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| <title>How do "fetchers" work?</title> | |
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| <h1>How do "fetchers" work?</h1> | |
| <p> | |
| Basically, "fetcher" is a simple object responsible for delivering external files to the script. | |
| Default fetcher object supplied with html2ps/pdf fetches HTML, images and CSS from remote sites using HTTP protocol. | |
| If you're using your own fetcher, you need to implement 'get_data' function returning contents of requested file and, | |
| probably, 'get_base_url', returning URL to be used as a base one while resolving relative URLs in recently fetched HTML file. | |
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| The image below illustrates simple html2ps session using default fetcher while converting html file from abstract test.com site. | |
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| <img src="uml/Simple_fetcher_session.PNG"/> | |
| <p> | |
| If you have pages stored on your local system or dynamically generated and kept in memory, you don't need to use HTTP protocol to fetch them. | |
| In this case, you should use custom fetcher, so session will look similar to image below. Note that fetcher processes <em>all</em> requests, | |
| returning valid content for all requests; this makes difference from the <em>very simple</em> fetcher supplied with html2ps, which <em>does always | |
| return</em> memory string content whatever the request is. Internals of the fully-featured fetcher will depend on your system architecture greatly, | |
| so most likely such fetcher will never be included to html2ps distribution. | |
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| <img src="uml/Custom_fetcher_session.PNG"/> | |
| <p> | |
| The image below illustrates why images and external stylesheets are not rendered when you're using <em>too simple</em> fetcher object. | |
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| <img src="uml/Simple_custom_fetcher_session.PNG"/> | |
| <p> | |
| Sometimes you need to fetch files from different places; for example, HTML code is generated locally, while images and CSS files should be fetched via | |
| HTTP protocol. In this case you'll need to use several fetchers at once, as illustrated below. Note that in this case you need to implement 'get_base_url' | |
| function returning correct URL so script will be able to resolve relative URLs contained in HTML code. | |
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| <img src="uml/Multiple_fetcher_session.PNG"/> | |
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