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# fast-redact very fast object redaction [](https://travis-ci.org/davidmarkclements/fast-redact) ## Default Usage By default, `fast-redact` serializes an object with `JSON.stringify`, censoring any data at paths specified: ```js const fastRedact = require('fast-redact') const fauxRequest = { headers: { host: 'http://example.com', cookie: `oh oh we don't want this exposed in logs in etc.`, referer: `if we're cool maybe we'll even redact this`, // Note: headers often contain hyphens and require bracket notation 'X-Forwarded-For': `192.168.0.1` } } const redact = fastRedact({ paths: ['headers.cookie', 'headers.referer', 'headers["X-Forwarded-For"]'] }) console.log(redact(fauxRequest)) // {"headers":{"host":"http://example.com","cookie":"[REDACTED]","referer":"[REDACTED]","X-Forwarded-For": "[REDACTED]"}} ``` ## API ### `require('fast-redact')({paths, censor, serialize}) => Function` When called without any options, or with a zero length `paths` array, `fast-redact` will return `JSON.stringify` or the `serialize` option, if set. #### `paths` – `Array` An array of strings describing the nested location of a key in an object. The syntax follows that of the EcmaScript specification, that is any JavaScript path is accepted – both bracket and dot notation is supported. For instance in each of the following cases, the `c` property will be redacted: `a.b.c`,`a['b'].c`, `a["b"].c`, `a[``b``].c`. Since bracket notation is supported, array indices are also supported `a[0].b` would redact the `b` key in the first object of the `a` array. Leading brackets are also allowed, for instance `["a"].b.c` will work. ##### Wildcards In addition to static paths, asterisk wildcards are also supported. When an asterisk is place in the final position it will redact all keys within the parent object. For instance `a.b.*` will redact all keys in the `b` object. Similarly for arrays `a.b[*]` will redact all elements of an array (in truth it actually doesn't matter whether `b` is in an object or array in either case, both notation styles will work). When an asterisk is in an intermediate or first position, the paths following the asterisk will be redacted for every object within the parent. For example: ```js const fastRedact = require('fast-redact') const redact = fastRedact({paths: ['*.c.d']}) const obj = { x: {c: {d: 'hide me', e: 'leave me be'}}, y: {c: {d: 'and me', f: 'I want to live'}}, z: {c: {d: 'and also I', g: 'I want to run in a stream'}} } console.log(redact(obj)) // {"x":{"c":{"d":"[REDACTED]","e":"leave me be"}},"y":{"c":{"d":"[REDACTED]","f":"I want to live"}},"z":{"c":{"d":"[REDACTED]","g":"I want to run in a stream"}}} ``` Another example with a nested array: ```js const fastRedact = require('..') const redact = fastRedact({paths: ['a[*].c.d']}) const obj = { a: [ {c: {d: 'hide me', e: 'leave me be'}}, {c: {d: 'and me', f: 'I want to live'}}, {c: {d: 'and also I', g: 'I want to run in a stream'}} ] } console.log(redact(obj)) // {"a":[{"c":{"d":"[REDACTED]","e":"leave me be"}},{"c":{"d":"[REDACTED]","f":"I want to live"}},{"c":{"d":"[REDACTED]","g":"I want to run in a stream"}}]} ``` #### `remove` - `Boolean` - `[false]` The `remove` option, when set to `true` will cause keys to be removed from the serialized output. Since the implementation exploits the fact that `undefined` keys are ignored by `JSON.stringify` the `remove` option may *only* be used when `JSON.stringify` is the serializer (this is the default) – otherwise `fast-redact` will throw. If supplying a custom serializer that has the same behavior (removing keys with `undefined` values), this restriction can be bypassed by explicitly setting the `censor` to `undefined`. #### `censor` – `<Any type>` – `('[REDACTED]')` This is the value which overwrites redacted properties. Setting `censor` to `undefined` will cause properties to removed as long as this is the behavior of the `serializer` – which defaults to `JSON.stringify`, which does remove `undefined` properties. Setting `censor` to a function will cause `fast-redact` to invoke it with the original value. The output of the `censor` function sets the redacted value. Please note that asynchronous functions are not supported. #### `serialize` – `Function | Boolean` – `(JSON.stringify)` The `serialize` option may either be a function or a boolean. If a function is supplied, this will be used to `serialize` the redacted object. It's important to understand that for performance reasons `fast-redact` *mutates* the original object, then serializes, then restores the original values. So the object passed to the serializer is the exact same object passed to the redacting function. The `serialize` option as a function example: ```js const fastRedact = require('fast-redact') const redact = fastRedact({ paths: ['a'], serialize: (o) => JSON.stringify(o, 0, 2) }) console.log(redact({a: 1, b: 2})) // { // "a": "[REDACTED]", // "b": 2 // } ``` For advanced usage the `serialize` option can be set to `false`. When `serialize` is set to `false`, instead of the serialized object, the output of the redactor function will be the mutated object itself (this is the exact same as the object passed in). In addition a `restore` method is supplied on the redactor function allowing