Add zstandard support for wheels (#15645)

## Summary

This PR allows pyx to send down hashes for zstandard-compressed
tarballs. If the hash is present, then the file is assumed to be present
at `${wheel_url}.tar.zst`, similar in design to PEP 658
`${wheel_metadata}.metadata` files. The intent here is that the index
must include the wheel (to support all clients and support
random-access), but can optionally include a zstandard-compressed
version alongside it.

Cargo.lock

@@ -5675,6 +5675,7 @@ dependencies = [
  "reqwest",
  "rustc-hash",
  "sha2",
+ "tar",
  "thiserror 2.0.16",
  "tokio",
  "tokio-util",
@@ -5685,6 +5686,7 @@ dependencies = [
  "uv-static",
  "xz2",
  "zip",
+ "zstd",
 ]
 
 [[package]]

Cargo.toml

@@ -201,6 +201,7 @@ windows-sys = { version = "0.59.0", features = ["Win32_Foundation", "Win32_Secur
 wiremock = { version = "0.6.4" }
 xz2 = { version = "0.1.7" }
 zip = { version = "2.2.3", default-features = false, features = ["deflate", "zstd", "bzip2", "lzma", "xz"] }
+zstd = { version = "0.13.3" }
 
 # dev-dependencies
 assert_cmd = { version = "2.0.16" }

crates/uv-client/src/flat_index.rs

@@ -305,6 +305,7 @@ impl<'a> FlatIndexClient<'a> {
                 upload_time_utc_ms: None,
                 url: FileLocation::AbsoluteUrl(UrlString::from(url)),
                 yanked: None,
+                zstd: None,
             };
 
             let Some(filename) = DistFilename::try_from_normalized_filename(filename) else {

crates/uv-distribution-types/src/file.rs

@@ -40,6 +40,7 @@ pub struct File {
     pub upload_time_utc_ms: Option<i64>,
     pub url: FileLocation,
     pub yanked: Option<Box<Yanked>>,
+    pub zstd: Option<Box<Zstd>>,
 }
 
 impl File {
@@ -63,6 +64,7 @@ impl File {
             upload_time_utc_ms: file.upload_time.map(Timestamp::as_millisecond),
             url: FileLocation::new(file.url, base),
             yanked: file.yanked,
+            zstd: None,
         })
     }
 
@@ -108,6 +110,13 @@ impl File {
             upload_time_utc_ms: file.upload_time.map(Timestamp::as_millisecond),
             url: FileLocation::new(file.url, base),
             yanked: file.yanked,
+            zstd: file
+                .zstd
+                .map(|zstd| Zstd {
+                    hashes: HashDigests::from(zstd.hashes),
+                    size: zstd.size,
+                })
+                .map(Box::new),
         })
     }
 }
@@ -289,6 +298,12 @@ pub enum ToUrlError {
     },
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, Hash, rkyv::Archive, rkyv::Deserialize, rkyv::Serialize)]
+pub struct Zstd {
+    pub hashes: HashDigests,
+    pub size: Option<u64>,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/uv-distribution/src/distribution_database.rs

@@ -20,8 +20,8 @@ use uv_client::{
 };
 use uv_distribution_filename::WheelFilename;
 use uv_distribution_types::{
-    BuildInfo, BuildableSource, BuiltDist, Dist, HashPolicy, Hashed, IndexUrl, InstalledDist, Name,
-    SourceDist,
+    BuildInfo, BuildableSource, BuiltDist, Dist, File, HashPolicy, Hashed, IndexUrl, InstalledDist,
+    Name, SourceDist, ToUrlError,
 };
 use uv_extract::hash::Hasher;
 use uv_fs::write_atomic;
@@ -179,7 +179,11 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
         match dist {
             BuiltDist::Registry(wheels) => {
                 let wheel = wheels.best_wheel();
-                let url = wheel.file.url.to_url()?;
+                let WheelTarget {
+                    url,
+                    extension,
+                    size,
+                } = WheelTarget::try_from(&*wheel.file)?;
 
