fix: Ignore quoted newlines when skipping lines in CSV (pola-rs#19543)

crates/polars-io/src/csv/read/read_impl.rs

@@ -15,8 +15,8 @@ use rayon::prelude::*;
 use super::buffer::init_buffers;
 use super::options::{CommentPrefix, CsvEncoding, NullValues, NullValuesCompiled};
 use super::parser::{
-    is_comment_line, next_line_position, next_line_position_naive, parse_lines, skip_bom,
-    skip_line_ending, skip_this_line, CountLines,
+    is_comment_line, parse_lines, skip_bom, skip_line_ending, skip_this_line, CountLines,
+    SplitLines,
 };
 use super::schema_inference::{check_decimal_comma, infer_file_schema};
 #[cfg(any(feature = "decompress", feature = "decompress-fast"))]
@@ -283,11 +283,19 @@ impl<'a> CoreReader<'a> {
 
         // skip 'n' leading rows
         if self.skip_rows_before_header > 0 {
+            let mut split_lines = SplitLines::new(bytes, quote_char, eol_char);
+            let mut current_line = &bytes[..0];
+
             for _ in 0..self.skip_rows_before_header {
-                let pos = next_line_position_naive(bytes, eol_char)
+                current_line = split_lines
+                    .next()
                     .ok_or_else(|| polars_err!(NoData: "not enough lines to skip"))?;
-                bytes = &bytes[pos..];
             }
+
+            current_line = split_lines
+                .next()
+                .unwrap_or(&current_line[current_line.len()..]);
+            bytes = &bytes[current_line.as_ptr() as usize - bytes.as_ptr() as usize..];
         }
 
         // skip lines that are comments
@@ -301,19 +309,19 @@ impl<'a> CoreReader<'a> {
         }
         // skip 'n' rows following the header
         if self.skip_rows_after_header > 0 {
-            for _ in 0..self.skip_rows_after_header {
-                let pos = if is_comment_line(bytes, self.comment_prefix.as_ref()) {
-                    next_line_position_naive(bytes, eol_char)
-                } else {
-                    // we don't pass expected fields
-                    // as we want to skip all rows
-                    // no matter the no. of fields
-                    next_line_position(bytes, None, self.separator, self.quote_char, eol_char)
-                }
-                .ok_or_else(|| polars_err!(NoData: "not enough lines to skip"))?;
+            let mut split_lines = SplitLines::new(bytes, quote_char, eol_char);
+            let mut current_line = &bytes[..0];
 
-                bytes = &bytes[pos..];
+            for _ in 0..self.skip_rows_after_header {
+                current_line = split_lines
+                    .next()
+                    .ok_or_else(|| polars_err!(NoData: "not enough lines to skip"))?;
             }
+
+            current_line = split_lines
+                .next()
+                .unwrap_or(&current_line[current_line.len()..]);
+            bytes = &bytes[current_line.as_ptr() as usize - bytes.as_ptr() as usize..];
         }
 
         let starting_point_offset = if bytes.is_empty() {

py-polars/tests/unit/io/test_csv.py

@@ -2307,3 +2307,18 @@ def test_csv_double_new_line() -> None:
         "column_2": ["b", None],
         "column_3": ["c", None],
     }
+
+
+def test_csv_quoted_newlines_skip_rows_19535() -> None:
+    assert_frame_equal(
+        pl.read_csv(
+            b"""\
+"a\nb"
+0
+""",
+            has_header=False,
+            skip_rows=1,
+            new_columns=["x"],
+        ),
+        pl.DataFrame({"x": 0}),
+    )