graphql-cost-analysis

by pa-bru

A Graphql query cost analyzer.

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GraphQL Query Cost Analysis for graphql-js

Travis npm version

A GraphQL request cost analyzer.

This can be used to protect your GraphQL servers against DoS attacks, compute the data consumption per user and limit it.

This package parses the request content and computes its cost with your GraphQL server cost configuration.

Backend operations have different complexities and dynamic arguments (like a limit of items to retrieve). With this package you can define a cost setting on each GraphQL field/type with directives or a Type Map Object.

Works with graphql-js reference implementation

Type Map Object: An object containing types supported by your GraphQL server.

Installation

Install the package with npm

$ npm install --save graphql-cost-analysis

Simple Setup

Init the cost analyzer

import costAnalysis from 'graphql-cost-analysis'

const costAnalyzer = costAnalysis({ maximumCost: 1000, })

Then add the validation rule to the GraphQL server (apollo-server, express-graphql...)

Setup with express-graphql

app.use(
  '/graphql',
  graphqlHTTP((req, res, graphQLParams) => ({
    schema: MyGraphQLSchema,
    graphiql: true,
    validationRules: [
      costAnalysis({
        variables: graphQLParams.variables,
        maximumCost: 1000,
      }),
    ],
  }))
)

Setup with apollo-server-express

app.use(
  '/graphql',
  graphqlExpress(req => {
    return {
      schema,
      rootValue: null,
      validationRules: [
        costAnalysis({
          variables: req.body.variables,
          maximumCost: 1000,
        }),
      ],
    }
  })
)

costAnalysis Configuration

The

costAnalysis
function accepts the following options:

| Argument | Description | Type | Default | Required | | ------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------- | --------- | -------- | | maximumCost | The maximum allowed cost. Queries above this threshold will be rejected. | Int | undefined | yes | | variables | The query variables. This is needed because the variables are not available in the visitor of the graphql-js library. | Object | undefined | no | | defaultCost | Fields without cost setting will have this default value. | Int | 0 | no | | costMap | A Type Map Object where you can define the cost setting of each field without adding cost directives to your schema.
If this object is defined, cost directives will be ignored.
Each field in the Cost Map Object can have 3 args:

multipliers
,
useMultipliers
,
complexity
. | Object | undefined | no | | complexityRange | An optional object defining a range the complexity must respect. It throws an error if it's not the case. | Object: {min: number, max: number} | undefined | no | | onComplete(cost) | Callback function to retrieve the determined query cost. It will be invoked whether the query is rejected or not.
This can be used for logging or to implement rate limiting (for example, to store the cost by session and define a max cost the user can have in a specific time). | Function | undefined | no | | createError(maximumCost, cost) | Function to create a custom error. | Function | undefined | no |

A Custom Cost for Each Field/Type

Now that your global configuration is set, you can define the cost calculation for each of your schema Field/Type.

2 Ways of defining Field/Type cost settings:

  • with a
    @cost
    directive
  • by passing a Type Map Object to the
    costAnalysis
    function (see
    costMap
    argument)

Cost Settings Arguments

| Argument | Description | Type | Default | Required | | -------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------- | --------- | -------- | | multipliers | An array containing names of parameters present in the GraphQL field. Use parameters values to compute the field's cost dynamically.
N.B: if the parameter is an array, its multiplier value will be the length of the array (cf EG2).

E.g: GraphQL field is

getUser(filters: {limit: 5})
. The
multipliers
array could be
["filters.limit"]
.

E.g 2:
posts(first: 5, last: 5, list: ["my", "list"])
. The
multipliers
array could be
["first", "last", "list"]
. Then the cost would be
complexity
* (
first
+
last
+
list.length
). | Array | undefined | no | | useMultipliers | Defines if the field's cost depends on the parent multipliers and field's multipliers. | Boolean | true | no | | complexity | The level of complexity to resolve the current field.
If the field needs to call an expensive service to resolve itself, then the complexity should be at a high level but if the field is easy to resolve and not an expensive operation, the complexity should be at a low level. | Object {min: number, max: number} | {min: 1} | no |

Defining the Cost Settings via Directives

To define the cost settings of fields for which you want a custom cost calculation, just add a

cost
directive to the concerned fields directly to your GraphQL schema.