                 // Create a cache entry for the wheel.
                 let wheel_entry = self.build_context.cache().entry(
@@ -194,7 +198,14 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                         .to_file_path()
                         .map_err(|()| Error::NonFileUrl(url.clone()))?;
                     return self
-                        .load_wheel(&path, &wheel.filename, wheel_entry, dist, hashes)
+                        .load_wheel(
+                            &path,
+                            &wheel.filename,
+                            WheelExtension::Whl,
+                            wheel_entry,
+                            dist,
+                            hashes,
+                        )
                         .await;
                 }
 
@@ -204,7 +215,8 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                         url.clone(),
                         dist.index(),
                         &wheel.filename,
-                        wheel.file.size,
+                        extension,
+                        size,
                         &wheel_entry,
                         dist,
                         hashes,
@@ -241,7 +253,8 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                                 url,
                                 dist.index(),
                                 &wheel.filename,
-                                wheel.file.size,
+                                extension,
+                                size,
                                 &wheel_entry,
                                 dist,
                                 hashes,
@@ -279,6 +292,7 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                         wheel.url.raw().clone(),
                         None,
                         &wheel.filename,
+                        WheelExtension::Whl,
                         None,
                         &wheel_entry,
                         dist,
@@ -310,6 +324,7 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                                 wheel.url.raw().clone(),
                                 None,
                                 &wheel.filename,
+                                WheelExtension::Whl,
                                 None,
                                 &wheel_entry,
                                 dist,
@@ -343,6 +358,7 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                 self.load_wheel(
                     &wheel.install_path,
                     &wheel.filename,
+                    WheelExtension::Whl,
                     cache_entry,
                     dist,
                     hashes,
@@ -547,6 +563,7 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
         url: DisplaySafeUrl,
         index: Option<&IndexUrl>,
         filename: &WheelFilename,
+        extension: WheelExtension,
         size: Option<u64>,
         wheel_entry: &CacheEntry,
         dist: &BuiltDist,
@@ -588,15 +605,31 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                 match progress {
                     Some((reporter, progress)) => {
                         let mut reader = ProgressReader::new(&mut hasher, progress, &**reporter);
+                        match extension {
+                            WheelExtension::Whl => {
                                 uv_extract::stream::unzip(&mut reader, temp_dir.path())
                                     .await
                                     .map_err(|err| Error::Extract(filename.to_string(), err))?;
                             }
-                    None => {
+                            WheelExtension::WhlZst => {
+                                uv_extract::stream::untar_zst(&mut reader, temp_dir.path())
+                                    .await
+                                    .map_err(|err| Error::Extract(filename.to_string(), err))?;
+                            }
+                        }
+                    }
+                    None => match extension {
+                        WheelExtension::Whl => {
                             uv_extract::stream::unzip(&mut hasher, temp_dir.path())
                                 .await
                                 .map_err(|err| Error::Extract(filename.to_string(), err))?;
                         }
+                        WheelExtension::WhlZst => {
+                            uv_extract::stream::untar_zst(&mut hasher, temp_dir.path())
+                                .await
+                                .map_err(|err| Error::Extract(filename.to_string(), err))?;
+                        }
+                    },
                 }
 
                 // If necessary, exhaust the reader to compute the hash.
@@ -701,6 +734,7 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
         url: DisplaySafeUrl,
         index: Option<&IndexUrl>,
         filename: &WheelFilename,
+        extension: WheelExtension,
         size: Option<u64>,
         wheel_entry: &CacheEntry,
         dist: &BuiltDist,
@@ -772,7 +806,14 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                         let target = temp_dir.path().to_owned();
                         move || -> Result<(), uv_extract::Error> {
                             // Unzip the wheel into a temporary directory.
+                            match extension {
+                                WheelExtension::Whl => {
                                     uv_extract::unzip(file, &target)?;
+                                }
+                                WheelExtension::WhlZst => {
+                                    uv_extract::stream::untar_zst_file(file, &target)?;
+                                }
+                            }
                             Ok(())
                         }
                     })
@@ -785,9 +826,19 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
                     let algorithms = hashes.algorithms();
                     let mut hashers = algorithms.into_iter().map(Hasher::from).collect::<Vec<_>>();
                     let mut hasher = uv_extract::hash::HashReader::new(file, &mut hashers);
+
+                    match extension {
+                        WheelExtension::Whl => {
                             uv_extract::stream::unzip(&mut hasher, temp_dir.path())
                                 .await
                                 .map_err(|err| Error::Extract(filename.to_string(), err))?;
+                        }
+                        WheelExtension::WhlZst => {
+                            uv_extract::stream::untar_zst(&mut hasher, temp_dir.path())
+                                .await
+                                .map_err(|err| Error::Extract(filename.to_string(), err))?;
+                        }
+                    }
 
