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 <errno.h>
11#include <poll.h>
12#include <stdlib.h>
13#include <string.h>
14#include <unistd.h>
15#include <linux/types.h>
16
17struct io {
18	/* File descriptor being read/ */
19	int fd;
20	/* Size of the read buffer. */
21	unsigned int buf_len;
22	/* Pointer to storage for buffering read. */
23	char *buf;
24	/* End of the storage. */
25	char *end;
26	/* Currently accessed data pointer. */
27	char *data;
28	/* Read timeout, 0 implies no timeout. */
29	int timeout_ms;
30	/* Set true on when the end of file on read error. */
31	bool eof;
32};
33
34static inline void io__init(struct io *io, int fd,
35			    char *buf, unsigned int buf_len)
36{
37	io->fd = fd;
38	io->buf_len = buf_len;
39	io->buf = buf;
40	io->end = buf;
41	io->data = buf;
42	io->timeout_ms = 0;
43	io->eof = false;
44}
45
46/* Reads one character from the "io" file with similar semantics to fgetc. */
47static inline int io__get_char(struct io *io)
48{
49	char *ptr = io->data;
50
51	if (io->eof)
52		return -1;
53
54	if (ptr == io->end) {
55		ssize_t n;
56
57		if (io->timeout_ms != 0) {
58			struct pollfd pfds[] = {
59				{
60					.fd = io->fd,
61					.events = POLLIN,
62				},
63			};
64
65			n = poll(pfds, 1, io->timeout_ms);
66			if (n == 0)
67				errno = ETIMEDOUT;
68			if (n > 0 && !(pfds[0].revents & POLLIN)) {
69				errno = EIO;
70				n = -1;
71			}
72			if (n <= 0) {
73				io->eof = true;
74				return -1;
75			}
76		}
77		n = read(io->fd, io->buf, io->buf_len);
78
79		if (n <= 0) {
80			io->eof = true;
81			return -1;
82		}
83		ptr = &io->buf[0];
84		io->end = &io->buf[n];
85	}
86	io->data = ptr + 1;
87	return *ptr;
88}
89
90/* Read a hexadecimal value with no 0x prefix into the out argument hex. If the
91 * first character isn't hexadecimal returns -2, io->eof returns -1, otherwise
92 * returns the character after the hexadecimal value which may be -1 for eof.
93 * If the read value is larger than a u64 the high-order bits will be dropped.
94 */
95static inline int io__get_hex(struct io *io, __u64 *hex)
96{
97	bool first_read = true;
98
99	*hex = 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			*hex = (*hex << 4) | (ch - '0');
107		else if (ch >= 'a' && ch <= 'f')
108			*hex = (*hex << 4) | (ch - 'a' + 10);
109		else if (ch >= 'A' && ch <= 'F')
110			*hex = (*hex << 4) | (ch - 'A' + 10);
111		else if (first_read)
112			return -2;
113		else
114			return ch;
115		first_read = false;
116	}
117}
118
119/* Read a positive decimal value with out argument dec. If the first character
120 * isn't a decimal returns -2, io->eof returns -1, otherwise returns the
121 * character after the decimal value which may be -1 for eof. If the read value
122 * is larger than a u64 the high-order bits will be dropped.
123 */
124static inline int io__get_dec(struct io *io, __u64 *dec)
125{
126	bool first_read = true;
127
128	*dec = 0;
129	while (true) {
130		int ch = io__get_char(io);
131
132		if (ch < 0)
133			return ch;
134		if (ch >= '0' && ch <= '9')
135			*dec = (*dec * 10) + ch - '0';
136		else if (first_read)
137			return -2;
138		else
139			return ch;
140		first_read = false;
141	}
142}
143
144/* Read up to and including the first delim. */
145static inline ssize_t io__getdelim(struct io *io, char **line_out, size_t *line_len_out, int delim)
146{
147	char buf[128];
148	int buf_pos = 0;
149	char *line = NULL, *temp;
150	size_t line_len = 0;
151	int ch = 0;
152
153	/* TODO: reuse previously allocated memory. */
154	free(*line_out);
155	while (ch != delim) {
156		ch = io__get_char(io);
157
158		if (ch < 0)
159			break;
160
161		if (buf_pos == sizeof(buf)) {
162			temp = realloc(line, line_len + sizeof(buf));
163			if (!temp)
164				goto err_out;
165			line = temp;
166			memcpy(&line[line_len], buf, sizeof(buf));
167			line_len += sizeof(buf);
168			buf_pos = 0;
169		}
170		buf[buf_pos++] = (char)ch;
171	}
172	temp = realloc(line, line_len + buf_pos + 1);
173	if (!temp)
174		goto err_out;
175	line = temp;
176	memcpy(&line[line_len], buf, buf_pos);
177	line[line_len + buf_pos] = '\0';
178	line_len += buf_pos;
179	*line_out = line;
180	*line_len_out = line_len;
181	return line_len;
182err_out:
183	free(line);
184	*line_out = NULL;
185	return -ENOMEM;
186}
187
188static inline ssize_t io__getline(struct io *io, char **line_out, size_t *line_len_out)
189{
190	return io__getdelim(io, line_out, line_len_out, /*delim=*/'\n');
191}
192
193#endif /* __API_IO__ */
194