dj(1): add a ton of assertions, fix if statement, fix io[i] mixups

src/dj.c

@@ -16,6 +16,7 @@
  * along with this program. If not, see https://www.gnu.org/licenses/.
  */
 
+#include <assert.h> /* assert(3) */
 #include <errno.h> /* errno */
 #include <fcntl.h> /* open(2) */
 #include <stdio.h> /* fprintf(3), stderr */
@@ -68,14 +69,18 @@ static int write_flags = O_WRONLY | O_CREAT;
 static void *
 Io_bufalloc(struct Io *io){
 
-	return (io->buf = malloc(io->bs * (sizeof *io->buf)));
+	return io != NULL
+		? (io->buf = malloc(io->bs * (sizeof *io->buf)))
+		: NULL;
 }
 
 /* Fills the unused portion of io's buffer with padding, updating io->bufuse.
  * Returns io. */
 static struct Io *
 Io_bufrpad(struct Io *io, int padding){
-	
+
+	assert(io != NULL);
+
 	memset(io->buf + io->bufuse, padding, io->bs - io->bufuse);
 	io->bufuse = io->bs;
 
@@ -90,6 +95,8 @@ static struct Io*
 Io_bufxapp(struct Io *dest, struct Io *src){
 	int n;
 
+	assert(dest != NULL && src != NULL);
+
 	n = MIN(src->bufuse, dest->bs - dest->bufuse);
 	memcpy(dest->buf + dest->bufuse, src->buf, n);
 	dest->bufuse += n;
@@ -106,6 +113,8 @@ Io_bufxapp(struct Io *dest, struct Io *src){
 static struct Io*
 Io_bufxfer(struct Io *dest, struct Io *src, int n){
 
+	assert(dest != NULL && src != NULL);
+
 	memcpy(dest->buf, src->buf, (dest->bufuse = n));
 	memmove(src->buf, src->buf + n, (src->bufuse -= n));
 
@@ -117,7 +126,9 @@ Io_bufxfer(struct Io *dest, struct Io *src, int n){
 static int
 Io_fdopen(struct Io *io, char *fn){
 	int fd;
-	
+
+	assert(io != NULL);
+
 	if((fd = open(fn, io->fl,
 					/* these are the flags used by touch(1p) */
 					S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH))
@@ -134,8 +145,15 @@ Io_fdopen(struct Io *io, char *fn){
  * of sought bytes from io->seek. This procedure leaves garbage in io->buf. */
 static void
 Io_fdseek(struct Io *io){
-	
+
-	if(io->seek != 0
+	assert(io != NULL);
+	assert(io->fd != STDIN_FILENO  || io->fl == read_flags);
+	assert(io->fd != STDOUT_FILENO || io->fl == write_flags);
+	assert(io->fd != STDERR_FILENO || io->fl == write_flags);
+
+	printf("%s\n", io->fn);
+
+	if(io->seek == 0
 			|| (!fdisstd(io->fd) && lseek(io->fd, io->seek, SEEK_SET) != -1))
 		return;
 
@@ -160,7 +178,8 @@ Io_fdseek(struct Io *io){
 				/* 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;
 
@@ -255,9 +274,9 @@ int main(int argc, char *argv[]){
 	for(i = 0; i < 2; ++i){
 		io[i].bs = 1024 /* 1 KiB */; /* GNU dd(1) default; POSIX says 512B */
 		io[i].bytes = 0;
-		io[i].fd = i ? STDIN_FILENO : STDOUT_FILENO;
+		io[i].fd = i == 0 ? STDIN_FILENO : STDOUT_FILENO;
-		io[i].fn = i ? stdin_name   : stdout_name;
+		io[i].fn = i == 0 ? stdin_name   : stdout_name;
-		io[i].fl = i ? read_flags   : write_flags;
+		io[i].fl = i == 0 ? read_flags   : write_flags;
 		io[i].prec = 0;
 		io[i].rec = 0;
 		io[i].seek = 0;
@@ -271,8 +290,8 @@ int main(int argc, char *argv[]){
 			switch(c){
 			case 'i': case 'o': i = (c == 'o');
 				if(optarg[0] == '-' && optarg[1] == '\0'){ /* optarg == "-" */
-					io[i].fd = i ? STDIN_FILENO : STDOUT_FILENO;
+					io[i].fd = i == 0 ? STDIN_FILENO : STDOUT_FILENO;
-					io[i].fn = i ? stdin_name   : stdout_name;
+					io[i].fn = i == 0 ? stdin_name   : stdout_name;
 					break;
 				}else if(Io_fdopen(&io[i], optarg) != -1)
 					break;
@@ -309,11 +328,12 @@ int main(int argc, char *argv[]){
 			fprintf(stderr, "%s: Failed to allocate %d bytes\n",
 				program_name, io[i].bs);
 			return EX_OSERR;
-		}else if(io[i].seek > 0)
+		}else if(io[i].seek > 0){
 			Io_fdseek(&io[i]);
 			if(io[i].seek > 0){
 				return oserr(io[i].fn);
 			}
+		}
 	}
 
 	do{	/* read */