1/* SPDX-License-Identifier: GPL-2.0 */
  2/*
  3 * Lightweight buffered reading library.
  4 *
  5 * Copyright 2019 Google LLC.
  6 */
  7#ifndef __API_IO__
  8#define __API_IO__
  9
 10#include <stdlib.h>
 11#include <unistd.h>
 12
 13struct io {
 14	/* File descriptor being read/ */
 15	int fd;
 16	/* Size of the read buffer. */
 17	unsigned int buf_len;
 18	/* Pointer to storage for buffering read. */
 19	char *buf;
 20	/* End of the storage. */
 21	char *end;
 22	/* Currently accessed data pointer. */
 23	char *data;
 24	/* Set true on when the end of file on read error. */
 25	bool eof;
 26};
 27
 28static inline void io__init(struct io *io, int fd,
 29			    char *buf, unsigned int buf_len)
 30{
 31	io->fd = fd;
 32	io->buf_len = buf_len;
 33	io->buf = buf;
 34	io->end = buf;
 35	io->data = buf;
 36	io->eof = false;
 37}
 38
 39/* Reads one character from the "io" file with similar semantics to fgetc. */
 40static inline int io__get_char(struct io *io)
 41{
 42	char *ptr = io->data;
 43
 44	if (io->eof)
 45		return -1;
 46
 47	if (ptr == io->end) {
 48		ssize_t n = read(io->fd, io->buf, io->buf_len);
 49
 50		if (n <= 0) {
 51			io->eof = true;
 52			return -1;
 53		}
 54		ptr = &io->buf[0];
 55		io->end = &io->buf[n];
 56	}
 57	io->data = ptr + 1;
 58	return *ptr;
 59}
 60
 61/* Read a hexadecimal value with no 0x prefix into the out argument hex. If the
 62 * first character isn't hexadecimal returns -2, io->eof returns -1, otherwise
 63 * returns the character after the hexadecimal value which may be -1 for eof.
 64 * If the read value is larger than a u64 the high-order bits will be dropped.
 65 */
 66static inline int io__get_hex(struct io *io, __u64 *hex)
 67{
 68	bool first_read = true;
 69
 70	*hex = 0;
 71	while (true) {
 72		int ch = io__get_char(io);
 73
 74		if (ch < 0)
 75			return ch;
 76		if (ch >= '0' && ch <= '9')
 77			*hex = (*hex << 4) | (ch - '0');
 78		else if (ch >= 'a' && ch <= 'f')
 79			*hex = (*hex << 4) | (ch - 'a' + 10);
 80		else if (ch >= 'A' && ch <= 'F')
 81			*hex = (*hex << 4) | (ch - 'A' + 10);
 82		else if (first_read)
 83			return -2;
 84		else
 85			return ch;
 86		first_read = false;
 87	}
 88}
 89
 90/* Read a positive decimal value with out argument dec. If the first character
 91 * isn't a decimal returns -2, io->eof returns -1, otherwise returns the
 92 * character after the decimal value which may be -1 for eof. If the read value
 93 * is larger than a u64 the high-order bits will be dropped.
 94 */
 95static inline int io__get_dec(struct io *io, __u64 *dec)
 96{
 97	bool first_read = true;
 98
 99	*dec = 0;
100	while (true) {
101		int ch = io__get_char(io);
102
103		if (ch < 0)
104			return ch;
105		if (ch >= '0' && ch <= '9')
106			*dec = (*dec * 10) + ch - '0';
107		else if (first_read)
108			return -2;
109		else
110			return ch;
111		first_read = false;
112	}
113}
114
115#endif /* __API_IO__ */