nbbio.c

[詳解]

/*++
/* NAME
/*  nbbio 3
/* SUMMARY
/*  non-blocking buffered I/O
/* SYNOPSIS
/*  #include <nbbio.h>
/*
/*  NBBIO   *nbbio_create(fd, bufsize, label, action, context)
/*  int fd;
/*  ssize_t bufsize;
/*  const char *label;
/*  void    (*action)(int event, void *context);
/*  char    *context;
/*
/*  void    nbbio_free(np)
/*  NBBIO   *np;
/*
/*  void    nbbio_enable_read(np, timeout)
/*  NBBIO   *np;
/*  int timeout;
/*
/*  void    nbbio_enable_write(np, timeout)
/*  NBBIO   *np;
/*  int timeout;
/*
/*  void    nbbio_disable_readwrite(np)
/*  NBBIO   *np;
/*
/*  void    nbbio_slumber(np, timeout)
/*  NBBIO   *np;
/*  int timeout;
/*
/*  int NBBIO_ACTIVE_FLAGS(np)
/*  NBBIO   *np;
/*
/*  int NBBIO_ERROR_FLAGS(np)
/*  NBBIO   *np;
/*
/*  const ssize_t NBBIO_BUFSIZE(np)
/*  NBBIO   *np;
/*
/*  ssize_t NBBIO_READ_PEND(np)
/*  NBBIO   *np;
/*
/*  char    *NBBIO_READ_BUF(np)
/*  NBBIO   *np;
/*
/*  const ssize_t NBBIO_WRITE_PEND(np)
/*  NBBIO   *np;
/*
/*  char    *NBBIO_WRITE_BUF(np)
/*  NBBIO   *np;
/* DESCRIPTION
/*  This module implements low-level support for event-driven
/*  I/O on a full-duplex stream. Read/write events are handled
/*  by pseudothreads that run under control by the events(5)
/*  module.  After each I/O operation, the application is
/*  notified via a call-back routine.
/*
/*  It is up to the call-back routine to turn on/off read/write
/*  events as appropriate.  It is an error to leave read events
/*  enabled for a buffer that is full, or to leave write events
/*  enabled for a buffer that is empty.
/*
/*  nbbio_create() creates a pair of buffers of the named size
/*  for the named stream. The label specifies the purpose of
/*  the stream, and is used for diagnostic messages.  The
/*  nbbio(3) event handler invokes the application call-back
/*  routine with the current event type (EVENT_READ etc.) and
/*  with the application-specified context.
/*
/*  nbbio_free() terminates any pseudothreads associated with
/*  the named buffer pair, closes the stream, and destroys the
/*  buffer pair.
/*
/*  nbbio_enable_read() enables a read pseudothread for the
/*  named buffer pair.  It is an error to enable a read
/*  pseudothread while the read buffer is full, or while a read
/*  or write pseudothread is still enabled.
/*
/*  nbbio_enable_write() enables a write pseudothread for the
/*  named buffer pair.  It is an error to enable a write
/*  pseudothread while the write buffer is empty, or while a
/*  read or write pseudothread is still enabled.
/*
/*  nbbio_disable_readwrite() disables any read/write pseudothreads
/*  for the named buffer pair, including timeouts. To ensure
/*  buffer liveness, use nbbio_slumber() instead of
/*  nbbio_disable_readwrite().  It is no error to call this
/*  function while no read/write pseudothread is enabled.
/*
/*  nbbio_slumber() disables any read/write pseudothreads for
/*  the named buffer pair, but keeps the timer active to ensure
/*  buffer liveness. It is no error to call this function while
/*  no read/write pseudothread is enabled.
/*
/*  NBBIO_ERROR_FLAGS() returns the error flags for the named buffer
/*  pair: zero or more of NBBIO_FLAG_EOF (read EOF), NBBIO_FLAG_ERROR
/*  (read/write error) or NBBIO_FLAG_TIMEOUT (time limit
/*  exceeded).
/*
/*  NBBIO_ACTIVE_FLAGS() returns the pseudothread flags for the
/*  named buffer pair: NBBIO_FLAG_READ (read pseudothread is
/*  active), NBBIO_FLAG_WRITE (write pseudothread is active),
/*  or zero (no pseudothread is active).
/*
/*  NBBIO_WRITE_PEND() and NBBIO_WRITE_BUF() evaluate to the
/*  number of to-be-written bytes and the write buffer for the
/*  named buffer pair. NBBIO_WRITE_PEND() must be updated by
/*  the application code that fills the write buffer; no more
/*  than NBBIO_BUFSIZE() bytes may be filled.
/*
/*  NBBIO_READ_PEND() and NBBIO_READ_BUF() evaluate to the
/*  number of unread bytes and the read buffer for the named
/*  buffer pair. NBBIO_READ_PEND() and NBBIO_READ_BUF() must
/*  be updated by the application code that drains the read
/*  buffer.
/* SEE ALSO
/*  events(3) event manager
/* DIAGNOSTICS
/*  Panic: interface violation.
/*
/*  Fatal: out of memory.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

