sftp.c

/*
 * sftp.c: SFTP generic client code.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <limits.h>

#include "misc.h"
#include "int64.h"
#include "tree234.h"
#include "sftp.h"

struct sftp_packet {
  char *data;
  unsigned length, maxlen;
  unsigned savedpos;
  int type;
};

static const char *fxp_error_message;
static int fxp_errtype;

static void fxp_internal_error(const char *msg);

/* ----------------------------------------------------------------------
 * SFTP packet construction functions.
 */
static void sftp_pkt_ensure(struct sftp_packet *pkt, int length)
{
  if ((int)pkt->maxlen < length) {
    pkt->maxlen = length + 256;
    pkt->data = sresize(pkt->data, pkt->maxlen, char);
  }
}
static void sftp_pkt_adddata(struct sftp_packet *pkt, const void *data, int len)
{
  pkt->length += len;
  sftp_pkt_ensure(pkt, pkt->length);
  memcpy(pkt->data + pkt->length - len, data, len);
}
static void sftp_pkt_addbyte(struct sftp_packet *pkt, unsigned char byte)
{
  sftp_pkt_adddata(pkt, &byte, 1);
}
static void sftp_pkt_adduint32(struct sftp_packet *pkt, unsigned long value)
{
  unsigned char x[4];
  PUT_32BIT(x, value);
  sftp_pkt_adddata(pkt, x, 4);
}
static struct sftp_packet *sftp_pkt_init(int pkt_type)
{
  struct sftp_packet *pkt;
  pkt = snew(struct sftp_packet);
  pkt->data = NULL;
  pkt->savedpos = -1;
  pkt->length = 0;
  pkt->maxlen = 0;
  sftp_pkt_adduint32(pkt, 0); /* length field will be filled in later */
  sftp_pkt_addbyte(pkt, (unsigned char)pkt_type);
  return pkt;
}
/*
static void sftp_pkt_addbool(struct sftp_packet *pkt, unsigned char value)
{
    sftp_pkt_adddata(pkt, &value, 1);
}
*/
static void sftp_pkt_adduint64(struct sftp_packet *pkt, uint64 value)
{
  unsigned char x[8];
  PUT_32BIT(x, value.hi);
  PUT_32BIT(x + 4, value.lo);
  sftp_pkt_adddata(pkt, x, 8);
}
static void sftp_pkt_addstring_start(struct sftp_packet *pkt)
{
  sftp_pkt_adduint32(pkt, 0);
  pkt->savedpos = pkt->length;
}
static void sftp_pkt_addstring_str(struct sftp_packet *pkt, const char *data)
{
  sftp_pkt_adddata(pkt, data, strlen(data));
  PUT_32BIT(pkt->data + pkt->savedpos - 4, pkt->length - pkt->savedpos);
}
static void sftp_pkt_addstring_data(struct sftp_packet *pkt,
                                    const char *data,
                                    int len)
{
  sftp_pkt_adddata(pkt, data, len);
  PUT_32BIT(pkt->data + pkt->savedpos - 4, pkt->length - pkt->savedpos);
}
static void sftp_pkt_addstring(struct sftp_packet *pkt, const char *data)
{
  sftp_pkt_addstring_start(pkt);
  sftp_pkt_addstring_str(pkt, data);
}
static void sftp_pkt_addattrs(struct sftp_packet *pkt, struct fxp_attrs attrs)
{
  sftp_pkt_adduint32(pkt, attrs.flags);
  if (attrs.flags & SSH_FILEXFER_ATTR_SIZE) {
    sftp_pkt_adduint32(pkt, attrs.size.hi);
    sftp_pkt_adduint32(pkt, attrs.size.lo);
  }
  if (attrs.flags & SSH_FILEXFER_ATTR_UIDGID) {
    sftp_pkt_adduint32(pkt, attrs.uid);
    sftp_pkt_adduint32(pkt, attrs.gid);
  }
  if (attrs.flags & SSH_FILEXFER_ATTR_PERMISSIONS) {
    sftp_pkt_adduint32(pkt, attrs.permissions);
  }
  if (attrs.flags & SSH_FILEXFER_ATTR_ACMODTIME) {
    sftp_pkt_adduint32(pkt, attrs.atime);
    sftp_pkt_adduint32(pkt, attrs.mtime);
  }
  if (attrs.flags & SSH_FILEXFER_ATTR_EXTENDED) {
    /*
     * We currently don't support sending any extended
     * attributes.
     */
  }
}

