paste: permit the delimiter list to be empty (#6714)

* paste: permit the delimiter list to be empty

Also: refactored the delimiter processing logic

* Extract duplicated code into function

* Address PR comments. Improve code structure.

* Fix additional paste bugs

* Fix additional paste bugs

* Simplify backslash delimiter validation

* Fix Clippy violations

src/uu/paste/src/paste.rs

@@ -3,13 +3,14 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// spell-checker:ignore (ToDO) delim
-
 use clap::{crate_version, Arg, ArgAction, Command};
+use std::cell::{OnceCell, RefCell};
 use std::fs::File;
-use std::io::{stdin, stdout, BufRead, BufReader, Read, Write};
-use std::path::Path;
-use uucore::error::{FromIo, UResult, USimpleError};
+use std::io::{stdin, stdout, BufRead, BufReader, Stdin, Write};
+use std::iter::Cycle;
+use std::rc::Rc;
+use std::slice::Iter;
+use uucore::error::{UResult, USimpleError};
 use uucore::line_ending::LineEnding;
 use uucore::{format_usage, help_about, help_usage};
 
@@ -23,18 +24,6 @@ mod options {
     pub const ZERO_TERMINATED: &str = "zero-terminated";
 }
 
-// Wraps BufReader and stdin
-fn read_until<R: Read>(
-    reader: Option<&mut BufReader<R>>,
-    byte: u8,
-    buf: &mut Vec<u8>,
-) -> std::io::Result<usize> {
-    match reader {
-        Some(reader) => reader.read_until(byte, buf),
-        None => stdin().lock().read_until(byte, buf),
-    }
-}
-
 #[uucore::main]
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let matches = uu_app().try_get_matches_from(args)?;
@@ -96,120 +85,292 @@ fn paste(
     delimiters: &str,
     line_ending: LineEnding,
 ) -> UResult<()> {
-    let mut files = Vec::with_capacity(filenames.len());
-    for name in filenames {
-        let file = if name == "-" {
-            None
-        } else {
-            let path = Path::new(&name);
-            let r = File::open(path).map_err_context(String::new)?;
-            Some(BufReader::new(r))
+    let unescaped_and_encoded_delimiters = parse_delimiters(delimiters)?;
+
+    let stdin_once_cell = OnceCell::<Rc<RefCell<Stdin>>>::new();
+
+    let mut input_source_vec = Vec::with_capacity(filenames.len());
+
+    for filename in filenames {
+        let input_source = match filename.as_str() {
+            "-" => InputSource::StandardInput(
+                stdin_once_cell
+                    .get_or_init(|| Rc::new(RefCell::new(stdin())))
+                    .clone(),
+            ),
+            st => {
+                let file = File::open(st)?;
+
+                InputSource::File(BufReader::new(file))
+            }
         };
-        files.push(file);
+
+        input_source_vec.push(input_source);
     }
 
