diff --git a/crates/csv/README.md b/crates/csv/README.md index c677ec9eb..6369ce8b4 100644 --- a/crates/csv/README.md +++ b/crates/csv/README.md @@ -11,7 +11,7 @@ mapping a SYLK sheet onto a document are the caller's work. | Function | What it does | |---|---| | `decode_text(bytes)` | UTF-8 and UTF-16 byte order marks; without one, valid UTF-8 is kept; other bytes are Windows-1256 when they read as Arabic, else Windows-1252 | -| `sniff_delimiter(text, quote)` | comma, semicolon or tab: the one with the most consistent count per line over the first 20 non-blank lines, outside quotes | +| `sniff_delimiter(text, quote)` | comma, semicolon or tab: the one with the most consistent field count over the first 20 non-blank records in a 64 KiB sample; quote boundaries must be coherent, and ties prefer tab, comma, then semicolon | | `parse_records(text, delim, quote, max_fields, on_record)` | records of fields, one callback per record (return `false` to stop); CR, LF and CRLF line ends; quoted fields with doubled quotes and line breaks; a quote in the middle of a field is text | | `records(text, delim, quote, max_records, max_fields)` | the same, collected | | `push_field(out, field, delim)`, `field_len(field, delim)` | one field as written, quoted only when it holds the delimiter, a quote or a line break; its exact length, to enforce a size cap before writing | diff --git a/crates/csv/src/lib.rs b/crates/csv/src/lib.rs index a773f066f..5cbdc28c5 100644 --- a/crates/csv/src/lib.rs +++ b/crates/csv/src/lib.rs @@ -29,44 +29,96 @@ pub mod sylk; pub use decode::decode_text; -/// Picks comma, semicolon or tab: the candidate with the most consistent count per line -/// (outside quotes) over the first non-blank lines. A candidate must appear on every such line, otherwise comma wins. +/// Picks comma, semicolon or tab by consistent field counts in the first non-blank records. +/// Quotes start only at a candidate field boundary; candidates with incoherent quoted fields +/// are discarded when another coherent candidate separates the records. Ties prefer tab, +/// then comma, then semicolon. Comma is the fallback when no candidate separates the text. pub fn sniff_delimiter(text: &str, quote: char) -> u8 { - let mut best = (b',', 0usize, 0usize); - for d in [',', ';', '\t'] { - let mut counts = vec![]; - let mut n = 0usize; - let mut in_q = false; - let mut blank = true; - for ch in text.chars().take(64 * 1024) { - if !in_q && ch == '\n' { - // Blank lines carry no delimiter evidence. - if !blank { - counts.push(n); - } - n = 0; - blank = true; - if counts.len() >= 20 { - break; + let mut candidates = [(b'\t', 0usize, 0usize, true), (b',', 0, 0, true), (b';', 0, 0, true)]; + const SAMPLE_BYTES: usize = 64 * 1024; + let mut sample_end = text.len().min(SAMPLE_BYTES); + while !text.is_char_boundary(sample_end) { + sample_end -= 1; + } + let sample = &text[..sample_end]; + let truncated = sample_end < text.len(); + for (delimiter, min_count, total, coherent) in &mut candidates { + let mut counts = Vec::new(); + let mut count = 0usize; + let mut quoted = false; + let mut after_quote = false; + let mut field_start = true; + let mut record_has_content = false; + let mut record_coherent = true; + let mut candidate_coherent = true; + let mut reached_record_limit = false; + let mut chars = sample.chars().peekable(); + while let Some(ch) = chars.next() { + if quoted { + if ch == quote { + if chars.peek() == Some("e) { + chars.next(); + record_has_content = true; + } else { + quoted = false; + after_quote = true; + } + } else if !ch.is_whitespace() { + record_has_content = true; } continue; } - if ch != '\r' { - blank = false; + if ch == '\r' || ch == '\n' { + if ch == '\r' && chars.peek() == Some(&'\n') { + chars.next(); + } + if record_has_content { + counts.push(count); + candidate_coherent &= record_coherent; + if counts.len() >= 20 { + reached_record_limit = true; + break; + } + } + count = 0; + quoted = false; + after_quote = false; + field_start = true; + record_has_content = false; + record_coherent = true; + continue; } - if ch == quote { - in_q = !in_q; - } else if !in_q && ch == d { - n += 1; + if ch == quote && field_start { + quoted = true; + field_start = false; + record_has_content = true; + } else if ch == char::from(*delimiter) { + count += 1; + field_start = true; + after_quote = false; + } else { + record_coherent &= !after_quote || ch.is_whitespace(); + record_has_content |= !ch.is_whitespace(); + field_start = false; } } - if !blank { - counts.push(n); + if !reached_record_limit && !truncated { + if quoted { + candidate_coherent = false; + } else if record_has_content { + candidate_coherent &= record_coherent; + counts.push(count); + } } - let min = counts.iter().copied().min().unwrap_or(0); - let total: usize = counts.iter().sum(); - if min > 0 && (min, total) > (best.1, best.2) { - best = (d as u8, min, total); + *coherent &= candidate_coherent; + *min_count = counts.iter().copied().min().unwrap_or(0); + *total = counts.iter().sum(); + } + let prefer_coherent = candidates.iter().any(|(_, min, _, coherent)| *min > 0 && *coherent); + let mut best = (b',', 0usize, 0usize); + for (delimiter, min, total, coherent) in candidates { + if min > 0 && (!prefer_coherent || coherent) && (min, total) > (best.1, best.2) { + best = (delimiter, min, total); } } best.0 @@ -204,6 +256,9 @@ mod tests { assert_eq!(sniff_delimiter("a\tb\n1\t2\n", '"'), b'\t'); assert_eq!(sniff_delimiter("a,b\n\"x;y;z\",2\n", '"'), b','); assert_eq!(sniff_delimiter("single", '"'), b','); + assert_eq!(sniff_delimiter("a,b\tc\n1,2\td\n", '"'), b'\t'); + assert_eq!(sniff_delimiter("a,b;c\n1,2;c\n", '"'), b','); + assert_eq!(sniff_delimiter("a;b\tc\n1;2\td\n", '"'), b'\t'); // A delimiter missing from some lines is text, not a separator (single-column export round trip). assert_eq!(sniff_delimiter("alpha;beta\r\ngamma\r\n", '"'), b','); assert_eq!(sniff_delimiter("alpha\tbeta\r\ngamma\r\n", '"'), b','); @@ -211,6 +266,48 @@ mod tests { assert_eq!(sniff_delimiter("x;y\n1,5;2", '"'), b';'); } + #[test] + fn delimiter_sniffing_preserves_candidate_quote_boundaries() { + for ending in ["\n", "\r\n", "\r"] { + for (text, expected) in [ + (format!("Name,\"preferred\tCity\"{ending}Ada\tLondon{ending}"), b'\t'), + (format!("\"Last, First\";City{ending}Ada;London{ending}"), b';'), + (format!("\"Name\";\"Last, First\"{ending}\"Ada\";\"Lovelace, Countess\"{ending}\"Grace\";\"Hopper, Admiral\"{ending}"), b';'), + (format!("\"Name\"suffix,Title\tCity{ending}\"Ada\"suffix,Analyst\tLondon\tignored{ending}"), b'\t'), + (format!("\r\n \r\n\"Name\";City{ending}Ada;London{ending}"), b';'), + ] { + assert_eq!(sniff_delimiter(&text, '"'), expected, "{text:?}"); + } + } + } + + #[test] + fn delimiter_sniffing_counts_empty_quoted_fields_and_ignores_whitespace_records() { + assert_eq!(sniff_delimiter("\"\";name\n\"\";Ada\n", '"'), b';'); + + let blank_rows = "\t \t\n".repeat(25); + assert_eq!(sniff_delimiter(&format!("{blank_rows}a;b\nc;d\n"), '"'), b';'); + } + + #[test] + fn delimiter_sniffing_does_not_count_the_twentieth_record_twice() { + let mut text = "a;b\tc\td\n".repeat(19); + text.push('a'); + text.push_str(&";".repeat(19)); + text.push_str("\tc\n"); + assert_eq!(sniff_delimiter(&text, '"'), b'\t'); + } + + #[test] + fn delimiter_sniffing_discards_an_incomplete_record_at_the_sample_boundary() { + let complete = "a\tb\tc\n1\t2\t3\n"; + let remaining = 64 * 1024 - complete.len(); + let partial = format!("{}x\t\"unfinished", "z".repeat(remaining - 4)); + assert!(partial.len() >= remaining); + let text = format!("{complete}{partial}\"\n"); + assert_eq!(sniff_delimiter(&text, '"'), b'\t'); + } + #[test] fn parser_stops_collecting_fields_at_the_cap() { let (max, extra) = (16_384usize, 50);