Introduction

Let’s start with an example. Imagine that you have several proxy servers and you want to route requests to the right one. You could define the following rules:

• site1.com →︎ us_proxy

• site2.com/uk →︎ uk_proxy

• site2.com/ie →︎ ie_proxy

All URLs from site1.com should use the US proxy. The situation for site2.com URLs are different: if the path starts with /uk, then the UK proxy should be used whereas if the path starts with /ie then the IE proxy should be used instead. This library allows to create a matcher that can be used to match URLs with the right proxy using these rules.

Let see how the library can handle this situation:

from url_matcher import URLMatcher, Patterns

matcher = URLMatcher()
matcher.add_or_update("us_proxy", Patterns(["site1.com"]))
matcher.add_or_update("uk_proxy", Patterns(["site2.com/uk"]))
matcher.add_or_update("ie_proxy", Patterns(["site2.com/ie"]))

proxy = matcher.match("http://site1.com/articles/article1")
# proxy is "us_proxy" here

proxy = matcher.match("http://site2.com/uk/a_page")
# proxy is "uk_proxy" here

proxy = matcher.match("https://www.site2.com/ie/a_page")
# proxy is "ie_proxy" here

proxy = matcher.match("http://example.com/a_differnt_page")
# proxy is None here

As can be seen the the class url_matcher.URLMatcher is handy to handle this use case.

Note

Relative URLs are not supported in the match method.

Patterns, include and exclude

A pattern is a URL that describes a set of URLs. For example, the pattern example.com describes any URL whose domain is example.com or any of its subdomains.

A single pattern is sometimes not enough to describe which URLs to match. This is why we can define instead a set of patterns that are matched against. There is then a list of positive patterns (include) and a list of negative ones (exclude).

A URL is a match if it matches at least one of the patterns in include and none of the patterns in exclude.

This is an example of a rule using such a set of patterns:

patterns = Patterns(include=["example.com", "example.org"],
                    exclude=["*.jpg|", "*.jpeg|"])
matcher.add_or_update("proxy_1", patterns))

Patterns

A pattern is a URL that describes a set of URLs. It itself is just a URL. The following diagram summarizes its different parts and what do they mean.

Note

Matching is always case-insensitive.

The best way to understand how the patterns work is to look at some examples:

Basic patterns

Pattern	Behaviour
The empty string	Universal pattern. Match any URL
example.com	Match any URL whose domain is example.com or any of its subdomains. Match: http://example.com/anything?id=24 https://www.example.com/page#with_fragment Don’t match: http://myexample.com
example.com/articles/	Match any URL whose domain is example.com or www.example.com and path starts by /articles/. Match: http://www.example.com/articles/article1 https://example.com/articles/another_article?id=23 Don’t match: http://example.com/articles http://shop.example.com/articles/article1

Domain patterns

Pattern	Behaviour
shop.example.com	Match any URL whose domain is shop.example.com or any of its subdomains. Match: https://shop.example.com/foo?id=34#fragment http://uk.shop.example.com/foo?id=34 Don’t match: http://myshop.example.com
shop.example.com/	Match any URL whose domain is shop.example.com or www.shop.example.com. Match: https://shop.example.com/foo?id=34#fragment http://www.shop.example.com/foo?id=34 Don’t match: http://myshop.example.com http://uk.shop.example.com/foo?id=34

Note

Rules above only differ by the / character and this is enough to change the matching behaviour. The general rule is that the pattern matches the domain or any of the subdomains only if the pattern does not contain a path, a query or a fragment. Otherwise, only URLs with the exact same domain after removing www. will match the pattern.

Path patterns

A URL matches if the pattern path is a prefix of it.

Besides, the following modifier characters can be used:

• The * character matches any number of characters.

• Use the | character at the end of the pattern path if a exact path matching is required.

Pattern	Behaviour
/articles/	Match any URL whose path starts by /articles/. Match: http://example.com/articles/an_article?id=23#main https://foo.com/articles/ Don’t match: https://foo.com/articles
example.com/index.html|	Match any URL whose domain is example.com or www.example.com and path is exactly /index.html Match: http://example.com/index.html?id=24 https://www.example.com/index.html#main Don’t match: http://shop.example.com/index.html http://shop.example.com/index.html_2
/images/*.jpg|	Match any URL whose path starts by /images/ and whose path ends by .jpg Match: http://example.com/images/foo.jpg https://example.org/images/other/subpath/FOO.JPG?id=23 Don’t match: http://example.com/images/foo.jpeg http://example.com/images/foo.jpg_2

Query patterns

It serves to match URLs that have some specific parameters in the URL. The order of parameters in the query string is irrelevant. The wildcard char * can be used for values.

If a parameter is repeated in the pattern it will match if any of the values provided is matched

Pattern	Behaviour
/product|?id=34	Match any URL whose path is /product and contains the query parameter id with the value 34 Match: http://example.com/product?cat=shoes&id=34 Don’t match: http://example.com/product?id=12 http://example.com/product/other?id=34
/product|?id=*	Match any URL whose path is /product and contains the query parameter id with any value Match: http://example.com/product?cat=shoes&id=34 https://example.com/product?id=12&cat=clothes https://example.com/product?id= Don’t match: http://example.com/product?cat=shoes http://example.com/product?cat=shoes&ids=34
?cat=shoes&cat=pants	Match any URL containing the query parameters cat with the values shoes or pants Match: http://example.com/product?cat=shoes&id=34 http://example.org/p?cat=pants Don’t match: http://example.org/p?cat=pant

Fragment patterns

It works exactly like the path.

Rules conflict resolution

Sometimes several rules can match the same URL. We have then a conflict. By default the library will prioritize the most specific rule. For example, if a URL is matching both a rule with a pattern example.com and another with the pattern example.com/articles then the later one will be final match because it is more specific.

Alternatively, it is possible to control manually the order of rules by using the priority parameter of the url_matcher.Patterns. In case of conflict, the rule with the highest priority will be chosen.

The full criteria applied to resolve a conflict between rules are:

1. universality (rules with non universal include patterns are prioritized over rules with universal ones)

2. priority (the highest wins)

3. specificity (the most specific include patterns for the concerning domain wins)

4. the rule id (the rule with the highest id wins)

Efficiency

Internally, the library clusters the rules by the top level domain of their include patterns. This is done to speed up the matching because it reduces the space of possible rules that can match a URL.

The drawback is that the rules with include patterns that do not belong to any top level domain are not supported. In fact, an error is raised.

An exception were done for the universal matching pattern. It is the only cross-top-level-domain include pattern that is allowed. The rationale is that is can be convenient to define defaults (e.g. to define the default proxy to use if no other rule matches).