The GNU libmicrohttpd Library

This manual documents GNU libmicrohttpd version 0.3.1, last updated 26 May 2008. It is built upon the documentation in the header file ‘microhttpd.h’.

Copyright © 2007, 2008 Christian Grothoff

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 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 libmicrohttpd is a GNU package.

Appendices

Indices

1. Introduction

All symbols defined in the public API start with MHD_. MHD is a small HTTP daemon library. As such, it does not have any API for logging errors (you can only enable or disable logging to stderr). Also, it may not support all of the HTTP features directly, where applicable, portions of HTTP may have to be handled by clients of the library.

The library is supposed to handle everything that it must handle (because the API would not allow clients to do this), such as basic connection management; however, detailed interpretations of headers — such as range requests — and HTTP methods are left to clients. The library does understand HEAD and will only send the headers of the response and not the body, even if the client supplied a body. The library also understands headers that control connection management (specifically, Connection: close and Expect: 100 continue are understood and handled automatically).

MHD understands POST data and is able to decode certain formats (at the moment only application/x-www-form-urlencoded and multipart/form-data) using the post processor API. The data stream of a POST is also provided directly to the main application, so unsupported encodings could still be processed, just not conveniently by MHD.

The header file defines various constants used by the HTTP protocol. This does not mean that MHD actually interprets all of these values. The provided constants are exported as a convenience for users of the library. MHD does not verify that transmitted HTTP headers are part of the standard specification; users of the library are free to define their own extensions of the HTTP standard and use those with MHD.

All functions are guaranteed to be completely reentrant and thread-safe. MHD checks for allocation failures and tries to recover gracefully (for example, by closing the connection). 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.

2. Constants

Enumeration: MHD_FLAG

Options for the MHD daemon.

Note that if neither MHD_USER_THREAD_PER_CONNECTION nor MHD_USE_SELECT_INTERNALLY are used, the client wants control over the process and will call the appropriate microhttpd callbacks.

Starting the daemon may also fail if a particular option is not implemented or not supported on the target platform (i.e. no support for SSL, threads or IPv6).

MHD_NO_FLAG

No options selected.

MHD_USE_DEBUG

Run in debug mode. If this flag is used, the library should print error messages and warnings to stderr. Note that MHD also needs to be compiled with the configure option --enable-messages for this run-time option to have any effect.

MHD_USE_SSL

Run in https mode (this is not yet supported).

MHD_USE_THREAD_PER_CONNECTION

Run using one thread per connection.

MHD_USE_SELECT_INTERNALLY

Run using an internal thread doing SELECT.

MHD_USE_IPv6

Run using the IPv6 protocol (otherwise, MHD will just support IPv4).

MHD_USE_PEDANTIC_CHECKS

Be pedantic about the protocol (as opposed to as tolerant as possible). Specifically, at the moment, this flag causes MHD 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 ON if you are testing clients against MHD, and OFF in production.

Enumeration: MHD_OPTION

MHD options. Passed in the varargs portion of MHD_start_daemon().

MHD_OPTION_END

No more options / last option. This is used to terminate the VARARGs list.

MHD_OPTION_CONNECTION_MEMORY_LIMIT

Maximum memory size per connection (followed by an unsigned int).

MHD_OPTION_CONNECTION_LIMIT

Maximum number of concurrenct connections to accept (followed by an unsigned int).

MHD_OPTION_CONNECTION_TIMEOUT

After how many seconds of inactivity should a connection automatically be timed out? (followed by an unsigned int; use zero for no timeout).

MHD_OPTION_NOTIFY_COMPLETED

Register a function that should be called whenever a request has been completed (this can be used for application-specific clean up). Requests that have never been presented to the application (via MHD_AccessHandlerCallback()) will not result in notifications.

This option should be followed by TWO pointers. First a pointer to a function of type MHD_RequestCompletedCallback() and second a pointer to a closure to pass to the request completed callback. The second pointer maybe NULL.

