gdb-server/request.c

#include <errno.h>
#include <hex.h>
#include <request.h>
#include <stdio.h>
#include <sys/socket.h>
#include <unistd.h>

void rdb_request_init(RdbRequest *req, int connfd, char *buf, size_t buflen) {
    req->connfd = connfd;
    req->outbuf = buf;
    req->blocking = true;
    rdb_request_reset(req);
}

void rdb_request_reset(RdbRequest *req) {
    req->state = read_state_header;
    req->inbuf.len = 0;
    req->inbuf.index = 0;
    req->chk = 0;
}

void rdb_request_set_blocking(RdbRequest *req, bool blocking) {
    req->blocking = blocking;
}

static rdb_read_result_t read_char(RdbRequest *req, char *in) {
    if (req->inbuf.index >= req->inbuf.len) {
        int flags = req->blocking ? 0 : MSG_DONTWAIT;
        ssize_t inlen = recv(req->connfd, req->inbuf.buf, INBUF_LEN, flags);
        if (inlen == 0) {
            return read_result_disconnected;
        }
        if (inlen < 0) {
            if (errno == EAGAIN || errno == EWOULDBLOCK) {
                return read_result_pending;
            } else {
                perror("could not read incoming packet");
                return read_result_error;
            }
        }
        req->inbuf.index = 0;
        req->inbuf.len = inlen;
    }
    *in = req->inbuf.buf[req->inbuf.index++];
    return read_result_success;
}

rdb_read_result_t rdb_request_read(RdbRequest *req, CommandBuf *cmd) {
    rdb_read_result_t res;
    char in;

    switch (req->state) {
    case read_state_header:
        cmd->buf = req->outbuf;
        cmd->len = 0;

        // read any acknowledgements and continue
        do {
            res = read_char(req, &in);
            if (res != read_result_success) return res;
        } while (in == '+');

        if (in == '-') {
            fprintf(stderr, "negative ack not supported\n");
            return read_result_error;
        }

        if (in == '\x03') {
            // interrupt from the server
            cmd->buf[0] = in;
            cmd->len = 1;
            return read_result_success;
        }

        // now, we should be at the start of a packet
        if (in != '$') {
            fprintf(stderr, "unexpected packet start \"%c\"\n", in);
            return read_result_error;
        }

        req->state = read_state_body;
        __attribute__ ((fallthrough));
    case read_state_body:
    case read_state_body_escape:
        while (1) {
            res = read_char(req, &in);
            if (res != read_result_success) return res;

            if (req->state == read_state_body && in == '#') {
                // end of packet body
                break;
            }

            req->chk += in;

            if (req->state == read_state_body && in == '}') {
                // escape sequence
                req->state = read_state_body_escape;
                continue;
            }

            if (cmd->len >= req->outbuflen) {
                // ran out of room in the buffer
                fprintf(stderr, "packet too big for buffer\n");
                return read_result_error;
            }

            if (req->state == read_state_body_escape) {
                cmd->buf[cmd->len++] = in ^ 0x20;
                req->state = read_state_body;
            } else {
                cmd->buf[cmd->len++] = in;
            }
        }
        req->state = read_state_checksum_1;
        __attribute__ ((fallthrough));
    case read_state_checksum_1:
        res = read_char(req, &in);
        if (res != read_result_success) return res;

        // check the high digit of the checksum
        char hi;
        if (!parse_hex_digit(in, &hi)) {
            fprintf(stderr, "invalid checksum1\n");
            return read_result_error;
        }
        if (((req->chk >> 4) & 0x000f) != hi) {
            fprintf(stderr, "invalid checksum2\n");
            return read_result_error;
        }
        req->state = read_state_checksum_2;
        __attribute__ ((fallthrough));
    case read_state_checksum_2:
        res = read_char(req, &in);
        if (res != read_result_success) return res;

        // check the high digit of the checksum
        char lo;
        if (!parse_hex_digit(in, &lo)) {
            fprintf(stderr, "invalid checksum3 %c\n", in);
            return read_result_error;
        }
        if ((req->chk & 0x000f) != lo) {
            fprintf(stderr, "invalid checksum4\n");
            return read_result_error;
        }

        return read_result_success;
    default:
        fprintf(stderr, "invalid state\n");
        return read_result_error;
    }
}