Abstract proc-macro-srv protocol format

crates/proc-macro-api/src/json.rs

@@ -0,0 +1,34 @@
+use std::io::{self, BufRead, Write};
+
+pub fn read_json<'a>(
+    inp: &mut impl BufRead,
+    buf: &'a mut String,
+) -> io::Result<Option<&'a String>> {
+    loop {
+        buf.clear();
+
+        inp.read_line(buf)?;
+        buf.pop(); // Remove trailing '\n'
+
+        if buf.is_empty() {
+            return Ok(None);
+        }
+
+        // Some ill behaved macro try to use stdout for debugging
+        // We ignore it here
+        if !buf.starts_with('{') {
+            tracing::error!("proc-macro tried to print : {}", buf);
+            continue;
+        }
+
+        return Ok(Some(buf));
+    }
+}
+
+pub fn write_json(out: &mut impl Write, msg: &str) -> io::Result<()> {
+    tracing::debug!("> {}", msg);
+    out.write_all(msg.as_bytes())?;
+    out.write_all(b"\n")?;
+    out.flush()?;
+    Ok(())
+}