 /*
  * System library.
  */
#include <sys_defs.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>         /* memmove() */

 /*
  * Utility library.
  */
#include <mymalloc.h>
#include <msg.h>
#include <events.h>
#include <nbbio.h>

/* nbbio_event - non-blocking event handler */

static void nbbio_event(int event, void *context)
{
    const char *myname = "nbbio_event";
    NBBIO  *np = (NBBIO *) context;
    ssize_t count;

    switch (event) {

    /*
     * Read data into the read buffer. Leave it up to the application to
     * drain the buffer until it is empty.
     */
    case EVENT_READ:
    if (np->read_pend == np->bufsize)
        msg_panic("%s: socket fd=%d: read buffer is full",
              myname, np->fd);
    if (np->read_pend < 0 || np->read_pend > np->bufsize)
        msg_panic("%s: socket fd=%d: bad pending read count %ld",
              myname, np->fd, (long) np->read_pend);
    count = read(np->fd, np->read_buf + np->read_pend,
             np->bufsize - np->read_pend);
    if (count > 0) {
        np->read_pend += count;
        if (msg_verbose)
        msg_info("%s: read %ld on %s fd=%d",
             myname, (long) count, np->label, np->fd);
    } else if (count == 0) {
        np->flags |= NBBIO_FLAG_EOF;
        if (msg_verbose)
        msg_info("%s: read EOF on %s fd=%d",
             myname, np->label, np->fd);
    } else {
        if (errno == EAGAIN)
        msg_warn("%s: read() returns EAGAIN on readable descriptor",
             myname);
        np->flags |= NBBIO_FLAG_ERROR;
        if (msg_verbose)
        msg_info("%s: read %s fd=%d: %m", myname, np->label, np->fd);
    }
    break;

    /*
     * Drain data from the output buffer.  Notify the application
     * whenever some bytes are written.
     * 
     * XXX Enforce a total time limit to ensure liveness when a hostile
     * receiver sets a very small TCP window size.
     */
    case EVENT_WRITE:
    if (np->write_pend == 0)
        msg_panic("%s: socket fd=%d: empty write buffer", myname, np->fd);
    if (np->write_pend < 0 || np->write_pend > np->bufsize)
        msg_panic("%s: socket fd=%d: bad pending write count %ld",
              myname, np->fd, (long) np->write_pend);
    count = write(np->fd, np->write_buf, np->write_pend);
    if (count > 0) {
        np->write_pend -= count;
        if (np->write_pend > 0)
        memmove(np->write_buf, np->write_buf + count, np->write_pend);
    } else {
        if (errno == EAGAIN)
        msg_warn("%s: write() returns EAGAIN on writable descriptor",
             myname);
        np->flags |= NBBIO_FLAG_ERROR;
        if (msg_verbose)
        msg_info("%s: write %s fd=%d: %m", myname, np->label, np->fd);
    }
    break;

    /*
     * Something bad happened.
     */
    case EVENT_XCPT:
    np->flags |= NBBIO_FLAG_ERROR;
    if (msg_verbose)
        msg_info("%s: error on %s fd=%d: %m", myname, np->label, np->fd);
    break;

