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winhandl.c

/*
 * winhandl.c: Module to give Windows front ends the general
 * ability to deal with consoles, pipes, serial ports, or any other
 * type of data stream accessed through a Windows API HANDLE rather
 * than a WinSock SOCKET.
 *
 * We do this by spawning a subthread to continuously try to read
 * from the handle. Every time a read successfully returns some
 * data, the subthread sets an event object which is picked up by
 * the main thread, and the main thread then sets an event in
 * return to instruct the subthread to resume reading.
 * 
 * Output works precisely the other way round, in a second
 * subthread. The output subthread should not be attempting to
 * write all the time, because it hasn't always got data _to_
 * write; so the output thread waits for an event object notifying
 * it to _attempt_ a write, and then it sets an event in return
 * when one completes.
 * 
 * (It's terribly annoying having to spawn a subthread for each
 * direction of each handle. Technically it isn't necessary for
 * serial ports, since we could use overlapped I/O within the main
 * thread and wait directly on the event objects in the OVERLAPPED
 * structures. However, we can't use this trick for some types of
 * file handle at all - for some reason Windows restricts use of
 * OVERLAPPED to files which were opened with the overlapped flag -
 * and so we must use threads for those. This being the case, it's
 * simplest just to use threads for everything rather than trying
 * to keep track of multiple completely separate mechanisms.)
 */

#include <assert.h>

#include "putty.h"

/* ----------------------------------------------------------------------
 * Generic definitions.
 */

/*
 * Maximum amount of backlog we will allow to build up on an input
 * handle before we stop reading from it.
 */
#define MAX_BACKLOG 32768

struct handle_generic {
    /*
     * Initial fields common to both handle_input and handle_output
     * structures.
     * 
     * The three HANDLEs are set up at initialisation time and are
     * thereafter read-only to both main thread and subthread.
     * `moribund' is only used by the main thread; `done' is
     * written by the main thread before signalling to the
     * subthread. `defunct' and `busy' are used only by the main
     * thread.
     */
    HANDLE h;                        /* the handle itself */
    HANDLE ev_to_main;               /* event used to signal main thread */
    HANDLE ev_from_main;             /* event used to signal back to us */
    int moribund;              /* are we going to kill this soon? */
    int done;                        /* request subthread to terminate */
    int defunct;               /* has the subthread already gone? */
    int busy;                        /* operation currently in progress? */
    void *privdata;                  /* for client to remember who they are */
};

/* ----------------------------------------------------------------------
 * Input threads.
 */

/*
 * Data required by an input thread.
 */
struct handle_input {
    /*
     * Copy of the handle_generic structure.
     */
    HANDLE h;                        /* the handle itself */
    HANDLE ev_to_main;               /* event used to signal main thread */
    HANDLE ev_from_main;             /* event used to signal back to us */
    int moribund;              /* are we going to kill this soon? */
    int done;                        /* request subthread to terminate */
    int defunct;               /* has the subthread already gone? */
    int busy;                        /* operation currently in progress? */
    void *privdata;                  /* for client to remember who they are */

    /*
     * Data set at initialisation and then read-only.
     */
    int flags;

    /*
     * Data set by the input thread before signalling ev_to_main,
     * and read by the main thread after receiving that signal.
     */
    char buffer[4096];               /* the data read from the handle */
    DWORD len;                       /* how much data that was */
    int readret;               /* lets us know about read errors */

    /*
     * Callback function called by this module when data arrives on
     * an input handle.
     */
    handle_inputfn_t gotdata;
};

/*
 * The actual thread procedure for an input thread.
 */
static DWORD WINAPI handle_input_threadfunc(void *param)
{
    struct handle_input *ctx = (struct handle_input *) param;
    OVERLAPPED ovl, *povl;
    HANDLE oev;
    int readlen;

    if (ctx->flags & HANDLE_FLAG_OVERLAPPED) {
      povl = &ovl;
      oev = CreateEvent(NULL, TRUE, FALSE, NULL);
    } else {
      povl = NULL;
    }

    if (ctx->flags & HANDLE_FLAG_UNITBUFFER)
      readlen = 1;
    else
      readlen = sizeof(ctx->buffer);

