From 0278b9e1801f64b2586fbb857d6ad2da4f6b7d09 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 2 Jun 2025 11:41:02 +0200
Subject: [PATCH 1/2] nix store copy-sigs: Use http-connections setting to
 control parallelism

Previously it used the `ThreadPool` default,
i.e. `std::thread::hardware_concurrency()`. But copying signatures is
not primarily CPU-bound so it makes more sense to use the
`http-connections` setting (since we're typically copying from/to a
binary cache).
---
 src/nix/sigs.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/nix/sigs.cc b/src/nix/sigs.cc
index fb868baa1..802c093cb 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -3,6 +3,7 @@
 #include "nix/main/shared.hh"
 #include "nix/store/store-open.hh"
 #include "nix/util/thread-pool.hh"
+#include "nix/store/filetransfer.hh"
 
 #include <atomic>
 
@@ -38,7 +39,7 @@ struct CmdCopySigs : StorePathsCommand
         for (auto & s : substituterUris)
             substituters.push_back(openStore(s));
 
-        ThreadPool pool;
+        ThreadPool pool{fileTransferSettings.httpConnections};
 
         std::atomic<size_t> added{0};
 

From b16fa06ff1dc8a2bac101a3daf1839b65f09bfbd Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 2 Jun 2025 12:06:21 +0200
Subject: [PATCH 2/2] nix store copy-sigs: Add docs

---
 src/nix/sigs.cc            |  7 +++++++
 src/nix/store-copy-sigs.md | 30 ++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 src/nix/store-copy-sigs.md

diff --git a/src/nix/sigs.cc b/src/nix/sigs.cc
index 802c093cb..89ed7b91d 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -29,6 +29,13 @@ struct CmdCopySigs : StorePathsCommand
         return "copy store path signatures from substituters";
     }
 
+    std::string doc() override
+    {
+        return
+          #include "store-copy-sigs.md"
+          ;
+    }
+
     void run(ref<Store> store, StorePaths && storePaths) override
     {
         if (substituterUris.empty())
diff --git a/src/nix/store-copy-sigs.md b/src/nix/store-copy-sigs.md
new file mode 100644
index 000000000..678756221
--- /dev/null
+++ b/src/nix/store-copy-sigs.md
@@ -0,0 +1,30 @@
+R""(
+
+# Examples
+
+* To copy signatures from a binary cache to the local store:
+
+  ```console
+  # nix store copy-sigs --substituter https://cache.nixos.org \
+      --recursive /nix/store/y1x7ng5bmc9s8lqrf98brcpk1a7lbcl5-hello-2.12.1
+  ```
+
+* To copy signatures from one binary cache to another:
+
+  ```console
+  # nix store copy-sigs --substituter https://cache.nixos.org \
+      --store file:///tmp/binary-cache \
+      --recursive -v \
+      /nix/store/y1x7ng5bmc9s8lqrf98brcpk1a7lbcl5-hello-2.12.1
+  imported 2 signatures
+  ```
+
+# Description
+
+`nix store copy-sigs` copies store path signatures from one store to another.
+
+It is not advised to copy signatures to binary cache stores. Binary cache signatures are stored in `.narinfo` files. Since these are cached aggressively, clients may not see the new signatures quickly. It is therefore better to set any required signatures when the paths are first uploaded to the binary cache.
+
+Store paths are processed in parallel. The amount of parallelism is controlled by the [`http-connections`](@docroot@/command-ref/conf-file.md#conf-http-connections) settings.
+
+)""