From 944feef43465caf4ffafc8106373bfbd0d9a090f Mon Sep 17 00:00:00 2001
From: DTB <trinity@trinity.moe>
Date: Wed, 3 Jul 2024 16:07:02 -0600
Subject: [PATCH] dj(1): Refactor out Io_fdseek entirely

---
 src/dj.c | 93 +++++++++++++++++++++++++-------------------------------
 1 file changed, 42 insertions(+), 51 deletions(-)

diff --git a/src/dj.c b/src/dj.c
index 8c9f327..96085e3 100644
--- a/src/dj.c
+++ b/src/dj.c
@@ -129,52 +129,6 @@ Io_fdopen(struct Io *io, char *fn){
 	return fd;
 }
 
-/* Seeks io->seek bytes through *io's file descriptor, subtracting the number
- * of sought bytes from io->seek. This procedure leaves garbage in io->buf.
- * Read/written bytes here aren't counted in the statistics because successful
- * seeking is guaranteed. */
-static void
-Io_fdseek(struct Io *io){
-
-	assert(io != NULL);
-	assert(io->fd != STDIN_FILENO  || io->fl == read_flags);
-	assert(io->fd != STDOUT_FILENO || io->fl == write_flags);
-
-	if(io->seek == 0
-			|| (!fdisstd(io->fd) && lseek(io->fd, io->seek, SEEK_SET) != -1)){
-		io->seek = 0;
-		return;
-	}
-
-	if(io->fl == write_flags)
-		memset(io->buf, '\0', io->bs);
-
-	if(io->fl == write_flags){
-		memset(io->buf, '\0', io->bs);
-		/* We're going to cheat and use bufuse as the retval for write(2),
-		 * which is fine because it'll be zeroed as this function returns
-		 * anyway. */
-		do{
-			if((io->bufuse = write(io->fd, io->buf, MIN(io->bs, io->seek)))
-					== 0)
-				/* second chance */
-				io->bufuse = write(io->fd, io->buf, MIN(io->bs, io->seek));
-		}while((io->seek -= io->bufuse) > 0 && io->bufuse != 0);
-	}else if(io->fl == read_flags){
-		do{
-			if((io->bufuse = read(io->fd, io->buf, MIN(io->bs, io->seek)))
-					== 0)
-				/* second chance */
-				io->bufuse = read(io->fd, io->buf, MIN(io->bs, io->seek));
-		}while((io->seek -= io->bufuse) > 0 && io->bufuse != 0);
-	}else
-		assert(0); /* UNREACHABLE */
-
-	io->bufuse = 0;
-
-	return;
-}
-
 /* Reads io->bs bytes from *io's file descriptor into io->buf, storing the
  * number of read bytes in io->bufuse and updating io->bytes. If io->bufuse is
  * 0, errno will probably be set. Returns io. */
@@ -307,24 +261,61 @@ int main(int argc, char *argv[]){
 			}
 	}
 
+	assert(io->fd != STDIN_FILENO  || io->fl == read_flags);
+	assert(io->fd != STDOUT_FILENO || io->fl == write_flags);
 
 	if(argc > optind){
 		return usage(program_name);
 	}
 
 	for(i = 0; i < 2; ++i){
+		/* buffer allocation */
 		if((io[i].buf = malloc(io[i].bs * (sizeof *(io[i].buf)))) == NULL){
 			fprintf(stderr, "%s: Failed to allocate %d bytes\n",
 				program_name, io[i].bs);
 			return EX_OSERR;
-		}else if(io[i].seek > 0){
-			Io_fdseek(&io[i]);
-			if(io[i].seek > 0){
-				return oserr(io[i].fn);
-			}
 		}
+		/* easy seeking */
+		if(!fdisstd(io[i].fd) && lseek(io[i].fd, io[i].seek, SEEK_SET) != -1)
+			io[i].seek = 0;
 	}
 
+	/* hard skipping */
+	if(io[0].seek > 0){
+		do{
+			if((io[0].bufuse = read(
+						io[0].fd, io[0].buf, MIN(io[0].bs, io[0].seek)))
+					== 0)
+				/* second chance */
+				io->bufuse = read(
+					io[0].fd, io[0].buf, MIN(io[0].bs, io[0].seek));
+		}while((io[0].seek -= io[0].bufuse) > 0 && io[0].bufuse != 0);
+		io[0].bufuse = 0;
+	}
+
+	/* hard seeking */
+	if(io[1].seek > 0){
+		memset(io[1].buf, '\0', io[1].bs);
+		/* We're going to cheat and use bufuse as the retval for write(2),
+		 * which is fine because it'll be zeroed as this function returns
+		 * anyway. */
+		do{
+			if((io[1].bufuse = write(
+						io[1].fd, io[1].buf, MIN(io[1].bs, io[1].seek)))
+					== 0)
+				/* second chance */
+				io[1].bufuse = write(
+					io[1].fd, io[1].buf, MIN(io[1].bs, io[1].seek));
+		}while((io[1].seek -= io[1].bufuse) > 0 && io[1].bufuse != 0);
+		io[1].bufuse = 0;
+	}
+
+	/* Sought bytes aren't counted in the statistics because successful seeking
+	 * is guaranteed here. */
+	for(i = 0; i < 2; ++i)
+		if(io[i].seek > 0)
+			return oserr(io[i].fn);
+
 	do{	/* read */
 		Io_read(&io[0]);
 		if(!noerror && io[0].bufuse == 0)