    while (1) {
      if (povl) {
          memset(povl, 0, sizeof(OVERLAPPED));
          povl->hEvent = oev;
      }
      ctx->readret = ReadFile(ctx->h, ctx->buffer, readlen,
                        &ctx->len, povl);
      if (povl && !ctx->readret && GetLastError() == ERROR_IO_PENDING) {
          WaitForSingleObject(povl->hEvent, INFINITE);
          ctx->readret = GetOverlappedResult(ctx->h, povl, &ctx->len, FALSE);
      }

      if (!ctx->readret)
          ctx->len = 0;

      if (ctx->readret && ctx->len == 0 &&
          (ctx->flags & HANDLE_FLAG_IGNOREEOF))
          continue;

      SetEvent(ctx->ev_to_main);

      if (!ctx->len)
          break;

      WaitForSingleObject(ctx->ev_from_main, INFINITE);
      if (ctx->done)
          break;               /* main thread told us to shut down */
    }

    if (povl)
      CloseHandle(oev);

    return 0;
}

/*
 * This is called after a succcessful read, or from the
 * `unthrottle' function. It decides whether or not to begin a new
 * read operation.
 */
static void handle_throttle(struct handle_input *ctx, int backlog)
{
    if (ctx->defunct)
      return;

    /*
     * If there's a read operation already in progress, do nothing:
     * when that completes, we'll come back here and be in a
     * position to make a better decision.
     */
    if (ctx->busy)
      return;

    /*
     * Otherwise, we must decide whether to start a new read based
     * on the size of the backlog.
     */
    if (backlog < MAX_BACKLOG) {
      SetEvent(ctx->ev_from_main);
      ctx->busy = TRUE;
    }
}

/* ----------------------------------------------------------------------
 * Output threads.
 */

/*
 * Data required by an output thread.
 */
struct handle_output {
    /*
     * Copy of the handle_generic structure.
     */
    HANDLE h;                        /* the handle itself */
    HANDLE ev_to_main;               /* event used to signal main thread */
    HANDLE ev_from_main;             /* event used to signal back to us */
    int moribund;              /* are we going to kill this soon? */
    int done;                        /* request subthread to terminate */
    int defunct;               /* has the subthread already gone? */
    int busy;                        /* operation currently in progress? */
    void *privdata;                  /* for client to remember who they are */

    /*
     * Data set at initialisation and then read-only.
     */
    int flags;

    /*
     * Data set by the main thread before signalling ev_from_main,
     * and read by the input thread after receiving that signal.
     */
    char *buffer;              /* the data to write */
    DWORD len;                       /* how much data there is */

    /*
     * Data set by the input thread before signalling ev_to_main,
     * and read by the main thread after receiving that signal.
     */
    DWORD lenwritten;                /* how much data we actually wrote */
    int writeret;              /* return value from WriteFile */

    /*
     * Data only ever read or written by the main thread.
     */
    bufchain queued_data;            /* data still waiting to be written */

    /*
     * Callback function called when the backlog in the bufchain
     * drops.
     */
    handle_outputfn_t sentdata;
};

static DWORD WINAPI handle_output_threadfunc(void *param)
{
    struct handle_output *ctx = (struct handle_output *) param;
    OVERLAPPED ovl, *povl;

    if (ctx->flags & HANDLE_FLAG_OVERLAPPED)
      povl = &ovl;
    else
      povl = NULL;

    while (1) {
      WaitForSingleObject(ctx->ev_from_main, INFINITE);
      if (ctx->done) {
          SetEvent(ctx->ev_to_main);
          break;
      }
      if (povl)
          memset(povl, 0, sizeof(OVERLAPPED));
      ctx->writeret = WriteFile(ctx->h, ctx->buffer, ctx->len,
                          &ctx->lenwritten, povl);
      if (povl && !ctx->writeret && GetLastError() == ERROR_IO_PENDING)
          ctx->writeret = GetOverlappedResult(ctx->h, povl,
                                    &ctx->lenwritten, TRUE);

