uri - Tcl Uniform Resource Identifier Management

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# uri(n) 1.2.7 tcllib "Tcl Uniform Resource Identifier Management"

## Name

uri - URI utilities

## Synopsis

- package require Tcl 8.2
- package require uri ?1.2.7?

- uri::setQuirkOption option ?value?
- uri::split url ?defaultscheme?
- uri::join ?key value?...
- uri::resolve base url
- uri::isrelative url
- uri::geturl url ?options...?
- uri::canonicalize uri
- uri::register schemeList script

## Description

This package does two things.

First, it provides a number of commands for manipulating URLs/URIs and fetching data specified by them. For fetching data this package analyses the requested URL/URI and then dispatches it to the appropriate package (http, ftp, ...) for actual retrieval. Currently these commands are defined for the schemes http, https, ftp, mailto, news, ldap, ldaps and file. The package uri::urn adds scheme urn.

Second, it provides regular expressions for a number of registered URL/URI schemes. Registered schemes are currently ftp, ldap, ldaps, file, http, https, gopher, mailto, news, wais and prospero. The package uri::urn adds scheme urn.

The commands of the package conform to RFC 3986 (https://www.rfc-editor.org/rfc/rfc3986.txt), with the exception of a loophole arising from RFC 1630 and described in RFC 3986 Sections 5.2.2 and 5.4.2. The loophole allows a relative URI to include a scheme if it is the same as the scheme of the base URI against which it is resolved. RFC 3986 recommends avoiding this usage.

## COMMANDS

uri::setQuirkOption option ?value?

  uri::setQuirkOption is an accessor command for a number of "quirk options". The command has the same semantics as the command set: when called with one argument it reads an existing value; with two arguments it writes a new value. The value of a "quirk option" is boolean: the value false requests conformance with RFC 3986, while true requests use of the quirk. See section QUIRK OPTIONS for discussion of the different options and their purpose.

uri::split url ?defaultscheme?

  uri::split takes a url, decodes it and then returns a list of key/value pairs suitable for array set containing the constituents of the url. If the scheme is missing from the url it defaults to the value of defaultscheme if it was specified, or http else. Currently the schemes http, https, ftp, mailto, news, ldap, ldaps and file are supported by the package itself. See section EXTENDING on how to expand that range.

  The set of constituents of a URL (= the set of keys in the returned dictionary) is dependent on the scheme of the URL. The only key which is therefore always present is scheme. For the following schemes the constituents and their keys are known:

  ftp

    user, pwd, host, port, path, type, pbare. The pbare is optional.

  http(s)

    user, pwd, host, port, path, query, fragment, pbare. The pbare is optional.

  file

    path, host. The host is optional.

  mailto

    user, host. The host is optional.

  ldap(s)

    host, port, dn, attrs, scope, filter, extensions

  news

    Either message-id or newsgroup-name.

  For discussion of the boolean pbare see options NoInitialSlash and NoExtraKeys in QUIRK OPTIONS.

  The constituents are returned as slices of the argument url, without removal of percent-encoding ("url-encoding") or other adaptations. Notably, on Windows® the path in scheme file is not a valid local filename. See EXAMPLES for more information.

uri::join ?key value?...

  uri::join takes a list of key/value pairs (generated by uri::split, for example) and returns the canonical URL they represent. Currently the schemes http, https, ftp, mailto, news, ldap, ldaps and file are supported by the package itself. See section EXTENDING on how to expand that range.

  The arguments are expected to be slices of a valid URL, with percent-encoding ("url-encoding") and any other necessary adaptations. Notably, on Windows the path in scheme file is not a valid local filename. See EXAMPLES for more information.

uri::resolve base url

  uri::resolve resolves the specified url relative to base, in conformance with RFC 3986. In other words: a non-relative url is returned unchanged, whereas for a relative url the missing parts are taken from base and prepended to it. The result of this operation is returned. For an empty url the result is base, without its URI fragment (if any). The command is available for schemes http, https, ftp, and file.

uri::isrelative url

  uri::isrelative determines whether the specified url is absolute or relative. The command is available for a url of any scheme.

uri::geturl url ?options...?

  uri::geturl decodes the specified url and then dispatches the request to the package appropriate for the scheme found in the URL. The command assumes that the package to handle the given scheme either has the same name as the scheme itself (including possible capitalization) followed by ::geturl, or, in case of this failing, has the same name as the scheme itself (including possible capitalization). It further assumes that whatever package was loaded provides a geturl-command in the namespace of the same name as the package itself. This command is called with the given url and all given options. Currently geturl does not handle any options itself.

