Add ZstdEncoder::with_quality_and_params to enable compression parame…

…ters

This allows enabling parameters such as long-distance matching mode or
rsyncable mode.

Add a type supporting a subset of zstd compression parameters, to
insulate against future changes to zstd.

src/codec/zstd/encoder.rs

@@ -1,5 +1,5 @@
 use crate::{codec::Encode, unshared::Unshared, util::PartialBuffer};
-use libzstd::stream::raw::{Encoder, Operation};
+use libzstd::stream::raw::{CParameter, Encoder, Operation};
 use std::io::Result;
 
 #[derive(Debug)]
@@ -13,6 +13,16 @@ impl ZstdEncoder {
             encoder: Unshared::new(Encoder::new(level).unwrap()),
         }
     }
+
+    pub(crate) fn new_with_params(level: i32, params: &[crate::zstd::CParameter]) -> Self {
+        let mut encoder = Encoder::new(level).unwrap();
+        for param in params {
+            encoder.set_parameter(param.as_zstd()).unwrap();
+        }
+        Self {
+            encoder: Unshared::new(encoder),
+        }
+    }
 }
 
 impl Encode for ZstdEncoder {

src/lib.rs

@@ -258,3 +258,110 @@ impl Level {
         }
     }
 }
+
+#[cfg(feature = "zstd")]
+/// This module contains zstd-specific types for async-compression.
+pub mod zstd {
+    use libzstd::stream::raw::CParameter::*;
+
+    /// A compression parameter for zstd. This is a stable wrapper around zstd's own `CParameter`
+    /// type, to abstract over different versions of the zstd library.
+    ///
+    /// See the [zstd documentation](https://facebook.github.io/zstd/zstd_manual.html) for more
+    /// information on these parameters.
+    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
+    pub struct CParameter(libzstd::stream::raw::CParameter);
+
+    impl CParameter {
+        /// Window size in bytes (as a power of two)
+        pub fn window_log(value: u32) -> Self {
+            Self(WindowLog(value))
+        }
+
+        /// Size of the initial probe table in 4-byte entries (as a power of two)
+        pub fn hash_log(value: u32) -> Self {
+            Self(HashLog(value))
+        }
+
+        /// Size of the multi-probe table in 4-byte entries (as a power of two)
+        pub fn chain_log(value: u32) -> Self {
+            Self(ChainLog(value))
+        }
+
+        /// Number of search attempts (as a power of two)
+        pub fn search_log(value: u32) -> Self {
+            Self(SearchLog(value))
+        }
+
+        /// Minimum size of matches searched for
+        pub fn min_match(value: u32) -> Self {
+            Self(MinMatch(value))
+        }
+
+        /// Strategy-dependent length modifier
+        pub fn target_length(value: u32) -> Self {
+            Self(TargetLength(value))
+        }
+
+        /// Enable long-distance matching mode to look for and emit long-distance references.
+        ///
+        /// This increases the default window size.
+        pub fn enable_long_distance_matching(value: bool) -> Self {
+            Self(EnableLongDistanceMatching(value))
+        }
+
+        /// Size of the long-distance matching table (as a power of two)
+        pub fn ldm_hash_log(value: u32) -> Self {
+            Self(LdmHashLog(value))
+        }
+
+        /// Minimum size of long-distance matches searched for
+        pub fn ldm_min_match(value: u32) -> Self {
+            Self(LdmMinMatch(value))
+        }
+
+        /// Size of each bucket in the LDM hash table for collision resolution (as a power of two)
+        pub fn ldm_bucket_size_log(value: u32) -> Self {
+            Self(LdmBucketSizeLog(value))
+        }
+
+        /// Frequency of using the LDM hash table (as a power of two)
+        pub fn ldm_hash_rate_log(value: u32) -> Self {
+            Self(LdmHashRateLog(value))
+        }
+
+        /// Emit the size of the content (default: true).
+        pub fn content_size_flag(value: bool) -> Self {
+            Self(ContentSizeFlag(value))
+        }
+
+        /// Emit a checksum (default: false).
+        pub fn checksum_flag(value: bool) -> Self {
+            Self(ChecksumFlag(value))
+        }
+
+        /// Emit a dictionary ID when using a custom dictionary (default: true).
+        pub fn dict_id_flag(value: bool) -> Self {
+            Self(DictIdFlag(value))
+        }
+
+        /// Number of threads to spawn.
+        ///
+        /// If set to 0, compression functions will block; if set to 1 or more, compression will
+        /// run in background threads and `flush` pushes bytes through the compressor.
+        pub fn nb_workers(value: u32) -> Self {
+            Self(NbWorkers(value))
+        }
+
+        /// Number of bytes given to each worker.
+        ///
+        /// If set to 0, zstd selects a job size based on compression parameters.
+        pub fn job_size(value: u32) -> Self {
+            Self(JobSize(value))
+        }
+
+        pub(crate) fn as_zstd(&self) -> libzstd::stream::raw::CParameter {
+            self.0
+        }
+    }
+}

src/macros.rs

@@ -89,6 +89,17 @@ macro_rules! algos {
                     ),
                 }
             }
+
+            /// Creates a new encoder, using the specified compression level and parameters, which
+            /// will read uncompressed data from the given stream and emit a compressed stream.
+            pub fn with_quality_and_params(inner: $inner, level: crate::Level, params: &[crate::zstd::CParameter]) -> Self {
+                Self {
+                    inner: crate::$($mod::)+generic::Encoder::new(
+                        inner,
+                        crate::codec::ZstdEncoder::new_with_params(level.into_zstd(), params),
+                    ),
+                }
+            }
         });
 
         algos!(@algo xz ["xz"] XzDecoder XzEncoder<$inner> {