CsvHelper Error "No header record found" on reading a csv stream

Question

Below is the code which i using to read a stream source of csv files but I get error as "No header record found". The library is 15.0 and I am already using .ToList() as suggested in some solutions, but still the error persists. Below is the method along with the tablefield class and the Read Stream method.

Also note here, I can get the desired result if I pass source as MemoryStream but it fails if I pass it as Stream because I need to avoid writing to memory each time.

public async Task<Stream> DownloadBlob(string containerName, string fileName, string connectionString)
        {
            //  MemoryStream memoryStream = new MemoryStream();           

            if (string.IsNullOrEmpty(connectionString))
            {
                connectionString = @"UseDevelopmentStorage=true";
                containerName = "testblobs";
            }

            Microsoft.Azure.Storage.CloudStorageAccount storageAccount = Microsoft.Azure.Storage.CloudStorageAccount.Parse(connectionString);
            CloudBlobClient serviceClient = storageAccount.CreateCloudBlobClient();
            CloudBlobContainer container = serviceClient.GetContainerReference(containerName);
            CloudBlockBlob blob = container.GetBlockBlobReference(fileName);
            if (!blob.Exists())
            {
                throw new Exception($"Blob Not found");
            }
          
            return await blob.OpenReadAsync();



public class TableField
    {
        public string Name { get; set; }
        public string Type { get; set; }

        public Type DataType
        {
            get
            {
                switch( Type.ToUpper() )
                {
                    case "STRING":
                        return typeof(string);

                    case "INT":
                        return typeof( int );

                    case "BOOL":
                    case "BOOLEAN":
                        return typeof( bool );

                    case "FLOAT":
                    case "SINGLE":
                    case "DOUBLE":
                        return typeof( double );

                    case "DATETIME":
                        return typeof( DateTime );

                    default:
                        throw new NotSupportedException( $"CSVColumn data type '{Type}' not supported" );
                }
            }
        }

 private IEnumerable<Dictionary<string, EntityProperty>> ReadCSV(Stream source, IEnumerable<TableField> cols)           

 {                
         using (TextReader reader = new StreamReader(source, Encoding.UTF8))
                {
                
                    var cache = new TypeConverterCache();
                    cache.AddConverter<float>(new CSVSingleConverter());
                    cache.AddConverter<double>(new CSVDoubleConverter());
                    var csv = new CsvReader(reader,
                        new CsvHelper.Configuration.CsvConfiguration(global::System.Globalization.CultureInfo.InvariantCulture)
                        {
                            Delimiter = ";",
                            HasHeaderRecord = true,
                            CultureInfo = global::System.Globalization.CultureInfo.InvariantCulture,
                            TypeConverterCache = cache
                        });
                    csv.Read();
                    csv.ReadHeader();


                    var map = (
                            from col in cols
                            from src in col.Sources()
                            let index = csv.GetFieldIndex(src, isTryGet: true)
                            where index != -1
                            select new { col.Name, Index = index, Type = col.DataType }).ToList();

                    while (csv.Read())
                    {
                        yield return map.ToDictionary(
                            col => col.Name,
                            col => EntityProperty.CreateEntityPropertyFromObject(csv.GetField(col.Type, col.Index)));
                    }
                
                }
            
        }

StreamReading code:

public async Task<Stream> ReadStream(string containerName, string digestFileName, string fileName, string connectionString)
        {
            string data = string.Empty;
            string fileExtension = Path.GetExtension(fileName);
            var contents = await DownloadBlob(containerName, digestFileName, connectionString);               
                
            
            return contents;
        }

Sample CSv to be read:

PartitionKey;Time;RowKey;State;RPM;Distance;RespirationConfidence;HeartBPM
te123;2020-11-06T13:33:37.593Z;10;1;8;20946;26;815
te123;2020-11-06T13:33:37.593Z;4;2;79944;8;36635;6
te123;2020-11-06T13:33:37.593Z;3;3;80042;9;8774;5
te123;2020-11-06T13:33:37.593Z;1;4;0;06642;6925;37
te123;2020-11-06T13:33:37.593Z;6;5;04740;74753;94628;21
te123;2020-11-06T13:33:37.593Z;7;6;6;2;14;629
te123;2020-11-06T13:33:37.593Z;9;7;126;86296;9157;05
te123;2020-11-06T13:33:37.593Z;5;8;5;3;7775;08
te123;2020-11-06T13:33:37.593Z;2;9;44363;65;70;229
te123;2020-11-06T13:33:37.593Z;8;10;02;24666;2;2

Answer 1

Related to my answer to your other question (it has more detail ; you can read it there) I didn't encounter any problem connecting CsvHelper to a blob storage sourced stream

This was the code used (I took the CSV data you posted, added it to a file, upped it to blob):

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private async void button1_Click(object sender, EventArgs e)
    {
        var cstr = "YOUR CONNSTR" HERE;

        var bbc = new BlockBlobClient(cstr, "temp", "ankit.csv");

        var s = await bbc.OpenReadAsync(new BlobOpenReadOptions(true) { BufferSize = 16384 });

        var sr = new StreamReader(s);

        var csv = new CsvHelper.CsvReader(sr, new CsvConfiguration(CultureInfo.CurrentCulture) { HasHeaderRecord = true, Delimiter = ";" });

        
        //try by read/getrecord
        while(await csv.ReadAsync())
        {
            var rec = csv.GetRecord<X>();
            Console.WriteLine(rec.PartitionKey);
        }

        var x = new X();
        //try by await foreach
        await foreach (var r in csv.EnumerateRecordsAsync(x))
        {
            Console.WriteLine(r.PartitionKey);
        }
    }
}

class X {
    public string PartitionKey { get; set; }
}