RUST-1881 Check integer conversions (#1045)

Author: abr-egn

src/bson_util.rs

@@ -5,12 +5,14 @@ use std::{
 
 use crate::{
     bson::{Bson, Document, RawArrayBuf, RawBson, RawBsonRef, RawDocumentBuf},
+    checked::Checked,
     error::{ErrorKind, Result},
     runtime::SyncLittleEndianRead,
 };
 
 /// Coerce numeric types into an `i64` if it would be lossless to do so. If this Bson is not numeric
 /// or the conversion would be lossy (e.g. 1.5 -> 1), this returns `None`.
+#[allow(clippy::cast_possible_truncation)]
 pub(crate) fn get_int(val: &Bson) -> Option<i64> {
     match *val {
         Bson::Int32(i) => Some(i64::from(i)),
@@ -33,6 +35,7 @@ pub(crate) fn get_int_raw(val: RawBsonRef<'_>) -> Option<i64> {
 
 /// Coerce numeric types into an `u64` if it would be lossless to do so. If this Bson is not numeric
 /// or the conversion would be lossy (e.g. 1.5 -> 1), this returns `None`.
+#[allow(clippy::cast_possible_truncation)]
 pub(crate) fn get_u64(val: &Bson) -> Option<u64> {
     match *val {
         Bson::Int32(i) => u64::try_from(i).ok(),
@@ -89,18 +92,18 @@ pub(crate) fn update_document_check(update: &Document) -> Result<()> {
 }
 
 /// The size in bytes of the provided document's entry in a BSON array at the given index.
-pub(crate) fn array_entry_size_bytes(index: usize, doc_len: usize) -> u64 {
+pub(crate) fn array_entry_size_bytes(index: usize, doc_len: usize) -> Result<usize> {
     //   * type (1 byte)
     //   * number of decimal digits in key
     //   * null terminator for the key (1 byte)
     //   * size of value
 
-    1 + num_decimal_digits(index) + 1 + doc_len as u64
+    (Checked::new(1) + num_decimal_digits(index) + 1 + doc_len).get()
 }
 
 /// The number of digits in `n` in base 10.
 /// Useful for calculating the size of an array entry in BSON.
-fn num_decimal_digits(mut n: usize) -> u64 {
+fn num_decimal_digits(mut n: usize) -> usize {
     let mut digits = 0;
 
     loop {