refactor: change extra_data to extra_fields

README.md

@@ -154,7 +154,7 @@ The zip creation fuzzer will try to print out a description of the kind of input
 # This input was translated into one or more test cases:
 <fuzz/write/in/id-000000,time-0,execs-0,orig-0011743621118ab6c5278ffbb8fd14bddd8369ee.min \
   cargo run --manifest-path=fuzz/Cargo.toml --quiet -p fuzz_write
-writer.start_file_from_path("", FileOptions { compression_method: Stored, compression_level: None, last_modified_time: DateTime::from_date_and_time(2048, 1, 1, 0, 0, 0)?, permissions: None, large_file: false, encrypt_with: None, extended_options: ExtendedFileOptions {extra_data: vec![].into(), central_extra_data: vec![].into()}, alignment: 0 })?;
+writer.start_file_from_path("", FileOptions { compression_method: Stored, compression_level: None, last_modified_time: DateTime::from_date_and_time(2048, 1, 1, 0, 0, 0)?, permissions: None, large_file: false, encrypt_with: None, extended_options: ExtendedFileOptions {extra_fields: vec![].into()}, alignment: 0 })?;
 writer.write_all(&[])?;
 writer
 let _ = writer.finish_into_readable()?;

src/extra_fields/mod.rs

@@ -1,5 +1,7 @@
 //! Types for extra fields
 
+use crate::result::ZipResult;
+use crate::result::invalid;
 use core::fmt::Display;
 
 mod aex_encryption;
@@ -180,3 +182,60 @@ pub const EXTRA_FIELD_MAPPING: [u16; 59] = [
     0xe57a, // Korean ZIP code page info
     0xfd4a, // SMS/QDOS
 ];
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub(crate) struct CustomExtraField {
+    pub(crate) central_only: bool,
+    header_id: u16,
+    data: Box<[u8]>,
+}
+
+impl CustomExtraField {
+    pub(crate) fn new(central_only: bool, header_id: u16, data: &[u8]) -> Self {
+        Self {
+            central_only,
+            header_id,
+            data: data.into(),
+        }
+    }
+
+    #[allow(unused)] // used for tests
+    pub(crate) fn new_from_raw(central_only: bool, data: &[u8]) -> ZipResult<Self> {
+        if data.len() < 2 {
+            return Err(invalid!("Cannot build a CustomExtraField: no header_id"));
+        }
+        let header_id = u16::from_le_bytes([data[0], data[1]]);
+        if data.len() < 4 {
+            return Err(invalid!("Cannot build a CustomExtraField: no size"));
+        }
+        let size = u16::from_le_bytes([data[2], data[3]]) as usize;
+        if size > u16::MAX as usize {
+            return Err(invalid!("Cannot build a CustomExtraField: size too big"));
+        }
+        let data_rest = &data[4..];
+        if size != data_rest.len() {
+            return Err(invalid!("Cannot build a CustomExtraField: incorrect size"));
+        }
+        Ok(Self {
+            central_only,
+            header_id,
+            data: data[2..].to_vec().into_boxed_slice(),
+        })
+    }
+
+    pub(crate) fn len(&self) -> usize {
+        let size = self.data.len();
+        2 + 2 + size
+    }
+
+    pub(crate) fn serialize(&self) -> Vec<u8> {
+        let mut out = Vec::with_capacity(4 + self.data.len());
+
+        out.extend_from_slice(&self.header_id.to_le_bytes());
+        let size = self.data.len() as u16;
+        out.extend_from_slice(&size.to_le_bytes());
+        out.extend_from_slice(&self.data);
+
+        out
+    }
+}

src/types.rs

@@ -404,8 +404,8 @@ impl ZipFileData {
             extra_field: Some(Arc::from(extra_field)),
             central_extra_field: options
                 .extended_options
-                .central_extra_data()
-                .map(|v| Arc::from(v.as_ref().as_slice())),
+                .central_extra_fields()
+                .map(Arc::<[u8]>::from),
             file_comment: String::with_capacity(0).into_boxed_str(),
             header_start,
             data_start: OnceLock::new(),