X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/7d2c1789c5a8ccf8a767fb11082bff34c1b7c5aa..479fe1ba750b1cda0ad3a159f2727619555436b0:/sftp.c

diff --git a/sftp.c b/sftp.c
index e1f60173..a55262a7 100644
--- a/sftp.c
+++ b/sftp.c
@@ -6,9 +6,11 @@
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>
+#include <limits.h>
 
 #include "misc.h"
 #include "int64.h"
+#include "tree234.h"
 #include "sftp.h"
 
 #define GET_32BIT(cp) \
@@ -33,6 +35,8 @@ struct sftp_packet {
 static const char *fxp_error_message;
 static int fxp_errtype;
 
+static void fxp_internal_error(char *msg);
+
 /* ----------------------------------------------------------------------
  * SFTP packet construction functions.
  */
@@ -40,7 +44,7 @@ static void sftp_pkt_ensure(struct sftp_packet *pkt, int length)
 {
     if (pkt->maxlen < length) {
 	pkt->maxlen = length + 256;
-	pkt->data = srealloc(pkt->data, pkt->maxlen);
+	pkt->data = sresize(pkt->data, pkt->maxlen, char);
     }
 }
 static void sftp_pkt_adddata(struct sftp_packet *pkt, void *data, int len)
@@ -56,7 +60,7 @@ static void sftp_pkt_addbyte(struct sftp_packet *pkt, unsigned char byte)
 static struct sftp_packet *sftp_pkt_init(int pkt_type)
 {
     struct sftp_packet *pkt;
-    pkt = smalloc(sizeof(struct sftp_packet));
+    pkt = snew(struct sftp_packet);
     pkt->data = NULL;
     pkt->savedpos = -1;
     pkt->length = 0;
@@ -64,10 +68,12 @@ static struct sftp_packet *sftp_pkt_init(int pkt_type)
     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_adduint32(struct sftp_packet *pkt,
 			       unsigned long value)
 {
@@ -228,10 +234,10 @@ struct sftp_packet *sftp_recv(void)
     if (!sftp_recvdata(x, 4))
 	return NULL;
 
-    pkt = smalloc(sizeof(struct sftp_packet));
+    pkt = snew(struct sftp_packet);
     pkt->savedpos = 0;
     pkt->length = pkt->maxlen = GET_32BIT(x);
-    pkt->data = smalloc(pkt->length);
+    pkt->data = snewn(pkt->length, char);
 
     if (!sftp_recvdata(pkt->data, pkt->length)) {
 	sftp_pkt_free(pkt);
@@ -244,12 +250,134 @@ struct sftp_packet *sftp_recv(void)
 }
 
 /* ----------------------------------------------------------------------
+ * 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;
+    struct sftp_request *req;
+
+    if (!pktin) {
+	fxp_internal_error("did not receive a valid SFTP packet\n");
+	return NULL;
+    }
+
+    id = sftp_pkt_getuint32(pktin);
+    req = find234(sftp_requests, &id, sftp_reqfind);
+
+    if (!req || !req->registered) {
+	fxp_internal_error("request ID mismatch\n");
+        sftp_pkt_free(pktin);
+	return NULL;
+    }
+
+    del234(sftp_requests, req);
+
+    return req;
+}
+
+/* ----------------------------------------------------------------------
  * String handling routines.
  */
 
