Fuzzing

.gitignore

@@ -1,2 +1,3 @@
 /target
 Cargo.lock
+*.swp

README.md

@@ -35,5 +35,7 @@ but it implements a different format.
 +
 +[dependencies]
 +diff = "0.1.10"
+~/unified-diff$ rustup override set nightly
+~/unified-diff$ cargo fuzz run fuzz_patch
 ```
 

fuzz/.gitignore

@@ -0,0 +1,4 @@
+
+target
+corpus
+artifacts

fuzz/Cargo.toml

@@ -0,0 +1,27 @@
+
+[package]
+name = "unified-diff-fuzz"
+version = "0.0.0"
+authors = ["Automatically generated"]
+publish = false
+edition = "2018"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.3"
+
+[dependencies.unified-diff]
+path = ".."
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "fuzz_patch"
+path = "fuzz_targets/fuzz_patch.rs"
+test = false
+doc = false
+

fuzz/fuzz_targets/fuzz_patch.rs

@@ -0,0 +1,55 @@
+#![no_main]
+#[macro_use] extern crate libfuzzer_sys;
+extern crate unified_diff;
+
+use std::fs::{self, File};
+use std::io::Write;
+use std::process::Command;
+
+fuzz_target!(|x: (Vec<u8>, Vec<u8>, u8)| {
+    let (from, to, context) = x;
+    if let Ok(s) = String::from_utf8(from.clone()) {
+        if !s.is_ascii() { return }
+        if s.find(|x| x < ' ' && x != '\n').is_some() { return }
+    } else {
+        return
+    }
+    if let Ok(s) = String::from_utf8(to.clone()) {
+        if !s.is_ascii() { return }
+        if s.find(|x| x < ' ' && x != '\n').is_some() { return }
+    } else {
+        return
+    }
+    let diff = unified_diff::diff(&from, "a/fuzz.file", &to, "target/fuzz.file", context as usize);
+    File::create("target/fuzz.file.original")
+        .unwrap()
+        .write_all(&from)
+        .unwrap();
+    File::create("target/fuzz.file.expected")
+        .unwrap()
+        .write_all(&to)
+        .unwrap();
+    File::create("target/fuzz.file")
+        .unwrap()
+        .write_all(&from)
+        .unwrap();
+    File::create("target/fuzz.diff")
+        .unwrap()
+        .write_all(&diff)
+        .unwrap();
+    let output = Command::new("patch")
+        .arg("-p0")
+        .arg("--binary")
+        .arg("--fuzz=0")
+        .stdin(File::open("target/fuzz.diff").unwrap())
+        .output()
+        .unwrap();
+    if !output.status.success() {
+        panic!("STDOUT:\n{}\nSTDERR:\n{}", String::from_utf8_lossy(&output.stdout), String::from_utf8_lossy(&output.stderr));
+    }
+    let result = fs::read("target/fuzz.file").unwrap();
+    if result != to {
+        panic!("STDOUT:\n{}\nSTDERR:\n{}", String::from_utf8_lossy(&output.stdout), String::from_utf8_lossy(&output.stderr));
+    }
+});
+

src/lib.rs

@@ -112,15 +112,24 @@ fn make_diff(expected: &[u8], actual: &[u8], context_size: usize) -> Vec<Mismatc
                 lines_since_mismatch = 0;
             }
             diff::Result::Both(str, _) => {
+
+                // if one of them is missing a newline and the other isn't, then they don't actually match
                 if (line_number_actual > actual_lines_count)
-                    || (line_number_expected > expected_lines_count)
+                    && (line_number_expected > expected_lines_count)
                 {
-                    // if one of them is missing a newline and the other isn't, then they don't actually match
-                    if lines_since_mismatch >= context_size
-                        && lines_since_mismatch > 0
-                        && (line_number_actual > actual_lines_count)
-                            != (line_number_expected > expected_lines_count)
-                    {
+                    if context_queue.len() < context_size {
+                        while let Some(line) = context_queue.pop_front() {
+                            assert!(mismatch.lines.last() != Some(&DiffLine::MissingNL));
+                            mismatch.lines.push(DiffLine::Context(line.to_vec()));
+                        }
+                        if lines_since_mismatch < context_size {
+                            mismatch.lines.push(DiffLine::Context(str.to_vec()));
+                            mismatch.lines.push(DiffLine::MissingNL);
+                        }
+                    }
+                    lines_since_mismatch = 0;
+                } else if line_number_actual > actual_lines_count {
+                    if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
                         results.push(mismatch);
                         mismatch = Mismatch::new(
                             line_number_expected - context_queue.len() as u32,
