feat: add MessagePack reader/writer (#56)

Implements MessagePack binary format support using rmpv:
- Parser: from_bytes/from_reader for binary input, from_str for hex
- Writer: to_bytes for binary output, to_string as hex for CLI pipeline
- All primitive types round-trip: null, bool, int, float, string, bytes
- Nested structures (maps, arrays) fully preserved with key order
- Binary data (Bytes variant) natively preserved
- Cross-format round-trip: MessagePack → JSON → MessagePack
- CLI integration: -f msgpack/-t msgpack, .msgpack/.mp extensions
- 30+ tests covering round-trips, edge cases, errors, hex encoding

Fixes #27

Author: alvinreal

Cargo.toml

@@ -15,6 +15,8 @@ toml = "0.8"
 csv = "1"
 clap = { version = "4", features = ["derive"] }
 quick-xml = "0.31"
+rmp-serde = "1"
+rmpv = "1"
 indexmap = { version = "2", features = ["serde"] }
 thiserror = "1"
 anyhow = "1"

src/cli.rs

@@ -11,6 +11,7 @@ pub enum Format {
     Toml,
     Csv,
     Xml,
+    Msgpack,
 }
 
 impl Format {
@@ -23,6 +24,7 @@ impl Format {
             (Format::Toml, "TOML", &["toml"]),
             (Format::Csv, "CSV", &["csv"]),
             (Format::Xml, "XML", &["xml"]),
+            (Format::Msgpack, "MessagePack", &["msgpack", "mp"]),
         ]
     }
 
@@ -35,6 +37,7 @@ impl Format {
             "toml" => Some(Format::Toml),
             "csv" => Some(Format::Csv),
             "xml" => Some(Format::Xml),
+            "msgpack" | "mp" => Some(Format::Msgpack),
             _ => None,
         }
     }
@@ -55,6 +58,7 @@ impl Format {
             "toml" => Some(Format::Toml),
             "csv" => Some(Format::Csv),
             "xml" => Some(Format::Xml),
+            "msgpack" | "mp" => Some(Format::Msgpack),
             _ => None,
         }
     }
@@ -69,6 +73,7 @@ impl fmt::Display for Format {
             Format::Toml => write!(f, "toml"),
             Format::Csv => write!(f, "csv"),
             Format::Xml => write!(f, "xml"),
+            Format::Msgpack => write!(f, "msgpack"),
         }
     }
 }
@@ -196,6 +201,7 @@ pub fn parse_input(input: &str, format: Format) -> crate::error::Result<crate::v
         Format::Toml => crate::formats::toml::from_str(input),
         Format::Csv => crate::formats::csv::from_str(input),
         Format::Xml => crate::formats::xml::from_str(input),
+        Format::Msgpack => crate::formats::msgpack::from_str(input),
     }
 }
 
@@ -218,6 +224,7 @@ pub fn serialize_output(
         Format::Toml => crate::formats::toml::to_string(value),
         Format::Csv => crate::formats::csv::to_string(value),
         Format::Xml => crate::formats::xml::to_string(value),
+        Format::Msgpack => crate::formats::msgpack::to_string(value),
     }
 }
 
@@ -378,6 +385,12 @@ mod tests {
         assert_eq!(Format::from_extension("ndjson"), Some(Format::Jsonl));
     }
 
+    #[test]
+    fn format_from_extension_msgpack() {
+        assert_eq!(Format::from_extension("msgpack"), Some(Format::Msgpack));
+        assert_eq!(Format::from_extension("mp"), Some(Format::Msgpack));
+    }
+
     #[test]
     fn format_from_path_json() {
         let p = PathBuf::from("data.json");
@@ -403,6 +416,8 @@ mod tests {
         assert_eq!(Format::from_name("xml"), Some(Format::Xml));
         assert_eq!(Format::from_name("jsonl"), Some(Format::Jsonl));
         assert_eq!(Format::from_name("ndjson"), Some(Format::Jsonl));
+        assert_eq!(Format::from_name("msgpack"), Some(Format::Msgpack));
+        assert_eq!(Format::from_name("mp"), Some(Format::Msgpack));
         assert_eq!(Format::from_name("nope"), None);
     }
 
@@ -518,6 +533,7 @@ mod tests {
         assert_eq!(Format::Toml.to_string(), "toml");
         assert_eq!(Format::Csv.to_string(), "csv");
         assert_eq!(Format::Xml.to_string(), "xml");
+        assert_eq!(Format::Msgpack.to_string(), "msgpack");
     }
 
     // -- Mapping CLI flags --------------------------------------------------

src/formats/mod.rs

@@ -1,6 +1,7 @@
 pub mod csv;
 pub mod json;
 pub mod jsonl;
+pub mod msgpack;
 pub mod toml;
 pub mod xml;
 pub mod yaml;