    /*
     * Something good didn't happen.
     */
    case EVENT_TIME:
    np->flags |= NBBIO_FLAG_TIMEOUT;
    if (msg_verbose)
        msg_info("%s: %s timeout on %s fd=%d",
             myname, NBBIO_OP_NAME(np), np->label, np->fd);
    break;

    default:
    msg_panic("%s: unknown event %d", myname, event);
    }

    /*
     * Application notification. The application will check for any error
     * flags, copy application data from or to our buffer pair, and decide
     * what I/O happens next.
     */
    np->action(event, np->context);
}

/* nbbio_enable_read - enable reading from socket into buffer */

void    nbbio_enable_read(NBBIO *np, int timeout)
{
    const char *myname = "nbbio_enable_read";

    /*
     * Sanity checks.
     */
    if (np->flags & NBBIO_MASK_ACTIVE)
    msg_panic("%s: socket fd=%d is enabled for %s",
          myname, np->fd, NBBIO_OP_NAME(np));
    if (timeout <= 0)
    msg_panic("%s: socket fd=%d: bad timeout %d",
          myname, np->fd, timeout);
    if (np->read_pend >= np->bufsize)
    msg_panic("%s: socket fd=%d: read buffer is full",
          myname, np->fd);

    /*
     * Enable events.
     */
    event_enable_read(np->fd, nbbio_event, (void *) np);
    event_request_timer(nbbio_event, (void *) np, timeout);
    np->flags |= NBBIO_FLAG_READ;
}

/* nbbio_enable_write - enable writing from buffer to socket */

void    nbbio_enable_write(NBBIO *np, int timeout)
{
    const char *myname = "nbbio_enable_write";

    /*
     * Sanity checks.
     */
    if (np->flags & NBBIO_MASK_ACTIVE)
    msg_panic("%s: socket fd=%d is enabled for %s",
          myname, np->fd, NBBIO_OP_NAME(np));
    if (timeout <= 0)
    msg_panic("%s: socket fd=%d bad timeout %d",
          myname, np->fd, timeout);
    if (np->write_pend <= 0)
    msg_panic("%s: socket fd=%d: empty write buffer",
          myname, np->fd);

    /*
     * Enable events.
     */
    event_enable_write(np->fd, nbbio_event, (void *) np);
    event_request_timer(nbbio_event, (void *) np, timeout);
    np->flags |= NBBIO_FLAG_WRITE;
}

/* nbbio_disable_readwrite - disable read/write/timer events */

void    nbbio_disable_readwrite(NBBIO *np)
{
    np->flags &= ~NBBIO_MASK_ACTIVE;
    event_disable_readwrite(np->fd);
    event_cancel_timer(nbbio_event, (void *) np);
}

/* nbbio_slumber - disable read/write events, keep timer */

void    nbbio_slumber(NBBIO *np, int timeout)
{
    np->flags &= ~NBBIO_MASK_ACTIVE;
    event_disable_readwrite(np->fd);
    event_request_timer(nbbio_event, (void *) np, timeout);
}

/* nbbio_create - create socket buffer */

NBBIO  *nbbio_create(int fd, ssize_t bufsize, const char *label,
                     NBBIO_ACTION action, void *context)
{
    NBBIO  *np;

    /*
     * Sanity checks.
     */
    if (fd < 0)
    msg_panic("nbbio_create: bad file descriptor: %d", fd);
    if (bufsize <= 0)
    msg_panic("nbbio_create: bad buffer size: %ld", (long) bufsize);

    /*
     * Create a new buffer pair.
     */
    np = (NBBIO *) mymalloc(sizeof(*np));
    np->fd = fd;
    np->bufsize = bufsize;
    np->label = mystrdup(label);
    np->action = action;
    np->context = context;
    np->flags = 0;

    np->read_buf = mymalloc(bufsize);
    np->read_pend = 0;

    np->write_buf = mymalloc(bufsize);
    np->write_pend = 0;

    return (np);
}

/* nbbio_free - destroy socket buffer */

void    nbbio_free(NBBIO *np)
{
    nbbio_disable_readwrite(np);
    (void) close(np->fd);
    myfree(np->label);
    myfree(np->read_buf);
    myfree(np->write_buf);
    myfree((void *) np);
}