MHD_OPTION_PER_IP_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 option should be followed by an unsigned int. The default is zero, which means no limit on the number of connections from the same IP address.

Enumeration: MHD_ValueKind

The MHD_ValueKind specifies the source of the key-value pairs in the HTTP protocol.

MHD_RESPONSE_HEADER_KIND

Response header.

MHD_HEADER_KIND

HTTP header.

MHD_COOKIE_KIND

Cookies. Note that the original HTTP header containing the cookie(s) will still be available and intact.

MHD_POSTDATA_KIND

POST data. This is available only if a content encoding supported by MHD is used (currently only URL encoding), and only if the posted content fits within the available memory pool. Note that in that case, the upload data given to the MHD_AccessHandlerCallback() will be empty (since it has already been processed).

MHD_GET_ARGUMENT_KIND

GET (URI) arguments.

MHD_HEADER_KIND

HTTP footer (only for http 1.1 chunked encodings).

Enumeration: MHD_RequestTerminationCode

The MHD_RequestTerminationCode specifies reasons why a request has been terminated (or completed).

MHD_REQUEST_TERMINATED_COMPLETED_OK

We finished sending the response.

MHD_REQUEST_TERMINATED_WITH_ERROR

Error handling the connection (resources exhausted, other side closed connection, application error accepting request, etc.)

MHD_REQUEST_TERMINATED_TIMEOUT_REACHED

No activity on the connection for the number of seconds specified using MHD_OPTION_CONNECTION_TIMEOUT.

MHD_REQUEST_TERMINATED_DAEMON_SHUTDOWN

We had to close the session since MHD was being shut down.

3. Structures type definition

C Struct: MHD_Daemon

Handle for the daemon (listening on a socket for HTTP traffic).

C Struct: MHD_Connection

Handle for a connection / HTTP request. With HTTP/1.1, multiple requests can be run over the same connection. However, MHD will only show one request per TCP connection to the client at any given time.

C Struct: MHD_Response

Handle for a response.

C Struct: MHD_PostProcessor

Handle for POST processing.

4. Callback functions definition

Function Pointer: int *MHD_AcceptPolicyCallback (void *cls, const struct sockaddr * addr, socklen_t addrlen)

Invoked in the context of a connection to allow or deny a client to connect. This callback return MHD_YES if connection is allowed, MHD_NO if not.

cls

custom value selected at callback registration time;

addr

address information from the client;

addrlen

length of the address information.

Function Pointer: int *MHD_AccessHandlerCallback (void *cls, struct MHD_Connection * connection, const char *url, const char *method, const char *version, const char *upload_data, unsigned int *upload_data_size, void **con_cls)

Invoked in the context of a connection to answer a request from the client. This callback must call MHD functions (example: the MHD_Response ones) to provide content to give back to the client and return an HTTP status code (i.e. 200 for OK, 404, etc.).

Adding a POST processor, for details on how to code this callback.

Must return MHD_YES if the connection was handled successfully, MHD_NO if the socket must be closed due to a serious error while handling the request

cls

custom value selected at callback registration time;

url

the URL requested by the client;

method

the HTTP method used by the client (GET, PUT, DELETE, POST, etc.);

version

the HTTP version string (i.e. HTTP/1.1);

upload_data

the data being uploaded (excluding headers):

• for a POST that fits into memory and that is encoded with a supported encoding, the POST data will NOT be given in upload_data and is instead available as part of MHD_get_connection_values();
• very large POST data will be made available incrementally in upload_data;

upload_data_size

set initially to the size of the upload_data provided; this callback must update this value to the number of bytes NOT processed; unless external select is used, the callback maybe required to process at least some data. If the callback fails to process data in multi-threaded or internal-select mode and if the read-buffer is already at the maximum size that MHD is willing to use for reading (about half of the maximum amount of memory allowed for the connection), then MHD will abort handling the connection and return an internal server error to the client. In order to avoid this, clients must be able to process upload data incrementally and reduce the value of upload_data_size.

con_cls

reference to a pointer, initially set to NULL, that this callback can set to some address and that will be preserved by MHD for future calls for this request;

since the access handler may be called many times (i.e., for a PUT/POST operation with plenty of upload data) this allows the application to easily associate some request-specific state;

if necessary, this state can be cleaned up in the global MHD_RequestCompletedCallback (which can be set with the MHD_OPTION_NOTIFY_COMPLETED).