-    if delimiters.ends_with('\\') && !delimiters.ends_with("\\\\") {
+    let mut stdout = stdout().lock();
+
+    let line_ending_byte = u8::from(line_ending);
+    let line_ending_byte_array_ref = &[line_ending_byte];
+
+    let input_source_vec_len = input_source_vec.len();
+
+    let mut delimiter_state = DelimiterState::new(&unescaped_and_encoded_delimiters);
+
+    let mut output = Vec::new();
+
+    if serial {
+        for input_source in &mut input_source_vec {
+            output.clear();
+
+            loop {
+                match input_source.read_until(line_ending_byte, &mut output)? {
+                    0 => break,
+                    _ => {
+                        remove_trailing_line_ending_byte(line_ending_byte, &mut output);
+
+                        delimiter_state.write_delimiter(&mut output);
+                    }
+                }
+            }
+
+            delimiter_state.remove_trailing_delimiter(&mut output);
+
+            stdout.write_all(&output)?;
+            stdout.write_all(line_ending_byte_array_ref)?;
+        }
+    } else {
+        let mut eof = vec![false; input_source_vec_len];
+
+        loop {
+            output.clear();
+
+            let mut eof_count = 0;
+
+            for (i, input_source) in input_source_vec.iter_mut().enumerate() {
+                if eof[i] {
+                    eof_count += 1;
+                } else {
+                    match input_source.read_until(line_ending_byte, &mut output)? {
+                        0 => {
+                            eof[i] = true;
+                            eof_count += 1;
+                        }
+                        _ => {
+                            remove_trailing_line_ending_byte(line_ending_byte, &mut output);
+                        }
+                    }
+                }
+
+                delimiter_state.write_delimiter(&mut output);
+            }
+
+            if eof_count == input_source_vec_len {
+                break;
+            }
+
+            delimiter_state.remove_trailing_delimiter(&mut output);
+
+            stdout.write_all(&output)?;
+            stdout.write_all(line_ending_byte_array_ref)?;
+
+            // Quote:
+            //     When the -s option is not specified:
+            //     [...]
+            //     The delimiter shall be reset to the first element of list after each file operand is processed.
+            // https://pubs.opengroup.org/onlinepubs/9799919799/utilities/paste.html
+            delimiter_state.reset_to_first_delimiter();
+        }
+    }
+
+    Ok(())
+}
+
+fn parse_delimiters(delimiters: &str) -> UResult<Box<[Box<[u8]>]>> {
+    /// A single backslash char
+    const BACKSLASH: char = '\\';
+
+    fn add_one_byte_single_char_delimiter(vec: &mut Vec<Box<[u8]>>, byte: u8) {
+        vec.push(Box::new([byte]));
+    }
+
+    // a buffer of length four is large enough to encode any char
+    let mut buffer = [0; 4];
+
+    let mut add_single_char_delimiter = |vec: &mut Vec<Box<[u8]>>, ch: char| {
+        let delimiter_encoded = ch.encode_utf8(&mut buffer);
+
+        vec.push(Box::from(delimiter_encoded.as_bytes()));
+    };
+
+    let mut vec = Vec::<Box<[u8]>>::with_capacity(delimiters.len());
+
+    let mut chars = delimiters.chars();
+
+    // Unescape all special characters
+    while let Some(char) = chars.next() {
+        match char {
+            BACKSLASH => match chars.next() {
+                // "Empty string (not a null character)"
+                // https://pubs.opengroup.org/onlinepubs/9799919799/utilities/paste.html
+                Some('0') => {
+                    vec.push(Box::<[u8; 0]>::new([]));
+                }
+                // "\\" to "\" (U+005C)
+                Some(BACKSLASH) => {
+                    add_one_byte_single_char_delimiter(&mut vec, b'\\');
+                }
+                // "\n" to U+000A
