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76 lines
3.2 KiB
Markdown
76 lines
3.2 KiB
Markdown
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# Chrome's URL library
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## Layers
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There are several conceptual layers in this directory. Going from the lowest
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level up, they are:
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### Parsing
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The `url_parse.*` files are the parser. This code does no string
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transformations. Its only job is to take an input string and splits out the
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components of the URL as best as it can deduce them, for a given type of URL.
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Parsing can never fail, it will take its best guess. This layer does not
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have logic for determining the type of URL parsing to apply, that needs to
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be applied at a higher layer (the "util" layer below).
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Because the parser code is derived (_very_ distantly) from some code in
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Mozilla, some of the parser files are in `url/third_party/mozilla/`.
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The main header to include for calling the parser is
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`url/third_party/mozilla/url_parse.h`.
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### Canonicalization
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The `url_canon*` files are the canonicalizer. This code will transform specific
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URL components or specific types of URLs into a standard form. For some
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dangerous or invalid data, the canonicalizer will report that a URL is invalid,
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although it will always try its best to produce output (so the calling code
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can, for example, show the user an error that the URL is invalid). The
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canonicalizer attempts to provide as consistent a representation as possible
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without changing the meaning of a URL.
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The canonicalizer layer is designed to be independent of the string type of
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the embedder, so all string output is done through a `CanonOutput` wrapper
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object. An implementation for `std::string` output is provided in
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`url_canon_stdstring.h`.
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The main header to include for calling the canonicalizer is
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`url/url_canon.h`.
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### Utility
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The `url_util*` files provide a higher-level wrapper around the parser and
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canonicalizer. While it can be called directly, it is designed to be the
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foundation for writing URL wrapper objects (The GURL later and Blink's KURL
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object use the Utility layer to implement the low-level logic).
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The Utility code makes decisions about URL types and calls the correct parsing
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and canonicalzation functions for those types. It provides an interface to
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register application-specific schemes that have specific requirements.
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Sharing this loigic between KURL and GURL is important so that URLs are
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handled consistently across the application.
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The main header to include is `url/url_util.h`.
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### GURL and Origin
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At the highest layer, a C++ object for representing URLs is provided. This
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object uses STL. Most uses need only this layer. Include `url/gurl.h`.
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Also at this layer is also the Origin object which exists to make security
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decisions on the web. Include `url/origin.h`.
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## Historical background
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This code was originally a separate library that was designed to be embedded
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into both Chrome (which uses STL) and WebKit (which didn't use any STL at the
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time). As a result, the parsing, canonicalization, and utility code could
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not use STL, or any other common code in Chromium like base.
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When WebKit was forked into the Chromium repo and renamed Blink, this
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restriction has been relaxed somewhat. Blink still provides its own URL object
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using its own string type, so the insulation that the Utility layer provides is
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still useful. But some STL strings and calls to base functions have gradually
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been added in places where doing so is possible.
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