Use boxed slices instead of Vec in public Rust API

None of the data returned is meaningfully extensible, so reflect that in the types used.

plugins_metadata() returns a Vec because the FFI layer needs a Vec, as
cbindgen doesn't support representing a Box<[T]> in a C header, so
there's no point converting back and forth.

ffi/src/plugin.rs

@@ -121,7 +121,7 @@ pub unsafe extern "C" fn esp_plugin_parse(plugin_ptr: *mut Plugin, load_header_o
 #[no_mangle]
 pub unsafe extern "C" fn esp_plugin_resolve_record_ids(
     plugin_ptr: *mut Plugin,
-    plugins_metadata: *mut Vec<PluginMetadata>,
+    plugins_metadata: *const Vec<PluginMetadata>,
 ) -> u32 {
     panic::catch_unwind(|| {
         if plugin_ptr.is_null() {

src/error.rs

@@ -30,8 +30,8 @@ pub enum Error {
     IoError(io::Error),
     NoFilename(PathBuf),
     ParsingIncomplete(MoreDataNeeded),
-    ParsingError(Vec<u8>, ParsingErrorKind),
-    DecodeError(Vec<u8>),
+    ParsingError(Box<[u8]>, ParsingErrorKind),
+    DecodeError(Box<[u8]>),
     UnresolvedRecordIds(PathBuf),
     PluginMetadataNotFound(String),
 }
@@ -46,7 +46,7 @@ impl From<Err<nom::error::Error<&[u8]>>> for Error {
                 Error::ParsingIncomplete(MoreDataNeeded::Size(size))
             }
             Err::Error(err) | Err::Failure(err) => Error::ParsingError(
-                err.input.to_vec(),
+                err.input.into(),
                 ParsingErrorKind::GenericParserError(err.code.description().to_string()),
             ),
         }

src/plugin.rs

@@ -199,7 +199,7 @@ impl Plugin {
             .map(std::string::ToString::to_string)
     }
 
-    pub fn masters(&self) -> Result<Vec<String>, Error> {
+    pub fn masters(&self) -> Result<Box<[String]>, Error> {
         masters(&self.data.header_record)
     }
 
@@ -288,7 +288,7 @@ impl Plugin {
             if subrecord.subrecord_type() == target_subrecord_type {
                 if subrecord.data().len() <= description_offset {
                     return Err(Error::ParsingError(
-                        subrecord.data().to_vec(),
+                        subrecord.data().into(),
                         ParsingErrorKind::SubrecordDataTooShort(description_offset),
                     ));
                 }
@@ -298,7 +298,7 @@ impl Plugin {
                 return WINDOWS_1252
                     .decode_without_bom_handling_and_without_replacement(data)
                     .map(|s| Some(s.to_string()))
-                    .ok_or(Error::DecodeError(data.to_vec()));
+                    .ok_or(Error::DecodeError(data.into()));
             }
         }
 
@@ -719,7 +719,7 @@ fn hashed_masters_for_starfield(
     Ok(hashed_masters)
 }
 
-fn masters(header_record: &Record) -> Result<Vec<String>, Error> {
+fn masters(header_record: &Record) -> Result<Box<[String]>, Error> {
     header_record
         .subrecords()
         .iter()
@@ -729,9 +729,9 @@ fn masters(header_record: &Record) -> Result<Vec<String>, Error> {
             WINDOWS_1252
                 .decode_without_bom_handling_and_without_replacement(d)
                 .map(|s| s.to_string())
-                .ok_or(Error::DecodeError(d.to_vec()))
+                .ok_or(Error::DecodeError(d.into()))
         })
-        .collect::<Result<Vec<String>, Error>>()
+        .collect()
 }
 
 fn read_form_ids<R: BufRead + Seek>(reader: &mut R, game_id: GameId) -> Result<Vec<u32>, Error> {

src/record.rs

@@ -72,7 +72,7 @@ impl Record {
         if &header_bytes[0..4] != expected_type {
             // Take a copy of 16 bytes so the output includes the FormID.
             return Err(Error::ParsingError(
-                header_bytes[..16].to_vec(),
+                header_bytes[..16].into(),
                 ParsingErrorKind::UnexpectedRecordType(expected_type.to_vec()),
             ));
         }