From 4ff015722bbebc845eb2e5a735e6e8b2eabd2457 Mon Sep 17 00:00:00 2001
From: Martin Liska <martin.liska@hey.com>
Date: Wed, 17 Jul 2024 20:27:51 +0200
Subject: [PATCH] Speed up parse_header of the binary IndexData
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The change makes a measurable performance gain for debuginfod-rs:

```
Before:
  Time (mean ± σ):      2.322 s ±  0.042 s    [User: 25.047 s, System: 4.994 s]
After:
  Time (mean ± σ):      2.269 s ±  0.023 s    [User: 24.264 s, System: 5.174 s]

1.02 ± 0.02 times faster than debuginfod-rs-before
```
---
 src/rpm/headers/header.rs | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/rpm/headers/header.rs b/src/rpm/headers/header.rs
index d1fbfd6..fd7c509 100644
--- a/src/rpm/headers/header.rs
+++ b/src/rpm/headers/header.rs
@@ -54,13 +54,14 @@ where
         // add data to entries
         for entry in &mut entries {
             let mut remaining = &bytes[entry.offset as usize..];
+
             match &mut entry.data {
                 IndexData::Null => {}
                 IndexData::Char(ref mut chars) => {
-                    parse_entry_data_number(remaining, entry.num_items, chars, be_u8)?;
+                    parse_binary_entry(remaining, entry.num_items, chars, "Char")?;
                 }
                 IndexData::Int8(ref mut ints) => {
-                    parse_entry_data_number(remaining, entry.num_items, ints, be_u8)?;
+                    parse_binary_entry(remaining, entry.num_items, ints, "Int8")?;
                 }
                 IndexData::Int16(ref mut ints) => {
                     parse_entry_data_number(remaining, entry.num_items, ints, be_u16)?;
@@ -76,7 +77,7 @@ where
                     string.push_str(String::from_utf8_lossy(raw_string).as_ref());
                 }
                 IndexData::Bin(ref mut bin) => {
-                    parse_entry_data_number(remaining, entry.num_items, bin, be_u8)?;
+                    parse_binary_entry(remaining, entry.num_items, bin, "Bin")?;
                 }
                 IndexData::StringArray(ref mut strings) => {
                     for _ in 0..entry.num_items {
@@ -480,6 +481,7 @@ where
     E: nom::error::ParseError<&'a [u8]>,
     F: Fn(&'a [u8]) -> nom::IResult<&'a [u8], T, E>,
 {
+    items.reserve_exact(num_items as usize);
     for _ in 0..num_items {
         let (rest, data) = parser(input)?;
         items.push(data);
@@ -489,6 +491,22 @@ where
     Ok((input, ()))
 }
 
+fn parse_binary_entry(
+    input: &[u8],
+    num_items: u32,
+    items: &mut Vec<u8>,
+    bin_type: &str,
+) -> Result<(), Error> {
+    let bin_bytes = input.get(..num_items as usize).ok_or_else(|| {
+        Error::Nom(format!(
+            "Insufficient bytes for IndexData::{} entry",
+            bin_type
+        ))
+    })?;
+    items.extend_from_slice(bin_bytes);
+    Ok(())
+}
+
 /// A header keeping track of all other header records.
 #[derive(Debug, PartialEq)]
 pub(crate) struct IndexHeader {