Fix regression: Allow FIFO / process substitution for --read-batch

batch.c

@@ -271,12 +271,12 @@ void open_batch_files(void)
 		exit_cleanup(RERR_FILEIO);
 	}
 
-	/* --read-batch: the file's bytes drive the protocol parser, so refuse
-	 * non-regular files (FIFO, device, socket) at the batch path. */
+	/* --read-batch: the file's bytes drive the protocol parser,
+	 * allow FIFOs used by shell process substitution while continuing to reject other non-regular inputs. */
 	if (!write_batch && batch_fd != STDIN_FILENO) {
 		STRUCT_STAT st;
-		if (do_fstat(batch_fd, &st) == 0 && !S_ISREG(st.st_mode)) {
-			rprintf(FERROR, "Batch file %s is not a regular file\n",
+		if (do_fstat(batch_fd, &st) == 0 && !S_ISREG(st.st_mode) && !S_ISFIFO(st.st_mode)) {
+			rprintf(FERROR, "Batch file %s is neither a regular file nor a FIFO\n",
 				full_fname(batch_name));
 			exit_cleanup(RERR_FILEIO);
 		}

testsuite/batch-file-symlink_test.py

@@ -209,7 +209,7 @@ def run_write_batch(batch_plant_path):
 # node fails first with ENXIO, which is an equally valid refusal at the open.
 # A clean (returncode 0) run would be the real failure -- rsync accepting the
 # device as a batch file.
-refused = ('is not a regular file' in proc.stderr
+refused = ('is neither a regular file nor a FIFO' in proc.stderr
            or ('open error' in proc.stderr and proc.returncode != 0))
 if not refused:
     test_fail(

testsuite/read-batch-pipe_test.py

@@ -0,0 +1,80 @@
+#!/usr/bin/env python3
+"""--read-batch process substitution /dev/fd/ pipe must not crash with strict file-type checks."""
+import os
+import shlex
+import shutil
+import subprocess
+import tempfile
+import sys
+from pathlib import Path
+
+from rsyncfns import SCRATCHDIR, makepath, rmtree, rsync_argv, test_fail, test_skipped
+
+# We require bash specifically because standard POSIX /bin/sh does not
+# guarantee support for <(...) process substitution syntax.
+if not sys.platform.startswith('linux'):
+    test_skipped('This test requires Linux platform')
+
+bash = shutil.which('bash')
+if bash is None:
+    test_skipped('bash is unavailable, cannot test process substitution')
+
+# Verify the host bash actually supports process substitution
+probe = subprocess.run(
+    [bash, '-c', 'cat <(echo "probe")'],
+    capture_output=True)
+
+if probe.returncode != 0:
+    test_skipped('bash process substitution is not supported on this system')
+
+base = Path(SCRATCHDIR / 'rsync-batch-fifo')
+src = base / 'src'
+dest = base / 'dest'
+batch_file = base / 'update.batch'
+makepath(src, dest)
+
+# 1. Create dummy data
+(src / 'payload.txt').write_text('batch payload data\n')
+
+# 2. Generate a valid batch file so `cat` actually has a real file to read.
+# Note: This operation also copies the file to `dest` as a side effect.
+subprocess.run([*rsync_argv('-a', f'--write-batch={batch_file}'), f'{src}/', f'{dest}/'], check=True)
+
+# must wipe and recreate the destination directory so the test can 
+# properly prove that --read-batch recreates the files from scratch.
+rmtree(dest)
+makepath(dest)
+
+# 3. Now we can test reading it via bash process substitution
+rsync_base_cmd = shlex.join(rsync_argv('-a'))
+batch_path = shlex.quote(str(batch_file))
+dest_path = shlex.quote(str(dest) + '/')
+
+# Construct the bash command: rsync -a --read-batch=<(cat /path/to/batch) /dest/
+bash_script = f"{rsync_base_cmd} --read-batch=<(cat {batch_path}) {dest_path}"
+
+try:
+    proc_read = subprocess.run(
+        [bash, '-c', bash_script],
+        capture_output=True,
+        text=True,
+        timeout=10,
+    )
+except subprocess.TimeoutExpired:
+    rmtree(base)
+    test_fail('process substitution batch test timed out')
+
+ctx = f'rc={proc_read.returncode}, stderr={proc_read.stderr.strip()!r}'
+
+# Evaluate result against the strict S_ISREG check bug
+if proc_read.returncode != 0:
+    rmtree(base)
+    test_fail(f'rsync crashed reading batch file from pipe ({ctx})')
+
+if not (dest / 'payload.txt').is_file():
+    rmtree(base)
+    test_fail(f'rsync exited successfully but payload is missing in target ({ctx})')
+
+rmtree(base)
+print('rsync successfully parsed batch stream via process substitution pseudo-path')
+raise SystemExit(0)

testsuite/skiplist/almalinux-8.txt

@@ -6,3 +6,4 @@
 # AlmaLinux 8 container additions to common.txt and linux.txt.
 
 pseudo-paths  # Bash process substitution is unavailable in the AlmaLinux 8 container
+read-batch-pipe

testsuite/skiplist/cygwin.txt

@@ -52,6 +52,7 @@ partial-protected-regular-retry-policy  # deterministic partial EACCES recovery
 password-file-symlink
 protected-regular
 pseudo-paths
+read-batch-pipe
 rename-mixed-parent-transfer
 rrsync-sender-leaf-flip
 rrsync-sender-parent-pin

testsuite/skiplist/macos.txt

@@ -22,6 +22,7 @@ partial-protected-regular-retry-linux
 preallocate
 protected-regular
 pseudo-paths  # dynamically skips on runners lacking bash process substitution
+read-batch-pipe
 readonly-partial-abort-mode-regression  # 
 rrsync-sender-leaf-flip
 rrsync-sender-parent-pin