/* ----------------------------------------------------------------------
 * SFTP packet decode functions.
 */

static int sftp_pkt_getbyte(struct sftp_packet *pkt, unsigned char *ret)
{
  if (pkt->length - pkt->savedpos < 1)
    return 0;
  *ret = (unsigned char)pkt->data[pkt->savedpos];
  pkt->savedpos++;
  return 1;
}
static int sftp_pkt_getuint32(struct sftp_packet *pkt, unsigned long *ret)
{
  if (pkt->length - pkt->savedpos < 4)
    return 0;
  *ret = GET_32BIT(pkt->data + pkt->savedpos);
  pkt->savedpos += 4;
  return 1;
}
static int sftp_pkt_getstring(struct sftp_packet *pkt, char **p, int *length)
{
  *p = NULL;
  if (pkt->length - pkt->savedpos < 4)
    return 0;
  *length = toint(GET_32BIT(pkt->data + pkt->savedpos));
  pkt->savedpos += 4;
  if ((int)(pkt->length - pkt->savedpos) < *length || *length < 0) {
    *length = 0;
    return 0;
  }
  *p = pkt->data + pkt->savedpos;
  pkt->savedpos += *length;
  return 1;
}
static int sftp_pkt_getattrs(struct sftp_packet *pkt, struct fxp_attrs *ret)
{
  if (!sftp_pkt_getuint32(pkt, &ret->flags))
    return 0;
  if (ret->flags & SSH_FILEXFER_ATTR_SIZE) {
    unsigned long hi, lo;
    if (!sftp_pkt_getuint32(pkt, &hi) || !sftp_pkt_getuint32(pkt, &lo))
      return 0;
    ret->size = uint64_make(hi, lo);
  }
  if (ret->flags & SSH_FILEXFER_ATTR_UIDGID) {
    if (!sftp_pkt_getuint32(pkt, &ret->uid) ||
        !sftp_pkt_getuint32(pkt, &ret->gid))
      return 0;
  }
  if (ret->flags & SSH_FILEXFER_ATTR_PERMISSIONS) {
    if (!sftp_pkt_getuint32(pkt, &ret->permissions))
      return 0;
  }
  if (ret->flags & SSH_FILEXFER_ATTR_ACMODTIME) {
    if (!sftp_pkt_getuint32(pkt, &ret->atime) ||
        !sftp_pkt_getuint32(pkt, &ret->mtime))
      return 0;
  }
  if (ret->flags & SSH_FILEXFER_ATTR_EXTENDED) {
    unsigned long count;
    if (!sftp_pkt_getuint32(pkt, &count))
      return 0;
    while (count--) {
      char *str;
      int len;
      /*
       * We should try to analyse these, if we ever find one
       * we recognise.
       */
      if (!sftp_pkt_getstring(pkt, &str, &len) ||
          !sftp_pkt_getstring(pkt, &str, &len))
        return 0;
    }
  }
  return 1;
}
static void sftp_pkt_free(struct sftp_packet *pkt)
{
  if (pkt->data)
    sfree(pkt->data);
  sfree(pkt);
}

/* ----------------------------------------------------------------------
 * Send and receive packet functions.
 */
int sftp_send(struct sftp_packet *pkt)
{
  int ret;
  PUT_32BIT(pkt->data, pkt->length - 4);
  ret = sftp_senddata(pkt->data, pkt->length);
  sftp_pkt_free(pkt);
  return ret;
}
struct sftp_packet *sftp_recv(void)
{
  struct sftp_packet *pkt;
  char x[4];
  unsigned char uc;

  if (!sftp_recvdata(x, 4))
    return NULL;

  pkt = snew(struct sftp_packet);
  pkt->savedpos = 0;
  pkt->length = pkt->maxlen = GET_32BIT(x);
  pkt->data = snewn(pkt->length, char);

  if (!sftp_recvdata(pkt->data, pkt->length)) {
    sftp_pkt_free(pkt);
    return NULL;
  }

  if (!sftp_pkt_getbyte(pkt, &uc)) {
    sftp_pkt_free(pkt);
    return NULL;
  } else {
    pkt->type = uc;
  }

  return pkt;
}

/* ----------------------------------------------------------------------
 * Request ID allocation and temporary dispatch routines.
 */

#define REQUEST_ID_OFFSET 256

struct sftp_request {
  unsigned id;
  int registered;
  void *userdata;
};

static int sftp_reqcmp(void *av, void *bv)
{
  struct sftp_request *a = (struct sftp_request *)av;
  struct sftp_request *b = (struct sftp_request *)bv;
  if (a->id < b->id)
    return -1;
  if (a->id > b->id)
    return +1;
  return 0;
}
static int sftp_reqfind(void *av, void *bv)
{
  unsigned *a = (unsigned *)av;
  struct sftp_request *b = (struct sftp_request *)bv;
  if (*a < b->id)
    return -1;
  if (*a > b->id)
    return +1;
  return 0;
}

static tree234 *sftp_requests;

static struct sftp_request *sftp_alloc_request(void)
{
  unsigned low, high, mid;
  int tsize;
  struct sftp_request *r;

  if (sftp_requests == NULL)
    sftp_requests = newtree234(sftp_reqcmp);

