use zlib-rs as a dynamic c library

.github/workflows/checks.yaml

@@ -192,3 +192,37 @@ jobs:
           for target in $(cargo fuzz list ${{ matrix.features }}) ; do
             RUST_BACKTRACE=1 cargo fuzz run ${{ matrix.features }} $target -- -max_total_time=10
           done
+
+  link-c-dynamic-library:
+    name: dynamic library
+    strategy:
+      matrix:
+        include:
+          - target: x86_64-unknown-linux-gnu
+        features:
+          - ''
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
+        with:
+          persist-credentials: false
+      - name: Install rust toolchain
+        uses: dtolnay/rust-toolchain@be73d7920c329f220ce78e0234b8f96b7ae60248
+        with:
+          toolchain: stable
+          targets: ${{matrix.target}}
+      - name: Rust cache
+        uses: Swatinem/rust-cache@3cf7f8cc28d1b4e7d01e3783be10a97d55d483c8
+        with:
+            shared-key: "stable-${{matrix.target}}"
+      - name: get zpipe.c
+        run: wget https://www.zlib.net/zpipe.c
+      - name: cargo build
+        run: cargo build --target ${{matrix.target}} -p libz-rs-sys --release
+      - name: cc
+        run: cc -o zpipe zpipe.c target/${{matrix.target}}/release/deps/liblibz_rs_sys.so
+      - name: execute
+        run: cat Cargo.toml | ./zpipe | ./zpipe -d > out.txt
+      - name: compare
+        run: cmp -s Cargo.toml out.txt

libz-rs-sys/src/lib.rs

@@ -650,36 +650,24 @@ pub unsafe extern "C" fn deflateTune(
     }
 }
 
-const LIBZ_RS_SYS_VERSION: &str = env!("CARGO_PKG_VERSION");
+// the first part of this version specifies the zlib that we're compatible with (in terms of
+// supported functions). In practice in most cases only the major version is checked, unless
+// specific functions that were added later are used.
+const LIBZ_RS_SYS_VERSION: &str = concat!("1.3.0-zlib-rs-", env!("CARGO_PKG_VERSION"), "\0");
 
 unsafe fn is_version_compatible(version: *const c_char, stream_size: i32) -> bool {
     if version.is_null() {
         return false;
     }
 
-    let cstr = core::ffi::CStr::from_ptr(version);
-
-    if LIBZ_RS_SYS_VERSION.as_bytes()[0] != cstr.to_bytes()[0] {
+    let expected_major_version = core::ptr::read(version);
+    if expected_major_version as u8 != LIBZ_RS_SYS_VERSION.as_bytes()[0] {
         return false;
     }
 
     core::mem::size_of::<z_stream>() as i32 == stream_size
 }
 
 pub const extern "C" fn zlibVersion() -> *const c_char {
-    const BUF: [u8; 16] = {
-        let mut buf = [0; 16];
-
-        let mut i = 0;
-        while i < LIBZ_RS_SYS_VERSION.len() {
-            buf[i] = LIBZ_RS_SYS_VERSION.as_bytes()[i];
-            i += 1;
-        }
-
-        assert!(matches!(buf.last(), Some(0)));
-
-        buf
-    };
-
-    BUF.as_ptr() as *const c_char
+    LIBZ_RS_SYS_VERSION.as_ptr() as *const c_char
 }