fix(CsvReader.cs): Add a read method to read without skipping headers

Author: omerbenda

src/CsvHelper/CsvReader.cs

@@ -237,6 +237,72 @@ protected virtual void ValidateHeader(ClassMap map, List<InvalidHeader> invalidH
 		}
 	}
 
+	/// <summary>
+	/// Advances the reader to the header record. Does not skip over records and should not be used to read records.
+	/// You need to call <see cref="Read"/> then <see cref="ReadHeader"/> 
+	/// for the headers to be read.
+	/// </summary>
+	/// <returns>True if there are more records, otherwise false.</returns>
+	public virtual bool PreHeaderRead()
+	{
+		// Don't forget about the async method below!
+
+		bool hasMoreData = parser.Read();
+		hasBeenRead = true;
+
+		currentIndex = -1;
+
+		if (detectColumnCountChanges && hasMoreData)
+		{
+			if (prevColumnCount > 0 && prevColumnCount != parser.Count)
+			{
+				var csvException = new BadDataException(string.Empty, parser.RawRecord, context, "An inconsistent number of columns has been detected.");
+
+				var args = new ReadingExceptionOccurredArgs(csvException);
+				if (readingExceptionOccurred?.Invoke(args) ?? true)
+				{
+					throw csvException;
+				}
+			}
+
+			prevColumnCount = parser.Count;
+		}
+
+		return hasMoreData;
+	}
+
+	/// <summary>
+	/// Advances the reader to the header record. Does not skip over records and should not be used to read records.
+	/// You need to call <see cref="ReadAsync"/> then <see cref="ReadHeader"/> 
+	/// for the headers to be read.
+	/// </summary>
+	/// <returns>True if there are more records, otherwise false.</returns>
+	public virtual async Task<bool> PreHeaderReadAsync()
+	{
+		bool hasMoreData = await parser.ReadAsync().ConfigureAwait(false);
+		hasBeenRead = true;
+
+		currentIndex = -1;
+
+		if (detectColumnCountChanges && hasMoreData)
+		{
+			if (prevColumnCount > 0 && prevColumnCount != parser.Count)
+			{
+				var csvException = new BadDataException(string.Empty, parser.RawRecord, context, "An inconsistent number of columns has been detected.");
+
+				var args = new ReadingExceptionOccurredArgs(csvException);
+				if (readingExceptionOccurred?.Invoke(args) ?? true)
+				{
+					throw csvException;
+				}
+			}
+
+			prevColumnCount = parser.Count;
+		}
+
+		return hasMoreData;
+	}
+
 	/// <inheritdoc/>
 	public virtual bool Read()
 	{
@@ -843,7 +909,7 @@ public virtual IEnumerable<T> GetRecords<T>()
 
 		if (hasHeaderRecord && headerRecord == null)
 		{
-			if (!Read())
+			if (!PreHeaderRead())
 			{
 				yield break;
 			}
@@ -924,7 +990,7 @@ public virtual IEnumerable<object> GetRecords(Type type)
 
 		if (hasHeaderRecord && headerRecord == null)
 		{
-			if (!Read())
+			if (!PreHeaderRead())
 			{
 				yield break;
 			}
@@ -989,7 +1055,7 @@ public virtual IEnumerable<T> EnumerateRecords<T>(T record)
 
 		if (hasHeaderRecord && headerRecord == null)
 		{
-			if (!Read())
+			if (!PreHeaderRead())
 			{
 				yield break;
 			}
@@ -1046,7 +1112,7 @@ public virtual IEnumerable<T> EnumerateRecords<T>(T record)
 
 		if (hasHeaderRecord && headerRecord == null)
 		{
-			if (!await ReadAsync().ConfigureAwait(false))
+			if (!await PreHeaderReadAsync().ConfigureAwait(false))
 			{
 				yield break;
 			}
@@ -1128,7 +1194,7 @@ public virtual async IAsyncEnumerable<object> GetRecordsAsync(Type type, [Enumer
 
 		if (hasHeaderRecord && headerRecord == null)
 		{
-			if (!await ReadAsync().ConfigureAwait(false))
+			if (!await PreHeaderReadAsync().ConfigureAwait(false))
 			{
 				yield break;
 			}
@@ -1194,7 +1260,7 @@ public virtual async IAsyncEnumerable<T> EnumerateRecordsAsync<T>(T record, [Enu
 
 		if (hasHeaderRecord && headerRecord == null)
 		{
-			if (!await ReadAsync().ConfigureAwait(false))
+			if (!await PreHeaderReadAsync().ConfigureAwait(false))
 			{
 				yield break;
 			}

tests/CsvHelper.Tests/Reading/ShouldSkipRecordTests.cs

@@ -83,5 +83,36 @@ public void ShouldSkipWithEmptyRows()
 			Assert.Equal("1", csv.GetField(0));
 			Assert.Equal("2", csv.GetField(1));
 		}
+
+		[Fact]
+		public void ShouldSkipIgnoreHeader()
+		{
+			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
+			{
+				ShouldSkipRecord = skipArgs => !skipArgs.Row[0]!.StartsWith("A")
+			};
+
+			var parser = new ParserMock(config)
+			{
+				{ "Name" },
+				{ "Arnold" },
+				{ "Andrew" },
+				{ "Betty" },
+				{ "Frank" }
+			};
+
+			var csv = new CsvReader(parser);
+			var csvReader = new CsvReader(parser);
+			var typeDef = new
+			{
+				Name = string.Empty
+			};
+
+			var records = csvReader.GetRecords(typeDef).ToList();
+
+			Assert.Equal(2, records.Count);
+			Assert.Equal("Arnold", records[0].Name);
+			Assert.Equal("Andrew", records[1].Name);
+		}
 	}
 }