feat: port csv2lp from influxdb (#37)

Co-authored-by: William Baker <55118525+wbaker85@users.noreply.github.com>

pkg/csv2lp/skip_header_lines_test.go

@@ -0,0 +1,93 @@
+package csv2lp
+
+import (
+	"io"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// simulates the reader that returns all data together with EOF
+type readOnceWithEOF struct {
+	reader io.Reader
+}
+
+func (r *readOnceWithEOF) Read(p []byte) (n int, err error) {
+	n, _ = r.reader.Read(p)
+	return n, io.EOF
+}
+
+// Test_SkipHeaderLines checks that first lines are skipped
+func Test_SkipHeaderLines(t *testing.T) {
+
+	var tests = []struct {
+		skipCount int
+		input     string
+		result    string
+	}{
+		{
+			10,
+			"1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n",
+			"",
+		},
+		{
+			0,
+			"1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n",
+			"1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n",
+		},
+		{
+			1,
+			"1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n",
+			"2\n3\n4\n5\n6\n7\n8\n9\n0\n",
+		},
+		{
+			5,
+			"1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n",
+			"6\n7\n8\n9\n0\n",
+		},
+		{
+			20,
+			"1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n",
+			"",
+		},
+		{
+			1,
+			"\"\n\"\"\n\"\n2",
+			"2",
+		},
+	}
+
+	for i, test := range tests {
+		input := test.input
+		bufferSizes := []int{1, 2, 7, 0, len(input), len(input) + 1}
+		for _, bufferSize := range bufferSizes {
+			t.Run(strconv.Itoa(i)+"_"+strconv.Itoa(bufferSize), func(t *testing.T) {
+				var reader io.Reader
+				if bufferSize == 0 {
+					// emulate a reader that returns EOF together with data
+					bufferSize = len(input)
+					reader = SkipHeaderLinesReader(test.skipCount, &readOnceWithEOF{strings.NewReader(input)})
+				} else {
+					reader = SkipHeaderLinesReader(test.skipCount, strings.NewReader(input))
+				}
+				buffer := make([]byte, bufferSize)
+				result := make([]byte, 0, 100)
+				for {
+					n, err := reader.Read(buffer)
+					if n > 0 {
+						result = append(result, buffer[:n]...)
+					}
+					if err != nil {
+						if err != io.EOF {
+							require.Nil(t, err.Error())
+						}
+						break
+					}
+				}
+				require.Equal(t, test.result, string(result))
+			})
+		}
+	}
+}