                     // If necessary, exhaust the reader to compute the hash.
                     hasher.finish().await.map_err(Error::HashExhaustion)?;
@@ -887,6 +938,7 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
         &self,
         path: &Path,
         filename: &WheelFilename,
+        extension: WheelExtension,
         wheel_entry: CacheEntry,
         dist: &BuiltDist,
         hashes: HashPolicy<'_>,
@@ -965,9 +1017,18 @@ impl<'a, Context: BuildContext> DistributionDatabase<'a, Context> {
             let mut hasher = uv_extract::hash::HashReader::new(file, &mut hashers);
 
             // Unzip the wheel to a temporary directory.
+            match extension {
+                WheelExtension::Whl => {
                     uv_extract::stream::unzip(&mut hasher, temp_dir.path())
                         .await
                         .map_err(|err| Error::Extract(filename.to_string(), err))?;
+                }
+                WheelExtension::WhlZst => {
+                    uv_extract::stream::untar_zst(&mut hasher, temp_dir.path())
+                        .await
+                        .map_err(|err| Error::Extract(filename.to_string(), err))?;
+                }
+            }
 
             // Exhaust the reader to compute the hash.
             hasher.finish().await.map_err(Error::HashExhaustion)?;
@@ -1227,3 +1288,90 @@ impl LocalArchivePointer {
         None
     }
 }
+
+#[derive(Debug, Clone)]
+struct WheelTarget {
+    /// The URL from which the wheel can be downloaded.
+    url: DisplaySafeUrl,
+    /// The expected extension of the wheel file.
+    extension: WheelExtension,
+    /// The expected size of the wheel file, if known.
+    size: Option<u64>,
+}
+
+impl TryFrom<&File> for WheelTarget {
+    type Error = ToUrlError;
+
+    /// Determine the [`WheelTarget`] from a [`File`].
+    fn try_from(file: &File) -> Result<Self, Self::Error> {
+        let url = file.url.to_url()?;
+        if let Some(zstd) = file.zstd.as_ref() {
+            Ok(Self {
+                url: add_tar_zst_extension(url),
+                extension: WheelExtension::WhlZst,
+                size: zstd.size,
+            })
+        } else {
+            Ok(Self {
+                url,
+                extension: WheelExtension::Whl,
+                size: file.size,
+            })
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum WheelExtension {
+    /// A `.whl` file.
+    Whl,
+    /// A `.whl.tar.zst` file.
+    WhlZst,
+}
+
+/// Add `.tar.zst` to the end of the URL path, if it doesn't already exist.
+#[must_use]
+fn add_tar_zst_extension(mut url: DisplaySafeUrl) -> DisplaySafeUrl {
+    let mut path = url.path().to_string();
+
+    if !path.ends_with(".tar.zst") {
+        path.push_str(".tar.zst");
+    }
+
+    url.set_path(&path);
+    url
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_add_tar_zst_extension() {
+        let url =
+            DisplaySafeUrl::parse("https://files.pythonhosted.org/flask-3.1.0-py3-none-any.whl")
+                .unwrap();
+        assert_eq!(
+            add_tar_zst_extension(url).as_str(),
+            "https://files.pythonhosted.org/flask-3.1.0-py3-none-any.whl.tar.zst"
+        );
+
+        let url = DisplaySafeUrl::parse(
+            "https://files.pythonhosted.org/flask-3.1.0-py3-none-any.whl.tar.zst",
+        )
+        .unwrap();
+        assert_eq!(
+            add_tar_zst_extension(url).as_str(),
+            "https://files.pythonhosted.org/flask-3.1.0-py3-none-any.whl.tar.zst"
+        );
+
+        let url = DisplaySafeUrl::parse(
+            "https://files.pythonhosted.org/flask-3.1.0%2Bcu124-py3-none-any.whl",
+        )
+        .unwrap();
+        assert_eq!(
+            add_tar_zst_extension(url).as_str(),
+            "https://files.pythonhosted.org/flask-3.1.0%2Bcu124-py3-none-any.whl.tar.zst"
+        );
+    }
+}

