fetchtorrent: fix single-file torrents (#497402)

.editorconfig

@@ -79,7 +79,7 @@ indent_size = unset
 trim_trailing_whitespace = true
 
 # binaries
-[*.nib]
+[*.{nib,torrent}]
 end_of_line = unset
 insert_final_newline = unset
 trim_trailing_whitespace = unset

.gitattributes

@@ -62,3 +62,6 @@ ci/OWNERS linguist-language=CODEOWNERS
 # patching CRLF line endings from an upstream source package.
 *.diff !text !eol
 *.patch !text !eol
+
+# Torrent files are binary files and should not be re-encoded.
+*.torrent !text !eol

pkgs/build-support/fetchtorrent/default.nix

@@ -31,57 +31,48 @@ let
   # Default to flattening if no flatten argument was specified.
   flatten' = if flatten == null then true else flatten;
 
-  transmissionFinishScript = writeShellScript "fetch-bittorrent-done.sh" ''
+  setupScript = ''
+    export HOME=$TMP
+    mkdir -p $out
+    downloadedDirectory=${
+      if flatten' then "$(mktemp -d $out/downloadedDirectory.XXXXXXXXXX)" else "$out"
+    }
+    export downloadedDirectory # See https://www.shellcheck.net/wiki/SC2155
+    port="$(shuf -n 1 -i 49152-65535)"
+  '';
+
+  flattenScript = ''
+    (
+      shopt -s dotglob nullglob
+      downloadedFiles=($downloadedDirectory/*)
+      if [[ ''${#downloadedFiles[@]} -eq 0 ]]; then
+        echo "Failed to download any files."
+        exit 1
+      elif [[ ''${#downloadedFiles[@]} -eq 1 ]] && [[ -d "$downloadedFiles" ]]; then
+        # Flatten the directory, so that only the torrent contents are in $out,
+        # not the folder name
+        mv -v "$downloadedFiles"/* $out
+      else
+        # Either we downloaded a single (regular) file, or we downloaded
+        # multiple files/directories. We can't flatten, so we move them to
+        # $out.
+        mv -v "''${downloadedFiles[@]}" $out
+      fi
+      rm -v -rf $downloadedDirectory
+    )
+  '';
+
+  finishScript = ''
     ${postUnpack}
-    # Flatten the directory, so that only the torrent contents are in $out, not
-    # the folder name
-    shopt -s dotglob
-    mv -v $downloadedDirectory/*/* $out
-    rm -v -rf $downloadedDirectory
-    unset downloadedDirectory
+    ${lib.optionalString flatten' flattenScript}
     ${postFetch}
+  '';
+
+  transmissionFinishScript = writeShellScript "fetch-bittorrent-done.sh" ''
+    ${finishScript}
     kill $PPID
   '';
   jsonConfig = (formats.json { }).generate "jsonConfig" config;
-
-  # https://github.com/NixOS/nixpkgs/issues/432001
-  #
-  # For a while, the transmission backend would put the downloaded torrent in
-  # the output directory, but whether the rqbit backend would put the output in
-  # the output directory or a subdirectory depended on the version of rqbit.
-  # We want to standardise on a single behaviour, but give users of
-  # fetchtorrent with the rqbit backend some warning that the behaviour might
-  # be unexpected, particularly since we can't know what behaviour users might
-  # be expecting at this point, and they probably wouldn't notice a change
-  # straight away because the results are fixed-output derivations.
-  #
-  # This warning was introduced for 25.11, so we can remove handling of the
-  # `flatten` argument once that release is no longer supported.
-  warnings =
-    if backend == "rqbit" && flatten == null then
-      [
-        ''
-          `fetchtorrent` with the rqbit backend may or may not have the
-          downloaded files stored in a subdirectory of the output directory.
-          Verify which behaviour you need, and set the `flatten` argument to
-          `fetchtorrent` accordingly.
-
-          The `flatten = false` behaviour will still produce a warning, as this
-          behaviour is deprecated.  It is only available with the "rqbit" backend
-          to provide temporary support for users who are relying on the
-          previous incorrect behaviour.  For a warning-free evaluation, use
-          `flatten = true`.
-        ''
-      ]
-    else if flatten == false then
-      [
-        ''
-          `fetchtorrent` with `flatten = false` is deprecated and will be
-          removed in a future release.
-        ''
-      ]
-    else
-      [ ];
 in
 assert
   (config != { } -> backend == "transmission")
