gdb-server/client.c

#include <client.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

static bool write_char(RdbClient *self, char out)  {
    if (self->len >= RDB_CLIENT_BUFLEN) {
        return false;
    }
    if (out == '#' || out == '$' || out == '}' || out == '*') {
        self->full_buf[self->len++] = '}';
        self->chk += '}';
        if (self->len >= RDB_CLIENT_BUFLEN) {
            return false;
        }
        out ^= 0x20;
    }
    self->full_buf[self->len++] = out;
    self->chk += out;
    return true;
}

bool char_to_hex_digit(char in, char *out) {
    if (in & 0xf0) {
        return false;
    }
    in &= 0x0f;
    if (in > 9) {
        *out = 'a' + in - 10;
    } else {
        *out = '0' + in;
    }
    return true;
}

bool hex_digit_to_char(char in, char *out) {
    if (in >= '0' && in <= '9') {
        *out = in - '0';
        return true;
    }
    if (in >= 'a' && in <= 'f') {
        *out = in - 'a' + 10;
        return true;
    }
    if (in >= 'A' && in <= 'F') {
        *out = in - 'A' + 10;
        return true;
    }
    return false;
}

bool char_to_hex_digits(char in, char *hi, char *lo) {
    return char_to_hex_digit((in & 0xf0) >> 4, hi)
        && char_to_hex_digit(in & 0x0f, lo);
}

void rdb_client_init(RdbClient *self, int connfd) {
    self->connfd = connfd;
    self->len = 0;
    self->chk = 0;
    self->should_ack = true;
}

#define BUFFER_LEN 8096

typedef struct Buffer {
    char buf[BUFFER_LEN];
    size_t len;
    size_t index;
} Buffer;

static Buffer INBUF = {
    .len = 0,
    .index = 0,
};

static ssize_t read_next_char(int connfd, char *in) {
    if (INBUF.index >= INBUF.len) {
        ssize_t inlen = read(connfd, INBUF.buf, BUFFER_LEN);
        if (inlen < 1) {
            // either we got an error (-1) or the connection closed (0)
            return inlen;
        }
        INBUF.index = 0;
        INBUF.len = inlen;
    }
    *in = INBUF.buf[INBUF.index++];
    return 1;
}

ssize_t rdb_client_read(RdbClient *self, char *buf, size_t len) {
    // read any acknowledgements and continue
    char in;
    do {
        ssize_t res = read_next_char(self->connfd, &in);
        if (res < 1) return res;
    } while (in == '+');

    if (in == '\x03') {
        // interrupt from the server
        *buf = in;
        return 1;
    }

    if (in == '-') {
        // we don't handle resending right now
        return -1;
    }

    // now, expect to be at the start of a packet
    if (in != '$') {
        fprintf(stderr, "unexpected packet start \"%c\"", in);
        return -1;
    }

    size_t outlen = 0;
    char chk = 0;
    while (1) {
        ssize_t res = read_next_char(self->connfd, &in);
        if (res < 1) return res;

        if (in == '#') {
            // end of packet, checksum next
            break;
        }
        if (outlen >= len) {
            // ran out of room in the buffer
            fprintf(stderr, "packet too big for buffer\n");
            return -1;
        }
        if (in == '}') {
            // escape sequence
            chk += in;
            res = read_next_char(self->connfd, &in);
            if (res < 1) return res;
            chk += in;
            buf[outlen++] = in ^ 0x20;
        } else {
            chk += in;
            buf[outlen++] = in;
        }
    };

    // validate the checksum
    char hi, lo;

    ssize_t res = read_next_char(self->connfd, &in);
    if (res < 1) return res;
    if (!hex_digit_to_char(in, &hi)) return -1;

    res = read_next_char(self->connfd, &in);
    if (res < 1) return res;
    if (!hex_digit_to_char(in, &lo)) return -1;

    char real_chk = (hi << 4) | lo;
    if (real_chk != chk) {
        fprintf(stderr, "invalid checksum\n");
        return -1;
    }

    return outlen;
}

void rdb_client_begin_packet(RdbClient *self) {
    self->len = 0;
    self->chk = 0;
    if (self->should_ack) {
        self->full_buf[self->len++] = '+';
    }
    self->full_buf[self->len++] = '$';
}

bool rdb_client_write_str(RdbClient *self, const char *str) {
    size_t len = strlen(str);
    for (size_t i = 0; i < len; ++i) {
        if (!write_char(self, str[i])) {
            return false;
        }
    }
    return true;
}

bool rdb_client_write_str_hex(RdbClient *self, const char *str) {
    size_t len = strlen(str);
    for (size_t i = 0; i < len; ++i) {
        char hi, lo;
        if (!char_to_hex_digits(str[i], &hi, &lo)
            || !write_char(self, hi)
            || !write_char(self, lo)) {
                return false;
        }
    }
    return true;
}

int rdb_client_send_packet(RdbClient *self) {
    if (self->len + 3 > RDB_CLIENT_BUFLEN) {
        return -1;
    }
    self->full_buf[self->len++] = '#';
    char hi, lo;
    if (!char_to_hex_digits(self->chk, &hi, &lo)) {
        return -1;
    }
    self->full_buf[self->len++] = hi;
    self->full_buf[self->len++] = lo;
    printf("sending command \"%.*s\" %d\n", (int) self->len, self->full_buf, (int)self->len);

    ssize_t rwrite = write(self->connfd, self->full_buf, self->len);
    if (rwrite == -1) {
        return -1;
    }
    return 0;
}