[PATCH win-vdagent] Support file transfer for existing files

[Jonathon Jongsma <jjongsma@xxxxxxxxxx>]

Previously, if the user attempted to transfer a file that had the same
name as a file that already exists on the guest, we would just fail the
transfer. This patch tries to match the behavior of the linux vdagent
where we try to append an integer onto the name of the new file to make
it unique. For example, if you tried to transfer 'file.doc' to the guest
and that file already existed, it would try to create 'file.doc (1)'
instead. If that also failed, it would attempt 'file.doc (2)', etc, up
to 63.

Resolves: rhbz#1410181
---
 vdagent/file_xfer.cpp | 38 ++++++++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/vdagent/file_xfer.cpp b/vdagent/file_xfer.cpp
index f763ed3..14e2098 100644
--- a/vdagent/file_xfer.cpp
+++ b/vdagent/file_xfer.cpp
@@ -61,6 +61,7 @@ void FileXfer::handle_start(VDAgentFileXferStartMessage* start,
     HANDLE handle;
     AsUser as_user;
     int wlen;
+    int attempt = 0;
 
     status->id = start->id;
     status->result = VD_AGENT_FILE_XFER_STATUS_ERROR;
@@ -99,15 +100,40 @@ void FileXfer::handle_start(VDAgentFileXferStartMessage* start,
 
     file_path[wlen++] = TEXT('\\');
     file_path[wlen] = TEXT('\0');
-    if((wlen = MultiByteToWideChar(CP_UTF8, 0, file_name, -1, file_path + wlen, MAX_PATH - wlen)) == 0){
-        vd_printf("failed converting file_name:%s to WideChar", file_name);
-        return;
+
+    const int MAX_ATTEMPTS = 64; // matches behavior of linux vdagent
+    const size_t POSTFIX_LEN = 6; // up to 2 digits in parentheses and final NULL: " (xx)"
+    size_t name_len = strlen(file_name);
+    for (attempt = 0; attempt < MAX_ATTEMPTS; attempt++) {
+        char *pos = &file_name[name_len];
+        if (attempt > 0) {
+            if (name_len + POSTFIX_LEN > MAX_PATH) {
+                vd_printf("failed creating %ls. Postfix makes name too long for the buffer.", file_path);
+                return;
+            }
+            snprintf(pos, POSTFIX_LEN, " (%d)", attempt);
+        }
+        if((MultiByteToWideChar(CP_UTF8, 0, file_name, -1, file_path + wlen, MAX_PATH - wlen)) == 0){
+            vd_printf("failed converting file_name:%s to WideChar", file_name);
+            return;
+        }
+        handle = CreateFile(file_path, GENERIC_WRITE, 0, NULL, CREATE_NEW, 0, NULL);
+        if (handle != INVALID_HANDLE_VALUE) {
+            break;
+        }
+
+        // If the file already exists, we can re-try with a new filename. If
+        // it's a different error, there's not much we can do.
+        if (GetLastError() != ERROR_FILE_EXISTS) {
+            return;
+        }
     }
-    handle = CreateFile(file_path, GENERIC_WRITE, 0, NULL, CREATE_NEW, 0, NULL);
-    if (handle == INVALID_HANDLE_VALUE) {
-        vd_printf("failed creating %ls %lu", file_path, GetLastError());
+
+    if (attempt == MAX_ATTEMPTS) {
+        vd_printf("Failed creating %ls. More than 63 copies exist?", file_path);
         return;
     }
+
     task = new FileXferTask(handle, file_size, file_path);
     _tasks[start->id] = task;
     status->result = VD_AGENT_FILE_XFER_STATUS_CAN_SEND_DATA;
-- 
2.9.3

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