crates/uv-extract/Cargo.toml

@@ -32,12 +32,14 @@ rayon = { workspace = true }
 reqwest = { workspace = true }
 rustc-hash = { workspace = true }
 sha2 = { workspace = true }
+tar = { workspace = true }
 thiserror = { workspace = true }
 tokio = { workspace = true }
 tokio-util = { workspace = true, features = ["compat"] }
 tracing = { workspace = true }
 xz2 = { workspace = true }
 zip = { workspace = true }
+zstd = { workspace = true }
 
 [features]
 default = []

crates/uv-extract/src/stream.rs

@@ -686,6 +686,16 @@ pub async fn untar_zst<R: tokio::io::AsyncRead + Unpin>(
         .map_err(Error::io_or_compression)
 }
 
+/// Unpack a `.tar.zst` archive from a file on disk into the target directory.
+pub fn untar_zst_file<R: std::io::Read>(reader: R, target: impl AsRef<Path>) -> Result<(), Error> {
+    let reader = std::io::BufReader::with_capacity(DEFAULT_BUF_SIZE, reader);
+    let decompressed = zstd::Decoder::new(reader).map_err(Error::Io)?;
+    let mut archive = tar::Archive::new(decompressed);
+    archive.set_preserve_mtime(false);
+    archive.unpack(target).map_err(Error::io_or_compression)?;
+    Ok(())
+}
+
 /// Unpack a `.tar.xz` archive into the target directory, without requiring `Seek`.
 ///
 /// This is useful for unpacking files as they're being downloaded.

crates/uv-pypi-types/src/simple_json.rs

@@ -150,6 +150,7 @@ pub struct PyxFile {
     pub upload_time: Option<Timestamp>,
     pub url: SmallString,
     pub yanked: Option<Box<Yanked>>,
+    pub zstd: Option<Zstd>,
 }
 
 impl<'de> Deserialize<'de> for PyxFile {
@@ -178,6 +179,7 @@ impl<'de> Deserialize<'de> for PyxFile {
                 let mut upload_time = None;
                 let mut url = None;
                 let mut yanked = None;
+                let mut zstd = None;
 
                 while let Some(key) = access.next_key::<String>()? {
                     match key.as_str() {
@@ -201,6 +203,9 @@ impl<'de> Deserialize<'de> for PyxFile {
                         "upload-time" => upload_time = Some(access.next_value()?),
                         "url" => url = Some(access.next_value()?),
                         "yanked" => yanked = Some(access.next_value()?),
+                        "zstd" => {
+                            zstd = Some(access.next_value()?);
+                        }
                         _ => {
                             let _: serde::de::IgnoredAny = access.next_value()?;
                         }
@@ -216,6 +221,7 @@ impl<'de> Deserialize<'de> for PyxFile {
                     upload_time,
                     url: url.ok_or_else(|| serde::de::Error::missing_field("url"))?,
                     yanked,
+                    zstd,
                 })
             }
         }
@@ -320,6 +326,13 @@ impl Default for Yanked {
     }
 }
 
+#[derive(Debug, Clone, Eq, PartialEq, Default, Deserialize, Serialize)]
+pub struct Zstd {
+    pub hashes: Hashes,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub size: Option<u64>,
+}
+
 /// A dictionary mapping a hash name to a hex encoded digest of the file.
 ///
 /// PEP 691 says multiple hashes can be included and the interpretation is left to the client.

