[PATCH spice-server v3 2/5] smartcard: Fix parsing multiple messages from the device

[Frediano Ziglio <fziglio@xxxxxxxxxx>]

This patch handles the scenario when a single read to guest device
brings multiple requests to be handled. When this happens, we will
iterate till all requests are handled and no more requests can be read
from guest device.

If the remaining buffer contains a full request we don't need to read
other bytes (note that there could be no bytes left), just parse the
request.

Signed-off-by: Frediano Ziglio <fziglio@xxxxxxxxxx>
---
 server/smartcard.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/server/smartcard.c b/server/smartcard.c
index bf5e90520..340118e18 100644
--- a/server/smartcard.c
+++ b/server/smartcard.c
@@ -130,19 +130,28 @@ static RedPipeItem *smartcard_read_msg_from_device(RedCharDevice *self,
     RedCharDeviceSmartcard *dev = RED_CHAR_DEVICE_SMARTCARD(self);
     SpiceCharDeviceInterface *sif = spice_char_device_get_interface(sin);
     VSCMsgHeader *vheader = (VSCMsgHeader*)dev->priv->buf;
-    int n;
     int remaining;
     int actual_length;
 
-    while ((n = sif->read(sin, dev->priv->buf_pos, dev->priv->buf_size - dev->priv->buf_used)) > 0) {
+    while (true) {
         RedMsgItem *msg_to_client;
 
-        dev->priv->buf_pos += n;
-        dev->priv->buf_used += n;
-        if (dev->priv->buf_used < sizeof(VSCMsgHeader)) {
-            continue;
+        // it's possible we already got a full message from a previous partial
+        // read. In this case we don't need to read any byte
+        if (dev->priv->buf_used < sizeof(VSCMsgHeader) ||
+            dev->priv->buf_used - sizeof(VSCMsgHeader) < ntohl(vheader->length)) {
+            int n = sif->read(sin, dev->priv->buf_pos, dev->priv->buf_size - dev->priv->buf_used);
+            if (n <= 0) {
+                break;
+            }
+            dev->priv->buf_pos += n;
+            dev->priv->buf_used += n;
+
+            if (dev->priv->buf_used < sizeof(VSCMsgHeader)) {
+                continue;
+            }
+            smartcard_read_buf_prepare(dev, vheader);
         }
-        smartcard_read_buf_prepare(dev, vheader);
         actual_length = ntohl(vheader->length);
         if (dev->priv->buf_used - sizeof(VSCMsgHeader) < actual_length) {
             continue;
-- 
2.21.0

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