fix(cpp): reject special input files before open to avoid FIFO hang

cpp/src/file/local_random_access_read_file.cc

@@ -175,6 +175,23 @@ int LocalRandomAccessReadFile::open(const std::string& file_path) {
         (preopen_stat.st_mode & _S_IFMT) != _S_IFREG) {
         return E_INVALID_PATH;
     }
+#endif
+#ifndef _WIN32
+    // POSIX open(O_RDONLY) blocks on a FIFO until a writer appears, and
+    // succeeds on directories/device files.  Preflight with stat() (which
+    // follows symlinks) so non-regular paths fail fast with the same stable
+    // E_INVALID_PATH code the post-open fstat() check below produces, instead
+    // of hanging forever.  If stat() itself fails (missing file, dangling
+    // symlink), fall through to the normal open() path so those continue to
+    // report E_FILE_OPEN_ERR.
+    // Close the stat/open race: regular files ignore O_NONBLOCK, while a FIFO
+    // replacement cannot block before the descriptor check below.
+    flags |= O_NONBLOCK;
+    struct stat preopen_stat;
+    if (::stat(file_path_.c_str(), &preopen_stat) == 0 &&
+        !S_ISREG(preopen_stat.st_mode)) {
+        return E_INVALID_PATH;
+    }
 #endif
     fd_ = file_internal::open_utf8(file_path_, flags);
     if (fd_ < 0) {

cpp/test/tools/model_format_e2e_test.cc

@@ -493,6 +493,24 @@ TEST(IndependentFixtures, EmptyTreeAndInputFailuresHaveExactDiagnostics) {
         expect_cli_exact(input_args(command, "."), 2, "",
                          "Error: cannot open .: invalid path (code 37)\n");
     }
+#ifndef _WIN32
+    // A FIFO (named pipe) is a special file, not a TsFile.  POSIX
+    // open(O_RDONLY) would otherwise block until a writer appears, so the
+    // reader must preflight the file type and fail fast with the same stable
+    // diagnostic instead of hanging.
+    {
+        const std::string fifo = tsfile_cli_test::unique_temp_path(
+            "tsfile_cli_fifo_input", ".tsfile");
+        ASSERT_EQ(mkfifo(fifo.c_str(), 0600), 0);
+        for (const std::string& command : commands) {
+            std::remove("tsfile_cli_input_error.csv");
+            expect_cli_exact(
+                input_args(command, fifo), 2, "",
+                "Error: cannot open " + fifo + ": invalid path (code 37)\n");
+        }
+        std::remove(fifo.c_str());
+    }
+#endif
     std::remove("tsfile_cli_input_error.csv");
 }