From c85467a1b65d2a8907fcab3303572f76c071776d Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Sun, 6 Feb 2022 14:47:07 +0100
Subject: [PATCH 1/2] Revert "TarArchive: Small refactoring"

This reverts commit 50a35860ee9237d341948437c5f70a7f0987d393.

With this change Nix fails to open bzip2 logfiles that were created from
builds with no stdout/stderr.
---
 src/libutil/tarfile.cc | 26 ++++++++++++++------------
 src/libutil/tarfile.hh |  3 ---
 2 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/src/libutil/tarfile.cc b/src/libutil/tarfile.cc
index 790bc943a..a7db58559 100644
--- a/src/libutil/tarfile.cc
+++ b/src/libutil/tarfile.cc
@@ -39,30 +39,32 @@ void TarArchive::check(int err, const std::string & reason)
         throw Error(reason, archive_error_string(this->archive));
 }
 
-TarArchive::TarArchive(Source & source, bool raw)
-    : source(&source), buffer(4096)
+TarArchive::TarArchive(Source & source, bool raw) : buffer(4096)
 {
-    init();
-    if (!raw)
+    this->archive = archive_read_new();
+    this->source = &source;
+
+    if (!raw) {
+        archive_read_support_filter_all(archive);
         archive_read_support_format_all(archive);
-    else
+    } else {
+        archive_read_support_filter_all(archive);
         archive_read_support_format_raw(archive);
+        archive_read_support_format_empty(archive);
+    }
     check(archive_read_open(archive, (void *)this, callback_open, callback_read, callback_close), "Failed to open archive (%s)");
 }
 
+
 TarArchive::TarArchive(const Path & path)
 {
-    init();
+    this->archive = archive_read_new();
+
+    archive_read_support_filter_all(archive);
     archive_read_support_format_all(archive);
     check(archive_read_open_filename(archive, path.c_str(), 16384), "failed to open archive: %s");
 }
 
-void TarArchive::init()
-{
-    archive = archive_read_new();
-    archive_read_support_filter_all(archive);
-}
-
 void TarArchive::close()
 {
     check(archive_read_close(this->archive), "Failed to close archive (%s)");
diff --git a/src/libutil/tarfile.hh b/src/libutil/tarfile.hh
index f107a7e2e..4d9141fd4 100644
--- a/src/libutil/tarfile.hh
+++ b/src/libutil/tarfile.hh
@@ -17,13 +17,10 @@ struct TarArchive {
     // disable copy constructor
     TarArchive(const TarArchive &) = delete;
 
-    void init();
-
     void close();
 
     ~TarArchive();
 };
-
 void unpackTarfile(Source & source, const Path & destDir);
 
 void unpackTarfile(const Path & tarFile, const Path & destDir);

From d02e34ef06e24f98404d7a50130ddced15a12279 Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Sun, 6 Feb 2022 14:52:04 +0100
Subject: [PATCH 2/2] Implement regression test for empty logs loaded via `nix
 log`

---
 tests/logging.sh | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tests/logging.sh b/tests/logging.sh
index c894ad3ff..1481b9b36 100644
--- a/tests/logging.sh
+++ b/tests/logging.sh
@@ -13,3 +13,14 @@ rm -rf $NIX_LOG_DIR
 (! nix-store -l $path)
 nix-build dependencies.nix --no-out-link --compress-build-log
 [ "$(nix-store -l $path)" = FOO ]
+
+# test whether empty logs work fine with `nix log`.
+builder="$(mktemp)"
+echo -e "#!/bin/sh\nmkdir \$out" > "$builder"
+outp="$(nix-build -E \
+    'with import ./config.nix; mkDerivation { name = "fnord"; builder = '"$builder"'; }' \
+    --out-link "$(mktemp -d)/result")"
+
+test -d "$outp"
+
+nix log "$outp"