Function Pointer: void *MHD_RequestCompletedCallback (void *cls, struct MHD_Connectionconnection, void **con_cls, enum MHD_RequestTerminationCode toe)

Signature of the callback used by MHD to notify the application about completed requests.

cls

custom value selected at callback registration time;

connection

connection handle;

con_cls

value as set by the last call to the MHD_AccessHandlerCallback;

toe

reason for request termination see MHD_OPTION_NOTIFY_COMPLETED.

Function Pointer: int *MHD_KeyValueIterator (void *cls, enum MHD_ValueKind kind, const char *key, const char *value)

Iterator over key-value pairs. This iterator can be used to iterate over all of the cookies, headers, or POST-data fields of a request, and also to iterate over the headers that have been added to a response.

Return MHD_YES to continue iterating, MHD_NO to abort the iteration.

Function Pointer: int *MHD_ContentReaderCallback (void *cls, size_t pos, char *buf, int max)

Callback used by MHD in order to obtain content. The callback has to copy at most max bytes of content into buf. The total number of bytes that has been placed into buf should be returned.

Note that returning zero will cause MHD to try again, either “immediately” if in multi-threaded mode (in which case the callback may want to do blocking operations) or in the next round if MHD_run is used. Returning zero for a daemon that runs in internal select() mode is an error (since it would result in busy waiting) and will cause the program to be aborted (abort()).

cls

custom value selected at callback registration time;

pos

position in the datastream to access; note that if an MHD_Response object is re-used, it is possible for the same content reader to be queried multiple times for the same data; however, if an MHD_Response is not re-used, MHD guarantees that pos will be the sum of all non-negative return values obtained from the content reader so far.

Return -1 on error (MHD will no longer try to read content and instead close the connection with the client).

Function Pointer: void *MHD_ContentReaderFreeCallback (void *cls)

This method is called by MHD if we are done with a content reader. It should be used to free resources associated with the content reader.

Function Pointer: int *MHD_PostDataIterator (void *cls, enum MHD_ValueKind kind, const char *key, const char *filename, const char *content_type, const char *transfer_encoding, const char *data, size_t off, size_t size)

Iterator over key-value pairs where the value maybe made available in increments and/or may not be zero-terminated. Used for processing POST data.

cls

custom value selected at callback registration time;

kind

type of the value;

key

zero-terminated key for the value;

filename

name of the uploaded file, NULL if not known;

content_type

mime-type of the data, NULL if not known;

transfer_encoding

encoding of the data, NULL if not known;

data

pointer to size bytes of data at the specified offset;

off

offset of data in the overall value;

size

number of bytes in data available.

Return MHD_YES to continue iterating, MHD_NO to abort the iteration.

5. Starting and stopping the server

Function: struct MHD_Daemon * MHD_start_daemon (unsigned int flags, unsigned short port, MHD_AcceptPolicyCallback apc, void *apc_cls, MHD_AccessHandlerCallback dh, void *dh_cls, ...)

Start a webserver on the given port.

flags

OR-ed combination of MHD_FLAG values;

port

port to bind to;

apc

callback to call to check which clients will be allowed to connect; you can pass NULL in which case connections from any IP will be accepted;

apc_cls

extra argument to apc;

dh

default handler for all URIs;

dh_cls

extra argument to dh.

Additional arguments are a list of options (type-value pairs, terminated with MHD_OPTION_END). It is mandatory to use MHD_OPTION_END as last argument, even when there are no additional arguments.

Return NULL on error, handle to daemon on success.

Function: void MHD_stop_daemon (struct MHD_Daemon *daemon)

Shutdown an HTTP daemon.

