Fix AES encryption streaming support

The update_aes_extra_data function requires the underlying writer to
support seeking to succeed. In effect, this function is only used to
switch the mode between AE2 and AE1 depending on file size. This is not
strictly necessary so long as we use the strong mode by default, so we
now only call this function for the non-streaming case.

Author: roblabla

src/write.rs

@@ -927,19 +927,26 @@ impl<W: Write + Seek> ZipWriter<W> {
             new_extra_data.append(&mut extra_data);
             extra_data = new_extra_data;
         }
+
+        // Figure out the underlying compression_method and aes mode when using
+        // AES encryption.
+        let (compression_method, aes_mode) = match options.encrypt_with {
+            // Preserve AES method for raw copies without needing a password
+            #[cfg(feature = "aes-crypto")]
+            None if options.aes_mode.is_some() => (CompressionMethod::Aes, options.aes_mode),
+            #[cfg(feature = "aes-crypto")]
+            Some(EncryptWith::Aes { mode, .. }) => (
+                CompressionMethod::Aes,
+                Some((mode, AesVendorVersion::Ae2, options.compression_method)),
+            ),
+            _ => (options.compression_method, None),
+        };
+
         // Write AES encryption extra data.
         #[allow(unused_mut)]
         let mut aes_extra_data_start = 0;
         #[cfg(feature = "aes-crypto")]
-        if let Some(EncryptWith::Aes { mode, .. }) = options.encrypt_with {
-            let aes_dummy_extra_data = [0x02, 0x00, 0x41, 0x45, mode as u8, 0x00, 0x00];
-            aes_extra_data_start = extra_data.len() as u64;
-            ExtendedFileOptions::add_extra_data_unchecked(
-                &mut extra_data,
-                0x9901,
-                &aes_dummy_extra_data,
-            )?;
-        } else if let Some((mode, vendor, underlying)) = options.aes_mode {
+        if let Some((mode, vendor, underlying)) = aes_mode {
             // For raw copies of AES entries, write the correct AES extra data immediately
             let mut body = [0; 7];
             [body[0], body[1]] = (vendor as u16).to_le_bytes(); // vendor version (1 or 2)
@@ -949,18 +956,6 @@ impl<W: Write + Seek> ZipWriter<W> {
             aes_extra_data_start = extra_data.len() as u64;
             ExtendedFileOptions::add_extra_data_unchecked(&mut extra_data, 0x9901, &body)?;
         }
-
-        let (compression_method, aes_mode) = match options.encrypt_with {
-            // Preserve AES method for raw copies without needing a password
-            #[cfg(feature = "aes-crypto")]
-            None if options.aes_mode.is_some() => (CompressionMethod::Aes, options.aes_mode),
-            #[cfg(feature = "aes-crypto")]
-            Some(EncryptWith::Aes { mode, .. }) => (
-                CompressionMethod::Aes,
-                Some((mode, AesVendorVersion::Ae2, options.compression_method)),
-            ),
-            _ => (options.compression_method, None),
-        };
         let header_end =
             header_start + size_of::<ZipLocalEntryBlock>() as u64 + name.to_string().len() as u64;
 
@@ -1090,29 +1085,40 @@ impl<W: Write + Seek> ZipWriter<W> {
             let file_end = writer.stream_position()?;
             debug_assert!(file_end >= self.stats.start);
             file.compressed_size = file_end - self.stats.start;
-            let mut crc = true;
-            if let Some(aes_mode) = &mut file.aes_mode {
-                // We prefer using AE-1 which provides an extra CRC check, but for small files we
-                // switch to AE-2 to prevent being able to use the CRC value to to reconstruct the
-                // unencrypted contents.
-                //
-                // C.f. https://www.winzip.com/en/support/aes-encryption/#crc-faq
-                aes_mode.1 = if self.stats.bytes_written < 20 {
-                    crc = false;
-                    AesVendorVersion::Ae2
-                } else {
-                    AesVendorVersion::Ae1
-                };
+
+            if !file.using_data_descriptor {
+                if let Some(aes_mode) = &mut file.aes_mode {
+                    // We prefer using AE-1 which provides an extra CRC check, but for small files we
+                    // switch to AE-2 to prevent being able to use the CRC value to to reconstruct the
+                    // unencrypted contents.
+                    //
+                    // We can only do this when the underlying writer supports
+                    // seek operations, so we gate this behind using_data_descriptor.
+                    //
+                    // C.f. https://www.winzip.com/en/support/aes-encryption/#crc-faq
+                    aes_mode.1 = if self.stats.bytes_written < 20 {
+                        AesVendorVersion::Ae2
+                    } else {
+                        AesVendorVersion::Ae1
+                    };
+                }
             }
+
+            let crc = !matches!(file.aes_mode, Some((_, AesVendorVersion::Ae2, _)));
+
             file.crc32 = if crc {
                 self.stats.hasher.clone().finalize()
             } else {
                 0
             };
-            update_aes_extra_data(writer, file)?;
+
             if file.using_data_descriptor {
                 write_data_descriptor(writer, file)?;
             } else {
+                // If using a data descriptor, it's because the underlying
+                // Write implementation doesn't support seek. In this case, we
+                // shouldn't update the AES Extra Data.
+                update_aes_extra_data(writer, file)?;
                 update_local_file_header(writer, file)?;
                 writer.seek(SeekFrom::Start(file_end))?;
             }