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request.js
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request.js
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'use strict';
var WxHParser = () => {
var parser = {}
parser.parseIntegerStrictly = (strel) => {
var dim = NaN;
var digits = strel.split(/[^\d]/)
if (digits.length === 1) {
dim = parseInt(strel);
}
return dim;
},
// parse image size from the specification string.
// Look for string with value "<width>x<height>" where width and height
// are integers strings, e.g. "300x200"
// Or simply an integer, e.g. "300"
// return { w: <width>, h: <height> } with <width> and <height> as
// numeric Integer values
// return null if the specification is not valid
parser.parseWxH = (dimSpec) => {
var dimension = null
var dimensionMatch = dimSpec.split("x");
if (dimensionMatch.length == 1) {
var dim = parser.parseIntegerStrictly(dimensionMatch[0])
dimension = { w: dim, h: dim }
} else if (dimensionMatch.length === 2) {
dimension = {
w: parser.parseIntegerStrictly(dimensionMatch[0]),
h: parser.parseIntegerStrictly(dimensionMatch[1])
}
}
if (dimension && (isNaN(dimension.w) || isNaN(dimension.h))) {
dimension = null
}
return dimension
}
return parser;
};
// parse the image dimensions from the query string.
// Look for parameter d with value <width>x<height> where width and height
// are integers, e.g. "d=300x200" returns { w:300, h:200 }
// A single integer dimension is valid as well, and is applied to both, e.g.
// "d=300" returns { w:300, h:300 }
// return null if d not present or formatted incorrectly, otherwise return
// { w: <width>, h: <height> } where <width> and <height> are integers
var QueryStringParser = {
dimension: (query) => {
//var querystring = require('querystring');
//var params = querystring.parse(query);
var dimension = null
if (query.d) {
dimension = WxHParser().parseWxH(query.d.value);
}
return dimension
}
};
// parse the image dimensions from the uri
// Look for second to last path element d with value <width>x<height>
// where width and height are integers,
// e.g. "https://300x200/image.jpeg" returns { w:300, h:200 }
// A single integer dimension is valid as well, and is applied to both,
// e.g. "https://300/image.jpeg" returns { w:300, h:300 }
// Memoize the path prefix before the dimensions specification,
// the image name and the image extension
// If the second to last path element d does not have a valid dimension
// specificaton, leave dimensions unspecified and include the last path
// element in the memoized prefix.
var URIParser = (uri) => {
var parser = {};
parser.parseElements = () => {
var elements = parser.elements;
if (elements === undefined) {
var match = uri.match(/(.*)\/([^\/]+)\.([^\/]+)/);
if (match) {
elements = {
prefix: match[1],
name: match[2],
extension: match[3]
}
}
parser.elements = elements;
}
return elements;
};
parser.prefix = () => {
var elems = parser.parseElements();
return (elems && elems.prefix) ? elems.prefix : null;
};
parser.imageName = () => {
var elems = parser.parseElements();
return (elems && elems.name) ? elems.name : null;
}
parser.imageExtension = () => {
var elems = parser.parseElements();
return (elems && elems.extension) ? elems.extension : null;
}
return parser;
};
var ImageRequestBuilder = (uri, query, accept) => {
var builder = {};
// defines the allowed dimension requests
builder.allowedDimensions = [
{ w:600, h:600 },
{ w:1200, h:1200 },
{ w:2400, h:2400 },
{ w:3600, h:3600 }
];
// file extension for requests that accept webp format
builder.webpExtension = 'webp';
builder.uriParser = () => {
if (builder.memoizedParser === undefined) {
builder.memoizedParser = URIParser(uri)
}
return builder.memoizedParser;
}
// determine requested image dimensions from the request
builder.requestDimension = () => {
var qsp = QueryStringParser;
return qsp.dimension(query);
};
// find the smallest allowed dimension greater than that requested
// not finding one, return the greatest allowed size
builder.allowedDimension = (dimRequested) => {
var allowed =
builder.allowedDimensions[builder.allowedDimensions.length - 1];
if (dimRequested && dimRequested.h && dimRequested.w) {
for (var i = 0; i < builder.allowedDimensions.length; ++i) {
var dimension = builder.allowedDimensions[i];
if (dimRequested.h <= dimension.h &&
dimRequested.w <= dimension.w
) {
allowed = dimension;
break;
}
}
}
return allowed;
}
// build edge request url of format /images/200x200/webp/image.jpg
builder.edgeRequest = () => {
var edgeURI = uri;
var dims = builder.requestDimension();
if (dims) {
var parser = builder.uriParser(uri);
var normalized = builder.allowedDimension(dims);
// build the new uri to be forwarded upstream
var parts = [];
parts.push(parser.prefix());
parts.push(normalized.w + "x" + normalized.h);
// check support for webp
if (accept.includes(builder.webpExtension)) {
parts.push(builder.webpExtension);
}
else{
parts.push(parser.imageExtension());
}
parts.push(parser.imageName() + "." + parser.imageExtension());
edgeURI = parts.join("/");
}
return edgeURI;
}
return builder;
};
var parseEvent = (event) => {
var request = event.request;
console.log("request is " + JSON.stringify(request));
return {
"request": request,
"uri": request.uri ?? "",
"query": request.querystring ?? "",
"accept": request.headers.accept.value ?? ""
}
};
var handler = (event, context, callback) => {
var params = parseEvent(event);
var irb = ImageRequestBuilder(
params.uri, params.query, params.accept);
var fwdURI = irb.edgeRequest()
var request = params.request
if (fwdURI) {
request.uri = fwdURI;
request.querystring = {};
}
console.log("Request going out is " + JSON.stringify(request));
if (callback) { callback(null, request) };
return request;
};