query-cost-analyzer.service.ts

import {
  parse,
  TypeInfo,
  ValidationContext,
  visit,
  visitWithTypeInfo,
  getNamedType,
  OperationDefinitionNode,
  FieldNode,
  GraphQLSchema,
  SelectionNode,
  DocumentNode,
  DefinitionNode,
  GraphQLNamedType,
} from 'graphql'
import createCostAnalysis from 'graphql-cost-analysis'
import { GraphQLRequestContext } from 'apollo-server-core'
import { Logger } from 'pino'

interface CostInput {
  requestContext: GraphQLRequestContext
  schema: GraphQLSchema
}

export class QueryCostAnalyzerService {
  errorMessage = 'The query exceeds the maximum cost'
  constructor() {}

  buildAnalyzer(variables) {
    return createCostAnalysis({
      maximumCost: 1000, // to be determined
      variables: variables,
      defaultCost: 1, // let's just blanket cost every field with this value for now
      onComplete: cost => {
        console.log(`graphql-cost-analysis cost for request was ${cost}`) // in prod we wouldn't have a console log here
      },
    })
  }

  // do some graphQL things to calculate the cost
  getCost({requestContext, schema}: CostInput ): number {

    const typeInfo = new TypeInfo(schema)
    if (!requestContext.source) {
      return 0
    }
    const ast = parse(requestContext.source)

    const onBudgetExceeded = () => { } // leaving this blank for now

    const validationContext = new ValidationContext(
      schema,
      ast,
      typeInfo,
      onBudgetExceeded
    )

    const analysisVisitor = this.buildAnalyzer(
      requestContext.request.variables,
    )(validationContext)

    // Unfortunately not functional approach
    // Go through AST and register all costs
    visit(ast, visitWithTypeInfo(typeInfo, analysisVisitor))
    return analysisVisitor.cost || 0
  }
}