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I am trying to retrieve filename and ID list with Google Drive API (the latest Drive API version v3 is used here) as a first step in order to analyze and manipulate these files on Google Drive. The experimental implementation is as below. (Note: credentials.json file is needed and the step to generate this file is here. )

The experimental implementation

using Google.Apis.Auth.OAuth2;
using Google.Apis.Drive.v3;
using Google.Apis.Drive.v3.Data;
using Google.Apis.Services;
using Google.Apis.Util.Store;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace GoogleDriveFileManager
{
    class Program
    {
        static string[] Scopes = { DriveService.Scope.DriveReadonly };
        static string ApplicationName = "GoogleDriveFileManager";

        static void Main(string[] args)
        {
            UserCredential credential;

            using (var stream =
                new FileStream("credentials.json", FileMode.Open, FileAccess.Read))
            {
                string credPath = "token.json";
                credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
                    GoogleClientSecrets.Load(stream).Secrets,
                    Scopes,
                    "user",
                    CancellationToken.None,
                    new FileDataStore(credPath, true)).Result;
                Console.WriteLine($"Credential file saved to: {credPath}");
            }

            // Create Drive API service.
            var service = new DriveService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = ApplicationName,
            });

            // Define parameters of request.
            FilesResource.ListRequest listRequest = service.Files.List();
            listRequest.PageSize = 1000;
            listRequest.Fields = "nextPageToken, files(id, name)";

            // List files.
            IList<Google.Apis.Drive.v3.Data.File> files = listRequest.Execute()
                .Files;
            Console.WriteLine("Files:");
            Console.WriteLine($"file.Name{new String('\t', 6)}file.Id{new String('\t', 8)}file.ModifiedTime");
            if (files != null && files.Count > 0)
            {
                foreach (var file in files)
                {
                    Console.WriteLine(
                        $"{file.Name.PadRight(56)}{file.Id.PadRight(36)}{file.ModifiedTime}"
                        );
                }
            }
            else
            {
                Console.WriteLine("No files found.");
            }
            Console.Read();
        }
    }
}

If there is any possible improvement about potential drawback or unnecessary overhead, please let me know.

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  • 2
    \$\begingroup\$ Which version of C# are you using? I'm asking it because for instance since C# 7.1 async main is supported. \$\endgroup\$ – Peter Csala Apr 13 at 7:35
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First of all let me clarify that I'm not familiar with the Google Drive API. I've done some refactoring but I haven't tested it (just make it compile).

If I can assume you are using greater C# version than 8 then you can refactor your code like this:

using static {YourMainNamespace}.Constants;

class Program
{
    static async Task Main(string[] args)
    {
        UserCredential credential = await AuthorizeAgainstGoogleDriveAsync();
        IList<Google.Apis.Drive.v3.Data.File> files = await GetFilesMetaInfoAsync(credential);
        DisplayFilesMetaInfoInTabularFashion(files);
        Console.ReadLine();
    }

    static async Task<UserCredential> AuthorizeAgainstGoogleDriveAsync(
        string sourceRelativePath = Authorize.RelativeFilePath.Source,
        string targetRelativePath = Authorize.RelativeFilePath.Target)
    {
        using var stream = new FileStream(sourceRelativePath, FileMode.Open, FileAccess.Read);

        var credential = await GoogleWebAuthorizationBroker.AuthorizeAsync(
            GoogleClientSecrets.Load(stream).Secrets,
            Authorize.Scopes,
            Authorize.User,
            CancellationToken.None,
            new FileDataStore(targetRelativePath, true));

        Console.WriteLine($"Credential file saved to: {Authorize.RelativeFilePath.Target}");

        return credential;
    }

    static async Task<IList<Google.Apis.Drive.v3.Data.File>> GetFilesMetaInfoAsync(
        UserCredential credential,
        string applicationName = GetFiles.ApplicationName,
        int pageSize = GetFiles.PageSize,
        string fields = GetFiles.Fields)
    {
        var service = new DriveService(new BaseClientService.Initializer()
        {
            HttpClientInitializer = credential,
            ApplicationName = applicationName,
        });

        FilesResource.ListRequest listRequest = service.Files.List();
        listRequest.PageSize = pageSize;
        listRequest.Fields = fields;

        var fileList = await listRequest.ExecuteAsync();

        return fileList.Files;
    }

    static void DisplayFilesMetaInfoInTabularFashion(IList<Google.Apis.Drive.v3.Data.File> files)
    {
        Console.WriteLine("Files:");
        Console.WriteLine($"{DisplayFiles.Name}{new string('\t', 6)}{DisplayFiles.Id}{new string('\t', 8)}{DisplayFiles.ModifiedTime}");

        if (files == null || files.Count <= 0)
        {
            Console.WriteLine(DisplayFiles.NoFileMessage);
            return;
        }

        foreach (var file in files)
        {
            Console.WriteLine($"{file.Name,-56}{file.Id,-36}{file.ModifiedTime}");
        }
            
    }
}

static class Constans
{
    public static class Authorize
    {
        public const string User = "user";
        public readonly static string[] Scopes = new[] { DriveService.Scope.DriveReadonly };

        public static class RelativeFilePath
        {
            public const string Source = "credentials.json";
            public const string Target = "token.json";
        }
    }

    public static class GetFiles
    {
        public const string ApplicationName = "GoogleDriveFileManager";
        public const int PageSize = 1000;
        public const string Fields = "nextPageToken, files(id, name)";
    }

    public static class DisplayFiles
    {
        private const string prefix = "file.";
        public const string Name = prefix + nameof(Name);
        public const string Id = prefix + nameof(Id);
        public const string ModifiedTime = prefix + nameof(ModifiedTime);
        public const string NoFileMessage = "No files found.";
    }
}