Function: int MHD_run (struct MHD_Daemon *daemon)

Run webserver operations (without blocking unless in client callbacks). This method should be called by clients in combination with MHD_get_fdset() if the client-controlled select() method is used.

Return MHD_YES on success, MHD_NO if this daemon was not started with the right options for this call.

6. Implementing external select

Function: int MHD_get_fdset (struct MHD_Daemon *daemon, fd_set * read_fd_set, fd_set * write_fd_set, fd_set * except_fd_set, int *max_fd)

Obtain the select() sets for this daemon. The daemon's socket is added to read_fd_set. The list of currently existent connections is scanned and their file descriptors added to the correct set.

see (libc), for details on file descriptor sets.

After the call completed successfully: the variable referenced by max_fd references the file descriptor with highest integer identifier. The variable must be set to zero before invoking this function.

Return MHD_YES on success, MHD_NO if: the arguments are invalid (example: NULL pointers); this daemon was not started with the right options for this call.

Function: int MHD_get_timeout (struct MHD_Daemon *daemon, unsigned long long *timeout)

Obtain timeout value for select for this daemon (only needed if connection timeout is used). The returned value is how long select() should at most block, not the timeout value set for connections.

timeout

set to the timeout (in milliseconds).

Return MHD_YES on success, MHD_NO if timeouts are not used (or no connections exist that would necessiate the use of a timeout right now).

7. Handling requests

Function: int MHD_get_connection_values (struct MHD_Connection *connection, enum MHD_ValueKind kind, MHD_KeyValueIterator iterator, void *iterator_cls)

Get all the headers matching kind from the request.

The iterator callback is invoked once for each header, with iterator_cls as first argument. Return the number of entries iterated over; this can be less than the number of headers if, while iterating, iterator returns MHD_NO.

iterator can be NULL: in this case this function just counts and returns the number of headers.

Function: const char * MHD_lookup_connection_value (struct MHD_Connection *connection, enum MHD_ValueKind kind, const char *key)

Get a particular header value. If multiple values match the kind, return one of them (the “first”, whatever that means). key must reference a zero-terminated ASCII-coded string representing the header to look for: it is compared against the headers using strcasecmp(), so case is ignored. Return NULL if no such item was found.

8. Building answers to responses

Response objects handling by MHD is asynchronous with respect to the application execution flow. Instances of the MHD_Response structure are not associated to a daemon and neither to a client connection: they are managed with reference counting.

In the simplest case: we allocate a new MHD_Response structure for each response, we use it once and finally we destroy it.

MHD allows more efficient resources usages.

Example: we allocate a new MHD_Response structure for each response kind, we use it every time we have to give that responce and we finally destroy it only when the daemon shuts down.

8.1 Enqueuing a response

Function: int MHD_queue_response (struct MHD_Connection *connection, unsigned int status_code, struct MHD_Response *response)

Queue a response to be transmitted to the client as soon as possible (increment the reference counter).

connection

the connection identifying the client;

status_code

HTTP status code (i.e. 200 for OK);

response

response to transmit.

Return MHD_YES on success or if message has been queued. Return MHD_NO: if arguments are invalid (example: NULL pointer); on error (i.e. reply already sent).

Function: void MHD_destroy_response (struct MHD_Response *response)

Destroy a response object and associated resources (decrement the reference counter). Note that MHD may keep some of the resources around if the response is still in the queue for some clients, so the memory may not necessarily be freed immediatley.

An explanation of reference counting(1):

1. a MHD_Response object is allocated:

   struct MHD_Response * response = MHD_create_response_from_data(...); /* here: reference counter = 1 */

2. the MHD_Response object is enqueued in a MHD_Connection:

   MHD_queue_response(connection, , response); /* here: reference counter = 2 */

3. the creator of the response object discharges responsibility for it:

   MHD_destroy_response(response); /* here: reference counter = 1 */

4. the daemon handles the connection sending the response's data to the client then decrements the reference counter by calling MHD_destroy_response(): the counter's value drops to zero and the MHD_Response object is released.