+                Some('n') => {
+                    add_one_byte_single_char_delimiter(&mut vec, b'\n');
+                }
+                // "\t" to U+0009
+                Some('t') => {
+                    add_one_byte_single_char_delimiter(&mut vec, b'\t');
+                }
+                Some(other_char) => {
+                    // "If any other characters follow the <backslash>, the results are unspecified."
+                    // https://pubs.opengroup.org/onlinepubs/9799919799/utilities/paste.html
+                    // However, other implementations remove the backslash
+                    // See "test_posix_unspecified_delimiter"
+                    add_single_char_delimiter(&mut vec, other_char);
+                }
+                None => {
                     return Err(USimpleError::new(
                         1,
                         format!("delimiter list ends with an unescaped backslash: {delimiters}"),
                     ));
                 }
-
-    let delimiters: Vec<char> = unescape(delimiters).chars().collect();
-    let mut delim_count = 0;
-    let mut delim_length = 1;
-    let stdout = stdout();
-    let mut stdout = stdout.lock();
-
-    let mut output = Vec::new();
-    if serial {
-        for file in &mut files {
-            output.clear();
-            loop {
-                match read_until(file.as_mut(), line_ending as u8, &mut output) {
-                    Ok(0) => break,
-                    Ok(_) => {
-                        if output.ends_with(&[line_ending as u8]) {
-                            output.pop();
-                        }
-                        // a buffer of length four is large enough to encode any char
-                        let mut buffer = [0; 4];
-                        let ch =
-                            delimiters[delim_count % delimiters.len()].encode_utf8(&mut buffer);
-                        delim_length = ch.len();
-
-                        for byte in buffer.iter().take(delim_length) {
-                            output.push(*byte);
+            },
+            non_backslash_char => {
+                add_single_char_delimiter(&mut vec, non_backslash_char);
             }
         }
-                    Err(e) => return Err(e.map_err_context(String::new)),
-                }
-                delim_count += 1;
-            }
-            // remove final delimiter
-            output.truncate(output.len() - delim_length);
-
-            write!(
-                stdout,
-                "{}{}",
-                String::from_utf8_lossy(&output),
-                line_ending
-            )?;
-        }
-    } else {
-        let mut eof = vec![false; files.len()];
-        loop {
-            output.clear();
-            let mut eof_count = 0;
-            for (i, file) in files.iter_mut().enumerate() {
-                if eof[i] {
-                    eof_count += 1;
-                } else {
-                    match read_until(file.as_mut(), line_ending as u8, &mut output) {
-                        Ok(0) => {
-                            eof[i] = true;
-                            eof_count += 1;
-                        }
-                        Ok(_) => {
-                            if output.ends_with(&[line_ending as u8]) {
-                                output.pop();
-                            }
-                        }
-                        Err(e) => return Err(e.map_err_context(String::new)),
-                    }
-                }
-                // a buffer of length four is large enough to encode any char
-                let mut buffer = [0; 4];
-                let ch = delimiters[delim_count % delimiters.len()].encode_utf8(&mut buffer);
-                delim_length = ch.len();
-
-                for byte in buffer.iter().take(delim_length) {
-                    output.push(*byte);
     }
 
