Apollo Graphql server depth limit plugin

apollo-depth-limit-plugin.ts

const depthLimitPlugin = (maxDepth: number): ApolloServerPlugin<GraphQLContext> => ({
  async requestDidStart() {
    return {
      async didResolveOperation(requestContext) {
        const document = requestContext.document

        // Skip depth limit for "IntrospectionQuery" operation
        if (requestContext.operationName === 'IntrospectionQuery') return

        let depth = 0
        let maxDepthReached = 0

        visit(document, {
          Field: {
            enter() {
              depth++
              if (depth > maxDepthReached) {
                maxDepthReached = depth
              }
            },
            leave() {
              depth--
            }
          }
        })

        if (maxDepthReached > maxDepth) {
          throw new GraphQLError(
            `Query depth limit exceeded. Max depth: ${maxDepth}, actual depth: ${maxDepthReached}`,
            {
              extensions: {
                operationName: requestContext.operationName,
                code: 'DEPTH_LIMIT_EXCEEDED',
                maxDepth,
                actualDepth: maxDepthReached
              }
            }
          )
        }
      }
    }
  }
})