Add a simple file header to binary files created by measureme.

measureme/src/file_header.rs

@@ -0,0 +1,103 @@
+//! All binary files generated by measureme have a simple file header that
+//! consists of a 4 byte file magic string and a 4 byte little-endian version
+//! number.
+
+use byteorder::{ByteOrder, LittleEndian};
+use crate::serialization::SerializationSink;
+use std::error::Error;
+
+pub const CURRENT_FILE_FORMAT_VERSION: u32 = 0;
+pub const FILE_MAGIC_EVENT_STREAM: &[u8; 4] = b"MMES";
+pub const FILE_MAGIC_STRINGTABLE_DATA: &[u8; 4] = b"MMSD";
+pub const FILE_MAGIC_STRINGTABLE_INDEX: &[u8; 4] = b"MMSI";
+
+/// The size of the file header in bytes. Note that functions in this module
+/// rely on this size to be `8`.
+pub const FILE_HEADER_SIZE: usize = 8;
+
+pub fn write_file_header<S: SerializationSink>(s: &S, file_magic: &[u8; 4]) {
+    // The implementation here relies on FILE_HEADER_SIZE to have the value 8.
+    // Let's make sure this assumption cannot be violated without being noticed.
+    assert_eq!(FILE_HEADER_SIZE, 8);
+
+    s.write_atomic(FILE_HEADER_SIZE, |bytes| {
+        bytes[0 .. 4].copy_from_slice(file_magic);
+        LittleEndian::write_u32(&mut bytes[4..8], CURRENT_FILE_FORMAT_VERSION);
+    });
+}
+
+pub fn read_file_header(
+    bytes: &[u8],
+    expected_magic: &[u8; 4]
+) -> Result<u32, Box<dyn Error>> {
+    // The implementation here relies on FILE_HEADER_SIZE to have the value 8.
+    // Let's make sure this assumption cannot be violated without being noticed.
+    assert_eq!(FILE_HEADER_SIZE, 8);
+
+    let actual_magic = &bytes[0 .. 4];
+
+    if actual_magic != expected_magic {
+        // FIXME: The error message should mention the file path in order to be
+        //        more useful.
+        let msg = format!(
+            "Unexpected file magic `{:?}`. Expected `{:?}`",
+            actual_magic,
+            expected_magic,
+        );
+
+        return Err(From::from(msg));
+    }
+
+    Ok(LittleEndian::read_u32(&bytes[4..8]))
+}
+
+pub fn strip_file_header(data: &[u8]) -> &[u8] {
+    &data[FILE_HEADER_SIZE ..]
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::serialization::test::TestSink;
+
+    #[test]
+    fn roundtrip() {
+        let data_sink = TestSink::new();
+
+        write_file_header(&data_sink, FILE_MAGIC_EVENT_STREAM);
+
+        let data = data_sink.into_bytes();
+
+        assert_eq!(read_file_header(&data, FILE_MAGIC_EVENT_STREAM).unwrap(),
+                   CURRENT_FILE_FORMAT_VERSION);
+    }
+
+    #[test]
+    fn invalid_magic() {
+        let data_sink = TestSink::new();
+        write_file_header(&data_sink, FILE_MAGIC_STRINGTABLE_DATA);
+        let mut data = data_sink.into_bytes();
+
+        // Invalidate the filemagic
+        data[2] = 0;
+        assert!(read_file_header(&data, FILE_MAGIC_STRINGTABLE_DATA).is_err());
+    }
+
+    #[test]
+    fn other_version() {
+        let data_sink = TestSink::new();
+
+        write_file_header(&data_sink, FILE_MAGIC_STRINGTABLE_INDEX);
+
+        let mut data = data_sink.into_bytes();
+
+        // Change version
+        data[4] = 0xFF;
+        data[5] = 0xFF;
+        data[6] = 0xFF;
+        data[7] = 0xFF;
+        assert_eq!(read_file_header(&data, FILE_MAGIC_STRINGTABLE_INDEX).unwrap(),
+                   0xFFFF_FFFF);
+    }
+}

measureme/src/lib.rs

@@ -1,4 +1,5 @@
 mod event;
+mod file_header;
 mod file_serialization_sink;
 mod mmap_serialization_sink;
 mod profiler;

