use crate::Result;
use crate::crypto::{Cipher, Nonce};
use crate::errors::PagedbError;
use super::auth::{footer_aad, mac_hk};
use super::fields::{
FOOTER_CLEARTEXT_END_V1, FOOTER_CLEARTEXT_END_V2, FOOTER_FIELDS_END_V1, FOOTER_FIELDS_END_V2,
FOOTER_HEADER_MAC_LEN, MANIFEST_TAG_LEN, SegmentFooterFields, max_manifest_len,
max_manifest_len_v2,
};
pub fn encode_segment_footer(
fields: &SegmentFooterFields,
manifest: &[u8],
hk: &crate::crypto::keys::DerivedKey,
cipher: &Cipher,
page_size: usize,
) -> Result<Vec<u8>> {
let (fields_end, cleartext_end) = match fields.format_version {
1 => (FOOTER_FIELDS_END_V1, FOOTER_CLEARTEXT_END_V1),
2 => (FOOTER_FIELDS_END_V2, FOOTER_CLEARTEXT_END_V2),
_ => return Err(PagedbError::Unsupported),
};
if page_size < cleartext_end + MANIFEST_TAG_LEN {
return Err(PagedbError::Unsupported);
}
let max_manifest = if fields.format_version == 1 {
max_manifest_len(page_size)
} else {
max_manifest_len_v2(page_size)
};
if manifest.len() > max_manifest {
return Err(PagedbError::ManifestTooLarge);
}
if cipher.id().as_byte() != fields.cipher_id {
return Err(PagedbError::Unsupported);
}
let manifest_offset = u32::try_from(cleartext_end).map_err(|_| PagedbError::Unsupported)?;
let manifest_len = u32::try_from(manifest.len()).map_err(|_| PagedbError::ManifestTooLarge)?;
let mut out = vec![0u8; page_size];
let mut offset = 0usize;
out[offset..offset + 8].copy_from_slice(&super::fields::MAGIC);
offset += 8;
out[offset..offset + 2].copy_from_slice(&fields.format_version.to_le_bytes());
offset += 2;
out[offset] = fields.cipher_id;
offset += 1;
out[offset..offset + 16].copy_from_slice(&fields.segment_id);
offset += 16;
out[offset..offset + 16].copy_from_slice(&fields.parent_file_id);
offset += 16;
out[offset..offset + 16].copy_from_slice(&fields.realm_id.0);
offset += 16;
out[offset..offset + 8].copy_from_slice(&fields.mk_epoch.to_le_bytes());
offset += 8;
out[offset..offset + 8].copy_from_slice(&fields.page_count.to_le_bytes());
offset += 8;
out[offset..offset + 8].copy_from_slice(&fields.total_bytes.to_le_bytes());
offset += 8;
out[offset..offset + 8].copy_from_slice(&fields.final_counter.to_le_bytes());
offset += 8;
out[offset..offset + 4].copy_from_slice(&manifest_offset.to_le_bytes());
offset += 4;
out[offset..offset + 4].copy_from_slice(&manifest_len.to_le_bytes());
offset += 4;
if fields.format_version == 2 {
out[offset..offset + 8].copy_from_slice(&fields.index_start_page.to_le_bytes());
offset += 8;
out[offset..offset + 4].copy_from_slice(&fields.index_page_count.to_le_bytes());
offset += 4;
}
debug_assert_eq!(offset, fields_end);
let mac = mac_hk(hk, &out[..offset])?;
out[offset..offset + FOOTER_HEADER_MAC_LEN].copy_from_slice(&mac);
offset += FOOTER_HEADER_MAC_LEN;
debug_assert_eq!(offset, cleartext_end);
let nonce_counter = fields
.final_counter
.checked_add(1)
.filter(|counter| *counter <= Nonce::COUNTER_MAX)
.ok_or(PagedbError::NonceCounterExhausted)?;
let mut file_id = [0u8; 6];
file_id.copy_from_slice(&fields.segment_id[..6]);
let nonce = Nonce::from_parts(&file_id, nonce_counter);
let manifest_end = cleartext_end
.checked_add(manifest.len())
.ok_or_else(|| PagedbError::arithmetic_overflow("footer manifest end"))?;
out[cleartext_end..manifest_end].copy_from_slice(manifest);
let tag = cipher.encrypt(
&nonce,
&footer_aad(fields),
&mut out[cleartext_end..manifest_end],
)?;
let tag_end = manifest_end
.checked_add(MANIFEST_TAG_LEN)
.ok_or_else(|| PagedbError::arithmetic_overflow("footer manifest tag end"))?;
out[manifest_end..tag_end].copy_from_slice(&tag);
Ok(out)
}