From 68f148ed45da0a8b827a96611e7825d5d2396454 Mon Sep 17 00:00:00 2001
From: eldritch horrors <pennae@lix.systems>
Date: Mon, 4 Mar 2024 08:12:15 +0100
Subject: [PATCH] Merge pull request #9798 from edolstra/remote-store-eof

Print a more helpful message if the daemon crashes

(cherry picked from commit 32706b14a7531c2c21b9f96da083a540a0031ec4)
Change-Id: Ief7c465bca7666e2b7e7c9d1dd0c01c5f9014146
---
 src/libstore/remote-store.cc | 1 +
 src/libutil/serialise.cc     | 2 +-
 src/libutil/serialise.hh     | 5 +++--
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 2f4933577..58fac40dc 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -65,6 +65,7 @@ void RemoteStore::initConnection(Connection & conn)
 {
     /* Send the magic greeting, check for the reply. */
     try {
+        conn.from.endOfFileError = "Nix daemon disconnected unexpectedly (maybe it crashed?)";
         conn.to << WORKER_MAGIC_1;
         conn.to.flush();
         StringSink saved;
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 910a760a9..6b0d87b03 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -128,7 +128,7 @@ size_t FdSource::readUnbuffered(char * data, size_t len)
         n = ::read(fd, data, len);
     } while (n == -1 && errno == EINTR);
     if (n == -1) { _good = false; throw SysError("reading from file"); }
-    if (n == 0) { _good = false; throw EndOfFile("unexpected end-of-file"); }
+    if (n == 0) { _good = false; throw EndOfFile(std::string(*endOfFileError)); }
     read += n;
     return n;
 }
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 333c254ea..d1c791823 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -151,12 +151,13 @@ struct FdSource : BufferedSource
 {
     int fd;
     size_t read = 0;
+    BackedStringView endOfFileError{"unexpected end-of-file"};
 
     FdSource() : fd(-1) { }
     FdSource(int fd) : fd(fd) { }
-    FdSource(FdSource&&) = default;
+    FdSource(FdSource &&) = default;
 
-    FdSource& operator=(FdSource && s)
+    FdSource & operator=(FdSource && s)
     {
         fd = s.fd;
         s.fd = -1;