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106 lines
4.9 KiB
Markdown
106 lines
4.9 KiB
Markdown
# go-imageproxy #
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go-imageproxy is a caching image proxy server written in golang. It supports
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dynamic image resizing and URL whitelisting.
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This project was inspired by, and is designed to be an alternative to,
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WordPress's [photon service][photon]. Photon is a great free service, but is
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limited to sites hosted on WordPress.com, or that use the [Jetpack
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plugin][jetpack]. If you don't want to use Jetpack, then you're asked to use a
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different service. If you're looking for an alternative hosted service, I'd
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recommend [resize.ly][], [embed.ly][], or [cloudinary][]. I decided to try
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building my own for fun.
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[photon]: http://developer.wordpress.com/docs/photon/
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[jetpack]: http://jetpack.me/
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[resize.ly]: https://resize.ly/
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[embed.ly]: http://embed.ly/display
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[cloudinary]: http://cloudinary.com/
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## URL Structure ##
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go-imageproxy URLs are of the form `http://localhost/{options}/{remote_url}`.
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### Options ###
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Options are specified as a comma delimited list of parameters, the first of
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which always specifies image size. The format is a superset of [resize.ly's
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options](https://resize.ly/#demo).
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#### Size ####
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The size option takes the general form `{width}x{height}`, where width and
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height are numbers. Integer values greater than 1 are interpreted as exact
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pixel values. Floats between 0 and 1 are interpreted as percentages of the
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original image size. If either value is omitted or set to 0, it will be
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automatically set to preserve the aspect ratio based on the other dimension.
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If a single number is provided (with no "x" separator), it will be used for
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both height and width.
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#### Crop Mode ####
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Depending on the options specified, an image may be cropped to fit the
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requested size. In all cases, the original aspect ratio of the image will be
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preserved; go-imageproxy will never stretch the original image.
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When no explicit crop mode is specified, the following rules are followed:
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- If both width and height values are specified, the image will be scaled to
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fill the space, cropping if necessary to fit the exact dimension.
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- If only one of the width or height values is specified, the image will be
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resized to fit the specified dimension, scaling the other dimension as
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needed to maintain the aspect ratio.
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If the `fit` option is specified together with a width and height value, the
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image will be resized to fit within a containing box of the specified size. As
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always, the original aspect ratio will be preserved. Specifying the `fit`
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option with only one of either width or height does the same thing as if `fit`
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had not been specified.
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#### Rotate ####
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The `r{degrees}` option will rotate the image the specified number of degrees,
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counter-clockwise. Valid degrees values are `90`, `180`, and `270`. Images
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are rotated **after** being resized.
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#### Flip ####
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The `fv` option will flip the image vertically. The `fh` option will flip the
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image horizontally. Images are flipped **after** being resized and rotated.
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### Remote URL ###
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The URL of the original image to load is specified as the remainder of the
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path, without any encoding. For example,
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`http://localhost/200/https://willnorris.com/logo.jpg`.
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In order to [optimize caching][], it is recommended that URLs not contain query
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strings.
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[optimize caching]: http://www.stevesouders.com/blog/2008/08/23/revving-filenames-dont-use-querystring/
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### Examples ###
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The following live examples demonstrate setting different options on [this
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source image][small-things], which measures 1024 by 678 pixels.
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[small-things]: https://willnorris.com/content/uploads/2013/12/small-things.jpg
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Options | Meaning | Image
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--------|------------------------------------------|------
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200x | 200px wide, proportional height | 
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0.15x | 15% original width, proportional height | 
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x100 | 100px tall, proportional width | 
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100x150 | 100 by 150 pixels, cropping as needed | 
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100 | 100px square, cropping as needed | 
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150,fit | scale to fit 150px square, no cropping | 
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100,r90 | 100px square, rotated 90 degrees | 
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100,fv,fh | 100px square, flipped horizontal and vertical | 
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## License ##
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This application is distributed under the Apache 2.0 license found in the
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[LICENSE](./LICENSE) file.
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