GraphQL Query Cost Analysis for graphql-js

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

Default multipliers

It's possible to define multipliers as an object of the form {limit: 100}, where the number is the default value of the "limit" argument, used in cost analysis. This is different from adding a default value to the actual GraphQL argument, because it's only used for cost analysis. If the query happens to return more items, the result is not truncated.

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.