8.2 Creating response objects

Function: struct MHD_Response * MHD_create_response_from_callback (size_t size, unsigned int block_size, MHD_ContentReaderCallback crc, void *crc_cls, MHD_ContentReaderFreeCallback crfc)

Create a response object. The response object can be extended with header information and then it can be used any number of times.

size

size of the data portion of the response, -1 for unknown;

block_size

preferred block size for querying crc (advisory only, MHD may still call crc using smaller chunks); this is essentially the buffer size used for IO, clients should pick a value that is appropriate for IO and memory performance requirements;

crc

callback to use to obtain response data;

crc_cls

extra argument to crc;

crfc

callback to call to free crc_cls resources.

Return NULL on error (i.e. invalid arguments, out of memory).

Function: struct MHD_Response * MHD_create_response_from_data (size_t size, void *data, int must_free, int must_copy)

Create a response object. The response object can be extended with header information and then it can be used any number of times.

size

size of the data portion of the response;

data

the data itself;

must_free

if true: MHD should free data when done;

must_copy

if true: MHD allocates a block of memory and use it to make a copy of data embedded in the returned MHD_Response structure; handling of the embedded memory is responsibility of MHD; data can be released anytime after this call returns.

Return NULL on error (i.e. invalid arguments, out of memory).

Example: create a response from a statically allocated string:

const char * data = "<html><body><p>Error!</p></body></html>";

struct MHD_Connection * connection = ...;
struct MHD_Response *   response;

response = MHD_create_response_from_data(strlen(data), data,
                                         MHD_NO, MHD_NO);
MHD_queue_response(connection, 404, response);
MHD_destroy_response(response);

8.3 Adding headers to a response

Function: int MHD_add_response_header (struct MHD_Response *response, const char *header, const char *content)

Add a header line to the response. The strings referenced by header and content must be zero-terminated and they are duplicated into memory blocks embedded in response.

Notice that the strings must not hold newlines, carriage returns or tab chars.

Return MHD_NO on error (i.e. invalid header or content format or memory allocation error).

Function: int MHD_del_response_header (struct MHD_Response *response, const char *header, const char *content)

Delete a header line from the response. Return MHD_NO on error (arguments are invalid or no such header known).

8.4 Inspecting a response object

Function: int MHD_get_response_headers (struct MHD_Response *response, MHD_KeyValueIterator iterator, void *iterator_cls)

Get all of the headers added to a response.

Invoke the iterator callback for each header in the response, using iterator_cls as first argument. Return number of entries iterated over. iterator can be NULL: in this case the function just counts headers.

iterator should not modify the its key and value arguments, unless we know what we are doing.

Function: const char * MHD_get_response_header (struct MHD_Response *response, const char *key)

Find and return a pointer to the value of a particular header from the response. key must reference a zero-terminated string representing the header to look for. The search is case sensitive. Return NULL if header does not exist or key is NULL.

We should not modify the value, unless we know what we are doing.

9. Adding a POST processor

MHD provides the post procesor API to make it easier for applications to parse the data of a client's POST request: the MHD_AccessHandlerCallback will be invoked multiple times to process data as it arrives; at each invocation a new chunk of data must be processed. The arguments upload_data and upload_data_size are used to reference the chunk of data.

When MHD_AccessHandlerCallback is invoked for a new connection: its *con_cls argument is set to NULL. When POST data comes in the upload buffer it is mandatory to use the con_cls to store a reference to per-connection data. The fact that the pointer was initially NULL can be used to detect that this is a new request.