measureme/src/profiler.rs

@@ -1,3 +1,4 @@
+use crate::file_header::{write_file_header, FILE_MAGIC_EVENT_STREAM};
 use crate::raw_event::{RawEvent, Timestamp, TimestampKind};
 use crate::serialization::SerializationSink;
 use crate::stringtable::{SerializableString, StringId, StringTableBuilder};
@@ -32,6 +33,10 @@ impl<S: SerializationSink> Profiler<S> {
     pub fn new(path_stem: &Path) -> Result<Profiler<S>, Box<dyn Error>> {
         let paths = ProfilerFiles::new(path_stem);
         let event_sink = Arc::new(S::from_path(&paths.events_file)?);
+
+        // The first thing in every file we generate must be the file header.
+        write_file_header(&*event_sink, FILE_MAGIC_EVENT_STREAM);
+
         let string_table = StringTableBuilder::new(
             Arc::new(S::from_path(&paths.string_data_file)?),
             Arc::new(S::from_path(&paths.string_index_file)?),

measureme/src/profiling_data.rs

@@ -1,5 +1,7 @@
+use crate::file_header::FILE_HEADER_SIZE;
 use crate::event::Event;
 use crate::{ProfilerFiles, RawEvent, StringTable, TimestampKind};
+use std::error::Error;
 use std::fs;
 use std::mem;
 use std::path::Path;
@@ -11,19 +13,19 @@ pub struct ProfilingData {
 }
 
 impl ProfilingData {
-    pub fn new(path_stem: &Path) -> ProfilingData {
+    pub fn new(path_stem: &Path) -> Result<ProfilingData, Box<dyn Error>> {
         let paths = ProfilerFiles::new(path_stem);
 
         let string_data = fs::read(paths.string_data_file).expect("couldn't read string_data file");
         let index_data = fs::read(paths.string_index_file).expect("couldn't read string_index file");
         let event_data = fs::read(paths.events_file).expect("couldn't read events file");
 
-        let string_table = StringTable::new(string_data, index_data);
+        let string_table = StringTable::new(string_data, index_data)?;
 
-        ProfilingData {
+        Ok(ProfilingData {
             string_table,
             event_data,
-        }
+        })
     }
 
     pub fn iter(&self) -> impl Iterator<Item = Event<'_>> {
@@ -53,15 +55,16 @@ impl<'a> Iterator for ProfilerEventIterator<'a> {
     type Item = Event<'a>;
 
     fn next(&mut self) -> Option<Event<'a>> {
-        let raw_idx = self.curr_event_idx * mem::size_of::<RawEvent>();
-        let raw_idx_end = raw_idx + mem::size_of::<RawEvent>();
-        if raw_idx_end > self.data.event_data.len() {
+        let event_start_addr = FILE_HEADER_SIZE +
+            self.curr_event_idx * mem::size_of::<RawEvent>();
+        let event_end_addr = event_start_addr + mem::size_of::<RawEvent>();
+        if event_end_addr > self.data.event_data.len() {
             return None;
         }
 
         self.curr_event_idx += 1;
 
-        let raw_event_bytes = &self.data.event_data[raw_idx..raw_idx_end];
+        let raw_event_bytes = &self.data.event_data[event_start_addr..event_end_addr];
 
         let mut raw_event = RawEvent::default();
         unsafe {

measureme/src/stringtable.rs

@@ -12,10 +12,13 @@
 //! UTF-8 bytes. The content of a `TAG_STR_REF` is the contents of the entry
 //! it references.
 
+use crate::file_header::{write_file_header, read_file_header, strip_file_header,
+                         FILE_MAGIC_STRINGTABLE_DATA, FILE_MAGIC_STRINGTABLE_INDEX};
 use crate::serialization::{Addr, SerializationSink};
 use byteorder::{ByteOrder, LittleEndian};
 use rustc_hash::FxHashMap;
 use std::borrow::Cow;
+use std::error::Error;
 use std::sync::atomic::{AtomicU32, Ordering};
 use std::sync::Arc;
 
@@ -117,6 +120,11 @@ fn deserialize_index_entry(bytes: &[u8]) -> (StringId, Addr) {
 
 impl<S: SerializationSink> StringTableBuilder<S> {
     pub fn new(data_sink: Arc<S>, index_sink: Arc<S>) -> StringTableBuilder<S> {
+
+        // The first thing in every file we generate must be the file header.
+        write_file_header(&*data_sink, FILE_MAGIC_STRINGTABLE_DATA);
+        write_file_header(&*index_sink, FILE_MAGIC_STRINGTABLE_INDEX);
+
         StringTableBuilder {
             data_sink,
             index_sink,
@@ -230,12 +238,27 @@ pub struct StringTable {
 }
 
 impl<'data> StringTable {
-    pub fn new(string_data: Vec<u8>, index_data: Vec<u8>) -> StringTable {
-        assert!(index_data.len() % 8 == 0);
+    pub fn new(string_data: Vec<u8>, index_data: Vec<u8>) -> Result<StringTable, Box<dyn Error>> {
 