the redacted keys to be restored with the original data. ```js const fastRedact = require('fast-redact') const redact = fastRedact({ paths: ['a'], serialize: false }) const o = {a: 1, b: 2} console.log(redact(o) === o) // true console.log(o) // { a: '[REDACTED]', b: 2 } console.log(redact.restore(o) === o) // true console.log(o) // { a: 1, b: 2 } ``` #### `strict` – `Boolean` - `[true]` The `strict` option, when set to `true`, will cause the redactor function to throw if instead of an object it finds a primitive. When `strict` is set to `false`, the redactor function will treat the primitive value as having already been redacted, and return it serialized (with `JSON.stringify` or the user's custom `serialize` function), or as-is if the `serialize` option was set to false. ## Approach In order to achieve lowest cost/highest performance redaction `fast-redact` creates and compiles a function (using the `Function` constructor) on initialization. It's important to distinguish this from the dangers of a runtime eval, no user input is involved in creating the string that compiles into the function. This is as safe as writing code normally and having it compiled by V8 in the usual way. Thanks to changes in V8 in recent years, state can be injected into compiled functions using `bind` at very low cost (whereas `bind` used to be expensive, and getting state into a compiled function by any means was difficult without a performance penalty). For static paths, this function simply checks that the path exists and then overwrites with the censor. Wildcard paths are processed with normal functions that iterate over the object redacting values as necessary. It's important to note, that the original object is mutated – for performance reasons a copy is not made. See [rfdc](https://github.com/davidmarkclements/rfdc) (Really Fast Deep Clone) for the fastest known way to clone – it's not nearly close enough in speed to editing the original object, serializing and then restoring values. A `restore` function is also created and compiled to put the original state back on to the object after redaction. This means that in the default usage case, the operation is essentially atomic - the object is mutated, serialized and restored internally which avoids any state management issues. ## Caveat As mentioned in approach, the `paths` array input is dynamically compiled into a function at initialization time. While the `paths` array is vigourously tested for any developer errors, it's strongly recommended against allowing user input to directly supply any paths to redact. It can't be guaranteed that allowing user input for `paths` couldn't feasibly expose an attack vector. ## Benchmarks The fastest known predecessor to `fast-redact` is the non-generic [`pino-noir`](http://npm.im/pino-noir) library (which was also written by myself). In the direct calling case, `fast-redact` is ~30x faster than `pino-noir`, however a more realistic comparison is overhead on `JSON.stringify`. For a static redaction case (no wildcards) `pino-noir` adds ~25% overhead on top of `JSON.stringify` whereas `fast-redact` adds ~1% overhead. In the basic last-position wildcard case,`fast-redact` is ~12% faster than `pino-noir`. The `pino-noir` module does not support intermediate wildcards, but `fast-redact` does, the cost of an intermediate wildcard that results in two keys over two nested objects being redacted is about 25% overhead on `JSON.stringify`. The cost of an intermediate wildcard that results in four keys across two objects being redacted is about 55% overhead on `JSON.stringify` and ~50% more expensive that explicitly declaring the keys. ```sh npm run bench ``` ``` benchNoirV2*500: 59.108ms benchFastRedact*500: 2.483ms benchFastRedactRestore*500: 10.904ms benchNoirV2Wild*500: 91.399ms benchFastRedactWild*500: 21.200ms benchFastRedactWildRestore*500: 27.304ms benchFastRedactIntermediateWild*500: 92.304ms benchFastRedactIntermediateWildRestore*500: 107.047ms benchJSONStringify*500: 210.573ms benchNoirV2Serialize*500: 281.148ms benchFastRedactSerialize*500: 215.845ms benchNoirV2WildSerialize*500: 281.168ms benchFastRedactWildSerialize*500: 247.140ms benchFastRedactIntermediateWildSerialize*500: 333.722ms benchFastRedactIntermediateWildMatchWildOutcomeSerialize*500: 463.667ms benchFastRedactStaticMatchWildOutcomeSerialize*500: 239.293ms ``` ## Tests ``` npm test ``` ``` 224 passing (499.544ms) ``` ### Coverage ``` npm run cov ``` ``` -----------------|----------|----------|----------|----------|-------------------| File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s | -----------------|----------|----------|----------|----------|-------------------| All files | 100 | 100 | 100 | 100 | | fast-redact | 100 | 100 | 100 | 100 | | index.js | 100 | 100 | 100 | 100 | | fast-redact/lib | 100 | 100 | 100 | 100 | | modifiers.js | 100 | 100 | 100 | 100 | | parse.js | 100 | 100 | 100 | 100 | | redactor.js | 100 | 100 | 100 | 100 | | restorer.js | 100 | 100 | 100 | 100 | | rx.js | 100 | 100 | 100 | 100 | | state.js | 100 | 100 | 100 | 100 | | validator.js | 100 | 100 | 100 | 100 | | -----------------|----------|----------|----------|----------|-------------------| ``` ## License MIT ## Acknowledgements Sponsored by [nearForm](http://www.nearform.com)