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Commit df1b7d1d authored by Marybeth Fair's avatar Marybeth Fair
Browse files

Add a function to fingerprint flag/offset info. 

Uses SipHasher implementation added to the project. Ideally the output
would remain consistent between builds (though the worst case of an
updated algorithm would be a string lookup for cross-container reads
only).

Sort the flags first so everything is always added to the hasher in the
same order - note this code is only run at build time, not runtime.

Next step is to write this fingerprint into the package.map file and
introduce a flag to guard this change.

Bug: 316357686
Test: atest aconfig.test
Change-Id: Ie5f34541d982dfa120ffb05fc0790603689d47c0
parent 0ad443b8

tools/aconfig/aconfig/src/commands.rs

+34 −1
Original line number Diff line number Diff line
@@ -17,7 +17,8 @@ 
use anyhow::{bail, ensure, Context, Result};

use itertools::Itertools;

use protobuf::Message;

use std::collections::HashMap;

use std::collections::{BTreeMap, HashMap};

use std::hash::Hasher;

use std::io::Read;

use std::path::PathBuf;
@@ -31,6 +32,7 @@ use aconfig_protos::{ 
    ParsedFlagExt, ProtoFlagMetadata, ProtoFlagPermission, ProtoFlagState, ProtoParsedFlag,

    ProtoParsedFlags, ProtoTracepoint,

};

use aconfig_storage_file::sip_hasher13::SipHasher13;

use aconfig_storage_file::StorageFileType;



pub struct Input {
@@ -410,11 +412,42 @@ where 
    Ok(flag_ids)

}



#[allow(dead_code)] // TODO: b/316357686 - Use fingerprint in codegen to

                    // protect hardcoded offset reads.

pub fn compute_flag_offsets_fingerprint(flags_map: &HashMap<String, u16>) -> Result<u64> {

    let mut hasher = SipHasher13::new();



    // Need to sort to ensure the data is added to the hasher in the same order

    // each run.

    let sorted_map: BTreeMap<&String, &u16> = flags_map.iter().collect();



    for (flag, offset) in sorted_map {

        // See https://docs.rs/siphasher/latest/siphasher/#note for use of write

        // over write_i16. Similarly, use to_be_bytes rather than to_ne_bytes to

        // ensure consistency.

        hasher.write(flag.as_bytes());

        hasher.write(&offset.to_be_bytes());

    }

    Ok(hasher.finish())

}



#[cfg(test)]

mod tests {

    use super::*;

    use aconfig_protos::ProtoFlagPurpose;



    #[test]

    fn test_offset_fingerprint() {

        let parsed_flags = crate::test::parse_test_flags();

        let package = find_unique_package(&parsed_flags.parsed_flag).unwrap().to_string();

        let flag_ids = assign_flag_ids(&package, parsed_flags.parsed_flag.iter()).unwrap();

        let expected_fingerprint = 10709892481002252132u64;



        let hash_result = compute_flag_offsets_fingerprint(&flag_ids);



        assert_eq!(hash_result.unwrap(), expected_fingerprint);

    }



    #[test]

    fn test_parse_flags() {

        let parsed_flags = crate::test::parse_test_flags(); // calls parse_flags