From 38edf7c067ff4938c1da3c8a8367b0e7b54f8aed Mon Sep 17 00:00:00 2001
From: daywalker90 <8257956+daywalker90@users.noreply.github.com>
Date: Mon, 24 Nov 2025 16:54:06 +0100
Subject: [PATCH] crates: improved json codec decoding performance

Changelog-None
---
 cln-rpc/src/codec.rs | 57 ++++++++++++++++----------------------------
 plugins/src/codec.rs | 52 ++++++++++++++++------------------------
 2 files changed, 41 insertions(+), 68 deletions(-)

diff --git a/cln-rpc/src/codec.rs b/cln-rpc/src/codec.rs
index 25af70258ea8..ccecc73449a5 100644
--- a/cln-rpc/src/codec.rs
+++ b/cln-rpc/src/codec.rs
@@ -12,22 +12,13 @@ use std::{io, str};
 use tokio_util::codec::{Decoder, Encoder};
 
 pub use crate::jsonrpc::JsonRpc;
-use crate::{
-    model::{Request},
-    notifications::Notification,
-};
+use crate::{model::Request, notifications::Notification};
 
 /// A simple codec that parses messages separated by two successive
 /// `\n` newlines.
 #[derive(Default)]
-pub struct MultiLineCodec {}
-
-/// Find two consecutive newlines, i.e., an empty line, signalling the
-/// end of one message and the start of the next message.
-fn find_separator(buf: &mut BytesMut) -> Option<usize> {
-    buf.iter()
-        .zip(buf.iter().skip(1))
-        .position(|b| *b.0 == b'\n' && *b.1 == b'\n')
+pub struct MultiLineCodec {
+    search_pos: usize,
 }
 
 fn utf8(buf: &[u8]) -> Result<&str, io::Error> {
@@ -39,14 +30,24 @@ impl Decoder for MultiLineCodec {
     type Item = String;
     type Error = Error;
     fn decode(&mut self, buf: &mut BytesMut) -> Result<Option<Self::Item>, Error> {
-        if let Some(newline_offset) = find_separator(buf) {
-            let line = buf.split_to(newline_offset + 2);
-            let line = &line[..line.len() - 2];
-            let line = utf8(line)?;
-            Ok(Some(line.to_string()))
-        } else {
-            Ok(None)
+        let bytes = &buf[..];
+        let mut i = self.search_pos;
+
+        while i + 1 < bytes.len() {
+            if bytes[i] == b'\n' && bytes[i + 1] == b'\n' {
+                let line = buf.split_to(i + 2);
+                let line = &line[..line.len() - 2];
+
+                self.search_pos = 0;
+
+                return Ok(Some(utf8(line)?.to_owned()));
+            }
+            i += 1;
         }
+
+        self.search_pos = bytes.len().saturating_sub(1);
+
+        Ok(None)
     }
 }
 
@@ -129,27 +130,11 @@ impl Decoder for JsonRpcCodec {
 
 #[cfg(test)]
 mod test {
-    use super::{find_separator, JsonCodec, MultiLineCodec};
+    use super::{JsonCodec, MultiLineCodec};
     use bytes::{BufMut, BytesMut};
     use serde_json::json;
     use tokio_util::codec::{Decoder, Encoder};
 
-    #[test]
-    fn test_separator() {
-        struct Test(String, Option<usize>);
-        let tests = vec![
-            Test("".to_string(), None),
-            Test("}\n\n".to_string(), Some(1)),
-            Test("\"hello\"},\n\"world\"}\n\n".to_string(), Some(18)),
-        ];
-
-        for t in tests.iter() {
-            let mut buf = BytesMut::new();
-            buf.put_slice(t.0.as_bytes());
-            assert_eq!(find_separator(&mut buf), t.1);
-        }
-    }
-
     #[test]
     fn test_ml_decoder() {
         struct Test(String, Option<String>, String);
diff --git a/plugins/src/codec.rs b/plugins/src/codec.rs
index ad512872202a..75068e7e5f75 100644
--- a/plugins/src/codec.rs
+++ b/plugins/src/codec.rs
@@ -17,14 +17,8 @@ use crate::messages::{Notification, Request};
 /// A simple codec that parses messages separated by two successive
 /// `\n` newlines.
 #[derive(Default)]
-pub struct MultiLineCodec {}
-
-/// Find two consecutive newlines, i.e., an empty line, signalling the
-/// end of one message and the start of the next message.
-fn find_separator(buf: &mut BytesMut) -> Option<usize> {
-    buf.iter()
-        .zip(buf.iter().skip(1))
-        .position(|b| *b.0 == b'\n' && *b.1 == b'\n')
+pub struct MultiLineCodec {
+    search_pos: usize,
 }
 
 fn utf8(buf: &[u8]) -> Result<&str, io::Error> {
@@ -36,14 +30,24 @@ impl Decoder for MultiLineCodec {
     type Item = String;
     type Error = Error;
     fn decode(&mut self, buf: &mut BytesMut) -> Result<Option<Self::Item>, Error> {
-        if let Some(newline_offset) = find_separator(buf) {
-            let line = buf.split_to(newline_offset + 2);
-            let line = &line[..line.len() - 2];
-            let line = utf8(line)?;
-            Ok(Some(line.to_string()))
-        } else {
-            Ok(None)
+        let bytes = &buf[..];
+        let mut i = self.search_pos;
+
+        while i + 1 < bytes.len() {
+            if bytes[i] == b'\n' && bytes[i + 1] == b'\n' {
+                let line = buf.split_to(i + 2);
+                let line = &line[..line.len() - 2];
+
+                self.search_pos = 0;
+
+                return Ok(Some(utf8(line)?.to_owned()));
+            }
+            i += 1;
         }
+
+        self.search_pos = bytes.len().saturating_sub(1);
+
+        Ok(None)
     }
 }
 
@@ -125,27 +129,11 @@ impl Decoder for JsonRpcCodec {
 
 #[cfg(test)]
 mod test {
-    use super::{find_separator, JsonCodec, MultiLineCodec};
+    use super::{JsonCodec, MultiLineCodec};
     use bytes::{BufMut, BytesMut};
     use serde_json::json;
     use tokio_util::codec::{Decoder, Encoder};
 
-    #[test]
-    fn test_separator() {
-        struct Test(String, Option<usize>);
-        let tests = vec![
-            Test("".to_string(), None),
-            Test("}\n\n".to_string(), Some(1)),
-            Test("\"hello\"},\n\"world\"}\n\n".to_string(), Some(18)),
-        ];
-
-        for t in tests.iter() {
-            let mut buf = BytesMut::new();
-            buf.put_slice(t.0.as_bytes());
-            assert_eq!(find_separator(&mut buf), t.1);
-        }
-    }
-
     #[test]
     fn test_ml_decoder() {
         struct Test(String, Option<String>, String);