crates/uv-resolver/src/lock/export/pylock_toml.rs

@@ -1369,6 +1369,7 @@ impl PylockTomlWheel {
             upload_time_utc_ms: self.upload_time.map(Timestamp::as_millisecond),
             url: FileLocation::AbsoluteUrl(file_url),
             yanked: None,
+            zstd: None,
         });
 
         Ok(RegistryBuiltWheel {
@@ -1525,6 +1526,7 @@ impl PylockTomlSdist {
             upload_time_utc_ms: self.upload_time.map(Timestamp::as_millisecond),
             url: FileLocation::AbsoluteUrl(file_url),
             yanked: None,
+            zstd: None,
         });
 
         Ok(RegistrySourceDist {

crates/uv-resolver/src/lock/mod.rs

@@ -2754,6 +2754,7 @@ impl Package {
                     upload_time_utc_ms: sdist.upload_time().map(Timestamp::as_millisecond),
                     url: FileLocation::AbsoluteUrl(file_url.clone()),
                     yanked: None,
+                    zstd: None,
                 });
 
                 let index = IndexUrl::from(VerbatimUrl::from_url(
@@ -2828,6 +2829,7 @@ impl Package {
                     upload_time_utc_ms: sdist.upload_time().map(Timestamp::as_millisecond),
                     url: file_url,
                     yanked: None,
+                    zstd: None,
                 });
 
                 let index = IndexUrl::from(
@@ -3076,6 +3078,9 @@ impl Package {
         }
         for wheel in &self.wheels {
             hashes.extend(wheel.hash.as_ref().map(|h| h.0.clone()));
+            if let Some(zstd) = wheel.zstd.as_ref() {
+                hashes.extend(zstd.hash.as_ref().map(|h| h.0.clone()));
+            }
         }
         HashDigests::from(hashes)
     }
@@ -3648,6 +3653,14 @@ impl Source {
         }
         table.insert("source", value(source_table));
     }
+
+    /// Check if a package is local by examining its source.
+    pub(crate) fn is_local(&self) -> bool {
+        matches!(
+            self,
+            Self::Path(_) | Self::Directory(_) | Self::Editable(_) | Self::Virtual(_)
+        )
+    }
 }
 
 impl Display for Source {
@@ -3696,14 +3709,6 @@ impl Source {
             }
         }
     }
-
-    /// Check if a package is local by examining its source.
-    pub(crate) fn is_local(&self) -> bool {
-        matches!(
-            self,
-            Self::Path(_) | Self::Directory(_) | Self::Editable(_) | Self::Virtual(_)
-        )
-    }
 }
 
 #[derive(Clone, Debug, serde::Deserialize)]
@@ -4315,6 +4320,12 @@ fn locked_git_url(git_dist: &GitSourceDist) -> DisplaySafeUrl {
     url
 }
 
+#[derive(Clone, Debug, serde::Deserialize, PartialEq, Eq)]
+struct ZstdWheel {
+    hash: Option<Hash>,
+    size: Option<u64>,
+}
+
 /// Inspired by: <https://discuss.python.org/t/lock-files-again-but-this-time-w-sdists/46593>
 #[derive(Clone, Debug, serde::Deserialize, PartialEq, Eq)]
 #[serde(try_from = "WheelWire")]
@@ -4345,6 +4356,8 @@ struct Wheel {
     /// deserialization time. Not being able to extract a wheel filename from a
     /// wheel URL is thus a deserialization error.
     filename: WheelFilename,
+    /// The zstandard-compressed wheel metadata, if any.
+    zstd: Option<ZstdWheel>,
 }
 
 impl Wheel {
@@ -4453,12 +4466,17 @@ impl Wheel {
             .map(Timestamp::from_millisecond)
             .transpose()
             .map_err(LockErrorKind::InvalidTimestamp)?;
+        let zstd = wheel.file.zstd.as_ref().map(|zstd| ZstdWheel {
+            hash: zstd.hashes.iter().max().cloned().map(Hash::from),
+            size: zstd.size,
+        });
         Ok(Self {
             url,
             hash,
             size,
             upload_time,
             filename,
+            zstd,
         })
     }
 