  /*
   * First-fit allocation of request IDs: always pick the lowest
   * unused one. To do this, binary-search using the counted
   * B-tree to find the largest ID which is in a contiguous
   * sequence from the beginning. (Precisely everything in that
   * sequence must have ID equal to its tree index plus
   * REQUEST_ID_OFFSET.)
   */
  tsize = count234(sftp_requests);

  low = -1;
  high = tsize;
  while (high - low > 1) {
    mid = (high + low) / 2;
    r = index234(sftp_requests, mid);
    if (r->id == mid + REQUEST_ID_OFFSET)
      low = mid; /* this one is fine */
    else
      high = mid; /* this one is past it */
  }
  /*
   * Now low points to either -1, or the tree index of the
   * largest ID in the initial sequence.
   */
  {
    unsigned i = low + 1 + REQUEST_ID_OFFSET;
    assert(NULL == find234(sftp_requests, &i, sftp_reqfind));
  }

  /*
   * So the request ID we need to create is
   * low + 1 + REQUEST_ID_OFFSET.
   */
  r = snew(struct sftp_request);
  r->id = low + 1 + REQUEST_ID_OFFSET;
  r->registered = 0;
  r->userdata = NULL;
  add234(sftp_requests, r);
  return r;
}

void sftp_cleanup_request(void)
{
  if (sftp_requests != NULL) {
    freetree234(sftp_requests);
    sftp_requests = NULL;
  }
}

void sftp_register(struct sftp_request *req)
{
  req->registered = 1;
}

struct sftp_request *sftp_find_request(struct sftp_packet *pktin)
{
  unsigned long id;
  unsigned fid;
  struct sftp_request *req;

  if (!pktin) {
    fxp_internal_error("did not receive a valid SFTP packet\n");
    return NULL;
  }

  if (!sftp_pkt_getuint32(pktin, &id)) {
    fxp_internal_error("did not receive a valid SFTP packet\n");
    return NULL;
  }
  fid = (unsigned)id;
  req = find234(sftp_requests, &fid, sftp_reqfind);

  if (!req || !req->registered) {
    fxp_internal_error("request ID mismatch\n");
    return NULL;
  }

  del234(sftp_requests, req);

  return req;
}

/* ----------------------------------------------------------------------
 * String handling routines.
 */

static char *mkstr(char *s, int len)
{
  char *p = snewn(len + 1, char);
  memcpy(p, s, len);
  p[len] = '\0';
  return p;
}

/* ----------------------------------------------------------------------
 * SFTP primitives.
 */

/*
 * Deal with (and free) an FXP_STATUS packet. Return 1 if
 * SSH_FX_OK, 0 if SSH_FX_EOF, and -1 for anything else (error).
 * Also place the status into fxp_errtype.
 */
static int fxp_got_status(struct sftp_packet *pktin)
{
  static const char *const messages[] = {
      /* SSH_FX_OK. The only time we will display a _message_ for this
       * is if we were expecting something other than FXP_STATUS on
       * success, so this is actually an error message! */
      "unexpected OK response",
      "end of file",
      "no such file or directory",
      "permission denied",
      "failure",
      "bad message",
      "no connection",
      "connection lost",
      "operation unsupported",
  };

  if (pktin->type != SSH_FXP_STATUS) {
    fxp_error_message = "expected FXP_STATUS packet";
    fxp_errtype = -1;
  } else {
    unsigned long ul;
    if (!sftp_pkt_getuint32(pktin, &ul)) {
      fxp_error_message = "malformed FXP_STATUS packet";
      fxp_errtype = -1;
    } else {
      fxp_errtype = ul;
      if (fxp_errtype < 0 ||
          fxp_errtype >= sizeof(messages) / sizeof(*messages))
        fxp_error_message = "unknown error code";
      else
        fxp_error_message = messages[fxp_errtype];
    }
  }

  if (fxp_errtype == SSH_FX_OK)
    return 1;
  else if (fxp_errtype == SSH_FX_EOF)
    return 0;
  else
    return -1;
}

static void fxp_internal_error(const char *msg)
{
  fxp_error_message = msg;
  fxp_errtype = -1;
}

const char *fxp_error(void)
{
  return fxp_error_message;
}

int fxp_error_type(void)
{
  return fxp_errtype;
}

/*
 * Perform exchange of init/version packets. Return 0 on failure.
 */
int fxp_init(void)
{
  struct sftp_packet *pktout, *pktin;
  unsigned long remotever;

  pktout = sftp_pkt_init(SSH_FXP_INIT);
  sftp_pkt_adduint32(pktout, SFTP_PROTO_VERSION);
  sftp_send(pktout);

  pktin = sftp_recv();
  if (!pktin) {
    fxp_internal_error("could not connect");
    return 0;
  }
  if (pktin->type != SSH_FXP_VERSION) {
    fxp_internal_error("did not receive FXP_VERSION");
    sftp_pkt_free(pktin);
    return 0;
  }
  if (!sftp_pkt_getuint32(pktin, &remotever)) {
    fxp_internal_error("malformed FXP_VERSION packet");
    sftp_pkt_free(pktin);
    return 0;
  }
  if (remotever > SFTP_PROTO_VERSION) {
    fxp_internal_error("remote protocol is more advanced than we support");
    sftp_pkt_free(pktin);
    return 0;
  }
  /*
   * In principle, this packet might also contain extension-
   * string pairs. We should work through them and look for any
   * we recognise. In practice we don't currently do so because
   * we know we don't recognise _any_.
   */
  sftp_pkt_free(pktin);