@@ -131,22 +140,28 @@ fn make_diff(expected: &[u8], actual: &[u8], context_size: usize) -> Vec<Mismatc
                         assert!(mismatch.lines.last() != Some(&DiffLine::MissingNL));
                         mismatch.lines.push(DiffLine::Context(line.to_vec()));
                     }
+                    mismatch.lines.push(DiffLine::Expected(str.to_vec()));
+                    mismatch.lines.push(DiffLine::Actual(str.to_vec()));
+                    mismatch.lines.push(DiffLine::MissingNL);
                     lines_since_mismatch = 0;
-                    if line_number_actual > actual_lines_count
-                        && line_number_expected > expected_lines_count
-                    {
-                        mismatch.lines.push(DiffLine::Context(str.to_vec()));
-                        mismatch.lines.push(DiffLine::MissingNL);
-                    } else if line_number_expected > expected_lines_count {
-                        mismatch.lines.push(DiffLine::Expected(str.to_vec()));
-                        mismatch.lines.push(DiffLine::MissingNL);
-                        mismatch.lines.push(DiffLine::Actual(str.to_vec()));
-                    } else if line_number_actual > actual_lines_count {
-                        mismatch.lines.push(DiffLine::Expected(str.to_vec()));
-                        mismatch.lines.push(DiffLine::Actual(str.to_vec()));
-                        mismatch.lines.push(DiffLine::MissingNL);
+                } else if line_number_expected > expected_lines_count {
+                    if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
+                        results.push(mismatch);
+                        mismatch = Mismatch::new(
+                            line_number_expected - context_queue.len() as u32,
+                            line_number_actual - context_queue.len() as u32,
+                        );
                     }
+                    while let Some(line) = context_queue.pop_front() {
+                        assert!(mismatch.lines.last() != Some(&DiffLine::MissingNL));
+                        mismatch.lines.push(DiffLine::Context(line.to_vec()));
+                    }
+                    mismatch.lines.push(DiffLine::Expected(str.to_vec()));
+                    mismatch.lines.push(DiffLine::MissingNL);
+                    mismatch.lines.push(DiffLine::Actual(str.to_vec()));
+                    lines_since_mismatch = 0;
                 } else {
+                    assert!(context_queue.len() <= context_size);
                     if context_queue.len() >= context_size {
                         let _ = context_queue.pop_front();
                     }
@@ -157,7 +172,6 @@ fn make_diff(expected: &[u8], actual: &[u8], context_size: usize) -> Vec<Mismatc
                     }
                     lines_since_mismatch += 1;
                 }
-
                 line_number_expected += 1;
                 line_number_actual += 1;
             }
@@ -220,14 +234,17 @@ pub fn diff(
         return Vec::new();
     };
     for result in diff_results {
-        let line_number_expected = result.line_number_expected;
-        let line_number_actual = result.line_number_actual;
+        let mut line_number_expected = result.line_number_expected;
+        let mut line_number_actual = result.line_number_actual;
         let mut expected_count = 0;
         let mut actual_count = 0;
+        let mut has_expected = false;
+        let mut has_actual = false;
         for line in &result.lines {
             match line {
                 DiffLine::Expected(_) => {
                     expected_count += 1;
+                    has_expected = true;
                 }
                 DiffLine::Context(_) => {
                     expected_count += 1;
@@ -235,10 +252,13 @@ pub fn diff(
                 }
                 DiffLine::Actual(_) => {
                     actual_count += 1;
+                    has_actual = true;
                 }
                 DiffLine::MissingNL => {}
             }
         }
+        if expected_count == 0 { line_number_expected -= 1 }
+        if actual_count == 0 { line_number_actual -= 1 }
         writeln!(
             output,
             "@@ -{},{} +{},{} @@",

src/main.rs

@@ -49,7 +49,7 @@ fn main() {
             &from.to_string_lossy(),
             &to_content,
             &to.to_string_lossy(),
-            3,
+            1,
         ))
         .unwrap();
 }