rewriting-proxy
v0.5.2
Published
Proxy for rewriting JavaScript on-the-fly
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rewriting-proxy
Simple proxy library for rewriting JavaScript on-the-fly.
Installation
npm install rewriting-proxyUsage
From proxy-example.js:
var proxy = require("rewriting-proxy");
var options = {
rewriter: function (src, metadata) {
console.log("instrumenting " + metadata.url);
return src;
},
rewriteOptions: {
onNodeVisited: function (node) {
// Tag every element in the HTML with its source location
if (node.tagName) {
var location = node.__location;
node.attrs.push({ name: "data-loc", value: location.line + ":" + location.col })
}
},
locationInfo: true
},
headerHTML: "<script>alert(\"hi\");</script>",
port: 8080
};
proxy.start(options);The start(options) function starts the proxy server on localhost. Possible options are:
rewriter: A function that takes JavaScript code as its first parameter and returns the instrumented version of the code. Any response with a MIME type suggesting JavaScript content is passed torewriter. The metadata object passed as the second parameter includes properties:type: the type of the script, either'script'for inline scripts or script files,'event-handler'for event handlers, or'javascript-url'for JavaScript URLs.inline: For scripts of type'script', indicates whether the script was inline.url: A URL for the script; these are auto-generated for inline scripts, event handlers, etc.
rewriteOptions: An object that allows instrumenting the HTML. The object includes properties:onBeforeNodeVisited: A function that is called with a HTML node when the entire subtree rooted at the node has been visited. The function return value is ignored; instead the function should mutate the subtree rooted at the node argument. Is unlikeonNodeVisitedinvoked prior to any JavaScript instrumentation performed byrewriter.onNodeVisited: A function that is called with a HTML node when the entire subtree rooted at the node has been visited. The function return value is ignored; instead the function should mutate the subtree rooted at the node argument.locationInfo: A boolean that is parsed to the parse5 HTML parser, indicating whether node locations should be made available. (Disabled by default for performance.)
headerHTML: HTML string to be injected at the beginning of any requested HTML file.headerURLs: an Array of script URLs. These URLs will be loaded via<script>tags at the beginning of any HTML file.port: The port on which the proxy server should listen, default8080.
The library also exposes a rewriteHTML(html, url, rewriter,
headerHTML, headerURLs, options) function that rewrites the inline scripts (and HTML)
in a given html string with URL url, using the rewriter
function, headerHTML string and headerURLs array as described above.
To see a real-world use of the library, look at jalangi_proxy.js from the Jalangi framework.
Example
Input:
<!DOCTYPE html>
<html>
<head>
<title>Proxy test</title>
</head>
<body>
<h1>Proxy test</h1>
</body>
</html>Output using proxy-example.js (modulo indentation):
<!DOCTYPE html>
<html data-loc="2:1">
<head data-loc="3:3">
<script>alert("hi");</script>
<title data-loc="4:5">Proxy test</title>
</head>
<body data-loc="6:3">
<h1 data-loc="7:5">Proxy test</h1>
</body>
</html>Limitations
Can't rewrite scripts requested via HTTPS.
Can't rewrite inline scripts inserted by other scripts, e.g.:
var x = "<script>" + ... + "</script>"; node.innerHTML = x;
License
This software is distributed under the Eclipse Public License.