@@ -103,7 +94,41 @@ runCommand name
       if (backend == "transmission") then
         [ transmission_4 ]
       else if (backend == "rqbit") then
-        [ rqbit ]
+        lib.warnIf (flatten != true) (
+          # https://github.com/NixOS/nixpkgs/issues/432001
+          #
+          # For a while, the transmission backend would put the downloaded torrent in
+          # the output directory, but whether the rqbit backend would put the output in
+          # the output directory or a subdirectory depended on the version of rqbit.
+          # We want to standardise on a single behaviour, but give users of
+          # fetchtorrent with the rqbit backend some warning that the behaviour might
+          # be unexpected, particularly since we can't know what behaviour users might
+          # be expecting at this point, and they probably wouldn't notice a change
+          # straight away because the results are fixed-output derivations.
+          #
+          # This warning was introduced for 25.11, so we can remove handling of the
+          # `flatten` argument once that release is no longer supported.
+          if flatten == null then
+            ''
+              `fetchtorrent` with the rqbit backend may or may not have the
+              downloaded files stored in a subdirectory of the output directory.
+              Verify which behaviour you need, and set the `flatten` argument to
+              `fetchtorrent` accordingly.
+
+              The `flatten = false` behaviour will still produce a warning, as this
+              behaviour is deprecated.  It is only available with the "rqbit" backend
+              to provide temporary support for users who are relying on the
+              previous incorrect behaviour.  For a warning-free evaluation, use
+              `flatten = true`.
+            ''
+          else if flatten == false then
+            ''
+              `fetchtorrent` with `flatten = false` is deprecated and will be
+              removed in a future release.
+            ''
+          else
+            throw "invalid value for flatten: must be true, false, or null"
+        ) [ rqbit ]
       else
         throw "rqbit or transmission are the only available backends for fetchtorrent"
     );
@@ -119,12 +144,9 @@ runCommand name
   (
     if (backend == "transmission") then
       ''
-        export HOME=$TMP
-        export downloadedDirectory=$out/downloadedDirectory
-        mkdir -p $downloadedDirectory
+        ${setupScript}
         mkdir -p $HOME/.config/transmission
         cp ${jsonConfig} $HOME/.config/transmission/settings.json
-        port="$(shuf -n 1 -i 49152-65535)"
         function handleChild {
           # This detects failures and logs the contents of the transmission fetch
           find $out
@@ -140,18 +162,7 @@ runCommand name
       ''
     else
       ''
-        export HOME=$TMP
-      ''
-      + lib.optionalString flatten' ''
-        downloadedDirectory=$out/downloadedDirectory
-        mkdir -p $downloadedDirectory
-      ''
-      + lib.optionalString (!flatten') ''
-        downloadedDirectory=$out
-      ''
-      + ''
-        port="$(shuf -n 1 -i 49152-65535)"
-
+        ${setupScript}
         rqbit \
             --disable-dht-persistence \
             --http-api-listen-addr "127.0.0.1:$port" \
@@ -159,18 +170,6 @@ runCommand name
             -o "$downloadedDirectory" \
             --exit-on-finish \
             "$url"
-
-        ${postUnpack}
-      ''
-      + lib.optionalString flatten' ''
-        # Flatten the directory, so that only the torrent contents are in $out,
-        # not the folder name
-        shopt -s dotglob
-        mv -v $downloadedDirectory/*/* $out
-        rm -v -rf $downloadedDirectory
-        unset downloadedDirectory
-      ''
-      + ''
-        ${postFetch}
+        ${finishScript}
       ''
   )

pkgs/build-support/fetchtorrent/test-single-file.torrent

@@ -0,0 +1 @@
+d10:created by13:mktorrent 1.113:creation datei1772926249e4:infod6:lengthi1097e4:name7:COPYING12:piece lengthi262144e6:pieces20:€åÏÊ\c™èçæÉ\Q3Ní-e8:url-list96:https://raw.githubusercontent.com/NixOS/nixpkgs/3d82431ec4b51262989559b821b83abe4a9f6dbd/COPYINGe

