Use safe transmute by default

Using the zerocopy crate, we can port all header conversions from pointer cast to safe transmutes. After this change, the code in `header.rs` does not use `unsafe` anymore when the `zerocopy` feature is activated.

Since this adds a derive crate without feature addition as dependency, zerocopy is an optional (but on-by-default) dependency.

Author: konstin

.github/workflows/ci.yml

@@ -27,6 +27,8 @@ jobs:
       - run: cargo hack check --all --ignore-private --each-feature --no-dev-deps
       - run: cargo check --all --all-targets --all-features
       - run: cargo test
+      # Test without zerocopy
+      - run: cargo test --no-default-features
       - run: cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
 
   msrv:

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 0.5.2
+
+* Use safe transmutes from the zerocopy crate by default
+
 ## 0.5.1
 
 * Add test to reproduce issue in `impl Stream for Entries` causing filename truncation by @charliermarsh in https://github.com/astral-sh/tokio-tar/pull/41

Cargo.lock

@@ -30,6 +30,7 @@ portable-atomic = "1"
 rustc-hash = "2.1.0"
 tokio = { version = "1", features = ["fs", "io-util", "rt"] }
 tokio-stream = "0.1"
+zerocopy = { version = "0.8.23", features = ["derive"], optional = true }
 
 [dev-dependencies]
 tempfile = "3"
@@ -40,7 +41,9 @@ xattr = { version = "1.0", optional = true }
 libc = "0.2"
 
 [features]
-default = ["xattr"]
+default = ["xattr", "zerocopy"]
+# Use safe transmute for headers (otherwise, unsafe pointer casts are used)
+zerocopy = ["dep:zerocopy"]
 
 [lib]
 name = "tokio_tar"