Refactor syscalls.h for ch8 exercises

The refactor includes implementations for fflush and fclose as well,
needed in 8-03.

1 files changed, 222 insertions, 0 deletions

diff --git a/ch8/syscalls.h b/ch8/syscalls.h
new file mode 100644
index 0000000..ff58db5
--- /dev/null
+++ b/ch8/syscalls.h
@@ -0,0 +1,222 @@
+/* syscalls.h
+ *
+ * A simpler stdio.h to aid in exercises within chapter 8
+ */
+
+/* Declarations */
+int puts(char *);
+long lseek(int fd, long offset, int origin);
+
+/* workarounds for GNU/Linux */
+#undef NULL
+
+#define PERMS 0666
+#define NULL 0
+#define EOF (-1)
+#define BUFSIZ 100
+#define FOPEN_MAX 20
+
+
+struct _flags {
+	unsigned int _READ : 1;
+	unsigned int _WRITE : 1;
+	unsigned int _UNBUF : 1;
+	unsigned int _EOF : 1;
+	unsigned int _ERR : 1;
+} flags;
+
+typedef struct _iobuf {
+	int cnt;
+	char *ptr;
+	char *base;
+	struct _flags flags;
+	int fd;
+} FILE;
+
+FILE _iob[FOPEN_MAX] = {
+	/* stdin is read-only */
+	{ 0, (char *) 0, (char *) 0, {1, 0, 0, 0, 0}, 0 },
+	/* stdout is write only */
+	{ 0, (char *) 0, (char *) 0, {0, 1, 0, 0, 0}, 1 },
+	/* stderr is written AND not buffered */
+	{ 0, (char *) 0, (char *) 0, {0, 1, 1, 0, 0}, 2 }
+};
+
+#define stdin  (&_iob[0])
+#define stdout (&_iob[1])
+#define stderr (&_iob[2])
+
+#define feof(p) (((p)->flags._EOF) != 0)
+#define ferror(p) (((p)->flags._ERR) != 0)
+#define fileno(p) ((p)->fd)
+
+#define getc(p) (--(p)->cnt >= 0 ? (unsigned char) *(p)->ptr++ : _fillbuf(p))
+#define putc(x,p) (--(p)->cnt >= 0 ? *(p)->ptr++ = (x) : _flushbuf((x),p))
+#define getchar() getc(stdin)
+#define putchar(x) putc((x), stdout)
+
+int fempty(struct _flags flags) {
+	if (!flags._READ && !flags._WRITE && !flags._UNBUF && !flags._EOF && !flags._ERR) {
+		return 1;
+	} else {
+		return 0;
+	}
+}
+
+FILE * fopen(char *name, char *mode) {
+	int fd;
+	FILE *fp;
+	if (*mode != 'r' && *mode != 'w' && *mode != 'a') {
+		return NULL;
+	}
+	for (fp = _iob; fp < _iob + FOPEN_MAX; fp++) {
+		if (fp->flags._READ == 0 && fp->flags._WRITE == 0) {
+			break;
+		}
+	}
+	if (fp >= _iob + FOPEN_MAX) {
+		return NULL;
+	}
+	if (*mode == 'w') {
+		fd = creat(name, PERMS);
+	} else if (*mode == 'a') {
+		if ((fd = open(name, O_WRONLY, 0)) == -1) {
+			fd = creat(name, PERMS);
+		}
+		lseek(fd, 0L, 2);
+	} else {
+		fd = open(name, O_RDONLY, 0);
+	}
+	if (fd == -1) {
+		return NULL;
+	}
+	fp->fd = fd;
+	fp->cnt = 0;
+	if (*mode == 'r') {
+		fp->flags._READ = 1;
+	} else {
+		fp->flags._WRITE = 1;
+	}
+	return fp;
+}
+
+/* int _fillbuf(FILE *); */
+
+int _fillbuf(FILE *fp) {
+	int bufsize;
+	if (fp->flags._READ == 0) {
+		return EOF;
+	}
+	bufsize = (fp->flags._UNBUF != 0) ? 1 : BUFSIZ;
+	if (fp->base == NULL) {
+		if ((fp->base = (char *) calloc(bufsize, sizeof (char))) == NULL) {
+			return EOF;
+		}
+	}
+	fp->ptr = fp->base;
+	fp->cnt = read(fp->fd, fp->ptr, bufsize);
+	if (--(fp)->cnt < 0) {
+		if (fp->cnt == -1) {
+			fp->flags._EOF = 1;
+		} else {
+			fp->flags._ERR = 1;
+		}
+		fp->cnt = 0;
+		return EOF;
+	}
+	return (unsigned char) *fp->ptr++;
+}
+
+int _cleanbuf(FILE *fp) {
+	int bufsize = (fp->flags._UNBUF != 0) ? 1 : BUFSIZ;
+	if (fp->base != NULL) {
+		free(fp->base);
+	}
+	fp->base = (char *) calloc(bufsize, sizeof (char));
+	if (fp->base == NULL) {
+		return EOF;
+	}
+	return 0;
+}
+
+/*
+ * write the buffer's contents to the file and reset the buffer
+ *
+ * Returns 0 on success, EOF on errors, with errno set.
+ */
+int _flushbuf(char c, FILE *fp) {
+	int bufsize = (fp->flags._UNBUF != 0) ? 1 : BUFSIZ;
+	if (fp->base == NULL) {
+		if (_cleanbuf(fp) != 0) {
+			errno = ENOMEM;
+			return EOF;
+		}
+	}
+	if (fp->flags._WRITE == 0) {
+		errno = EBADF;
+		return EOF;
+	}
+	int written = write(fp->fd, fp->base, bufsize);
+	if (errno > 0) {
+		fp->flags._ERR = 1;
+		strerror(errno);
+		return EOF;
+	}
+	if (_cleanbuf(fp) != 0) {
+		errno = ENOMEM;
+		return EOF;
+	}
+	fp->ptr = fp->base;
+	fp->cnt = bufsize;
+	if (c != NULL) {
+		putc(c,fp);
+	}
+	return 0;
+}
+
+int fflush(FILE *fp) {
+	if (fp == NULL) {
+		int i;
+		for (i=0; i < FOPEN_MAX; i++) {
+			/* maybe check flags and buffers? */
+			if (fp->flags._WRITE == 1) {
+				if (_flushbuf(NULL, &_iob[i]) == EOF) {
+					strerror(errno);
+				}
+			}
+		}
+		return 0;
+	}
+	if (fp->flags._WRITE == 1) {
+		if (_flushbuf(NULL, fp) == EOF) {
+			strerror(errno);
+		}
+	}
+	return 0;
+}
+
+int fclose(FILE *fp) {
+	struct _flags f = {0,0,0,0,0};
+	if (fp->flags._WRITE == 1) {
+		fflush(fp);
+	}
+	if (fp->base != NULL) {
+		free(fp->base);
+		fp->base = NULL;
+		fp->ptr = NULL;
+	}
+	fp->cnt = 0;
+	fp->flags = f;
+	close(fp->fd);
+	fp->fd = -1;
+	return 0;
+}
+
+int puts(char *s) {
+	int i;
+	for (i=0; s[i] != '\0' && s[i] != EOF; i++) {
+		putchar(s[i]);
+	}
+	putchar('\n');
+	return i;
+}