-z threads fix for unlikely file read errors

when a file read error occurs (unlikely, but may happen), option -z decompression threads will shut down (can't read input to decompress) and ugrep search ends, but must also make sure to close an open pipe from decompression threads that msy stay open under error conditions, and a minor change to move filter() invocation up above fcntl() non-blocking input

Author: genivia-inc

src/ugrep.cpp

@@ -3446,31 +3446,32 @@ struct Grep {
       return false;
     }
 
+    // --filter: fork process to filter file, when applicable
+    if (!filter(file_in, pathname))
+      return false;
+
 #if defined(__linux__)
     if (file_in != stdin && file_in != Static::source)
     {
       // Linux has system "regular files" that can be set non-blocking to raise EAGAIN e.g. in /proc and /sys
       if (flag_devices_action != Action::READ)
       {
         int fd = fileno(file_in);
-        int fl = fcntl(fd, F_GETFL);
-        if (fl >= 0)
-          fcntl(fd, F_SETFL, fl | O_NONBLOCK);
+        struct stat buf;
+        if (fstat(fd, &buf) == 0 && S_ISREG(buf.st_mode))
+          fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);
       }
     }
 #endif
 
-    // --filter: fork process to filter file, when applicable
-    if (!filter(file_in, pathname))
-      return false;
-
 #ifdef HAVE_LIBZ
     if (flag_decompress)
     {
 #ifdef WITH_DECOMPRESSION_THREAD
 
       // start decompression thread if not running, get pipe with decompressed input
       FILE *pipe_in = zthread.start(flag_zmax, pathname, file_in, find);
+
       if (pipe_in == NULL)
       {
         fclose(file_in);
@@ -3482,6 +3483,7 @@ struct Grep {
       input = reflex::Input(pipe_in, flag_encoding_type);
 
 #else
+
       (void)find; // appease -Wunused
 
       // create or open a new zstreambuf
@@ -3827,14 +3829,28 @@ struct Grep {
 
 #ifdef HAVE_LIBZ
 #ifdef WITH_DECOMPRESSION_THREAD
+
       if (flag_decompress)
+      {
+        // close the input FILE* and its underlying pipe previously created with pipe() and fdopen()
+        if (input.file() != NULL)
+        {
+          // close and unassign input, i.e. input.file() == NULL, also closes pipe_fd[0] per fdopen()
+          fclose(input.file());
+          input.clear();
+        }
+
         zthread.cancel();
+      }
+
 #else
+
       if (stream != NULL)
       {
         delete stream;
         stream = NULL;
       }
+
 #endif
 #endif
 
@@ -3954,7 +3970,7 @@ struct Grep {
 #endif
 
 #ifndef OS_WIN
-      if (!flag_quiet && !flag_files_with_matches && !flag_count)
+      if (!flag_decompress && !flag_quiet && !flag_files_with_matches && !flag_count)
       {
         int fd = fileno(file_in);
         struct stat buf;