neon — HTTP and WebDAV client library
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.
Some conventions are used throughout the neon API, to provide a consistent and simple interface; these are documented below.
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:
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.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 neon.
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.
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_debug_init and
ne_debug, if enabled at compile time; for
debugging outputmalloc failureTo 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) |
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. |
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.
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.
As a pure library interface, neon will never produce
output on stdout or
stderr; all user interaction is the
responsibilty of the application.
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.
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.
Since version 0.27.0, neon transparently uses the "LFS
transitional" interfaces in places where file-backed file
descriptors are manipulated. This means files larger than 2GiB
can be handled on platforms with a native 32-bit
off_t type, where LFS support is
available.
Some 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.