From f65fac147dbb36e620cf23374cae50fcc7482f62 Mon Sep 17 00:00:00 2001
From: Edward Houston <ehouston@blockstream.com>
Date: Tue, 16 Jun 2026 08:33:32 +0200
Subject: [PATCH] fix(electrum): stop logging full response payload on client
 disconnect

  Broken-pipe/reset errors during send embedded the entire JSON-RPC reply
  (e.g. a large get_history result) into the error context, which was then
  logged at ERROR and split across many Cloud Logging entries. Truncate the
  send-failure context to a byte count and route client disconnects to debug!.
---
 src/electrum/server.rs | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/src/electrum/server.rs b/src/electrum/server.rs
index 873a8dc20..5bedb3a3c 100644
--- a/src/electrum/server.rs
+++ b/src/electrum/server.rs
@@ -553,7 +553,7 @@ impl Connection {
             let line = value.to_string() + "\n";
             self.stream
                 .write_all(line.as_bytes())
-                .chain_err(|| format!("failed to send {}", value))?;
+                .chain_err(|| format!("failed to send response ({} bytes)", line.len()))?;
         }
         Ok(())
     }
@@ -676,11 +676,16 @@ impl Connection {
         let sender = self.sender.clone();
         let child = spawn_thread("reader", || Connection::reader_thread(reader, sender));
         if let Err(e) = self.handle_replies(receiver) {
-            error!(
-                "[{}] connection handling failed: {}",
-                self.addr,
-                e.display_chain().to_string()
-            );
+            if is_disconnect(&e) {
+                // client went away mid-exchange (broken pipe / reset) — not actionable
+                debug!("[{}] connection closed by client: {}", self.addr, e);
+            } else {
+                error!(
+                    "[{}] connection handling failed: {}",
+                    self.addr,
+                    e.display_chain().to_string()
+                );
+            }
         }
         self.stats.clients.dec();
         self.stats
@@ -697,6 +702,25 @@ impl Connection {
     }
 }
 
+/// True if the error chain is rooted in a client disconnect (broken pipe /
+/// connection reset / aborted), which is expected and shouldn't be logged as ERROR.
+fn is_disconnect(err: &Error) -> bool {
+    use std::io::ErrorKind::*;
+    let mut cause: Option<&(dyn std::error::Error + 'static)> = Some(err);
+    while let Some(e) = cause {
+        if let Some(io_err) = e.downcast_ref::<std::io::Error>() {
+            if matches!(
+                io_err.kind(),
+                BrokenPipe | ConnectionReset | ConnectionAborted | UnexpectedEof
+            ) {
+                return true;
+            }
+        }
+        cause = e.source();
+    }
+    false
+}
+
 #[trace]
 fn get_history(
     query: &Query,