  return 1;
}

/*
 * Canonify a pathname.
 */
struct sftp_request *fxp_realpath_send(const char *path)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_REALPATH);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring_start(pktout);
  sftp_pkt_addstring_str(pktout, path);
  sftp_send(pktout);

  return req;
}

char *fxp_realpath_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  sfree(req);

  if (pktin->type == SSH_FXP_NAME) {
    unsigned long count;
    char *path;
    int len;

    if (!sftp_pkt_getuint32(pktin, &count) || count != 1) {
      fxp_internal_error("REALPATH did not return name count of 1\n");
      sftp_pkt_free(pktin);
      return NULL;
    }
    if (!sftp_pkt_getstring(pktin, &path, &len)) {
      fxp_internal_error("REALPATH returned malformed FXP_NAME\n");
      sftp_pkt_free(pktin);
      return NULL;
    }
    path = mkstr(path, len);
    sftp_pkt_free(pktin);
    return path;
  } else {
    fxp_got_status(pktin);
    sftp_pkt_free(pktin);
    return NULL;
  }
}

/*
 * Open a file.
 */
struct sftp_request *fxp_open_send(const char *path,
                                   int type,
                                   struct fxp_attrs *attrs)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_OPEN);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring(pktout, path);
  sftp_pkt_adduint32(pktout, type);
  if (attrs)
    sftp_pkt_addattrs(pktout, *attrs);
  else
    sftp_pkt_adduint32(pktout, 0); /* empty ATTRS structure */
  sftp_send(pktout);

  return req;
}

struct fxp_handle *fxp_open_recv(struct sftp_packet *pktin,
                                 struct sftp_request *req)
{
  sfree(req);

  if (pktin->type == SSH_FXP_HANDLE) {
    char *hstring;
    struct fxp_handle *handle;
    int len;

    if (!sftp_pkt_getstring(pktin, &hstring, &len)) {
      fxp_internal_error("OPEN returned malformed FXP_HANDLE\n");
      sftp_pkt_free(pktin);
      return NULL;
    }
    handle = snew(struct fxp_handle);
    handle->hstring = mkstr(hstring, len);
    handle->hlen = len;
    sftp_pkt_free(pktin);
    return handle;
  } else {
    fxp_got_status(pktin);
    sftp_pkt_free(pktin);
    return NULL;
  }
}

/*
 * Open a directory.
 */
struct sftp_request *fxp_opendir_send(const char *path)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_OPENDIR);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring(pktout, path);
  sftp_send(pktout);

  return req;
}

struct fxp_handle *fxp_opendir_recv(struct sftp_packet *pktin,
                                    struct sftp_request *req)
{
  sfree(req);
  if (pktin->type == SSH_FXP_HANDLE) {
    char *hstring;
    struct fxp_handle *handle;
    int len;

    if (!sftp_pkt_getstring(pktin, &hstring, &len)) {
      fxp_internal_error("OPENDIR returned malformed FXP_HANDLE\n");
      sftp_pkt_free(pktin);
      return NULL;
    }
    handle = snew(struct fxp_handle);
    handle->hstring = mkstr(hstring, len);
    handle->hlen = len;
    sftp_pkt_free(pktin);
    return handle;
  } else {
    fxp_got_status(pktin);
    sftp_pkt_free(pktin);
    return NULL;
  }
}

/*
 * Close a file/dir.
 */
struct sftp_request *fxp_close_send(struct fxp_handle *handle)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_CLOSE);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring_start(pktout);
  sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
  sftp_send(pktout);

  sfree(handle->hstring);
  sfree(handle);

  return req;
}

int fxp_close_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  sfree(req);
  fxp_got_status(pktin);
  sftp_pkt_free(pktin);
  return fxp_errtype == SSH_FX_OK;
}

struct sftp_request *fxp_mkdir_send(const char *path)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_MKDIR);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring(pktout, path);
  sftp_pkt_adduint32(pktout, 0); /* (FIXME) empty ATTRS structure */
  sftp_send(pktout);

  return req;
}

int fxp_mkdir_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  int id;
  sfree(req);
  id = fxp_got_status(pktin);
  sftp_pkt_free(pktin);
  if (id != 1) {
    return 0;
  }
  return 1;
}

struct sftp_request *fxp_rmdir_send(const char *path)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_RMDIR);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring(pktout, path);
  sftp_send(pktout);

  return req;
}

int fxp_rmdir_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  int id;
  sfree(req);
  id = fxp_got_status(pktin);
  sftp_pkt_free(pktin);
  if (id != 1) {
    return 0;
  }
  return 1;
}

