Escape U+0085, U+2028 and U+2029 in NDJSON records

crates/diffr-core/src/protocol/mod.rs

@@ -11,10 +11,17 @@
 //! last line. Columns are 0-based byte offsets into the UTF-8 text on the
 //! wire. All ranges are half-open.
 //!
+//! Records end at `\n` only. U+0085, U+2028 and U+2029 are written as
+//! `\u0085`, `\u2028` and `\u2029`, because some line readers also end a
+//! line at them.
+//!
 //! Sides are always `lhs` (before) and `rhs` (after). A `Pairing` says which
 //! sides exist and serializes by presence: `{lhs, rhs}`, `{lhs}`, or `{rhs}`.
 
+use std::io::{self, Write};
+
 use serde::{Deserialize, Serialize};
+use serde_json::ser::Formatter;
 
 use crate::pairing::Pairing;
 
@@ -23,6 +30,40 @@ pub mod project;
 /// The current wire version. Changes within a version are additive.
 pub const VERSION: u32 = 3;
 
+/// Write `event` as one record: compact JSON and a `\n`.
+pub fn write_record<W: Write>(writer: &mut W, event: &Event) -> serde_json::Result<()> {
+    event.serialize(&mut serde_json::Serializer::with_formatter(
+        &mut *writer,
+        RecordFormatter,
+    ))?;
+    writer.write_all(b"\n").map_err(serde_json::Error::io)
+}
+
+/// Compact JSON that also escapes U+0085, U+2028 and U+2029.
+struct RecordFormatter;
+
+impl Formatter for RecordFormatter {
+    fn write_string_fragment<W: ?Sized + Write>(
+        &mut self,
+        writer: &mut W,
+        fragment: &str,
+    ) -> io::Result<()> {
+        fragment
+            .split_inclusive(['\u{85}', '\u{2028}', '\u{2029}'])
+            .try_for_each(|piece| {
+                let mut chars = piece.chars();
+                let escape: &[u8] = match chars.next_back() {
+                    Some('\u{85}') => b"\\u0085",
+                    Some('\u{2028}') => b"\\u2028",
+                    Some('\u{2029}') => b"\\u2029",
+                    _ => return writer.write_all(piece.as_bytes()),
+                };
+                writer.write_all(chars.as_str().as_bytes())?;
+                writer.write_all(escape)
+            })
+    }
+}
+
 // ── stream ────────────────────────────────────────────────────────────────
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -590,6 +631,26 @@ mod tests {
         }
     }
 
+    #[test]
+    fn records_escape_line_separators() {
+        let event = Event::Complete {
+            succeeded: 0,
+            failed: 1,
+            aborted: Some(Problem {
+                code: "x".to_owned(),
+                message: "a\u{2028}b\u{2029}c\u{85}d\u{2028}".to_owned(),
+            }),
+        };
+        let mut record = Vec::new();
+        write_record(&mut record, &event).unwrap();
+        let line = String::from_utf8(record).unwrap();
+        assert!(
+            line.ends_with("\"message\":\"a\\u2028b\\u2029c\\u0085d\\u2028\"}}\n"),
+            "{line}"
+        );
+        assert_eq!(serde_json::from_str::<Event>(&line).unwrap(), event);
+    }
+
     #[test]
     fn defaults_are_omitted() {
         let line = serde_json::to_string(&example_file()).unwrap();

src/run.rs

@@ -7,7 +7,7 @@ use crate::options::DiffOptions;
 use crate::plugin::{Classifier, MutationFailed, Pipeline};
 use crate::present::present;
 use crate::protocol::project::{self, Inputs};
-use crate::protocol::{Diff, Event, FileChange, Outcome, Problem, VERSION};
+use crate::protocol::{self, Diff, Event, FileChange, Outcome, Problem, VERSION};
 use crate::summary::{DiffResult, FallbackCause, FileContent, FileFormat};
 use crate::tags;
 use std::io::{BufWriter, Write};
@@ -102,8 +102,7 @@ pub(crate) fn stream(
                 ended.failed |= *failed > 0;
                 ended.aborted = aborted.is_some();
             }
-            serde_json::to_writer(&mut output, &event)?;
-            output.write_all(b"\n")?;
+            protocol::write_record(&mut output, &event)?;
             output.flush()?;
         }
         Ok(ended)