rust: fix build with MSRV

Ticket: 6876

Do not backport try_string_from_bytes as it uses try_reserve
And just use string_from_bytes instead

Fixes: b9963b3 ("ssh: limit length for banner logs")

rust/src/jsonbuilder.rs

@@ -17,7 +17,6 @@
 
 #![allow(clippy::missing_safety_doc)]
 
-use std::collections::TryReserveError;
 use std::ffi::CStr;
 use std::os::raw::c_char;
 use std::str::Utf8Error;
@@ -28,7 +27,6 @@ const INIT_SIZE: usize = 4096;
 pub enum JsonError {
     InvalidState,
     Utf8Error(Utf8Error),
-    Memory,
 }
 
 impl std::error::Error for JsonError {}
@@ -38,17 +36,10 @@ impl std::fmt::Display for JsonError {
         match self {
             JsonError::InvalidState => write!(f, "invalid state"),
             JsonError::Utf8Error(ref e) => e.fmt(f),
-            JsonError::Memory => write!(f, "memory error"),
         }
     }
 }
 
-impl From<TryReserveError> for JsonError {
-    fn from(_: TryReserveError) -> Self {
-        JsonError::Memory
-    }
-}
-
 impl From<Utf8Error> for JsonError {
     fn from(e: Utf8Error) -> Self {
         JsonError::Utf8Error(e)
@@ -448,7 +439,7 @@ impl JsonBuilder {
         };
         match std::str::from_utf8(val) {
             Ok(s) => self.set_string(key, s),
-            Err(_) => self.set_string(key, &try_string_from_bytes(val)?),
+            Err(_) => self.set_string(key, &string_from_bytes(val)),
         }
     }
 
@@ -595,26 +586,6 @@ fn string_from_bytes(input: &[u8]) -> String {
     return out;
 }
 
-/// A Suricata specific function to create a string from bytes when UTF-8 decoding fails.
-///
-/// For bytes over 0x0f, we encode as hex like "\xf2".
-fn try_string_from_bytes(input: &[u8]) -> Result<String, JsonError> {
-    let mut out = String::new();
-
-    // Allocate enough data to handle the worst case scenario of every
-    // byte needing to be presented as a byte.
-    out.try_reserve(input.len() * 4)?;
-
-    for b in input.iter() {
-        if *b < 128 {
-            out.push(*b as char);
-        } else {
-            out.push_str(&format!("\\x{:02x}", *b));
-        }
-    }
-    return Ok(out);
-}
-
 #[no_mangle]
 pub extern "C" fn jb_new_object() -> *mut JsonBuilder {
     let boxed = Box::new(JsonBuilder::new_object());