How can I debug my Golang API code to show me what is wrong?

I have this module that use Google Cloud API to retrieve a list of all running Virtual Machine instances for a particular project. I'm new to Go, and followed the intro tutorial to help me out. I'm still trying to debug my code but no luck.

The problem is I'm able to communicate to Google Cloud API and pass authentication but that is all I can get through

compute.go module:

compute.go is able to communicate to Google Cloud servers and pass authentication (I'm not getting an auth error)

// Copyright 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package compute
// [START compute_instances_list_all]
import (
"context"
"fmt"
"io"
compute "cloud.google.com/go/compute/apiv1"
"google.golang.org/api/iterator"
computepb "google.golang.org/genproto/googleapis/cloud/compute/v1"
"google.golang.org/protobuf/proto"
)
// listAllInstances prints all instances present in a project, grouped by their zone.
func ListAllInstances(w io.Writer, projectID string) error {
// projectID := "your_project_id"
ctx := context.Background()
instancesClient, err := compute.NewInstancesRESTClient(ctx)
// instancesClient, err := compute.NewInstancesRESTClient(ctx, option.WithCredentialsFile(`C:\path\to\jsonkey.json`))
if err != nil {
return fmt.Errorf("NewInstancesRESTClient: %v", err)
}
defer instancesClient.Close()
// Use the `MaxResults` parameter to limit the number of results that the API returns per response page.
req := &computepb.AggregatedListInstancesRequest{
Project:    projectID,
MaxResults: proto.Uint32(6),
}
it := instancesClient.AggregatedList(ctx, req)
fmt.Fprintf(w, "Instances found:\n")
// Despite using the `MaxResults` parameter, you don't need to handle the pagination
// yourself. The returned iterator object handles pagination
// automatically, returning separated pages as you iterate over the results.
for {
pair, err := it.Next()
if err == iterator.Done {
break
}
if err != nil {
return err
}
instances := pair.Value.Instances
if len(instances) > 0 {
fmt.Fprintf(w, "%s\n", pair.Key)
for _, instance := range instances {
fmt.Fprintf(w, "- %s %s\n", instance.GetName(), instance.GetMachineType())
}
}
}
return nil
}
// [END compute_instances_list_all]

However the problem is when I run my main function that calls ListAllInstances, it returns a <nil>. Not allowing me to know what is wrong.

caller api.go module where I run go run .:

package main
import (
"fmt"
"example.com/compute"
"bytes"
)
func main() {
buf := new(bytes.Buffer)
// Get a message and print it.
respone := compute.ListAllInstances(buf, "project-unique-id")
fmt.Println(respone)
}

How else can I further debug this to figure out what is wrong with my code?

You're not printing buf. Your function returns an object of type error, which is nil (no error!), the actual output is written to buf.

Either print it out:

func main() {
buf := new(bytes.Buffer)
// Get a message and print it.
err := compute.ListAllInstances(buf, "project-unique-id")
if err != nil {
panic(err)
}
fmt.Println(buf.String())  // <======= Print buf contents!
}

Or just use os.Stdout:

func main() {
err := compute.ListAllInstances(os.Stdout, "project-unique-id")
if err != nil {
panic(err)
}
}

To answer your question about debugging, try using VSCode with the Go extension, in there you can run a debugger, set breakpoints and step through the code line-by-line, watching how variables change.

See also Debug Go programs in VS Code.