watch_socket.cc

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// Copyright (C) 2014-2025 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

 
#include <config.h>
 
#include <util/watch_socket.h>
 
#include <fcntl.h>
#include <errno.h>
#include <sstream>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>
 
namespace isc {
namespace util {
 
const int WatchSocket::SOCKET_NOT_VALID = -1;
 
const uint32_t WatchSocket::MARKER = 0xDEADBEEF;
 
WatchSocket::WatchSocket()
    : source_(SOCKET_NOT_VALID), sink_(SOCKET_NOT_VALID) {
    // Open the pipe.
    int fds[2];
    if (pipe(fds)) {
        const char* errstr = strerror(errno);
        isc_throw(WatchSocketError, "Cannot construct pipe: " << errstr);
    }
 
    source_ = fds[1];
    sink_ = fds[0];
 
    if (fcntl(source_, F_SETFD, FD_CLOEXEC)) {
        const char* errstr = strerror(errno);
        isc_throw(WatchSocketError, "Cannot set source to close-on-exec: "
                                     << errstr);
    }
 
    if (fcntl(sink_, F_SETFD, FD_CLOEXEC)) {
        const char* errstr = strerror(errno);
        isc_throw(WatchSocketError, "Cannot set sink to close-on-exec: "
                                     << errstr);
    }
 
    if (fcntl(sink_, F_SETFL, O_NONBLOCK)) {
        const char* errstr = strerror(errno);
        isc_throw(WatchSocketError, "Cannot set sink to non-blocking: "
                                     << errstr);
    }
}
 
WatchSocket::~WatchSocket() {
    closeSocket();
}
 
void
WatchSocket::markReady() {
    // Make sure it hasn't been orphaned!  Otherwise we may get SIGPIPE.  We
    // use fcntl to check as select() on some systems may show it as ready to
    // read.
    if (fcntl(sink_, F_GETFL) < 0) {
        closeSocket();
        isc_throw(WatchSocketError, "WatchSocket markReady failed:"
                  " select_fd was closed!");
    }
 
    if (!isReady()) {
        int nbytes = write (source_, &MARKER, sizeof(MARKER));
        if (nbytes != sizeof(MARKER)) {
            // If there's an error get the error message than close
            // the pipe.  This should ensure any further use of the socket
            // or testing the fd with select_fd will fail.
            const char* errstr = strerror(errno);
            closeSocket();
            isc_throw(WatchSocketError, "WatchSocket markReady failed:"
                      << " bytes written: " << nbytes << " : " << errstr);
        }
    }
}
 
bool
WatchSocket::isReady() {
    // Report it as not ready rather than error here.
    if (sink_ == SOCKET_NOT_VALID) {
        return (false);
    }
 
    // Use ioctl FIONREAD vs polling select as it is faster.
    int len;
    int result = ioctl(sink_, FIONREAD, &len);
    // Return true only if read ready, treat error same as not ready.
    return ((result == 0) && (len > 0));
}
 
void
WatchSocket::clearReady() {
    if (isReady()) {
        uint32_t buf = 0;
        int nbytes = read (sink_, &buf, sizeof(buf));
        if ((nbytes != sizeof(MARKER) || (buf != MARKER))) {
            // If there's an error get the error message than close
            // the pipe.  This should ensure any further use of the socket
            // or testing the fd with select_fd will fail.
            const char* errstr = strerror(errno);
            closeSocket();
            isc_throw(WatchSocketError, "WatchSocket clearReady failed: "
                      "bytes read: " << nbytes << " : "
                      "value read: " << buf << " error :" << errstr);
        }
    }
}
 
bool
WatchSocket::closeSocket(std::string& error_string) {
    std::ostringstream s;
    // Close the pipe fds.  Technically a close can fail (hugely unlikely)
    // but there's no recovery for it either.  If one does fail we log it
    // and go on. Plus this is called by the destructor and no one likes
    // destructors that throw.
    if (source_ != SOCKET_NOT_VALID) {
        if (close(source_)) {
            // An error occurred.
            s << "Could not close source: " << strerror(errno);
        }
 
        source_ = SOCKET_NOT_VALID;
    }
 
    if (sink_ != SOCKET_NOT_VALID) {
        if (close(sink_)) {
            // An error occurred.
            if (error_string.empty()) {
                s << "could not close sink: " << strerror(errno);
            }
        }
 
        sink_ = SOCKET_NOT_VALID;
    }
 
    error_string = s.str();
 
    // If any errors have been reported, return false.
    return (error_string.empty() ? true : false);
}
 
void
WatchSocket::closeSocket() {
    std::string error_string;
    closeSocket(error_string);
}
 
int
WatchSocket::getSelectFd() {
    return (sink_);
}
 
} // namespace isc::util
} // namespace isc