struct sftp_request *fxp_remove_send(const char *fname)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_REMOVE);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring(pktout, fname);
  sftp_send(pktout);

  return req;
}

int fxp_remove_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  int id;
  sfree(req);
  id = fxp_got_status(pktin);
  sftp_pkt_free(pktin);
  if (id != 1) {
    return 0;
  }
  return 1;
}

struct sftp_request *fxp_rename_send(const char *srcfname, const char *dstfname)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_RENAME);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring(pktout, srcfname);
  sftp_pkt_addstring(pktout, dstfname);
  sftp_send(pktout);

  return req;
}

int fxp_rename_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  int id;
  sfree(req);
  id = fxp_got_status(pktin);
  sftp_pkt_free(pktin);
  if (id != 1) {
    return 0;
  }
  return 1;
}

/*
 * Retrieve the attributes of a file. We have fxp_stat which works
 * on filenames, and fxp_fstat which works on open file handles.
 */
struct sftp_request *fxp_stat_send(const char *fname)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_STAT);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring(pktout, fname);
  sftp_send(pktout);

  return req;
}

int fxp_stat_recv(struct sftp_packet *pktin,
                  struct sftp_request *req,
                  struct fxp_attrs *attrs)
{
  sfree(req);
  if (pktin->type == SSH_FXP_ATTRS) {
    if (!sftp_pkt_getattrs(pktin, attrs)) {
      fxp_internal_error("malformed SSH_FXP_ATTRS packet");
      sftp_pkt_free(pktin);
      return 0;
    }
    sftp_pkt_free(pktin);
    return 1;
  } else {
    fxp_got_status(pktin);
    sftp_pkt_free(pktin);
    return 0;
  }
}

struct sftp_request *fxp_fstat_send(struct fxp_handle *handle)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_FSTAT);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring_start(pktout);
  sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
  sftp_send(pktout);

  return req;
}

int fxp_fstat_recv(struct sftp_packet *pktin,
                   struct sftp_request *req,
                   struct fxp_attrs *attrs)
{
  sfree(req);
  if (pktin->type == SSH_FXP_ATTRS) {
    if (!sftp_pkt_getattrs(pktin, attrs)) {
      fxp_internal_error("malformed SSH_FXP_ATTRS packet");
      sftp_pkt_free(pktin);
      return 0;
    }
    sftp_pkt_free(pktin);
    return 1;
  } else {
    fxp_got_status(pktin);
    sftp_pkt_free(pktin);
    return 0;
  }
}

/*
 * Set the attributes of a file.
 */
struct sftp_request *fxp_setstat_send(const char *fname, struct fxp_attrs attrs)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_SETSTAT);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring(pktout, fname);
  sftp_pkt_addattrs(pktout, attrs);
  sftp_send(pktout);

  return req;
}

int fxp_setstat_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  int id;
  sfree(req);
  id = fxp_got_status(pktin);
  sftp_pkt_free(pktin);
  if (id != 1) {
    return 0;
  }
  return 1;
}

struct sftp_request *fxp_fsetstat_send(struct fxp_handle *handle,
                                       struct fxp_attrs attrs)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_FSETSTAT);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring_start(pktout);
  sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
  sftp_pkt_addattrs(pktout, attrs);
  sftp_send(pktout);

  return req;
}

int fxp_fsetstat_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  int id;
  sfree(req);
  id = fxp_got_status(pktin);
  sftp_pkt_free(pktin);
  if (id != 1) {
    return 0;
  }
  return 1;
}

/*
 * Read from a file. Returns the number of bytes read, or -1 on an
 * error, or possibly 0 if EOF. (I'm not entirely sure whether it
 * will return 0 on EOF, or return -1 and store SSH_FX_EOF in the
 * error indicator. It might even depend on the SFTP server.)
 */
struct sftp_request *fxp_read_send(struct fxp_handle *handle,
                                   uint64 offset,
                                   int len)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_READ);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring_start(pktout);
  sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
  sftp_pkt_adduint64(pktout, offset);
  sftp_pkt_adduint32(pktout, len);
  sftp_send(pktout);

  return req;
}

int fxp_read_recv(struct sftp_packet *pktin,
                  struct sftp_request *req,
                  char *buffer,
                  int len)
{
  sfree(req);
  if (pktin->type == SSH_FXP_DATA) {
    char *str;
    int rlen;

    if (!sftp_pkt_getstring(pktin, &str, &rlen)) {
      fxp_internal_error("READ returned malformed SSH_FXP_DATA packet");
      sftp_pkt_free(pktin);
      return -1;
    }

    if (rlen > len || rlen < 0) {
      fxp_internal_error("READ returned more bytes than requested");
      sftp_pkt_free(pktin);
      return -1;
    }

    memcpy(buffer, str, rlen);
    sftp_pkt_free(pktin);
    return rlen;
  } else {
    fxp_got_status(pktin);
    sftp_pkt_free(pktin);
    return -1;
  }
}