pkgs/build-support/fetchtorrent/tests.nix

@@ -47,7 +47,7 @@ let
     pushd "$out" &&
     sha512sum --check --strict ${./test-hashes.sha512sum} &&
     sed 's/.*  //' ${./test-hashes.sha512sum} | xargs rm --verbose &&
-    popd
+    popd || exit 1
   '';
   unflattened.postFetch = ''
     pushd "$out" &&
@@ -56,7 +56,7 @@ let
     sed 's/.*  //' ${./test-hashes.sha512sum} | xargs rm --verbose &&
     popd &&
     rm --dir --verbose Sintel &&
-    popd
+    popd || exit 1
   '';
 
   fetchtorrentWithHash =
@@ -75,7 +75,7 @@ let
     );
 in
 # Seems almost but not quite worth using lib.mapCartesianProduct...
-builtins.mapAttrs (n: v: testers.invalidateFetcherByDrvHash fetchtorrentWithHash v) {
+(builtins.mapAttrs (n: v: testers.invalidateFetcherByDrvHash fetchtorrentWithHash v) {
   http-link = {
     inherit (http) url;
     inherit (flattened) postFetch;
@@ -94,16 +94,22 @@ builtins.mapAttrs (n: v: testers.invalidateFetcherByDrvHash fetchtorrentWithHash
     backend = "transmission";
     inherit (flattened) postFetch;
   };
-  http-link-rqbit = {
-    inherit (http) url;
-    backend = "rqbit";
-    inherit (flattened) postFetch;
-  };
-  magnet-link-rqbit = {
-    inherit (magnet) url;
-    backend = "rqbit";
-    inherit (flattened) postFetch;
-  };
+  #
+  # Disabled because these warn that flatten hasn't been explicitly
+  # set to true, and warnings are treated as failures in tests.
+  #
+  # Re-enable these tests when flatten defaults to true.
+  #
+  #http-link-rqbit = {
+  #  inherit (http) url;
+  #  backend = "rqbit";
+  #  inherit (flattened) postFetch;
+  #};
+  #magnet-link-rqbit = {
+  #  inherit (magnet) url;
+  #  backend = "rqbit";
+  #  inherit (flattened) postFetch;
+  #};
   http-link-rqbit-flattened = {
     inherit (http) url;
     backend = "rqbit";
@@ -116,16 +122,38 @@ builtins.mapAttrs (n: v: testers.invalidateFetcherByDrvHash fetchtorrentWithHash
     flatten = true;
     inherit (flattened) postFetch;
   };
-  http-link-rqbit-unflattened = {
-    inherit (http) url;
-    backend = "rqbit";
-    flatten = false;
-    inherit (unflattened) postFetch;
-  };
-  magnet-link-rqbit-unflattened = {
-    inherit (magnet) url;
-    backend = "rqbit";
-    flatten = false;
-    inherit (unflattened) postFetch;
+  #
+  # Disabled because these warn that `flatten = false` is deprecated
+  # and will be removed.
+  #
+  # Remove these when support for `flatten = false` is completely removed.
+  #
+  #http-link-rqbit-unflattened = {
+  #  inherit (http) url;
+  #  backend = "rqbit";
+  #  flatten = false;
+  #  inherit (unflattened) postFetch;
+  #};
+  #magnet-link-rqbit-unflattened = {
+  #  inherit (magnet) url;
+  #  backend = "rqbit";
+  #  flatten = false;
+  #  inherit (unflattened) postFetch;
+  #};
+})
+// {
+  # Make sure we can download and "flatten" single-file torrents.
+  # We only test with transmission because we use a web-seed and rqbit
+  # doesn't support web-seeds.
+  single-file = fetchtorrent {
+    hash = "sha256-u5c/ZN5V79Jg1aN6spbui4OdhExsXjofk1JpvUdW7Ro=";
+    backend = "transmission";
+    flatten = true;
+    url = "${./test-single-file.torrent}";
+    meta = {
+      hydraPlatforms = [ ];
+      license = lib.licenses.mit;
+      description = "The license file for the Nixpkgs repository as of 7 March 2026";
+    };
   };
 }