 static char *mkstr(char *s, int len)
 {
-    char *p = smalloc(len + 1);
+    char *p = snewn(len + 1, char);
     memcpy(p, s, len);
     p[len] = '\0';
     return p;
@@ -360,27 +488,24 @@ int fxp_init(void)
 /*
  * Canonify a pathname.
  */
-char *fxp_realpath(char *path)
+struct sftp_request *fxp_realpath_send(char *path)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_REALPATH);
-    sftp_pkt_adduint32(pktout, 0x123); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring_start(pktout);
     sftp_pkt_addstring_str(pktout, path);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return NULL;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x123) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return NULL;
-    }
+
+    return req;
+}
+
+char *fxp_realpath_recv(struct sftp_packet *pktin, struct sftp_request *req)
+{
+    sfree(req);
+
     if (pktin->type == SSH_FXP_NAME) {
 	int count;
 	char *path;
@@ -411,28 +536,26 @@ char *fxp_realpath(char *path)
 /*
  * Open a file.
  */
-struct fxp_handle *fxp_open(char *path, int type)
+struct sftp_request *fxp_open_send(char *path, int type)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_OPEN);
-    sftp_pkt_adduint32(pktout, 0x567); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring(pktout, path);
     sftp_pkt_adduint32(pktout, type);
     sftp_pkt_adduint32(pktout, 0);     /* (FIXME) empty ATTRS structure */
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return NULL;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x567) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return NULL;
-    }
+
+    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;
@@ -444,7 +567,7 @@ struct fxp_handle *fxp_open(char *path, int type)
             sftp_pkt_free(pktin);
 	    return NULL;
 	}
-	handle = smalloc(sizeof(struct fxp_handle));
+	handle = snew(struct fxp_handle);
 	handle->hstring = mkstr(hstring, len);
 	handle->hlen = len;
 	sftp_pkt_free(pktin);
@@ -459,26 +582,23 @@ struct fxp_handle *fxp_open(char *path, int type)
 /*
  * Open a directory.
  */
-struct fxp_handle *fxp_opendir(char *path)
+struct sftp_request *fxp_opendir_send(char *path)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_OPENDIR);
-    sftp_pkt_adduint32(pktout, 0x456); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring(pktout, path);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return NULL;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x456) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return NULL;
-    }
+
+    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;
@@ -490,7 +610,7 @@ struct fxp_handle *fxp_opendir(char *path)
             sftp_pkt_free(pktin);
 	    return NULL;
 	}
-	handle = smalloc(sizeof(struct fxp_handle));
+	handle = snew(struct fxp_handle);
 	handle->hstring = mkstr(hstring, len);
 	handle->hlen = len;
 	sftp_pkt_free(pktin);
@@ -505,54 +625,48 @@ struct fxp_handle *fxp_opendir(char *path)
 /*
  * Close a file/dir.
  */
-void fxp_close(struct fxp_handle *handle)
+struct sftp_request *fxp_close_send(struct fxp_handle *handle)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_CLOSE);
-    sftp_pkt_adduint32(pktout, 0x789); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring_start(pktout);
     sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x789) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return;
-    }
-    fxp_got_status(pktin);
-    sftp_pkt_free(pktin);
+
     sfree(handle->hstring);
     sfree(handle);
+
+    return req;
 }
 
-int fxp_mkdir(char *path)
+void fxp_close_recv(struct sftp_packet *pktin, struct sftp_request *req)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    sfree(req);
+    fxp_got_status(pktin);
+    sftp_pkt_free(pktin);
+}
+
+struct sftp_request *fxp_mkdir_send(char *path)
+{
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_MKDIR);
-    sftp_pkt_adduint32(pktout, 0x234); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring(pktout, path);
     sftp_pkt_adduint32(pktout, 0);     /* (FIXME) empty ATTRS structure */
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x234) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
+
+    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) {
@@ -561,26 +675,23 @@ int fxp_mkdir(char *path)
     return 1;
 }
 
-int fxp_rmdir(char *path)
+struct sftp_request *fxp_rmdir_send(char *path)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_RMDIR);
-    sftp_pkt_adduint32(pktout, 0x345); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring(pktout, path);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x345) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
+
+    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) {
@@ -589,26 +700,23 @@ int fxp_rmdir(char *path)
     return 1;
 }
 
-int fxp_remove(char *fname)
+struct sftp_request *fxp_remove_send(char *fname)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_REMOVE);
-    sftp_pkt_adduint32(pktout, 0x678); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring(pktout, fname);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x678) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
+
+    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) {
@@ -617,27 +725,24 @@ int fxp_remove(char *fname)
     return 1;
 }
 
-int fxp_rename(char *srcfname, char *dstfname)
+struct sftp_request *fxp_rename_send(char *srcfname, char *dstfname)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_RENAME);
-    sftp_pkt_adduint32(pktout, 0x678); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring(pktout, srcfname);
     sftp_pkt_addstring(pktout, dstfname);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x678) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
+
+    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) {
@@ -650,27 +755,23 @@ int fxp_rename(char *srcfname, char *dstfname)
  * Retrieve the attributes of a file. We have fxp_stat which works
  * on filenames, and fxp_fstat which works on open file handles.
  */
-int fxp_stat(char *fname, struct fxp_attrs *attrs)
+struct sftp_request *fxp_stat_send(char *fname)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_STAT);
-    sftp_pkt_adduint32(pktout, 0x678); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring(pktout, fname);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x678) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
 
+    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) {
 	*attrs = sftp_pkt_getattrs(pktin);
         sftp_pkt_free(pktin);
@@ -682,28 +783,24 @@ int fxp_stat(char *fname, struct fxp_attrs *attrs)
     }
 }
 
-int fxp_fstat(struct fxp_handle *handle, struct fxp_attrs *attrs)
+struct sftp_request *fxp_fstat_send(struct fxp_handle *handle)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_FSTAT);
-    sftp_pkt_adduint32(pktout, 0x678); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring_start(pktout);
     sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x678) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
 
