lib: c: io: implement standard FILE and DIR interfaces

lib/libc/io/stdio/file.c

@@ -0,0 +1,76 @@
+#include "file.h"
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define DEFAULT_BUFFER_SIZE 4096
+
+#define FILE_UNUSABLE(f)    (((f)->f_flags & (FILE_EOF | FILE_ERR)) != 0)
+
+int __libc_file_refill(struct __opaque_file *f)
+{
+	f->f_buf_datalen = 0;
+	f->f_buf_readptr = 0;
+
+	if (f->f_fd < 0) {
+		return EBADF;
+	}
+
+	if (f->f_flags & FILE_ERR) {
+		return EIO;
+	}
+
+	if (f->f_flags & FILE_EOF) {
+		return SUCCESS;
+	}
+
+	if (!f->f_buf) {
+		f->f_buf_max = DEFAULT_BUFFER_SIZE;
+		f->f_buf = malloc(f->f_buf_max);
+		if (!f->f_buf) {
+			f->f_buf_max = 0;
+			return ENOMEM;
+		}
+	}
+
+	long r = read(f->f_fd, f->f_buf, f->f_buf_max);
+	if (r < 0) {
+		return -r;
+	}
+
+	f->f_buf_datalen = r;
+	return SUCCESS;
+}
+
+int __libc_file_read(struct __opaque_file *f, void *out, size_t count)
+{
+	if (f->f_fd < 0) {
+		return EBADF;
+	}
+
+	if (f->f_flags & FILE_ERR) {
+		return EIO;
+	}
+
+	if (f->f_flags & FILE_EOF) {
+		return SUCCESS;
+	}
+
+	size_t available = f->f_buf_datalen - f->f_buf_readptr;
+	if (count > available) {
+		count = available;
+	}
+
+	memcpy(out, f->f_buf + f->f_buf_readptr, count);
+
+	f->f_buf_readptr += count;
+
+	return count;
+}
+
+size_t __libc_file_available(struct __opaque_file *f)
+{
+	return f->f_buf_datalen - f->f_buf_readptr;
+}