vendor/measureme/src/file_header.rs

   1 //! All binary files generated by measureme have a simple file header that
   2 //! consists of a 4 byte file magic string and a 4 byte little-endian version
   3 //! number.
   4
   5 use crate::serialization::SerializationSink;
   6 use byteorder::{ByteOrder, LittleEndian};
   7 use std::error::Error;
   8
   9 pub const CURRENT_FILE_FORMAT_VERSION: u32 = 0;
  10 pub const FILE_MAGIC_EVENT_STREAM: &[u8; 4] = b"MMES";
  11 pub const FILE_MAGIC_STRINGTABLE_DATA: &[u8; 4] = b"MMSD";
  12 pub const FILE_MAGIC_STRINGTABLE_INDEX: &[u8; 4] = b"MMSI";
  13
  14 /// The size of the file header in bytes. Note that functions in this module
  15 /// rely on this size to be `8`.
  16 pub const FILE_HEADER_SIZE: usize = 8;
  17
  18 pub fn write_file_header<S: SerializationSink>(s: &S, file_magic: &[u8; 4]) {
  19     // The implementation here relies on FILE_HEADER_SIZE to have the value 8.
  20     // Let's make sure this assumption cannot be violated without being noticed.
  21     assert_eq!(FILE_HEADER_SIZE, 8);
  22
  23     s.write_atomic(FILE_HEADER_SIZE, |bytes| {
  24         bytes[0..4].copy_from_slice(file_magic);
  25         LittleEndian::write_u32(&mut bytes[4..8], CURRENT_FILE_FORMAT_VERSION);
  26     });
  27 }
  28
  29 pub fn read_file_header(bytes: &[u8], expected_magic: &[u8; 4]) -> Result<u32, Box<dyn Error>> {
  30     // The implementation here relies on FILE_HEADER_SIZE to have the value 8.
  31     // Let's make sure this assumption cannot be violated without being noticed.
  32     assert_eq!(FILE_HEADER_SIZE, 8);
  33
  34     let actual_magic = &bytes[0..4];
  35
  36     if actual_magic != expected_magic {
  37         // FIXME: The error message should mention the file path in order to be
  38         //        more useful.
  39         let msg = format!(
  40             "Unexpected file magic `{:?}`. Expected `{:?}`",
  41             actual_magic, expected_magic,
  42         );
  43
  44         return Err(From::from(msg));
  45     }
  46
  47     Ok(LittleEndian::read_u32(&bytes[4..8]))
  48 }
  49
  50 pub fn strip_file_header(data: &[u8]) -> &[u8] {
  51     &data[FILE_HEADER_SIZE..]
  52 }
  53
  54 #[cfg(test)]
  55 mod tests {
  56     use super::*;
  57     use crate::serialization::test::TestSink;
  58
  59     #[test]
  60     fn roundtrip() {
  61         let data_sink = TestSink::new();
  62
  63         write_file_header(&data_sink, FILE_MAGIC_EVENT_STREAM);
  64
  65         let data = data_sink.into_bytes();
  66
  67         assert_eq!(
  68             read_file_header(&data, FILE_MAGIC_EVENT_STREAM).unwrap(),
  69             CURRENT_FILE_FORMAT_VERSION
  70         );
  71     }
  72
  73     #[test]
  74     fn invalid_magic() {
  75         let data_sink = TestSink::new();
  76         write_file_header(&data_sink, FILE_MAGIC_STRINGTABLE_DATA);
  77         let mut data = data_sink.into_bytes();
  78
  79         // Invalidate the filemagic
  80         data[2] = 0;
  81         assert!(read_file_header(&data, FILE_MAGIC_STRINGTABLE_DATA).is_err());
  82     }
  83
  84     #[test]
  85     fn other_version() {
  86         let data_sink = TestSink::new();
  87
  88         write_file_header(&data_sink, FILE_MAGIC_STRINGTABLE_INDEX);
  89
  90         let mut data = data_sink.into_bytes();
  91
  92         // Change version
  93         data[4] = 0xFF;
  94         data[5] = 0xFF;
  95         data[6] = 0xFF;
  96         data[7] = 0xFF;
  97         assert_eq!(
  98             read_file_header(&data, FILE_MAGIC_STRINGTABLE_INDEX).unwrap(),
  99             0xFFFF_FFFF
 100         );
 101     }
 102 }