imageproxy

README

imageproxy

imageproxy is a caching image proxy server written in golang. It supports dynamic image resizing and URL whitelisting.

This project was inspired by, and is designed to be an alternative to, WordPress's photon service. Photon is a great free service, but is limited to sites hosted on WordPress.com, or that use the Jetpack plugin. If you don't want to use Jetpack, then you're asked to use a different service. If you're looking for an alternative hosted service, I'd recommend resize.ly, embed.ly, or cloudinary. I decided to try building my own for fun.

URL Structure

imageproxy URLs are of the form http://localhost/{options}/{remote_url}.

Options

Options are specified as a comma delimited list of parameters, which can be supplied in any order. Duplicate parameters overwrite previous values.

The format is a superset of resize.ly's options.

Size

The size option takes the general form {width}x{height}, where width and height are numbers. Integer values greater than 1 are interpreted as exact pixel values. Floats between 0 and 1 are interpreted as percentages of the original image size. If either value is omitted or set to 0, it will be automatically set to preserve the aspect ratio based on the other dimension. If a single number is provided (with no "x" separator), it will be used for both height and width.

Crop Mode

Depending on the options specified, an image may be cropped to fit the requested size. In all cases, the original aspect ratio of the image will be preserved; imageproxy will never stretch the original image.

When no explicit crop mode is specified, the following rules are followed:

• If both width and height values are specified, the image will be scaled to fill the space, cropping if necessary to fit the exact dimension.

• If only one of the width or height values is specified, the image will be resized to fit the specified dimension, scaling the other dimension as needed to maintain the aspect ratio.

If the fit option is specified together with a width and height value, the image will be resized to fit within a containing box of the specified size. As always, the original aspect ratio will be preserved. Specifying the fit option with only one of either width or height does the same thing as if fit had not been specified.

Rotate

The r{degrees} option will rotate the image the specified number of degrees, counter-clockwise. Valid degrees values are 90, 180, and 270. Images are rotated after being resized.

Flip

The fv option will flip the image vertically. The fh option will flip the image horizontally. Images are flipped after being resized and rotated.

Remote URL

The URL of the original image to load is specified as the remainder of the path, without any encoding. For example, http://localhost/200/https://willnorris.com/logo.jpg.

In order to optimize caching, it is recommended that URLs not contain query strings.

Examples

The following live examples demonstrate setting different options on this source image, which measures 1024 by 678 pixels.

Options	Meaning	Image
200x	200px wide, proportional height
0.15x	15% original width, proportional height
x100	100px tall, proportional width
100x150	100 by 150 pixels, cropping as needed
100	100px square, cropping as needed
150,fit	scale to fit 150px square, no cropping
100,r90	100px square, rotated 90 degrees
100,fv,fh	100px square, flipped horizontal and vertical

License

This application is distributed under the Apache 2.0 license found in the LICENSE file.

Documentation

Overview

Package data provides common shared data structures for imageproxy.

Package proxy provides the image proxy.

Index

• Variables
• func Transform(img []byte, opt *Options) ([]byte, error)
• type Cache
• type Options
  • func ParseOptions(str string) *Options
  • func (o Options) String() string
• type Proxy
  • func NewProxy(transport http.RoundTripper, cache Cache) *Proxy
  • func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request)
• type Request
  • func NewRequest(r *http.Request) (*Request, error)
• type TransformingTransport
  • func (t *TransformingTransport) RoundTrip(req *http.Request) (*http.Response, error)
• type URLError
  • func (e URLError) Error() string

Variables

var NopCache = new(nopCache)

NopCache provides a no-op cache implementation that doesn't actually cache anything.

Functions

func Transform

func Transform(img []byte, opt *Options) ([]byte, error)

Transform the provided image.

Types

type Cache

type Cache interface {
	// Get retrieves the cached data for the provided key.
	Get(key string) (data []byte, ok bool)

	// Set caches the provided data.
	Set(key string, data []byte)

	// Delete deletes the cached data at the specified key.
	Delete(key string)
}

The Cache interface defines a cache for storing arbitrary data. The interface is designed to align with httpcache.Cache.

type Options

type Options struct {
	Width  float64 // requested width, in pixels
	Height float64 // requested height, in pixels

	// If true, resize the image to fit in the specified dimensions.  Image
	// will not be cropped, and aspect ratio will be maintained.
	Fit bool

	// Rotate image the specified degrees counter-clockwise.  Valid values are 90, 180, 270.
	Rotate int

	FlipVertical   bool
	FlipHorizontal bool
}

Options specifies transformations that can be performed on a requested image.

func ParseOptions

func ParseOptions(str string) *Options

func (Options) String

func (o Options) String() string

type Proxy

type Proxy struct {
	Client *http.Client // client used to fetch remote URLs
	Cache  Cache

	// Whitelist specifies a list of remote hosts that images can be proxied from.  An empty list means all hosts are allowed.
	Whitelist []string
}

Proxy serves image requests.

func NewProxy

func NewProxy(transport http.RoundTripper, cache Cache) *Proxy

NewProxy constructs a new proxy. The provided http Client will be used to fetch remote URLs. If nil is provided, http.DefaultClient will be used.

func (*Proxy) ServeHTTP

func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request)

ServeHTTP handles image requests.

type Request

type Request struct {
	URL     *url.URL // URL of the image to proxy
	Options *Options // Image transformation to perform
}

func NewRequest

func NewRequest(r *http.Request) (*Request, error)

NewRequest parses an http.Request into an image request.

type TransformingTransport

type TransformingTransport struct {
	// Transport is used to satisfy non-transform requests (those that do not include a URL fragment)
	Transport http.RoundTripper

	// Client is used to fetch images to be resized.
	Client *http.Client
}

TransformingTransport is an implementation of http.RoundTripper that optionally transforms images using the options specified in the request URL fragment.

func (*TransformingTransport) RoundTrip

func (t *TransformingTransport) RoundTrip(req *http.Request) (*http.Response, error)

RoundTrip implements http.RoundTripper.

type URLError

type URLError struct {
	Message string
	URL     *url.URL
}

URLError reports a malformed URL error.

func (URLError) Error

func (e URLError) Error() string