When splice() is available but neither the input nor the output are pipes, splice the input through an intermediary pipe (#188).

src/include/pv-internal.h

@@ -160,6 +160,8 @@ struct pvstate_s {
 		bool terminal_supports_utf8;	 /* whether the terminal supports UTF-8 */
 		bool terminal_supports_colour;	 /* whether the terminal supports colour */
 		bool checked_colour_support;	 /* whether we have checked colour support yet */
+		bool current_input_is_pipe;	 /* whether the current input file is a pipe */
+		bool output_is_pipe;		 /* whether the output is a pipe */
 	} status;
 
 	/***************
@@ -456,6 +458,15 @@ struct pvstate_s {
 		int last_read_skip_fd;
 		/* read_error_warning_shown is defined below. */
 #ifdef HAVE_SPLICE
+		/*
+		 * File descriptors for an intermediate pipe, used when
+		 * neither input nor output are pipes; the size of the pipe
+		 * buffer; and how much input data is in the intermediate
+		 * pipe waiting to be passed to the output.
+		 */
+		int intermediate_pipe[2];
+		int intermediate_pipe_buffer_size;
+		int intermediate_pipe_buffer_used;
 		/*
 		 * These variables are used to keep track of whether
 		 * splice() was used; splice_failed_fd is the file