rfb: keep failure_reason as Vec<u8>

And log it with from_utf8_lossy

Since we may now cut a too big failure_reason breaking a valid
utf-8 string

Ticket: 8731

rust/src/rfb/logger.rs

@@ -81,7 +81,10 @@ fn log_rfb(tx: &RFBTransaction, js: &mut JsonBuilder) -> Result<(), JsonError> {
     js.close()?; // Close authentication.
 
     if let Some(ref reason) = tx.tc_failure_reason {
-        js.set_string("server_security_failure_reason", &reason.reason_string)?;
+        js.set_string(
+            "server_security_failure_reason",
+            &String::from_utf8_lossy(&reason.reason_string),
+        )?;
     }
 
     // Client/Server init

rust/src/rfb/parser.rs

@@ -93,7 +93,7 @@ pub struct SecurityResult {
 }
 
 pub struct FailureReason {
-    pub reason_string: String,
+    pub reason_string: Vec<u8>,
     pub to_skip: u32,
 }
 
@@ -182,11 +182,11 @@ pub fn parse_security_result(i: &[u8]) -> IResult<&[u8], SecurityResult> {
 pub fn parse_failure_reason(i: &[u8], max_len: u32) -> IResult<&[u8], FailureReason> {
     let (i, reason_length) = be_u32(i)?;
     let to_skip = reason_length.saturating_sub(max_len);
-    let (i, reason_string) = map_res(take((reason_length - to_skip) as usize), str::from_utf8).parse(i)?;
+    let (i, reason_string) = take((reason_length - to_skip) as usize).parse(i)?;
     Ok((
         i,
         FailureReason {
-            reason_string: reason_string.to_string(),
+            reason_string: reason_string.to_vec(),
             to_skip,
         },
     ))