      SetEvent(ctx->ev_to_main);
      if (!ctx->writeret)
          break;
    }

    return 0;
}

static void handle_try_output(struct handle_output *ctx)
{
    void *senddata;
    int sendlen;

    if (!ctx->busy && bufchain_size(&ctx->queued_data)) {
      bufchain_prefix(&ctx->queued_data, &senddata, &sendlen);
      ctx->buffer = senddata;
      ctx->len = sendlen;
      SetEvent(ctx->ev_from_main);
      ctx->busy = TRUE;
    }
}

/* ----------------------------------------------------------------------
 * Unified code handling both input and output threads.
 */

struct handle {
    int output;
    union {
      struct handle_generic g;
      struct handle_input i;
      struct handle_output o;
    } u;
};

static tree234 *handles_by_evtomain;

static int handle_cmp_evtomain(void *av, void *bv)
{
    struct handle *a = (struct handle *)av;
    struct handle *b = (struct handle *)bv;

    if ((unsigned)a->u.g.ev_to_main < (unsigned)b->u.g.ev_to_main)
      return -1;
    else if ((unsigned)a->u.g.ev_to_main > (unsigned)b->u.g.ev_to_main)
      return +1;
    else
      return 0;
}

static int handle_find_evtomain(void *av, void *bv)
{
    HANDLE *a = (HANDLE *)av;
    struct handle *b = (struct handle *)bv;

    if ((unsigned)*a < (unsigned)b->u.g.ev_to_main)
      return -1;
    else if ((unsigned)*a > (unsigned)b->u.g.ev_to_main)
      return +1;
    else
      return 0;
}

struct handle *handle_input_new(HANDLE handle, handle_inputfn_t gotdata,
                        void *privdata, int flags)
{
    struct handle *h = snew(struct handle);
    DWORD in_threadid; /* required for Win9x */

    h->output = FALSE;
    h->u.i.h = handle;
    h->u.i.ev_to_main = CreateEvent(NULL, FALSE, FALSE, NULL);
    h->u.i.ev_from_main = CreateEvent(NULL, FALSE, FALSE, NULL);
    h->u.i.gotdata = gotdata;
    h->u.i.defunct = FALSE;
    h->u.i.moribund = FALSE;
    h->u.i.done = FALSE;
    h->u.i.privdata = privdata;
    h->u.i.flags = flags;

    if (!handles_by_evtomain)
      handles_by_evtomain = newtree234(handle_cmp_evtomain);
    add234(handles_by_evtomain, h);

    CreateThread(NULL, 0, handle_input_threadfunc,
             &h->u.i, 0, &in_threadid);
    h->u.i.busy = TRUE;

    return h;
}

struct handle *handle_output_new(HANDLE handle, handle_outputfn_t sentdata,
                         void *privdata, int flags)
{
    struct handle *h = snew(struct handle);
    DWORD out_threadid; /* required for Win9x */

    h->output = TRUE;
    h->u.o.h = handle;
    h->u.o.ev_to_main = CreateEvent(NULL, FALSE, FALSE, NULL);
    h->u.o.ev_from_main = CreateEvent(NULL, FALSE, FALSE, NULL);
    h->u.o.busy = FALSE;
    h->u.o.defunct = FALSE;
    h->u.o.moribund = FALSE;
    h->u.o.done = FALSE;
    h->u.o.privdata = privdata;
    bufchain_init(&h->u.o.queued_data);
    h->u.o.sentdata = sentdata;
    h->u.o.flags = flags;

    if (!handles_by_evtomain)
      handles_by_evtomain = newtree234(handle_cmp_evtomain);
    add234(handles_by_evtomain, h);

    CreateThread(NULL, 0, handle_output_threadfunc,
             &h->u.i, 0, &out_threadid);

    return h;
}

int handle_write(struct handle *h, const void *data, int len)
{
    assert(h->output);
    bufchain_add(&h->u.o.queued_data, data, len);
    handle_try_output(&h->u.o);
    return bufchain_size(&h->u.o.queued_data);
}

HANDLE *handle_get_events(int *nevents)
{
    HANDLE *ret;
    struct handle *h;
    int i, n, size;