/*
 * Read from a directory.
 */
struct sftp_request *fxp_readdir_send(struct fxp_handle *handle)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_READDIR);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring_start(pktout);
  sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
  sftp_send(pktout);

  return req;
}

struct fxp_names *fxp_readdir_recv(struct sftp_packet *pktin,
                                   struct sftp_request *req)
{
  sfree(req);
  if (pktin->type == SSH_FXP_NAME) {
    struct fxp_names *ret;
    unsigned long i;

    /*
     * Sanity-check the number of names. Minimum is obviously
     * zero. Maximum is the remaining space in the packet
     * divided by the very minimum length of a name, which is
     * 12 bytes (4 for an empty filename, 4 for an empty
     * longname, 4 for a set of attribute flags indicating that
     * no other attributes are supplied).
     */
    if (!sftp_pkt_getuint32(pktin, &i) ||
        i > (pktin->length - pktin->savedpos) / 12) {
      fxp_internal_error("malformed FXP_NAME packet");
      sftp_pkt_free(pktin);
      return NULL;
    }

    /*
     * Ensure the implicit multiplication in the snewn() call
     * doesn't suffer integer overflow and cause us to malloc
     * too little space.
     */
    if (i > INT_MAX / sizeof(struct fxp_name)) {
      fxp_internal_error("unreasonably large FXP_NAME packet");
      sftp_pkt_free(pktin);
      return NULL;
    }

    ret = snew(struct fxp_names);
    ret->nnames = i;
    ret->names = snewn(ret->nnames, struct fxp_name);
    for (i = 0; i < (unsigned long)ret->nnames; i++) {
      char *str1, *str2;
      int len1, len2;
      if (!sftp_pkt_getstring(pktin, &str1, &len1) ||
          !sftp_pkt_getstring(pktin, &str2, &len2) ||
          !sftp_pkt_getattrs(pktin, &ret->names[i].attrs)) {
        fxp_internal_error("malformed FXP_NAME packet");
        while (i--) {
          sfree(ret->names[i].filename);
          sfree(ret->names[i].longname);
        }
        sfree(ret->names);
        sfree(ret);
        sfree(pktin);
        return NULL;
      }
      ret->names[i].filename = mkstr(str1, len1);
      ret->names[i].longname = mkstr(str2, len2);
    }
    sftp_pkt_free(pktin);
    return ret;
  } else {
    fxp_got_status(pktin);
    sftp_pkt_free(pktin);
    return NULL;
  }
}

/*
 * Write to a file. Returns 0 on error, 1 on OK.
 */
struct sftp_request *fxp_write_send(struct fxp_handle *handle,
                                    char *buffer,
                                    uint64 offset,
                                    int len)
{
  struct sftp_request *req = sftp_alloc_request();
  struct sftp_packet *pktout;

  pktout = sftp_pkt_init(SSH_FXP_WRITE);
  sftp_pkt_adduint32(pktout, req->id);
  sftp_pkt_addstring_start(pktout);
  sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
  sftp_pkt_adduint64(pktout, offset);
  sftp_pkt_addstring_start(pktout);
  sftp_pkt_addstring_data(pktout, buffer, len);
  sftp_send(pktout);

  return req;
}

int fxp_write_recv(struct sftp_packet *pktin, struct sftp_request *req)
{
  sfree(req);
  fxp_got_status(pktin);
  sftp_pkt_free(pktin);
  return fxp_errtype == SSH_FX_OK;
}

/*
 * Free up an fxp_names structure.
 */
void fxp_free_names(struct fxp_names *names)
{
  int i;

  for (i = 0; i < names->nnames; i++) {
    sfree(names->names[i].filename);
    sfree(names->names[i].longname);
  }
  sfree(names->names);
  sfree(names);
}

/*
 * Duplicate an fxp_name structure.
 */
struct fxp_name *fxp_dup_name(struct fxp_name *name)
{
  struct fxp_name *ret;
  ret = snew(struct fxp_name);
  ret->filename = dupstr(name->filename);
  ret->longname = dupstr(name->longname);
  ret->attrs = name->attrs; /* structure copy */
  return ret;
}

/*
 * Free up an fxp_name structure.
 */
void fxp_free_name(struct fxp_name *name)
{
  sfree(name->filename);
  sfree(name->longname);
  sfree(name);
}

/*
 * Store user data in an sftp_request structure.
 */
void *fxp_get_userdata(struct sftp_request *req)
{
  return req->userdata;
}

void fxp_set_userdata(struct sftp_request *req, void *data)
{
  req->userdata = data;
}

