x-www-form-urlencoded
ormultipart/form-data
formats and the postprocessor is enabled in the webserver (enabled by default). - const std::map<std::string, std::string, http::header_comparator> get_headers() const: Returns a map containing all the headers present in the HTTP request.
- const std::map<std::string, std::string, http::header_comparator> get_cookies() const: Returns a map containing all the cookies present in the HTTP request.
- const std::map<std::string, std::string, http::header_comparator> get_footers() const: Returns a map containing all the footers present in the HTTP request (only for http 1.1 chunked encodings).
- const std::map<std::string, std::string, http::arg_comparator> get_args() const: Returns all the arguments present in the HTTP request. Arguments can be (1) querystring parameters, (2) path argument (in case of parametric endpoint, (3) parameters parsed from the HTTP request body if the body is in
application/x-www-form-urlencoded
ormultipart/form-data
formats and the postprocessor is enabled in the webserver (enabled by default). - const std::map<std::string, std::map<std::string, http::file_info>> get_files() const: Returns information about all the uploaded files (if the files are stored to disk). This information includes the key (as identifier of the outer map), the original file name (as identifier of the inner map) and a class
file_info
, which includes the size of the file and the path to the file in the file system. - const std::string& get_content() const: Returns the body of the HTTP request.
- bool content_too_large() const: Returns
true
if the body length of the HTTP request sent by the client is longer than the max allowed on the server. - const std::string get_querystring() const: Returns the
querystring
of the HTTP request. - const std::string& get_version() const: Returns the HTTP version of the client request.
- const std::string get_requestor() const: Returns the IP from which the client is sending the request.
- unsigned short get_requestor_port() const: Returns the port from which the client is sending the request.
- const std::string get_user() const: Returns the
user
as self-identified through basic authentication. The content of the user header will be parsed only if basic authentication is enabled on the server (enabled by default). - const std::string get_pass() const: Returns the
password
as self-identified through basic authentication. The content of the password header will be parsed only if basic authentication is enabled on the server (enabled by default). - const std::string get_digested_user() const: Returns the
digested user
as self-identified through digest authentication. The content of the user header will be parsed only if digest authentication is enabled on the server (enabled by default). - bool check_digest_auth(const std::string& realm, const std::string& password, int nonce_timeout, bool* reload_nonce) const: Allows to check the validity of the authentication token sent through digest authentication (if the provided values in the WWW-Authenticate header are valid and sound according to RFC2716). Takes in input the
realm
of validity of the authentication, thepassword
as known to the server to compare against, thenonce_timeout
to indicate how long the nonce is valid andreload_nonce
a boolean that will be set by the method to indicate a nonce being reloaded. The method returnstrue
if the authentication is valid,false
otherwise. - gnutls_session_t get_tls_session() const: Tests if there is am underlying TLS state of the current request.
- gnutls_session_t get_tls_session() const: Returns the underlying TLS state of the current request for inspection. (It is an error to call this if the state does not exist.)
Details on the http::file_info
structure.
- size_t get_file_size() const: Returns the size of the file uploaded through the HTTP request.
- const std::string get_file_system_file_name() const: Returns the name of the file uploaded through the HTTP request as stored on the filesystem.
- const std::string get_content_type() const: Returns the content type of the file uploaded through the HTTP request.
- const std::string get_transfer_encoding() const: Returns the transfer encoding of the file uploaded through the HTTP request.
Example of handler reading arguments from a request
#include <httpserver.hpp>
using namespace httpserver;
class hello_world_resource : public http_resource {
public:
const std::shared_ptr<http_response> render(const http_request& req) {
return std::shared_ptr<http_response>(new string_response("Hello: " + 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.
