Add [De]Compress::new_gzip (rust-lang#261)

* Add [De]Compress::new_gzip

* Add new_gzip test

src/ffi/c.rs

@@ -164,10 +164,6 @@ pub struct Inflate {
 
 impl InflateBackend for Inflate {
     fn make(zlib_header: bool, window_bits: u8) -> Self {
-        assert!(
-            window_bits > 8 && window_bits < 16,
-            "window_bits must be within 9 ..= 15"
-        );
         unsafe {
             let mut state = StreamWrapper::default();
             let ret = mz_inflateInit2(
@@ -258,10 +254,6 @@ pub struct Deflate {
 
 impl DeflateBackend for Deflate {
     fn make(level: Compression, zlib_header: bool, window_bits: u8) -> Self {
-        assert!(
-            window_bits > 8 && window_bits < 16,
-            "window_bits must be within 9 ..= 15"
-        );
         unsafe {
             let mut state = StreamWrapper::default();
             let ret = mz_deflateInit2(

src/ffi/rust.rs

@@ -41,12 +41,7 @@ impl fmt::Debug for Inflate {
 }
 
 impl InflateBackend for Inflate {
-    fn make(zlib_header: bool, window_bits: u8) -> Self {
-        assert!(
-            window_bits > 8 && window_bits < 16,
-            "window_bits must be within 9 ..= 15"
-        );
-
+    fn make(zlib_header: bool, _window_bits: u8) -> Self {
         let format = format_from_bool(zlib_header);
 
         Inflate {
@@ -119,12 +114,7 @@ impl fmt::Debug for Deflate {
 }
 
 impl DeflateBackend for Deflate {
-    fn make(level: Compression, zlib_header: bool, window_bits: u8) -> Self {
-        assert!(
-            window_bits > 8 && window_bits < 16,
-            "window_bits must be within 9 ..= 15"
-        );
-
+    fn make(level: Compression, zlib_header: bool, _window_bits: u8) -> Self {
         // Check in case the integer value changes at some point.
         debug_assert!(level.level() <= 10);
 

src/mem.rs

@@ -215,11 +215,43 @@ impl Compress {
         zlib_header: bool,
         window_bits: u8,
     ) -> Compress {
+        assert!(
+            window_bits > 8 && window_bits < 16,
+            "window_bits must be within 9 ..= 15"
+        );
         Compress {
             inner: Deflate::make(level, zlib_header, window_bits),
         }
     }
 
+    /// Creates a new object ready for compressing data that it's given.
+    ///
+    /// The `level` argument here indicates what level of compression is going
+    /// to be performed.
+    ///
+    /// The Compress object produced by this constructor outputs gzip headers
+    /// for the compressed data.
+    ///
+    /// # Panics
+    ///
+    /// If `window_bits` does not fall into the range 9 ..= 15,
+    /// `new_with_window_bits` will panic.
+    ///
+    /// # Note
+    ///
+    /// This constructor is only available when the `zlib` feature is used.
+    /// Other backends currently do not support gzip headers for Compress.
+    #[cfg(feature = "zlib")]
+    pub fn new_gzip(level: Compression, window_bits: u8) -> Compress {
+        assert!(
+            window_bits > 8 && window_bits < 16,
+            "window_bits must be within 9 ..= 15"
+        );
+        Compress {
+            inner: Deflate::make(level, true, window_bits + 16),
+        }
+    }
+
     /// Returns the total number of input bytes which have been processed by
     /// this compression object.
     pub fn total_in(&self) -> u64 {
@@ -355,11 +387,40 @@ impl Decompress {
     /// Other backends currently do not support custom window bits.
     #[cfg(feature = "any_zlib")]
     pub fn new_with_window_bits(zlib_header: bool, window_bits: u8) -> Decompress {
+        assert!(
+            window_bits > 8 && window_bits < 16,
+            "window_bits must be within 9 ..= 15"
+        );
         Decompress {
             inner: Inflate::make(zlib_header, window_bits),
         }
     }
 
+    /// Creates a new object ready for decompressing data that it's given.
+    ///
+    /// The Deompress object produced by this constructor expects gzip headers
+    /// for the compressed data.
+    ///
+    /// # Panics
+    ///
+    /// If `window_bits` does not fall into the range 9 ..= 15,
+    /// `new_with_window_bits` will panic.
+    ///
+    /// # Note
+    ///
+    /// This constructor is only available when the `zlib` feature is used.
+    /// Other backends currently do not support gzip headers for Decompress.
+    #[cfg(feature = "zlib")]
+    pub fn new_gzip(window_bits: u8) -> Decompress {
+        assert!(
+            window_bits > 8 && window_bits < 16,
+            "window_bits must be within 9 ..= 15"
+        );
+        Decompress {
+            inner: Inflate::make(true, window_bits + 16),
+        }
+    }
+
     /// Returns the total number of input bytes which have been processed by
     /// this decompression object.
     pub fn total_in(&self) -> u64 {
@@ -645,4 +706,30 @@ mod tests {
 
         assert_eq!(&decoded[..decoder.total_out() as usize], string);
     }
+
+    #[cfg(feature = "zlib")]
+    #[test]
+    fn test_gzip_flate() {
+        let string = "hello, hello!".as_bytes();
+
+        let mut encoded = Vec::with_capacity(1024);
+
+        let mut encoder = Compress::new_gzip(Compression::default(), 9);
+
+        encoder
+            .compress_vec(string, &mut encoded, FlushCompress::Finish)
+            .unwrap();
+
+        assert_eq!(encoder.total_in(), string.len() as u64);
+        assert_eq!(encoder.total_out(), encoded.len() as u64);
+
+        let mut decoder = Decompress::new_gzip(9);
+
+        let mut decoded = [0; 1024];
+        decoder
+            .decompress(&encoded, &mut decoded, FlushDecompress::Finish)
+            .unwrap();
+
+        assert_eq!(&decoded[..decoder.total_out() as usize], string);
+    }
 }