Fix SFTP Upload Stall

1. Update README for the change in the default channel receive window size.
2. In the SFTP client, add rekeying as a error that's OK to ignore.
3. In wolfSSH_stream_read(), clear the SSH object's error register.

README.md

@@ -53,10 +53,10 @@ For building under Windows with Visual Studio, see the file
 
 NOTE: On resource constrained devices the `DEFAULT_WINDOW_SZ` may need
 to be set to a lower size. It can also be increased in desktop use cases
-to help with large file transfers. By default channels are set to handle
-16,384 bytes of data being sent and received. An example of setting a
-window size for new channels would be as follows
-`./configure CPPFLAGS=-DDEFAULT_WINDOW_SZ=16384`
+to help with large file transfers. By default channels are set to receive
+up to 128kB of data before sending a channel window adjust message. An
+example of setting a window size for new channels would be as follows
+`./configure CPPFLAGS="-DDEFAULT_WINDOW_SZ=16384"`
 
 For 32bit Linux platforms you can add support for files > 2GB by compling
 with `CFLAGS=-D_FILE_OFFSET_BITS=64`.

examples/sftpclient/sftpclient.c

@@ -1017,7 +1017,7 @@ static int doCmds(func_args* args)
                     ret = wolfSSH_get_error(ssh);
                 }
             } while (ret == WS_WANT_READ || ret == WS_WANT_WRITE ||
-                    ret == WS_CHAN_RXD);
+                    ret == WS_CHAN_RXD || ret == WS_REKEYING);
 
 #ifndef WOLFSSH_NO_TIMESTAMP
             WMEMSET(currentFile, 0, WOLFSSH_MAX_FILENAME);
@@ -1113,7 +1113,8 @@ static int doCmds(func_args* args)
                 ret = wolfSSH_SFTP_Put(ssh, pt, to, resume, &myStatusCb);
                 err = wolfSSH_get_error(ssh);
             } while ((err == WS_WANT_READ || err == WS_WANT_WRITE ||
-                        err == WS_CHAN_RXD) && ret == WS_FATAL_ERROR);
+                        err == WS_CHAN_RXD || err == WS_REKEYING) &&
+                    ret == WS_FATAL_ERROR);
 
 #ifndef WOLFSSH_NO_TIMESTAMP
             WMEMSET(currentFile, 0, WOLFSSH_MAX_FILENAME);

src/ssh.c

@@ -1031,6 +1031,7 @@ int wolfSSH_stream_read(WOLFSSH* ssh, byte* buf, word32 bufSz)
         return WS_BAD_ARGUMENT;
 
     inputBuffer = &ssh->channelList->inputBuffer;
+    ssh->error = WS_SUCCESS;
 
     if (ret == WS_SUCCESS) {
         WLOG(WS_LOG_DEBUG, "    Stream read index of %u", inputBuffer->idx);

wolfssh/internal.h

@@ -344,6 +344,7 @@ enum {
     #define DEFAULT_WINDOW_SZ (128 * 1024)
 #endif
 #ifndef DEFAULT_MAX_PACKET_SZ
+    /* This is from RFC 4253 section 6.1. */
     #define DEFAULT_MAX_PACKET_SZ 32768
 #endif
 #ifndef DEFAULT_NEXT_CHANNEL