@@ -4471,6 +4489,7 @@ impl Wheel {
             size: None,
             upload_time: None,
             filename: direct_dist.filename.clone(),
+            zstd: None,
         }
     }
 
@@ -4483,6 +4502,7 @@ impl Wheel {
             size: None,
             upload_time: None,
             filename: path_dist.filename.clone(),
+            zstd: None,
         }
     }
 
@@ -4516,6 +4536,14 @@ impl Wheel {
                     upload_time_utc_ms: self.upload_time.map(Timestamp::as_millisecond),
                     url: file_location,
                     yanked: None,
+                    zstd: self
+                        .zstd
+                        .as_ref()
+                        .map(|zstd| uv_distribution_types::Zstd {
+                            hashes: zstd.hash.iter().map(|h| h.0.clone()).collect(),
+                            size: zstd.size,
+                        })
+                        .map(Box::new),
                 });
                 let index = IndexUrl::from(VerbatimUrl::from_url(
                     url.to_url().map_err(LockErrorKind::InvalidUrl)?,
@@ -4558,6 +4586,14 @@ impl Wheel {
                     upload_time_utc_ms: self.upload_time.map(Timestamp::as_millisecond),
                     url: file_location,
                     yanked: None,
+                    zstd: self
+                        .zstd
+                        .as_ref()
+                        .map(|zstd| uv_distribution_types::Zstd {
+                            hashes: zstd.hash.iter().map(|h| h.0.clone()).collect(),
+                            size: zstd.size,
+                        })
+                        .map(Box::new),
                 });
                 let index = IndexUrl::from(
                     VerbatimUrl::from_absolute_path(root.join(index_path))
@@ -4593,6 +4629,9 @@ struct WheelWire {
     /// This is only present for wheels that come from registries.
     #[serde(alias = "upload_time")]
     upload_time: Option<Timestamp>,
+    /// The zstandard-compressed wheel metadata, if any.
+    #[serde(alias = "zstd")]
+    zstd: Option<ZstdWheel>,
 }
 
 #[derive(Clone, Debug, serde::Deserialize, PartialEq, Eq)]
@@ -4648,6 +4687,19 @@ impl Wheel {
         if let Some(upload_time) = self.upload_time {
             table.insert("upload-time", Value::from(upload_time.to_string()));
         }
+        if let Some(zstd) = &self.zstd {
+            let mut inner = InlineTable::new();
+            if let Some(ref hash) = zstd.hash {
+                inner.insert("hash", Value::from(hash.to_string()));
+            }
+            if let Some(size) = zstd.size {
+                inner.insert(
+                    "size",
+                    toml_edit::ser::ValueSerializer::new().serialize_u64(size)?,
+                );
+            }
+            table.insert("zstd", Value::from(inner));
+        }
         Ok(table)
     }
 }
@@ -4682,6 +4734,7 @@ impl TryFrom<WheelWire> for Wheel {
             hash: wire.hash,
             size: wire.size,
             upload_time: wire.upload_time,
+            zstd: wire.zstd,
             filename,
         })
     }

crates/uv-resolver/src/lock/snapshots/uv_resolver__lock__tests__hash_optional_missing.snap

@@ -83,6 +83,7 @@ Ok(
                                 },
                             },
                         },
+                        zstd: None,
                     },
                 ],
                 fork_markers: [],

crates/uv-resolver/src/lock/snapshots/uv_resolver__lock__tests__hash_optional_present.snap

@@ -90,6 +90,7 @@ Ok(
                                 },
                             },
                         },
+                        zstd: None,
                     },
                 ],
                 fork_markers: [],

crates/uv-resolver/src/lock/snapshots/uv_resolver__lock__tests__hash_required_present.snap

@@ -86,6 +86,7 @@ Ok(
                                 },
                             },
                         },
+                        zstd: None,
                     },
                 ],
                 fork_markers: [],