    /*
     * Go through our tree counting the handle objects currently
     * engaged in useful activity.
     */
    ret = NULL;
    n = size = 0;
    if (handles_by_evtomain) {
      for (i = 0; (h = index234(handles_by_evtomain, i)) != NULL; i++) {
          if (h->u.g.busy) {
            if (n >= size) {
                size += 32;
                ret = sresize(ret, size, HANDLE);
            }
            ret[n++] = h->u.g.ev_to_main;
          }
      }
    }

    *nevents = n;
    return ret;
}

static void handle_destroy(struct handle *h)
{
    if (h->output)
      bufchain_clear(&h->u.o.queued_data);
    CloseHandle(h->u.g.ev_from_main);
    CloseHandle(h->u.g.ev_to_main);
    del234(handles_by_evtomain, h);
    sfree(h);
}

void handle_free(struct handle *h)
{
    /*
     * If the handle is currently busy, we cannot immediately free
     * it. Instead we must wait until it's finished its current
     * operation, because otherwise the subthread will write to
     * invalid memory after we free its context from under it.
     */
    assert(h && !h->u.g.moribund);
    if (h->u.g.busy) {
      /*
       * Just set the moribund flag, which will be noticed next
       * time an operation completes.
       */
      h->u.g.moribund = TRUE;
    } else if (h->u.g.defunct) {
      /*
       * There isn't even a subthread; we can go straight to
       * handle_destroy.
       */
      handle_destroy(h);
    } else {
      /*
       * The subthread is alive but not busy, so we now signal it
       * to die. Set the moribund flag to indicate that it will
       * want destroying after that.
       */
      h->u.g.moribund = TRUE;
      h->u.g.done = TRUE;
      h->u.g.busy = TRUE;
      SetEvent(h->u.g.ev_from_main);
    }
}

void handle_got_event(HANDLE event)
{
    struct handle *h;

    assert(handles_by_evtomain);
    h = find234(handles_by_evtomain, &event, handle_find_evtomain);
    if (!h) {
      /*
       * This isn't an error condition. If two or more event
       * objects were signalled during the same select operation,
       * and processing of the first caused the second handle to
       * be closed, then it will sometimes happen that we receive
       * an event notification here for a handle which is already
       * deceased. In that situation we simply do nothing.
       */
      return;
    }

    if (h->u.g.moribund) {
      /*
       * A moribund handle is already treated as dead from the
       * external user's point of view, so do nothing with the
       * actual event. Just signal the thread to die if
       * necessary, or destroy the handle if not.
       */
      if (h->u.g.done) {
          handle_destroy(h);
      } else {
          h->u.g.done = TRUE;
          h->u.g.busy = TRUE;
          SetEvent(h->u.g.ev_from_main);
      }
      return;
    }

    if (!h->output) {
      int backlog;

      h->u.i.busy = FALSE;

      /*
       * A signal on an input handle means data has arrived.
       */
      if (h->u.i.len == 0) {
          /*
           * EOF, or (nearly equivalently) read error.
           */
          h->u.i.gotdata(h, NULL, (h->u.i.readret ? 0 : -1));
          h->u.i.defunct = TRUE;
      } else {
          backlog = h->u.i.gotdata(h, h->u.i.buffer, h->u.i.len);
          handle_throttle(&h->u.i, backlog);
      }
    } else {
      h->u.o.busy = FALSE;

      /*
       * A signal on an output handle means we have completed a
       * write. Call the callback to indicate that the output
       * buffer size has decreased, or to indicate an error.
       */
      if (!h->u.o.writeret) {
          /*
           * Write error. Send a negative value to the callback,
           * and mark the thread as defunct (because the output
           * thread is terminating by now).
           */
          h->u.o.sentdata(h, -1);
          h->u.o.defunct = TRUE;
      } else {
          bufchain_consume(&h->u.o.queued_data, h->u.o.lenwritten);
          h->u.o.sentdata(h, bufchain_size(&h->u.o.queued_data));
          handle_try_output(&h->u.o);
      }
    }
}

void handle_unthrottle(struct handle *h, int backlog)
{
    assert(!h->output);
    handle_throttle(&h->u.i, backlog);
}

int handle_backlog(struct handle *h)
{
    assert(h->output);
    return bufchain_size(&h->u.o.queued_data);
}

void *handle_get_privdata(struct handle *h)
{
    return h->u.g.privdata;
}

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