-                delim_count += 1;
-            }
-            if files.len() == eof_count {
-                break;
-            }
-            // Remove final delimiter
-            output.truncate(output.len() - delim_length);
-
-            write!(
-                stdout,
-                "{}{}",
-                String::from_utf8_lossy(&output),
-                line_ending
-            )?;
-            delim_count = 0;
-        }
-    }
-    Ok(())
+    Ok(vec.into_boxed_slice())
 }
 
-// Unescape all special characters
-fn unescape(s: &str) -> String {
-    s.replace("\\n", "\n")
-        .replace("\\t", "\t")
-        .replace("\\\\", "\\")
+fn remove_trailing_line_ending_byte(line_ending_byte: u8, output: &mut Vec<u8>) {
+    if let Some(&byte) = output.last() {
+        if byte == line_ending_byte {
+            assert!(output.pop() == Some(line_ending_byte));
+        }
+    }
+}
+
+enum DelimiterState<'a> {
+    NoDelimiters,
+    OneDelimiter(&'a [u8]),
+    MultipleDelimiters {
+        current_delimiter: &'a [u8],
+        delimiters: &'a [Box<[u8]>],
+        delimiters_iterator: Cycle<Iter<'a, Box<[u8]>>>,
+    },
+}
+
+impl<'a> DelimiterState<'a> {
+    fn new(unescaped_and_encoded_delimiters: &'a [Box<[u8]>]) -> DelimiterState<'a> {
+        match unescaped_and_encoded_delimiters {
+            [] => DelimiterState::NoDelimiters,
+            [only_delimiter] => {
+                // -d '\0' is equivalent to -d ''
+                if only_delimiter.is_empty() {
+                    DelimiterState::NoDelimiters
+                } else {
+                    DelimiterState::OneDelimiter(only_delimiter)
+                }
+            }
+            [first_delimiter, ..] => DelimiterState::MultipleDelimiters {
+                current_delimiter: first_delimiter,
+                delimiters: unescaped_and_encoded_delimiters,
+                delimiters_iterator: unescaped_and_encoded_delimiters.iter().cycle(),
+            },
+        }
+    }
+
+    /// This should only be used to return to the start of the delimiter list after a file has been processed.
+    /// This should only be used when the "serial" option is disabled.
+    /// This is a no-op unless there are multiple delimiters.
+    fn reset_to_first_delimiter(&mut self) {
+        if let DelimiterState::MultipleDelimiters {
+            delimiters_iterator,
+            delimiters,
+            ..
+        } = self
+        {
+            *delimiters_iterator = delimiters.iter().cycle();
+        }
+    }
+
+    /// Remove the trailing delimiter.
+    /// If there are no delimiters, this is a no-op.
+    fn remove_trailing_delimiter(&mut self, output: &mut Vec<u8>) {
+        let delimiter_length = match self {
+            DelimiterState::OneDelimiter(only_delimiter) => only_delimiter.len(),
+            DelimiterState::MultipleDelimiters {
+                current_delimiter, ..
+            } => current_delimiter.len(),
+            _ => {
+                return;
+            }
+        };
+
+        // `delimiter_length` will be zero if the current delimiter is a "\0" delimiter
+        if delimiter_length > 0 {
+            let output_len = output.len();
+
+            if let Some(output_without_delimiter_length) = output_len.checked_sub(delimiter_length)
+            {
+                output.truncate(output_without_delimiter_length);
+            } else {
+                // This branch is NOT unreachable, must be skipped
+                // `output` should be empty in this case
+                assert!(output_len == 0);
+            }
+        }
+    }
+
+    /// Append the current delimiter to `output`.
+    /// If there are no delimiters, this is a no-op.
+    fn write_delimiter(&mut self, output: &mut Vec<u8>) {
+        match self {
+            DelimiterState::OneDelimiter(only_delimiter) => {
+                output.extend_from_slice(only_delimiter);
+            }
+            DelimiterState::MultipleDelimiters {
+                current_delimiter,
+                delimiters_iterator,
+                ..
+            } => {
+                // Unwrap because `delimiters_iterator` is a cycle iter and was created from a non-empty slice
+                let bo = delimiters_iterator.next().unwrap();
+
+                output.extend_from_slice(bo);
+
+                *current_delimiter = bo;
+            }
+            _ => {}
+        }
+    }
+}
+
+enum InputSource {
+    File(BufReader<File>),
+    StandardInput(Rc<RefCell<Stdin>>),
+}
+
+impl InputSource {
+    fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> UResult<usize> {
+        let us = match self {
+            Self::File(bu) => bu.read_until(byte, buf)?,
+            Self::StandardInput(rc) => rc
+                .try_borrow()
+                .map_err(|bo| USimpleError::new(1, format!("{bo}")))?
+                .lock()
+                .read_until(byte, buf)?,
+        };
+
+        Ok(us)
+    }
 }

tests/by-util/test_paste.rs

@@ -2,6 +2,9 @@
 //
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
+
+// spell-checker:ignore bsdutils toybox
+
 use crate::common::util::TestScenario;
 
 struct TestData<'b> {
@@ -11,7 +14,7 @@ struct TestData<'b> {
     out: &'b str,
 }
 
