This module is a quite flexible parser for various kinds of URLs occuring in practice. The syntax is configurable such that one URL module can handle a lot of URL types in a generic way.
In order to parse an absolute URL (beginning with a scheme identifier like "http:...") of unknown type just call
let url = parse_url "http://me@server/directory"
By default, this function can parse all URL types listed
Neturl.common_url_syntax. However, the default configuration
implies also that
The latter two features can be simply enabled by passing the
The restriction that relative URLs are rejected has to do with
the problem that context information is missing. Because the scheme
identifier (like "http") is not available, the function does not
know which syntax the relative URL should have. For example,
the relative URL
dir/file?x=1 is differently parsed when
it is taken relative to an
http URL and when it is interpreted
relative to an
ftp URL. In the first case, the path component
of the URL is
"dir/file" and the query component is
but in the latter case the path component is
and a query component is not allowed.
The solution is that the syntax of the base URL, relative to which
the URL is seen, must be passed as additional argument. Under the
base_url is the base URL, use
let url = parse_url ~base_syntax:(url_syntax_of_url base_url) "/dir/file?x=1"
Of course, this assumes that the base URL is known when the url is parsed.
url_of_string is also a parser, but you must pass
the URL syntax as argument, e.g.
let url = url_of_string syntax "ipp://server/printer"
syntax one of the elements of
let syntax = Hashtbl.find common_url_syntax "ipp"
or a self-defined syntax.
This is much easier, just call
string_of_url to convert an URL
to a string. It is ensured that every URL always has an
unambiguous representation as string.
Internally, the parsed URL is decomposed into its components. This module supports two ways of decomposition:
The first form is used for services that directly connect to a certain service running on a certain host. The second form can be used for everything else not falling under this category.
It is important to mention that the decomposition is not fully
performed, but only down to a certain level. For example, the
"x=5" could be further analysed and be split into
the syntactic parts
"5". However, this is not done,
just because the author seeked a compromise between the depth
of analysis and the genericy of application.
In order to represent the so-called unsafe characters, one can
%-escaping in URLs. For example, this URL contains a
@, an unsafe character encoded as
The question is how this module handles such escapings.
It is surprising that the URL parser does not decode these
escaped forms (it checks, however, whether they are syntactically
correct). Internally, the components are stored as parsed,
and one can even retrieve them in their original form.
url_password returns the password component.
Applied to the above URL, one can get the password in
its original, "encoded" form, or as decoded string:
url_password ~encoded:true urlreturns
The URL components can be retrieved with the functions
Most components are just strings. Of course, the port number is an integer.
The path component (
url_path) has a non-obvious representation. The path
is represented as string list, e.g. "a/b/c" is represented
["a";"b";"c"] . Note, however, that absolute paths have
an empty string at the beginning of the list, e.g.
[""; "a"; "b"; "" ] . In most cases, the paths
found in URLs are absolute, and because of this it is quite
common to find this empty string at the beginning of the
path list. The corner cases are:
is used when the path is missing in the URL
[ "" ]is "/"
[ ""; "" ]is considered as illegal
The last two cases are somewhat arbitrary.
There is the helper function
split_path to convert the string
representation of paths into the list representation.
The parameters (
url_param) are lists, too.
A parameter starts with a semicolon as delimiter and runs until
the next component, which can be another parameter. The contents,
i.e. the values after the semicolons are put into the list. For example,
the parameter ";auth=unix;type=i" is represented as
["auth=unix"; "type=i"] .
The query component is represented as a single string. When queries use the standard syntax "name1=value1&name2=value2&...", one can parse this string using
let args = Netencoding.Url.dest_url_encoded_parameters (url_query ~encoded:true url)
encoded:true is needed.
In order to create a URL for a certain syntax, call
let url = make_url ~scheme:"http" ~user:"user" ~password:"!$@?" ~host:"server" syntax
It is checked whether the URL conforms to the passed syntax. By default,
the components are passed in decoded form, and
encodes them if necessary (here, for example, the at sign in the
password). Alternatively, one can set
~encoded:true, and pass the
already escaped components. In this case,
make_url checks whether
the encoding is sufficient to represent the URL as string.
remove_from_url can be used to modify an existing URL.
A URL is relative when the scheme identifier at the beginning is
omitted. In this case, the URL can be transformed to an absolute
URL when the base URL is known. The algorithm for this is defined
in RFC 1808, and quite complicated. It is implemented in
apply_relative_url, but usually
is the more convenient function. Just call
let url' = ensure_absolute_url ~base url
url to its absolute counterpart
url' when it is
relative, and to pass the URL unchanged when it is already