NEON(3) neon 0.30.2 NEON(3)
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30 September 2016
NAME
neon - HTTP and WebDAV client library
DESCRIPTION
neon is an HTTP and WebDAV client library. The major abstractions
exposed are the HTTP session, created by ne_session_create; and the
HTTP request, created by ne_request_create. HTTP authentication is
handled transparently for server and proxy servers, see
ne_set_server_auth; complete SSL/TLS support is also included, see
ne_ssl_set_verify.
CONVENTIONS
Some conventions are used throughout the neon API, to provide a
consistent and simple interface; these are documented below.
Thread-safeness and global initialization
neon itself is implemented to be thread-safe (avoiding any use of
global state), but relies on the operating system providing a
thread-safe resolver interface. Modern operating systems offer the
thread-safe getaddrinfo interface, which neon supports; some others
implement gethostbyname using thread-local storage.
To allow thread-safe use of SSL in the OpenSSL and GnuTLS libraries
neon must be configured using the --enable-threadsafe-ssl; if this is
done, locking callbacks will be registered by ne_sock_init; note that
care must be exercised if neon is used in conjunction with another
library which uses OpenSSL or GnuTLS.
Some platforms and libraries used by neon require global
initialization before use; notably:
+ The SIGPIPE signal disposition must be set to ignored or otherwise
handled to avoid process termination when writing to a socket
which has been shutdown by the peer.
+ OpenSSL and GnuTLS require global initialization to load shared
lookup tables.
+ The Win32 socket library requires initialization before use.
The ne_sock_init function should be called before any other use of
neon to perform any necessary initialization needed for the particular
platform. Applications wishing to perform all the necessary
process-global initialization steps themselves may omit to call
ne_sock_init (and ne_sock_exit); neon neither checks whether these
functions are called nor calls them itself.
For some applications and configurations it may be necessary to call
ne_i18n_init to initialize the support for internationalization in
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neon.
Asynchronous signal safety
No function in neon is defined to be async-signal safe - that is, no
function is safe to call from a signal handler. Any call into the neon
library from a signal handler will have undefined behaviour - in other
words, it may crash the process.
Functions using global state
Any function in neon may modify the errno global variable as a
side-effect. Except where explicitly documented, the value of errno is
unspecified after any neon function call.
Other than in the use of errno, the only functions which use or modify
process-global state in neon are as follows:
+ ne_sock_init, ne_i18n_init, and ne_sock_exit, as described above
+ ne_debug_init and ne_debug, if enabled at compile time; for
debugging output
+ ne_oom_callback for installing a process-global callback to be
invoked on malloc failure
Namespaces
To avoid possible collisions between names used for symbols and
preprocessor macros by an application and the libraries it uses, it is
good practice for each library to reserve a particular namespace
prefix. An application which ensures it uses no names with these
prefixes is then guaranteed to avoid such collisions.
The neon library reserves the use of the namespace prefixes ne_ and
NE_. The libraries used by neon may also reserve certain namespaces;
collisions between these libraries and a neon-based application will
not be detected at compile time, since the underlying library
interfaces are not exposed through the neon header files. Such
collisions can only be detected at link time, when the linker attempts
to resolve symbols. The following list documents some of the
namespaces claimed by libraries used by neon; this list may be
incomplete.
SSL, ssl, TLS, tls, ERR_, BIO_, d2i_, i2d_, ASN1_
Some of the many prefixes used by the OpenSSL library; little
attempt has been made to keep exported symbols within any
particular prefixes for this library.
gnutls_, gcry_, gpg_
Namespaces used by the GnuTLS library (and dependencies thereof)
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XML_, Xml[A-Z]
Namespaces used by the expat library.
xml[A-Z], html[A-Z], docb[A-Z]
Namespaces used by the libxml2 library; a relatively small number
of symbols are used without these prefixes.
inflate, deflate, crc32, compress, uncompres, adler32, zlib
Namespaces used by the zlib library; a relatively small number of
symbols are used without these prefixes.
krb5, gss, GSS, asn1, decode_krb5, encode_krb5, profile, mit
Some of the prefixes used by the MIT GSSAPI library and
dependencies thereof; a number of symbols lie outside these
prefixes.
pakchois_
Namespace used by the pakchois library.
px_
Namespace used by the libproxy library.
Argument validation
neon does not attempt to validate that the parameters passed to
functions conform to the API (for instance, checking that pointer
arguments are not NULL). Any use of the neon API which is not
documented to produce a certain behaviour results is said to produce
undefined behaviour; it is likely that neon will segfault under these
conditions.
URI paths, WebDAV metadata
The path strings passed to any function must be URI-encoded by the
application; neon never performs any URI encoding or decoding
internally. WebDAV property names and values must be valid UTF-8
encoded Unicode strings.
User interaction
As a pure library interface, neon will never produce output on stdout
or stderr; all user interaction is the responsibilty of the
application.
Memory handling
neon does not attempt to cope gracefully with an out-of-memory
situation; instead, by default, the abort function is called to
immediately terminate the process. An application may register a
custom function which will be called before abort in such a situation;
see ne_oom_callback.
Callbacks and userdata
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Whenever a callback is registered, a userdata pointer is also used to
allow the application to associate a context with the callback. The
userdata is of type void *, allowing any pointer to be used.
Large File Support
Since version 0.27.0, neon transparently uses the "LFS transitional"
interfaces in functions which use file descriptors. This allows use of
files larger than 2GiB on platforms with a native 32-bit off_t type,
where LFS support is available.
Some neon interfaces use the ne_off_t type, which is defined to be
either off_t or off64_t according to whether LFS support is detected
at build time. neon does not use or require the -D_FILE_OFFSET_BITS=64
macro definition.
SEE ALSO
ne_session_create(3), ne_oom_callback
AUTHOR
Joe Orton <neon@lists.manyfish.co.uk>
Author.
COPYRIGHT
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