  Note: file-URLs are an exception to the rule described above. They are handled internally.

  It is not possible to specify results of the command. They depend on the geturl-command for the scheme the request was dispatched to.

uri::canonicalize uri

  uri::canonicalize returns the canonical form of a URI. The canonical form of a URI is one where relative path specifications, i.e. "." and "..", have been resolved. The command is available for all URI schemes that have uri::split and uri::join commands. The command returns a canonicalized URI if the URI scheme has a path component (i.e. http, https, ftp, and file). For schemes that have uri::split and uri::join commands but no path component (i.e. mailto, news, ldap, and ldaps), the command returns the uri unchanged.

uri::register schemeList script

  uri::register registers the first element of schemeList as a new scheme and the remaining elements as aliases for this scheme. It creates the namespace for the scheme and executes the script in the new namespace. The script has to declare variables containing regular expressions relevant to the scheme. At least the variable schemepart has to be declared as that one is used to extend the variables keeping track of the registered schemes.

## SCHEMES

In addition to the commands mentioned above this package provides regular expression to recognize URLs for a number of URL schemes.

For each supported scheme a namespace of the same name as the scheme itself is provided inside of the namespace uri containing the variable url whose contents are a regular expression to recognize URLs of that scheme. Additional variables may contain regular expressions for parts of URLs for that scheme.

The variable uri::schemes contains a list of all registered schemes. Currently these are ftp, ldap, ldaps, file, http, https, gopher, mailto, news, wais and prospero.

## EXTENDING

Extending the range of schemes supported by uri::split and uri::join is easy because both commands do not handle the request by themselves but dispatch it to another command in the uri namespace using the scheme of the URL as criterion.

uri::split and uri::join call Split[string totitle <scheme>] and Join[string totitle <scheme>] respectively.

The provision of split and join commands is sufficient to extend the commands uri::canonicalize and uri::geturl (the latter subject to the availability of a suitable package with a geturl command). In contrast, to extend the command uri::resolve to a new scheme, the command itself must be modified.

To extend the range of schemes for which pattern information is available, use the command uri::register.

An example of a package that provides both commands and pattern information for a new scheme is uri::urn, which adds scheme urn.

## QUIRK OPTIONS

The value of a "quirk option" is boolean: the value false requests conformance with RFC 3986, while true requests use of the quirk. Use command uri::setQuirkOption to access the values of quirk options.

Quirk options are useful both for allowing backwards compatibility when a command specification changes, and for adding useful features that are not included in RFC specifications. The following quirk options are currently defined:

NoInitialSlash

  This quirk option concerns the leading character of path (if non-empty) in the schemes http, https, and ftp.

  RFC 3986 defines path in an absolute URI to have an initial "/", unless the value of path is the empty string. For the scheme file, all versions of package uri follow this rule. The quirk option NoInitialSlash does not apply to scheme file.

  For the schemes http, https, and ftp, versions of uri before 1.2.7 define the path NOT to include an initial "/". When the quirk option NoInitialSlash is true (the default), this behavior is also used in version 1.2.7. To use instead values of path as defined by RFC 3986, set this quirk option to false.

  This setting does not affect RFC 3986 conformance. If NoInitialSlash is true, then the value of path in the schemes http, https, or ftp, cannot distinguish between URIs in which the full "RFC 3986 path" is the empty string "" or a single slash "/" respectively. The missing information is recorded in an additional uri::split key pbare.

  The boolean pbare is defined when quirk options NoInitialSlash and NoExtraKeys have values true and false respectively. In this case, if the value of path is the empty string "", pbare is true if the full "RFC 3986 path" is "", and pbare is false if the full "RFC 3986 path" is "/".

  Using this quirk option NoInitialSlash is a matter of preference.

NoExtraKeys

  This quirk option permits full backward compatibility with versions of uri before 1.2.7, by omitting the uri::split key pbare described above (see quirk option NoInitialSlash). The outcome is greater backward compatibility of the uri::split command, but an inability to distinguish between URIs in which the full "RFC 3986 path" is the empty string "" or a single slash "/" respectively - i.e. a minor non-conformance with RFC 3986.

