/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Lightweight buffered reading library.
 *
 * Copyright 2019 Google LLC.
 */
#ifndef __API_IO__
#define __API_IO__

#include <errno.h>
#include <poll.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/types.h>

struct io {
        /* File descriptor being read/ */
        int fd;
        /* Size of the read buffer. */
        unsigned int buf_len;
        /* Pointer to storage for buffering read. */
        char *buf;
        /* End of the storage. */
        char *end;
        /* Currently accessed data pointer. */
        char *data;
        /* Read timeout, 0 implies no timeout. */
        int timeout_ms;
        /* Set true on when the end of file on read error. */
        bool eof;
};

static inline void io__init(struct io *io, int fd,
                            char *buf, unsigned int buf_len)
{
        io->fd = fd;
        io->buf_len = buf_len;
        io->buf = buf;
        io->end = buf;
        io->data = buf;
        io->timeout_ms = 0;
        io->eof = false;
}

/* Read from fd filling the buffer. Called when io->data == io->end. */
static inline int io__fill_buffer(struct io *io)
{
        ssize_t n;

        if (io->eof)
                return -1;

        if (io->timeout_ms != 0) {
                struct pollfd pfds[] = {
                        {
                                .fd = io->fd,
                                .events = POLLIN,
                        },
                };

                n = poll(pfds, 1, io->timeout_ms);
                if (n == 0)
                        errno = ETIMEDOUT;
                if (n > 0 && !(pfds[0].revents & POLLIN)) {
                        errno = EIO;
                        n = -1;
                }
                if (n <= 0) {
                        io->eof = true;
                        return -1;
                }
        }
        n = read(io->fd, io->buf, io->buf_len);

        if (n <= 0) {
                io->eof = true;
                return -1;
        }
        io->data = &io->buf[0];
        io->end = &io->buf[n];
        return 0;
}

/* Reads one character from the "io" file with similar semantics to fgetc. */
static inline int io__get_char(struct io *io)
{
        if (io->data == io->end) {
                int ret = io__fill_buffer(io);

                if (ret)
                        return ret;
        }
        return *io->data++;
}

/* Read a hexadecimal value with no 0x prefix into the out argument hex. If the
 * first character isn't hexadecimal returns -2, io->eof returns -1, otherwise
 * returns the character after the hexadecimal value which may be -1 for eof.
 * If the read value is larger than a u64 the high-order bits will be dropped.
 */
static inline int io__get_hex(struct io *io, __u64 *hex)
{
        bool first_read = true;

        *hex = 0;
        while (true) {
                int ch = io__get_char(io);

                if (ch < 0)
                        return ch;
                if (ch >= '0' && ch <= '9')
                        *hex = (*hex << 4) | (ch - '0');
                else if (ch >= 'a' && ch <= 'f')
                        *hex = (*hex << 4) | (ch - 'a' + 10);
                else if (ch >= 'A' && ch <= 'F')
                        *hex = (*hex << 4) | (ch - 'A' + 10);
                else if (first_read)
                        return -2;
                else
                        return ch;
                first_read = false;
        }
}

/* Read a positive decimal value with out argument dec. If the first character
 * isn't a decimal returns -2, io->eof returns -1, otherwise returns the
 * character after the decimal value which may be -1 for eof. If the read value
 * is larger than a u64 the high-order bits will be dropped.
 */
static inline int io__get_dec(struct io *io, __u64 *dec)
{
        bool first_read = true;

        *dec = 0;
        while (true) {
                int ch = io__get_char(io);

                if (ch < 0)
                        return ch;
                if (ch >= '0' && ch <= '9')
                        *dec = (*dec * 10) + ch - '0';
                else if (first_read)
                        return -2;
                else
                        return ch;
                first_read = false;
        }
}

/* Read up to and including the first delim. */
static inline ssize_t io__getdelim(struct io *io, char **line_out, size_t *line_len_out, int delim)
{
        char buf[128];
        int buf_pos = 0;
        char *line = NULL, *temp;
        size_t line_len = 0;
        int ch = 0;

        /* TODO: reuse previously allocated memory. */
        free(*line_out);
        while (ch != delim) {
                ch = io__get_char(io);

                if (ch < 0)
                        break;

                if (buf_pos == sizeof(buf)) {
                        temp = realloc(line, line_len + sizeof(buf));
                        if (!temp)
                                goto err_out;
                        line = temp;
                        memcpy(&line[line_len], buf, sizeof(buf));
                        line_len += sizeof(buf);
                        buf_pos = 0;
                }
                buf[buf_pos++] = (char)ch;
        }
        temp = realloc(line, line_len + buf_pos + 1);
        if (!temp)
                goto err_out;
        line = temp;
        memcpy(&line[line_len], buf, buf_pos);
        line[line_len + buf_pos] = '\0';
        line_len += buf_pos;
        *line_out = line;
        *line_len_out = line_len;
        return line_len;
err_out:
        free(line);
        *line_out = NULL;
        *line_len_out = 0;
        return -ENOMEM;
}

static inline ssize_t io__getline(struct io *io, char **line_out, size_t *line_len_out)
{
        return io__getdelim(io, line_out, line_len_out, /*delim=*/'\n');
}

#endif /* __API_IO__ */