/*
 * A wrapper to go round fxp_read_* and fxp_write_*, which manages
 * the queueing of multiple read/write requests.
 */

struct req {
  char *buffer;
  int len, retlen, complete;
  uint64 offset;
  struct req *next, *prev;
};

struct fxp_xfer {
  uint64 offset, furthestdata, filesize;
  int req_totalsize, req_maxsize, eof, err;
  struct fxp_handle *fh;
  struct req *head, *tail;
};

static struct fxp_xfer *xfer_init(struct fxp_handle *fh, uint64 offset)
{
  struct fxp_xfer *xfer = snew(struct fxp_xfer);

  xfer->fh = fh;
  xfer->offset = offset;
  xfer->head = xfer->tail = NULL;
  xfer->req_totalsize = 0;
  xfer->req_maxsize = 1048576;
  xfer->err = 0;
  xfer->filesize = uint64_make(ULONG_MAX, ULONG_MAX);
  xfer->furthestdata = uint64_make(0, 0);

  return xfer;
}

int xfer_done(struct fxp_xfer *xfer)
{
  /*
   * We're finished if we've seen EOF _and_ there are no
   * outstanding requests.
   */
  return (xfer->eof || xfer->err) && !xfer->head;
}

void xfer_download_queue(struct fxp_xfer *xfer)
{
  while (xfer->req_totalsize < xfer->req_maxsize && !xfer->eof && !xfer->err) {
    /*
     * Queue a new read request.
     */
    struct req *rr;
    struct sftp_request *req;

    rr = snew(struct req);
    rr->offset = xfer->offset;
    rr->complete = 0;
    if (xfer->tail) {
      xfer->tail->next = rr;
      rr->prev = xfer->tail;
    } else {
      xfer->head = rr;
      rr->prev = NULL;
    }
    xfer->tail = rr;
    rr->next = NULL;

    rr->len = 32768;
    rr->buffer = snewn(rr->len, char);
    sftp_register(req = fxp_read_send(xfer->fh, rr->offset, rr->len));
    fxp_set_userdata(req, rr);

    xfer->offset = uint64_add32(xfer->offset, rr->len);
    xfer->req_totalsize += rr->len;

#ifdef DEBUG_DOWNLOAD
    {
      char buf[40];
      uint64_decimal(rr->offset, buf);
      printf("queueing read request %p at %s\n", rr, buf);
    }
#endif
  }
}

struct fxp_xfer *xfer_download_init(struct fxp_handle *fh, uint64 offset)
{
  struct fxp_xfer *xfer = xfer_init(fh, offset);

  xfer->eof = FALSE;
  xfer_download_queue(xfer);

  return xfer;
}

/*
 * Returns INT_MIN to indicate that it didn't even get as far as
 * fxp_read_recv and hence has not freed pktin.
 */
int xfer_download_gotpkt(struct fxp_xfer *xfer, struct sftp_packet *pktin)
{
  struct sftp_request *rreq;
  struct req *rr;

  rreq = sftp_find_request(pktin);
  if (!rreq)
    return INT_MIN; /* this packet doesn't even make sense */
  rr = (struct req *)fxp_get_userdata(rreq);
  if (!rr) {
    fxp_internal_error("request ID is not part of the current download");
    return INT_MIN; /* this packet isn't ours */
  }
  rr->retlen = fxp_read_recv(pktin, rreq, rr->buffer, rr->len);
#ifdef DEBUG_DOWNLOAD
  printf("read request %p has returned [%d]\n", rr, rr->retlen);
#endif

  if ((rr->retlen < 0 && fxp_error_type() == SSH_FX_EOF) || rr->retlen == 0) {
    xfer->eof = TRUE;
    rr->retlen = 0;
    rr->complete = -1;
#ifdef DEBUG_DOWNLOAD
    printf("setting eof\n");
#endif
  } else if (rr->retlen < 0) {
    /* some error other than EOF; signal it back to caller */
    xfer_set_error(xfer);
    rr->complete = -1;
    return -1;
  }

  rr->complete = 1;

  /*
   * Special case: if we have received fewer bytes than we
   * actually read, we should do something. For the moment I'll
   * just throw an ersatz FXP error to signal this; the SFTP
   * draft I've got says that it can't happen except on special
   * files, in which case seeking probably has very little
   * meaning and so queueing an additional read request to fill
   * up the gap sounds like the wrong answer. I'm not sure what I
   * should be doing here - if it _was_ a special file, I suspect
   * I simply shouldn't have been queueing multiple requests in
   * the first place...
   */
  if (rr->retlen > 0 && uint64_compare(xfer->furthestdata, rr->offset) < 0) {
    xfer->furthestdata = rr->offset;
#ifdef DEBUG_DOWNLOAD
    {
      char buf[40];
      uint64_decimal(xfer->furthestdata, buf);
      printf("setting furthestdata = %s\n", buf);
    }
#endif
  }

