util

package main

import (
	"encoding/json"
	"fmt"
	"time"

	"github.com/onflow/flow-go/engine/access/rest/models"
	"github.com/onflow/flow-go/engine/access/rest/util"
)

func main() {

	blocks := make([]models.Block, 2)
	for i := range blocks {
		block, err := generateBlock()
		if err != nil {
			fmt.Println(err)
			return
		}
		blocks[i] = block
	}

	selectKeys := []string{
		"header.id",
		"payload.collection_guarantees.signature",
		"payload.block_seals.aggregated_approval_signatures.signer_ids",
		"payload.collection_guarantees.signer_ids",
		"execution_result.events.event_index",
		"something.nonexisting",
	}

	filteredBlock, err := util.SelectFilter(blocks, selectKeys)
	if err != nil {
		fmt.Println(err)
		return
	}

	marshalled, err := json.MarshalIndent(filteredBlock, "", "\t")
	if err != nil {
		panic(err.Error())
	}
	fmt.Println(string(marshalled))
}

func generateBlock() (models.Block, error) {

	dummySignature := "abcdef0123456789"
	multipleDummySignatures := []string{dummySignature, dummySignature}
	dummyID := "abcd"
	dateString := "2021-11-20T11:45:26.371Z"
	t, err := time.Parse(time.RFC3339, dateString)
	if err != nil {
		return models.Block{}, err
	}

	return models.Block{
		Header: &models.BlockHeader{
			Id:                   dummyID,
			ParentId:             dummyID,
			Height:               "100",
			Timestamp:            t,
			ParentVoterSignature: dummySignature,
		},
		Payload: &models.BlockPayload{
			CollectionGuarantees: []models.CollectionGuarantee{
				{
					CollectionId: "abcdef0123456789",
					SignerIds:    multipleDummySignatures,
					Signature:    dummySignature,
				},
			},
			BlockSeals: []models.BlockSeal{
				{
					BlockId:    dummyID,
					ResultId:   dummyID,
					FinalState: "final",
					AggregatedApprovalSignatures: []models.AggregatedSignature{
						{
							VerifierSignatures: multipleDummySignatures,
							SignerIds:          multipleDummySignatures,
						},
					},
				},
			},
		},
		ExecutionResult: &models.ExecutionResult{
			Id:      dummyID,
			BlockId: dummyID,
			Events: []models.Event{
				{
					Type_:            "type",
					TransactionId:    dummyID,
					TransactionIndex: "1",
					EventIndex:       "2",
					Payload:          "payload",
				},
				{
					Type_:            "type",
					TransactionId:    dummyID,
					TransactionIndex: "1",
					EventIndex:       "3",
					Payload:          "payload",
				},
			},
			Links: &models.Links{
				Self: "link",
			},
		},
	}, nil
}

Output:

[
	{
		"execution_result": {
			"events": [
				{
					"event_index": "2"
				},
				{
					"event_index": "3"
				}
			]
		},
		"header": {
			"id": "abcd"
		},
		"payload": {
			"block_seals": [
				{
					"aggregated_approval_signatures": [
						{
							"signer_ids": [
								"abcdef0123456789",
								"abcdef0123456789"
							]
						}
					]
				}
			],
			"collection_guarantees": [
				{
					"signature": "abcdef0123456789",
					"signer_ids": [
						"abcdef0123456789",
						"abcdef0123456789"
					]
				}
			]
		}
	},
	{
		"execution_result": {
			"events": [
				{
					"event_index": "2"
				},
				{
					"event_index": "3"
				}
			]
		},
		"header": {
			"id": "abcd"
		},
		"payload": {
			"block_seals": [
				{
					"aggregated_approval_signatures": [
						{
							"signer_ids": [
								"abcdef0123456789",
								"abcdef0123456789"
							]
						}
					]
				}
			],
			"collection_guarantees": [
				{
					"signature": "abcdef0123456789",
					"signer_ids": [
						"abcdef0123456789",
						"abcdef0123456789"
					]
				}
			]
		}
	}
]