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:
- string_response(const std::string& content, int response_code =
200
, const std::string& content_type ="text/plain"
): The most basic type of response. It uses thecontent
string passed in construction as body of the HTTP response. The other two optional parameters are theresponse_code
and thecontent_type
. You can find constant definition for the various response codes within the http_utils library file. - file_response(const std::string& filename, int response_code =
200
, const std::string& content_type ="text/plain"
): Uses thefilename
passed in construction as pointer to a file on disk. The body of the HTTP response will be set using the content of the file. The file must be a regular file and exist on disk. Otherwise libhttpserver will return an error 500 (Internal Server Error). The other two optional parameters are theresponse_code
and thecontent_type
. You can find constant definition for the various response codes within the http_utils library file. - basic_auth_fail_response(const std::string& content, const std::string& realm =
""
, int response_code =200
, const std::string& content_type ="text/plain"
): A response in return to a failure during basic authentication. It allows to specify acontent
string as a message to send back to the client. Therealm
parameter should contain your realm of authentication (if any). The other two optional parameters are theresponse_code
and thecontent_type
. You can find constant definition for the various response codes within the http_utils library file. - digest_auth_fail_response(const std::string& content, const std::string& realm =
""
, const std::string& opaque =""
, bool reload_nonce =false
, int response_code =200
, const std::string& content_type ="text/plain"
): A response in return to a failure during digest authentication. It allows to specify acontent
string as a message to send back to the client. Therealm
parameter should contain your realm of authentication (if any). Theopaque
represents a value that gets passed to the client and expected to be passed again to the server as-is. This value can be a hexadecimal or base64 string. Thereload_nonce
parameter tells the server to reload the nonce (you should use the value returned by thecheck_digest_auth
method on thehttp_request
. The other two optional parameters are theresponse_code
and thecontent_type
. You can find constant definition for the various response codes within the http_utils library file. - deferred_response(ssize_t(*cycle_callback_ptr)(shared_ptr<T>, char*, size_t) cycle_callback, const std::string& content =
""
, int response_code =200
, const std::string& content_type ="text/plain"
): A response that obtains additional content from a callback executed in a deferred way. It leaves the client in pending state (returning a100 CONTINUE
message) and suspends the connection. Besides the callback, optionally, you can provide acontent
parameter that sets the initial message sent immediately to the client. The other two optional parameters are theresponse_code
and thecontent_type
. You can find constant definition for the various response codes within the http_utils library file. To usedeferred_response
you need to have thedeferred
option active on your webserver (enabled by default).- The
cycle_callback_ptr
has this shape: ssize_t cycle_callback(shared_ptr<T> closure_data, char* buf, size_t max_size). You are supposed to implement a function in this shape and provide it to thedeferred_repsonse
method. The webserver will provide achar*
to the function. It is responsibility of the function to allocate it and fill its content. The method is supposed to respect themax_size
parameter passed in input. The function must return assize_t
value representing the actual size you filled thebuf
with. Any value different from-1
will keep the resume the connection, deliver the content and suspend it again (with a100 CONTINUE
). If the method returns-1
, the webserver will complete the communication with the client and close the connection. You can also pass ashared_ptr
pointing to a data object of your choice (this will be templetized with a class of your choice). The server will guarantee that this object is passed at each invocation of the method allowing the client code to use it as a memory buffer during computation.
- The
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:
- void with_header(const std::string& key, const std::string& value): Sets an HTTP header with name set to
key
and value set tovalue
. - void with_footer(const std::string& key, const std::string& value): Sets an HTTP footer with name set to
key
and value set tovalue
. - void with_cookie(const std::string& key, const std::string& value): Sets an HTTP cookie with name set to
key
and value set tovalue
(only for http 1.1 chunked encodings). - void shoutCAST(): Mark the response as a
shoutCAST
one.
Example of response setting headers
#include <httpserver.hpp>
using namespace httpserver;
class hello_world_resource : public http_resource {
public:
const 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.
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:
- void ban_ip(const std::string& ip): Adds one IP (or a range of IPs) to the list of the banned ones. Takes in input a
string
that contains the IP (or range of IPs) to ban. To use when thedefault_policy
isACCEPT
. - void allow_ip(const std::string& ip): Adds one IP (or a range of IPs) to the list of the allowed ones. Takes in input a
string
that contains the IP (or range of IPs) to allow. To use when thedefault_policy
isREJECT
. - void unban_ip(const std::string& ip): Removes one IP (or a range of IPs) from the list of the banned ones. Takes in input a
string
that contains the IP (or range of IPs) to remove from the list. To use when thedefault_policy
isREJECT
. - void disallow_ip(const std::string& ip): Removes one IP (or a range of IPs) from the list of the allowed ones. Takes in input a
string
that contains the IP (or range of IPs) to remove from the list. To use when thedefault_policy
isREJECT
.
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:
"192.168.5.5"
: standard IPV4"192.168.*.*"
: range of IPV4 addresses. In the example, everything between192.168.0.0
and192.168.255.255
."2001:db8:8714:3a90::12"
: standard IPV6 - clustered empty ranges are fully supported."2001:db8:8714:3a90:*:*"
: range of IPV6 addresses."::ffff:192.0.2.128"
: IPV4 IPs nested into IPV6."::192.0.2.128"
: IPV4 IPs nested into IPV6 (without'ffff'
prefix)"::ffff:192.0.*.*"
: ranges of IPV4 IPs nested into IPV6.
Example of IP Whitelisting/Blacklisting
#include <httpserver.hpp>
using namespace httpserver;
class hello_world_resource : public http_resource {
public:
const 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.
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:
const 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:
const 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.
HTTP Utils
libhttpserver provides a set of constants to help you develop your HTTP server. It would be redudant to list them here; so, please, consult the list directly here.
Other Examples
Example of returning a response from a file
#include <httpserver.hpp>
using namespace httpserver;
class file_response_resource : public http_resource {
public:
const 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:
const 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:
const 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.
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.
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.
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That's all there is to it!
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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.
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1. APPLICABILITY AND DEFINITIONS
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2. VERBATIM COPYING
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3. COPYING IN QUANTITY
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4. MODIFICATIONS
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- I. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
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ADDENDUM: How to use this License for your documents
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Copyright (c) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
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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”.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the with...Texts.
line with this:
with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
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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1101 1010001100 111 001 01 1010 101100 1001 100
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For further information: visit our website https://zencoders.github.io
Author: Sebastiano Merlino