-static EXAMPLE_DATA: &[TestData] = &[
+const EXAMPLE_DATA: &[TestData] = &[
     // Ensure that paste properly handles files lacking a final newline.
     TestData {
         name: "no-nl-1",
@@ -172,7 +175,7 @@ fn test_delimiter_list_ending_with_escaped_backslash() {
             at.write(&file, one_in);
             ins.push(file);
         }
-        ucmd.args(&[d, "\\\\"])
+        ucmd.args(&[d, r"\\"])
             .args(&ins)
             .succeeds()
             .stdout_is("a\\b\n");
@@ -183,13 +186,174 @@ fn test_delimiter_list_ending_with_escaped_backslash() {
 fn test_delimiter_list_ending_with_unescaped_backslash() {
     for d in ["-d", "--delimiters"] {
         new_ucmd!()
-            .args(&[d, "\\"])
+            .args(&[d, r"\"])
             .fails()
-            .stderr_contains("delimiter list ends with an unescaped backslash: \\");
+            .stderr_contains(r"delimiter list ends with an unescaped backslash: \");
+
         new_ucmd!()
-            .args(&[d, "_\\"])
+            .args(&[d, r"\\\"])
             .fails()
-            .stderr_contains("delimiter list ends with an unescaped backslash: _\\");
+            .stderr_contains(r"delimiter list ends with an unescaped backslash: \\\");
+
+        new_ucmd!()
+            .args(&[d, r"_\"])
+            .fails()
+            .stderr_contains(r"delimiter list ends with an unescaped backslash: _\");
+    }
+}
+
+#[test]
+fn test_delimiter_list_empty() {
+    for option_style in ["-d", "--delimiters"] {
+        new_ucmd!()
+            .args(&[option_style, "", "-s"])
+            .pipe_in(
+                "\
+A ALPHA 1 _
+B BRAVO 2 _
+C CHARLIE 3 _
+",
+            )
+            .succeeds()
+            .stdout_only(
+                "\
+A ALPHA 1 _B BRAVO 2 _C CHARLIE 3 _
+",
+            );
+    }
+}
+
+// Was panicking (usize subtraction that would have resulted in a negative number)
+// Not observable in release builds, since integer overflow checking is not enabled
+#[test]
+fn test_delimiter_truncation() {
+    for option_style in ["-d", "--delimiters"] {
+        new_ucmd!()
+            .args(&[option_style, "!@#", "-s", "-", "-", "-"])
+            .pipe_in(
+                "\
+FIRST
+SECOND
+THIRD
+FOURTH
+ABCDEFG
+",
+            )
+            .succeeds()
+            .stdout_only(
+                "\
+FIRST!SECOND@THIRD#FOURTH!ABCDEFG
+
+
+",
+            );
+    }
+}
+
+#[test]
+fn test_non_utf8_input() {
+    // 0xC0 is not valid UTF-8
+    const INPUT: &[u8] = b"Non-UTF-8 test: \xC0\x00\xC0.\n";
+
+    new_ucmd!()
+        .pipe_in(INPUT)
+        .succeeds()
+        .stdout_only_bytes(INPUT);
+}
+
+#[test]
+fn test_three_trailing_backslashes_delimiter() {
+    const ONE_BACKSLASH_STR: &str = r"\";
+
+    let three_backslashes_string = ONE_BACKSLASH_STR.repeat(3);
+
+    for option_style in ["-d", "--delimiters"] {
+        new_ucmd!()
+            .args(&[option_style, &three_backslashes_string])
+            .fails()
+            .no_stdout()
+            .stderr_str_check(|st| {
+                st.ends_with(&format!(
+                    ": delimiter list ends with an unescaped backslash: {three_backslashes_string}\n"
+                ))
+            });
+    }
+}
+
+// "If any other characters follow the <backslash>, the results are unspecified."
+// https://pubs.opengroup.org/onlinepubs/9799919799/utilities/paste.html
+// However, other implementations remove the backslash
+#[test]
+fn test_posix_unspecified_delimiter() {
+    for option_style in ["-d", "--delimiters"] {
+        new_ucmd!()
+            .args(&[option_style, r"\z", "-s"])
+            .pipe_in(
+                "\
+1
+2
+3
+4
+",
+            )
+            .succeeds()
+            .stdout_only(
+                "\
+1z2z3z4
+",
+            );
+    }
+}
+
+// "Empty string (not a null character)"
+// https://pubs.opengroup.org/onlinepubs/9799919799/utilities/paste.html
+#[test]
+fn test_backslash_zero_delimiter() {
+    for option_style in ["-d", "--delimiters"] {
+        new_ucmd!()
+            .args(&[option_style, r"\0z\0", "-s"])
+            .pipe_in(
+                "\
+1
+2
+3
+4
+5
+6
+",
+            )
+            .succeeds()
+            .stdout_only(
+                "\
+12z345z6
+",
+            );
+    }
+}
+
+// As of 2024-10-09, only bsdutils (https://github.com/dcantrell/bsdutils, derived from FreeBSD) and toybox handle
+// multibyte delimiter characters in the way a user would likely expect. BusyBox and GNU Core Utilities do not.
+#[test]
+fn test_multi_byte_delimiter() {
+    for option_style in ["-d", "--delimiters"] {
+        new_ucmd!()
+            .args(&[option_style, "!ß@", "-s"])
+            .pipe_in(
+                "\
+1
+2
+3
+4
+5
+6
+",
+            )
+            .succeeds()
+            .stdout_only(
+                "\
+1!2ß3@4!5ß6
+",
+            );
     }
 }