Example:

# you can define a cost directive on a type
type TypeCost @cost(complexity: 3) {
  string: String
  int: Int
}

type Query {

will have the default cost value

defaultCost: Int

will have a cost of 2 because this field does not depend on its parent fields

customCost: Int @cost(useMultipliers: false, complexity: 2)

complexity should be between 1 and 10

badComplexityArgument: Int @cost(complexity: 12)

the cost will depend on the limit parameter passed to the field

then the multiplier will be added to the parent multipliers array

customCostWithResolver(limit: Int): Int @cost(multipliers: ["limit"], complexity: 4)

for recursive cost

first(limit: Int): First @cost(multipliers: ["limit"], useMultipliers: true, complexity: 2)

you can override the cost setting defined directly on a type

overrideTypeCost: TypeCost @cost(complexity: 2) getCostByType: TypeCost

You can specify several field parameters in the multipliers array

then the values of the corresponding parameters will be added together.

here, the cost will be parent multipliers * (first + last) * `complexity

severalMultipliers(first: Int, last: Int): Int @cost(multipliers: ["first", "last"]) }

type First {

will have the default cost value

myString: String

the cost will depend on the limit value passed to the field and the value of complexity

and the parent multipliers args: here the limit value of the Query.first field

second(limit: Int): String @cost(multipliers: ["limit"], complexity: 2)

the cost will be the value of the complexity arg even if you pass a multipliers array

because useMultipliers is false

costWithoutMultipliers(limit: Int): Int @cost(useMultipliers: false, multipliers: ["limit"]) }

Defining the Cost Settings in a Type Map Object

Use a Type Map Object when you don't want to contaminate your GraphQL schema definition, so every cost setting field will be reported in a specific object.

If you dispatch your GraphQL schema in several modules, you can divide your Cost Map Object into several objects to put them in their specific modules and then merge them into one Cost Map object that you can pass to the

costAnalysis
function.

Create a type Map Object representing your GraphQL schema and pass cost settings to each field for which you want a custom cost.

Example:

const myCostMap = {
  Query: {
    first: {
      multipliers: ['limit'],
      useMultipliers: true,
      complexity: 3,
    },
  },
}

app.use( '/graphql', graphqlHTTP({ schema: MyGraphQLSchema, validationRules: [ costAnalysis({ maximumCost: 1000, costMap: myCostMap, }), ], }) )

Using complex types (UnionType or InterfaceType)

When using a UnionType or Interfaces, the highest of the nested fragments cost is used.

Common interface fields outside of fragments are treated like regular fields.

Given types:

interface CommonType {
  common: Int @cost(useMultipliers: false, complexity: 3)
}

type First implements CommonType { common: Int firstField: String @cost(useMultipliers: false, complexity: 5) }

type Second implements CommonType { common: Int secondField: String @cost(useMultipliers: false, complexity: 8) }

union FirstOrSecond = First | Second

type Query { firstOrSecond: FirstOrSecond commonType: CommonType }

and a query like

query {
  firstOrSecond {
    ... on First {
      firstField
    }
    ...secondFields
  }
  commonType {
    common
    ...secondFields
  }
}

fragment secondFields on Second { secondField }

the complexity of the query will be

8
,
  • firstOrSecond
    has a complexity of 8
    • Second.secondField
      field has a defined complexity of 8 which exceeds the complexity of 5 for
      First.firstField
  • commonType
    has a complexity of 11
    • secondFields
      has a complexity of 8
    • common
      has a complexity of 3 and is added to the previous value of 8

So the whole query has a complexity of 19

Note

If you just need a simple query complexity analysis without the GraphQL Schema Language and without multipliers and/or depth of parent multipliers, I suggest you install graphql-query-complexity

License

graphql-cost-analysis is MIT-licensed.

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