One method to detect that a new connection was established is to set *con_cls to anunused integer:

int
access_handler (void *cls,
                struct MHD_Connection * connection,
                const char *url,
                const char *method, const char *version,
                const char *upload_data, unsigned int *upload_data_size,
                void **con_cls)
{
  static int old_connection_marker;
  int new_connection = (MYNULL == *con_cls);

  if (new_connection) 
    {
      /* new connection with POST */
      *con_cls = &old_connection_marker;
    }

  ...
}

In contrast to the previous example, for POST requests in particular, it is more common to use the value of *con_cls to keep track of actual state used during processing, such as the post processor (or a struct containing a post processor):

int
access_handler (void *cls,
                struct MHD_Connection * connection,
                const char *url,
                const char *method, const char *version,
                const char *upload_data, unsigned int *upload_data_size,
                void **con_cls)
{
  struct MHD_PostProcessor * pp = *con_cls;

  if (pp == NULL) 
    {
      pp = MHD_create_post_processor(connection, ...);
      *con_cls = pp;
      return MHD_YES;
    }
  if (*upload_data_size) 
    {
      MHD_post_process(pp, upload_data, *upload_data_size);
      *upload_data_size = 0;
      return MHD_YES;
    }
  else
    {
      MHD_destroy_post_processor(pp);
      return MHD_queue_response(...);
    }
}

Note that the callback from MHD_OPTION_NOTIFY_COMPLETED should be used to destroy the post processor. This cannot be done inside of the access handler since the connection may not always terminate normally.

9.1 Programming interface for the POST processor

Function: struct MHD_PostProcessor * MHD_create_post_processor (struct MHD_Connection *connection, unsigned int buffer_size, MHD_PostDataIterator iterator, void *iterator_cls)

Create a PostProcessor. A PostProcessor can be used to (incrementally) parse the data portion of a POST request.

connection

the connection on which the POST is happening (used to determine the POST format);

buffer_size

maximum number of bytes to use for internal buffering (used only for the parsing, specifically the parsing of the keys). A tiny value (256-1024) should be sufficient; do NOT use a value smaller than 256;

iterator

iterator to be called with the parsed data; must NOT be NULL;

iterator_cls

custom value to be used as first argument to iterator.

Return NULL on error (out of memory, unsupported encoding), otherwise a PP handle.

Function: int MHD_post_process (struct MHD_PostProcessor *pp, const char *post_data, unsigned int post_data_len)

Parse and process POST data. Call this function when POST data is available (usually during an MHD_AccessHandlerCallback) with the upload_data and upload_data_size. Whenever possible, this will then cause calls to the MHD_IncrementalKeyValueIterator.

pp

the post processor;

post_data

post_data_len bytes of POST data;

post_data_len

length of post_data.

Return MHD_YES on success, MHD_NO on error (out-of-memory, iterator aborted, parse error).

Function: int MHD_destroy_post_processor (struct MHD_PostProcessor *pp)

Release PostProcessor resources. After this function is being called, the PostProcessor is guaranteed to no longer call its iterator. There is no special call to the iterator to indicate the end of the post processing stream. After destroying the PostProcessor, the programmer should perform any necessary work to complete the processing of the iterator.

Return MHD_YES if processing completed nicely, MHD_NO if there were spurious characters or formatting problems with the post request. It is common to ignore the return value of this function.

Copying

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.]

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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.

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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:

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That's all there is to it!

GNU-FDL

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1. 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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2. 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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   The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

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   The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

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   The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

3. 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.

4. 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.

5. 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:

   1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
   2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
   3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
   4. Preserve all the copyright notices of the Document.
   5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
   6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
   7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
   8. Include an unaltered copy of this License.
   9. 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.
   10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
   11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
   12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
   13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
   14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
   15. Preserve any Warranty Disclaimers.

   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.

6. 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.”

7. 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.

8. 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.

9. 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.

10. TERMINATION

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11. FUTURE REVISIONS OF THIS LICENSE

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ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

  Copyright (C)  year  your name.
  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.2
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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.

Concept Index

Function and Data Index

Type Index

Footnotes

(1)

Note to readers acquainted to the Tcl API: reference counting on MHD_Connection structures is handled in the same way as Tcl handles Tcl_Obj structures through Tcl_IncrRefCount() and Tcl_DecrRefCount().

Table of Contents

Short Table of Contents

About This Document

This document was generated by Christian Grothoff on May, 26 2008 using texi2html 1.78.

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