cat: check if the input file is also the output file

Cargo.lock

@@ -2023,6 +2023,7 @@ dependencies = [
  "unix_socket",
  "uucore",
  "uucore_procs",
+ "winapi-util",
 ]
 
 [[package]]

src/uu/cat/Cargo.toml

@@ -23,9 +23,10 @@ uucore_procs = { version=">=0.0.6", package="uucore_procs", path="../../uucore_p
 
 [target.'cfg(unix)'.dependencies]
 unix_socket = "0.5.0"
+nix = "0.20.0"
 
-[target.'cfg(any(target_os = "linux", target_os = "android"))'.dependencies]
-nix = "0.20"
+[target.'cfg(windows)'.dependencies]
+winapi-util = "0.1.5"
 
 [[bin]]
 name = "cat"

src/uu/cat/src/cat.rs

@@ -22,11 +22,14 @@ use std::io::{self, Read, Write};
 use thiserror::Error;
 use uucore::error::UResult;
 
+#[cfg(unix)]
+use std::os::unix::io::AsRawFd;
+
 /// Linux splice support
 #[cfg(any(target_os = "linux", target_os = "android"))]
 mod splice;
 #[cfg(any(target_os = "linux", target_os = "android"))]
-use std::os::unix::io::{AsRawFd, RawFd};
+use std::os::unix::io::RawFd;
 
 /// Unix domain socket support
 #[cfg(unix)]
@@ -59,6 +62,8 @@ enum CatError {
     },
     #[error("Is a directory")]
     IsDirectory,
+    #[error("input file is output file")]
+    OutputIsInput,
 }
 
 type CatResult<T> = Result<T, CatError>;
@@ -297,7 +302,13 @@ fn cat_handle<R: Read>(
     }
 }
 
-fn cat_path(path: &str, options: &OutputOptions, state: &mut OutputState) -> CatResult<()> {
+fn cat_path(
+    path: &str,
+    options: &OutputOptions,
+    state: &mut OutputState,
+    #[cfg(unix)] out_info: &nix::sys::stat::FileStat,
+    #[cfg(windows)] out_info: &winapi_util::file::Information,
+) -> CatResult<()> {
     if path == "-" {
         let stdin = io::stdin();
         let mut handle = InputHandle {
@@ -324,6 +335,10 @@ fn cat_path(path: &str, options: &OutputOptions, state: &mut OutputState) -> Cat
         }
         _ => {
             let file = File::open(path)?;
+            #[cfg(any(windows, unix))]
+            if same_file(out_info, &file) {
+                return Err(CatError::OutputIsInput);
+            }
             let mut handle = InputHandle {
                 #[cfg(any(target_os = "linux", target_os = "android"))]
                 file_descriptor: file.as_raw_fd(),
@@ -335,7 +350,26 @@ fn cat_path(path: &str, options: &OutputOptions, state: &mut OutputState) -> Cat
     }
 }
 
+#[cfg(unix)]
+fn same_file(a_info: &nix::sys::stat::FileStat, b: &File) -> bool {
+    let b_info = nix::sys::stat::fstat(b.as_raw_fd()).unwrap();
+    b_info.st_size != 0 && b_info.st_dev == a_info.st_dev && b_info.st_ino == a_info.st_ino
+}
+
+#[cfg(windows)]
+fn same_file(a_info: &winapi_util::file::Information, b: &File) -> bool {
+    let b_info = winapi_util::file::information(b).unwrap();
+    b_info.file_size() != 0
+        && b_info.volume_serial_number() == a_info.volume_serial_number()
+        && b_info.file_index() == a_info.file_index()
+}
+
 fn cat_files(files: Vec<String>, options: &OutputOptions) -> UResult<()> {
+    #[cfg(windows)]
+    let out_info = winapi_util::file::information(&std::io::stdout()).unwrap();
+    #[cfg(unix)]
+    let out_info = nix::sys::stat::fstat(std::io::stdout().as_raw_fd()).unwrap();
+
     let mut state = OutputState {
         line_number: 1,
         at_line_start: true,
@@ -343,7 +377,7 @@ fn cat_files(files: Vec<String>, options: &OutputOptions) -> UResult<()> {
     let mut error_messages: Vec<String> = Vec::new();
 
     for path in &files {
-        if let Err(err) = cat_path(path, options, &mut state) {
+        if let Err(err) = cat_path(path, options, &mut state, &out_info) {
             error_messages.push(format!("{}: {}", path, err));
         }
     }

tests/by-util/test_cat.rs

@@ -1,5 +1,4 @@
 use crate::common::util::*;
-#[cfg(unix)]
 use std::fs::OpenOptions;
 #[cfg(unix)]
 use std::io::Read;
@@ -443,3 +442,49 @@ fn test_domain_socket() {
 
     thread.join().unwrap();
 }
+
+#[test]
+fn test_write_to_self_empty() {
+    // it's ok if the input file is also the output file if it's empty
+    let s = TestScenario::new(util_name!());
+    let file_path = s.fixtures.plus("file.txt");
+
+    let file = OpenOptions::new()
+        .create_new(true)
+        .write(true)
+        .append(true)
+        .open(&file_path)
+        .unwrap();
+
+    s.ucmd().set_stdout(file).arg(&file_path).succeeds();
+}
+
+#[test]
+fn test_write_to_self() {
+    let s = TestScenario::new(util_name!());
+    let file_path = s.fixtures.plus("first_file");
+    s.fixtures.write("second_file", "second_file_content.");
+
+    let file = OpenOptions::new()
+        .create_new(true)
+        .write(true)
+        .append(true)
+        .open(&file_path)
+        .unwrap();
+
+    s.fixtures.append("first_file", "first_file_content.");
+
+    s.ucmd()
+        .set_stdout(file)
+        .arg("first_file")
+        .arg("first_file")
+        .arg("second_file")
+        .fails()
+        .code_is(2)
+        .stderr_only("cat: first_file: input file is output file\ncat: first_file: input file is output file");
+
+    assert_eq!(
+        s.fixtures.read("first_file"),
+        "first_file_content.second_file_content."
+    );
+}