Let me give you some context for each part:

Main

static async Task Main(string[] args)
{
    UserCredential credential = await AuthorizeAgainstGoogleDriveAsync();
    IList<Google.Apis.Drive.v3.Data.File> files = await GetFilesMetaInfoAsync(credential);
    DisplayFilesMetaInfoInTabularFashion(files);
    Console.ReadLine();
}
  • I've made your Main async (supported since C# 7.1) to be able to use async-await
  • I've split your logic into three smaller functions to make your Main short and concise
    • If the scope of the application is this small then you can use shorter names of course, like
      • AuthorizeAsync
      • GetFiles
      • DisplayFiles

Constants

using static {YourMainNamespace}.Constants;

...

static class Constans
{
    public static class Authorize
    {
        public const string User = "user";
        public readonly static ImmutableArray<string> Scopes = new[] { DriveService.Scope.DriveReadonly }.ToImmutableArray();

        public static class RelativeFilePath
        {
            public const string Source = "credentials.json";
            public const string Target = "token.json";
        }
    }

    public static class GetFiles
    {
        public const string ApplicationName = "GoogleDriveFileManager";
        public const int PageSize = 1000;
        public const string Fields = "nextPageToken, files(id, name)";
    }

    public static class DisplayFiles
    {
        private const string prefix = "file.";
        public const string Name = prefix + nameof(Name);
        public const string Id = prefix + nameof(Id);
        public const string ModifiedTime = prefix + nameof(ModifiedTime);
        public const string NoFileMessage = "No files found.";
    }
}
  • I've put all of the hardcoded values into a hierarchical structure
    • Because I'm unfamiliar with the domain I've organize them based on the usage
    • In normal cases you should organize them based on their semantics
  • I've used const (which is implicit static) to prevent modification
  • In case of Scope I've used ImmutableArray to prevent modification
    • Here I can't use const but it could (and should) be marked as readonly
  • I've used using static to avoid prefixing with Constants each and every time

AuthorizeAgainstGoogleDriveAsync

static async Task<UserCredential> AuthorizeAgainstGoogleDriveAsync(
    string sourceRelativePath = Authorize.RelativeFilePath.Source,
    string targetRelativePath = Authorize.RelativeFilePath.Target)
{
    using var stream = new FileStream(sourceRelativePath, FileMode.Open, FileAccess.Read);

    var credential = await GoogleWebAuthorizationBroker.AuthorizeAsync(
        GoogleClientSecrets.Load(stream).Secrets,
        Authorize.Scopes,
        Authorize.User,
        CancellationToken.None,
        new FileDataStore(targetRelativePath, true));

    Console.WriteLine($"Credential file saved to: {Authorize.RelativeFilePath.Target}");

    return credential;
}
  • I've made the source and target file paths configurable (but with default values)
    • If you wish you can make the same with user and scopes
  • One can argue whether the Console.WriteLine should belong here or inside the Main
    • I've put it here to make the main as concise as possible
    • But from reusability point of view it should not belong here
  • I've used using declaration (which is a C# 8 feature) to avoid the block operator ({ ... })

GetFilesMetaInfoAsync

static async Task<IList<Google.Apis.Drive.v3.Data.File>> GetFilesMetaInfoAsync(
    UserCredential credential,
    string applicationName = GetFiles.ApplicationName,
    int pageSize = GetFiles.PageSize,
    string fields = GetFiles.Fields)
{
    var service = new DriveService(new BaseClientService.Initializer()
    {
        HttpClientInitializer = credential,
        ApplicationName = applicationName,
    });

    FilesResource.ListRequest listRequest = service.Files.List();
    listRequest.PageSize = pageSize;
    listRequest.Fields = fields;

    var fileList = await listRequest.ExecuteAsync();

    return fileList.Files;
}
  • I've made this API call to async (Execute >> ExecuteAsync) to make use of the async non-blocking I/O
  • I've declared the function with three optional parameters to be able to customize the request if needed
  • I've realized that you are not making use of the nextPageToken but I did not remove it
    • I've assumed that the implementation of paging will be your next step

DisplayFilesMetaInfoInTabularFashion

static void DisplayFilesMetaInfoInTabularFashion(IList<Google.Apis.Drive.v3.Data.File> files)
{
    Console.WriteLine("Files:");
    Console.WriteLine($"{DisplayFiles.Name}{new string('\t', 6)}{DisplayFiles.Id}{new string('\t', 8)}{DisplayFiles.ModifiedTime}");

    if (files == null || files.Count <= 0)
    {
        Console.WriteLine(DisplayFiles.NoFileMessage);
        return;
    }

    foreach (var file in files)
    {
        Console.WriteLine($"{file.Name,-56}{file.Id,-36}{file.ModifiedTime}");
    } 
}
  • This operation is tightly coupled to the request
    • It highly relies on the retrieved fields
    • So, it might make sense to it make more dynamic if needed
  • I've used new string instead of new String
  • I've reverted the if statement to use the early exit pattern
    • With this the main logic (foreach) is not indented
  • I've also used the capabilities of string interpolation to avoid calls like PadRight
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