-        let index: FxHashMap<_, _> = index_data.chunks(8).map(deserialize_index_entry).collect();
+        let string_data_format = read_file_header(&string_data, FILE_MAGIC_STRINGTABLE_DATA)?;
+        let index_data_format = read_file_header(&index_data, FILE_MAGIC_STRINGTABLE_INDEX)?;
+
+        if string_data_format != index_data_format {
+            Err("Mismatch between StringTable DATA and INDEX format version")?;
+        }
+
+        if string_data_format != 0 {
+            Err(format!("StringTable file format version '{}' is not supported
+                         by this version of `measureme`.", string_data_format))?;
+        }
+
+        assert!(index_data.len() % 8 == 0);
+        let index: FxHashMap<_, _> = strip_file_header(&index_data)
+            .chunks(8)
+            .map(deserialize_index_entry)
+            .collect();
 
-        StringTable { string_data, index }
+        Ok(StringTable { string_data, index })
     }
 
     #[inline]
@@ -245,7 +268,7 @@ impl<'data> StringTable {
 }
 
 #[cfg(test)]
-mod test {
+mod tests {
     use super::*;
 
     #[test]
@@ -278,7 +301,7 @@ mod test {
         let data_bytes = Arc::try_unwrap(data_sink).unwrap().into_bytes();
         let index_bytes = Arc::try_unwrap(index_sink).unwrap().into_bytes();
 
-        let string_table = StringTable::new(data_bytes, index_bytes);
+        let string_table = StringTable::new(data_bytes, index_bytes).unwrap();
 
         for (&id, &expected_string) in string_ids.iter().zip(expected_strings.iter()) {
             let str_ref = string_table.get(id);

measureme/src/testing_common.rs

@@ -88,7 +88,7 @@ fn generate_profiling_data<S: SerializationSink>(filestem: &Path) -> Vec<Event>
 // Process some profiling data. This is the part that would run in a
 // post processing tool.
 fn process_profiling_data(filestem: &Path, expected_events: &[Event]) {
-    let profiling_data = ProfilingData::new(filestem);
+    let profiling_data = ProfilingData::new(filestem).unwrap();
 
     let mut count = 0;
 

mmview/src/main.rs

@@ -1,3 +1,4 @@
+use std::error::Error;
 use std::path::PathBuf;
 use measureme::ProfilingData;
 
@@ -8,12 +9,14 @@ struct Opt {
     file_prefix: PathBuf,
 }
 
-fn main() {
+fn main() -> Result<(), Box<dyn Error>> {
     let opt = Opt::from_args();
 
-    let data = ProfilingData::new(&opt.file_prefix);
+    let data = ProfilingData::new(&opt.file_prefix)?;
 
     for event in data.iter() {
         println!("{:?}", event);
     }
+
+    Ok(())
 }

stack_collapse/src/main.rs

@@ -1,3 +1,4 @@
+use std::error::Error;
 use std::fs::File;
 use std::io::{BufWriter, Write};
 use std::path::PathBuf;
@@ -20,10 +21,10 @@ struct Opt {
     interval: u64,
 }
 
-fn main() -> Result<(), Box<std::error::Error>> {
+fn main() -> Result<(), Box<dyn Error>> {
     let opt = Opt::from_args();
 
-    let profiling_data = ProfilingData::new(&opt.file_prefix);
+    let profiling_data = ProfilingData::new(&opt.file_prefix)?;
 
     let first_event_time = {
         let current_time = profiling_data.iter().next().unwrap().timestamp;

summarize/src/main.rs

@@ -1,6 +1,7 @@
 #[macro_use]
 extern crate prettytable;
 
+use std::error::Error;
 use std::fs::File;
 use std::io::BufWriter;
 use std::path::PathBuf;
@@ -24,10 +25,10 @@ struct Opt {
     percent_above: f64,
 }
 
-fn main() -> Result<(), Box<std::error::Error>> {
+fn main() -> Result<(), Box<dyn Error>> {
     let opt = Opt::from_args();
 
-    let data = ProfilingData::new(&opt.file_prefix);
+    let data = ProfilingData::new(&opt.file_prefix)?;
 
     let mut results = analysis::perform_analysis(data);