  if (rr->retlen < rr->len) {
    uint64 filesize =
        uint64_add32(rr->offset, (rr->retlen < 0 ? 0 : rr->retlen));
#ifdef DEBUG_DOWNLOAD
    {
      char buf[40];
      uint64_decimal(filesize, buf);
      printf("short block! trying filesize = %s\n", buf);
    }
#endif
    if (uint64_compare(xfer->filesize, filesize) > 0) {
      xfer->filesize = filesize;
#ifdef DEBUG_DOWNLOAD
      printf("actually changing filesize\n");
#endif
    }
  }

  if (uint64_compare(xfer->furthestdata, xfer->filesize) > 0) {
    fxp_error_message = "received a short buffer from FXP_READ, but not"
                        " at EOF";
    fxp_errtype = -1;
    xfer_set_error(xfer);
    return -1;
  }

  return 1;
}

void xfer_set_error(struct fxp_xfer *xfer)
{
  xfer->err = 1;
}

int xfer_download_data(struct fxp_xfer *xfer, void **buf, int *len)
{
  void *retbuf = NULL;
  int retlen = 0;

  /*
   * Discard anything at the head of the rr queue with complete <
   * 0; return the first thing with complete > 0.
   */
  while (xfer->head && xfer->head->complete && !retbuf) {
    struct req *rr = xfer->head;

    if (rr->complete > 0) {
      retbuf = rr->buffer;
      retlen = rr->retlen;
#ifdef DEBUG_DOWNLOAD
      printf("handing back data from read request %p\n", rr);
#endif
    }
#ifdef DEBUG_DOWNLOAD
    else
      printf("skipping failed read request %p\n", rr);
#endif

    xfer->head = xfer->head->next;
    if (xfer->head)
      xfer->head->prev = NULL;
    else
      xfer->tail = NULL;
    xfer->req_totalsize -= rr->len;
    sfree(rr);
  }

  if (retbuf) {
    *buf = retbuf;
    *len = retlen;
    return 1;
  } else
    return 0;
}

struct fxp_xfer *xfer_upload_init(struct fxp_handle *fh, uint64 offset)
{
  struct fxp_xfer *xfer = xfer_init(fh, offset);

  /*
   * We set `eof' to 1 because this will cause xfer_done() to
   * return true iff there are no outstanding requests. During an
   * upload, our caller will be responsible for working out
   * whether all the data has been sent, so all it needs to know
   * from us is whether the outstanding requests have been
   * handled once that's done.
   */
  xfer->eof = 1;

  return xfer;
}

int xfer_upload_ready(struct fxp_xfer *xfer)
{
  if (sftp_sendbuffer() == 0)
    return 1;
  else
    return 0;
}

void xfer_upload_data(struct fxp_xfer *xfer, char *buffer, int len)
{
  struct req *rr;
  struct sftp_request *req;

  rr = snew(struct req);
  rr->offset = xfer->offset;
  rr->complete = 0;
  if (xfer->tail) {
    xfer->tail->next = rr;
    rr->prev = xfer->tail;
  } else {
    xfer->head = rr;
    rr->prev = NULL;
  }
  xfer->tail = rr;
  rr->next = NULL;

  rr->len = len;
  rr->buffer = NULL;
  sftp_register(req = fxp_write_send(xfer->fh, buffer, rr->offset, len));
  fxp_set_userdata(req, rr);

  xfer->offset = uint64_add32(xfer->offset, rr->len);
  xfer->req_totalsize += rr->len;

#ifdef DEBUG_UPLOAD
  {
    char buf[40];
    uint64_decimal(rr->offset, buf);
    printf("queueing write request %p at %s [len %d]\n", rr, buf, len);
  }
#endif
}

/*
 * Returns INT_MIN to indicate that it didn't even get as far as
 * fxp_write_recv and hence has not freed pktin.
 */
int xfer_upload_gotpkt(struct fxp_xfer *xfer, struct sftp_packet *pktin)
{
  struct sftp_request *rreq;
  struct req *rr, *prev, *next;
  int ret;

  rreq = sftp_find_request(pktin);
  if (!rreq)
    return INT_MIN; /* this packet doesn't even make sense */
  rr = (struct req *)fxp_get_userdata(rreq);
  if (!rr) {
    fxp_internal_error("request ID is not part of the current upload");
    return INT_MIN; /* this packet isn't ours */
  }
  ret = fxp_write_recv(pktin, rreq);
#ifdef DEBUG_UPLOAD
  printf("write request %p has returned [%d]\n", rr, ret);
#endif

  /*
   * Remove this one from the queue.
   */
  prev = rr->prev;
  next = rr->next;
  if (prev)
    prev->next = next;
  else
    xfer->head = next;
  if (next)
    next->prev = prev;
  else
    xfer->tail = prev;
  xfer->req_totalsize -= rr->len;
  sfree(rr);

  if (!ret)
    return -1;

  return 1;
}

void xfer_cleanup(struct fxp_xfer *xfer)
{
  struct req *rr;
  while (xfer->head) {
    rr = xfer->head;
    xfer->head = xfer->head->next;
    sfree(rr->buffer);
    sfree(rr);
  }
  sfree(xfer);
}