+    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) {
 	*attrs = sftp_pkt_getattrs(pktin);
         sftp_pkt_free(pktin);
@@ -718,27 +815,24 @@ int fxp_fstat(struct fxp_handle *handle, struct fxp_attrs *attrs)
 /*
  * Set the attributes of a file.
  */
-int fxp_setstat(char *fname, struct fxp_attrs attrs)
+struct sftp_request *fxp_setstat_send(char *fname, struct fxp_attrs attrs)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_SETSTAT);
-    sftp_pkt_adduint32(pktout, 0x678); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring(pktout, fname);
     sftp_pkt_addattrs(pktout, attrs);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x678) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
+
+    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) {
@@ -746,28 +840,27 @@ int fxp_setstat(char *fname, struct fxp_attrs attrs)
     }
     return 1;
 }
-int fxp_fsetstat(struct fxp_handle *handle, struct fxp_attrs attrs)
+
+struct sftp_request *fxp_fsetstat_send(struct fxp_handle *handle,
+				       struct fxp_attrs attrs)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_FSETSTAT);
-    sftp_pkt_adduint32(pktout, 0x678); /* request id */
+    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);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0x678) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
+
+    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) {
@@ -782,30 +875,27 @@ int fxp_fsetstat(struct fxp_handle *handle, struct fxp_attrs attrs)
  * 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.)
  */
-int fxp_read(struct fxp_handle *handle, char *buffer, uint64 offset,
-	     int len)
+struct sftp_request *fxp_read_send(struct fxp_handle *handle,
+				   uint64 offset, int len)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_READ);
-    sftp_pkt_adduint32(pktout, 0xBCD); /* request id */
+    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);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return -1;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0xBCD) {
-	fxp_internal_error("request ID mismatch");
-        sftp_pkt_free(pktin);
-	return -1;
-    }
+
+    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;
@@ -831,33 +921,30 @@ int fxp_read(struct fxp_handle *handle, char *buffer, uint64 offset,
 /*
  * Read from a directory.
  */
-struct fxp_names *fxp_readdir(struct fxp_handle *handle)
+struct sftp_request *fxp_readdir_send(struct fxp_handle *handle)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_READDIR);
-    sftp_pkt_adduint32(pktout, 0xABC); /* request id */
+    sftp_pkt_adduint32(pktout, req->id);
     sftp_pkt_addstring_start(pktout);
     sftp_pkt_addstring_data(pktout, handle->hstring, handle->hlen);
     sftp_send(pktout);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return NULL;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0xABC) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return NULL;
-    }
+
+    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;
 	int i;
-	ret = smalloc(sizeof(struct fxp_names));
+	ret = snew(struct fxp_names);
 	ret->nnames = sftp_pkt_getuint32(pktin);
-	ret->names = smalloc(ret->nnames * sizeof(struct fxp_name));
+	ret->names = snewn(ret->nnames, struct fxp_name);
 	for (i = 0; i < ret->nnames; i++) {
 	    char *str;
 	    int len;
@@ -879,31 +966,27 @@ struct fxp_names *fxp_readdir(struct fxp_handle *handle)
 /*
  * Write to a file. Returns 0 on error, 1 on OK.
  */
-int fxp_write(struct fxp_handle *handle, char *buffer, uint64 offset,
-	      int len)
+struct sftp_request *fxp_write_send(struct fxp_handle *handle,
+				    char *buffer, uint64 offset, int len)
 {
-    struct sftp_packet *pktin, *pktout;
-    int id;
+    struct sftp_request *req = sftp_alloc_request();
+    struct sftp_packet *pktout;
 
     pktout = sftp_pkt_init(SSH_FXP_WRITE);
-    sftp_pkt_adduint32(pktout, 0xDCB); /* request id */
+    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);
-    pktin = sftp_recv();
-    if (!pktin) {
-	fxp_internal_error("did not receive a valid SFTP packet\n");
-	return 0;
-    }
-    id = sftp_pkt_getuint32(pktin);
-    if (id != 0xDCB) {
-	fxp_internal_error("request ID mismatch\n");
-        sftp_pkt_free(pktin);
-	return 0;
-    }
+
+    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;
@@ -930,7 +1013,7 @@ void fxp_free_names(struct fxp_names *names)
 struct fxp_name *fxp_dup_name(struct fxp_name *name)
 {
     struct fxp_name *ret;
-    ret = smalloc(sizeof(struct fxp_name));
+    ret = snew(struct fxp_name);
     ret->filename = dupstr(name->filename);
     ret->longname = dupstr(name->longname);
     ret->attrs = name->attrs;	       /* structure copy */
@@ -942,9 +1025,339 @@ struct fxp_name *fxp_dup_name(struct fxp_name *name)
  */
 void fxp_free_name(struct fxp_name *name)
 {
-    int i;
-
     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 = 16384;
+    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 = 4096;
+	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;
+}
+
+int xfer_download_gotpkt(struct fxp_xfer *xfer, struct sftp_packet *pktin)
+{
+    struct sftp_request *rreq;
+    struct req *rr;
+
+    rreq = sftp_find_request(pktin);
+    rr = (struct req *)fxp_get_userdata(rreq);
+    if (!rr)
+	return 0;		       /* 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->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 (xfer->req_totalsize < xfer->req_maxsize)
+	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
+}
+
+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);
+    rr = (struct req *)fxp_get_userdata(rreq);
+    if (!rr)
+	return 0;		       /* 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);
+}