Add compression using zstd (#173)

fix #27

Co-authored-by: Trinity Pointard <trinity.pointard@gmail.com>
Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/173
Co-authored-by: trinity-1686a <trinity.pointard@gmail.com>
Co-committed-by: trinity-1686a <trinity.pointard@gmail.com>

src/util/config.rs

@@ -30,6 +30,13 @@ pub struct Config {
 	// (we can add more aliases for this later)
 	pub replication_mode: String,
 
+	/// Zstd compression level used on data blocks
+	#[serde(
+		deserialize_with = "deserialize_compression",
+		default = "default_compression"
+	)]
+	pub compression_level: Option<i32>,
+
 	/// RPC secret key: 32 bytes hex encoded
 	pub rpc_secret: String,
 
@@ -123,3 +130,57 @@ where
 
 	Ok(ret)
 }
+
+fn default_compression() -> Option<i32> {
+	Some(1)
+}
+
+fn deserialize_compression<'de, D>(deserializer: D) -> Result<Option<i32>, D::Error>
+where
+	D: de::Deserializer<'de>,
+{
+	use std::convert::TryFrom;
+
+	struct OptionVisitor;
+
+	impl<'de> serde::de::Visitor<'de> for OptionVisitor {
+		type Value = Option<i32>;
+		fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+			formatter.write_str("int or 'none'")
+		}
+
+		fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+		where
+			E: de::Error,
+		{
+			if value.eq_ignore_ascii_case("none") {
+				Ok(None)
+			} else {
+				Err(E::custom(format!(
+					"Invalid compression level: '{}', should be a number, or 'none'",
+					value
+				)))
+			}
+		}
+
+		fn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>
+		where
+			E: de::Error,
+		{
+			i32::try_from(v)
+				.map(Some)
+				.map_err(|_| E::custom("Compression level out of bound".to_owned()))
+		}
+
+		fn visit_u64<E>(self, v: u64) -> Result<Self::Value, E>
+		where
+			E: de::Error,
+		{
+			i32::try_from(v)
+				.map(Some)
+				.map_err(|_| E::custom("Compression level out of bound".to_owned()))
+		}
+	}
+
+	deserializer.deserialize_any(OptionVisitor)
+}