  If the quirk option NoExtraKeys is false (the default), command uri::split returns an additional key pbare, and the commands comply with RFC 3986. If the quirk option NoExtraKeys is true, the key pbare is not defined and there is not full conformance with RFC 3986.

  Using the quirk option NoExtraKeys is NOT recommended, because if set to true it will reduce conformance with RFC 3986. The option is included only for compatibility with code, written for earlier versions of uri, that needs values of path without a leading "/", AND ALSO cannot tolerate unexpected keys in the results of uri::split.

HostAsDriveLetter

  When handling the scheme file on the Windows platform, versions of uri before 1.2.7 use the host field to represent a Windows drive letter and the colon that follows it, and the path field to represent the filename path after the colon. Such URIs are invalid, and are not recognized by any RFC. When the quirk option HostAsDriveLetter is true, this behavior is also used in version 1.2.7. To use file URIs on Windows that conform to RFC 3986, set this quirk option to false (the default).

  Using this quirk is NOT recommended, because if set to true it will cause the uri commands to expect and produce invalid URIs. The option is included only for compatibility with legacy code.

RemoveDoubleSlashes

  When a URI is canonicalized by uri::canonicalize, its path is normalized by removal of segments "." and "..". RFC 3986 does not mandate the removal of empty segments "" (i.e. the merger of double slashes, which is a feature of filename normalization but not of URI path normalization): it treats URIs with excess slashes as referring to different resources. When the quirk option RemoveDoubleSlashes is true (the default), empty segments will be removed from path. To prevent removal, and thereby conform to RFC 3986, set this quirk option to false.

  Using this quirk is a matter of preference. A URI with double slashes in its path was most likely generated by error, certainly so if it has a straightforward mapping to a file on a server. In some cases it may be better to sanitize the URI; in others, to keep the URI and let the server handle the possible error.

### BACKWARD COMPATIBILITY

To behave as similarly as possible to versions of uri earlier than 1.2.7, set the following quirk options:

- uri::setQuirkOption NoInitialSlash 1

- uri::setQuirkOption NoExtraKeys 1

- uri::setQuirkOption HostAsDriveLetter 1

- uri::setQuirkOption RemoveDoubleSlashes 0

In code that can tolerate the return by uri::split of an additional key pbare, set

- uri::setQuirkOption NoExtraKeys 0

in order to achieve greater compliance with RFC 3986.

### NEW DESIGNS

For new projects, the following settings are recommended:

- uri::setQuirkOption NoInitialSlash 0

- uri::setQuirkOption NoExtraKeys 0

- uri::setQuirkOption HostAsDriveLetter 0

- uri::setQuirkOption RemoveDoubleSlashes 0|1

### DEFAULT VALUES

The default values for package uri version 1.2.7 are intended to be a compromise between backwards compatibility and improved features. Different default values may be chosen in future versions of package uri.

- uri::setQuirkOption NoInitialSlash 1

- uri::setQuirkOption NoExtraKeys 0

- uri::setQuirkOption HostAsDriveLetter 0

- uri::setQuirkOption RemoveDoubleSlashes 1

## EXAMPLES

A Windows® local filename such as "C:\Other Files\startup.txt" is not suitable for use as the path element of a URI in the scheme file.

The Tcl command file normalize will convert the backslashes to forward slashes. To generate a valid path for the scheme file, the normalized filename must be prepended with "/", and then any characters that do not match the regexp bracket expression

        [a-zA-Z0-9$_.+!*'(,)?:@&=-]

must be percent-encoded.

The result in this example is "/C:/Other%20Files/startup.txt" which is a valid value for path.

    % uri::join path /C:/Other%20Files/startup.txt scheme file
    file:///C:/Other%20Files/startup.txt
    % uri::split file:///C:/Other%20Files/startup.txt
    path /C:/Other%20Files/startup.txt scheme file

On UNIX® systems filenames begin with "/" which is also used as the directory separator. The only action needed to convert a filename to a valid path is percent-encoding.

## CREDITS

Original code (regular expressions) by Andreas Kupries. Modularisation by Steve Ball, also the split/join/resolve functionality. RFC 3986 conformance by Keith Nash.

## Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category uri of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

## Keywords

fetching information, file, ftp, gopher, http, https, ldap, mailto, news, prospero, rfc 1630, rfc 2255, rfc 2396, rfc 3986, uri, url, wais, www

## Category

Networking