fix: spec-compliant MP ext marker type

It used to serialize MP ext marker type as char, while it is signed
integer due to MP specification.
On most platforms char is mapped to i8, so no runtime errors were
normally seen. It was detected on linux aarch64, where char is u8.

Markdown spec [reference](https://github.com/msgpack/msgpack/blob/master/spec.md#ext-format-family).

Author: ftelnov

CHANGELOG.md

@@ -12,6 +12,7 @@
 ### Fixed
 
 - Use after free in `fiber::Builder::start_non_joinable` when the fiber exits without yielding.
+- Incorrect, off-spec MP Ext type: caused runtime errors on some platforms.
 
 ### Deprecated
 

tarantool/src/datetime.rs

@@ -2,7 +2,6 @@ use crate::ffi::datetime as ffi;
 use once_cell::sync::Lazy;
 use serde::{Deserialize, Serialize};
 use std::fmt::Display;
-use std::os::raw::c_char;
 use time::{Duration, UtcOffset};
 
 type Inner = time::OffsetDateTime;
@@ -132,7 +131,7 @@ impl serde::Serialize for Datetime {
         S: serde::Serializer,
     {
         #[derive(Serialize)]
-        struct _ExtStruct<'a>((c_char, &'a serde_bytes::Bytes));
+        struct _ExtStruct<'a>((i8, &'a serde_bytes::Bytes));
 
         let data = self.as_bytes_tt();
         let mut data = data.as_slice();
@@ -149,7 +148,7 @@ impl<'de> serde::Deserialize<'de> for Datetime {
         D: serde::Deserializer<'de>,
     {
         #[derive(Deserialize)]
-        struct _ExtStruct((c_char, serde_bytes::ByteBuf));
+        struct _ExtStruct((i8, serde_bytes::ByteBuf));
 
         let _ExtStruct((kind, bytes)) = serde::Deserialize::deserialize(deserializer)?;
 

tarantool/src/decimal.rs

@@ -438,7 +438,7 @@ mod tarantool_decimal {
             S: serde::Serializer,
         {
             #[derive(Serialize)]
-            struct _ExtStruct((std::os::raw::c_char, serde_bytes::ByteBuf));
+            struct _ExtStruct((i8, serde_bytes::ByteBuf));
 
             let data = unsafe {
                 let len = ffi::decimal_len(&self.inner) as usize;
@@ -457,7 +457,7 @@ mod tarantool_decimal {
             D: serde::Deserializer<'de>,
         {
             #[derive(Deserialize)]
-            struct _ExtStruct((std::os::raw::c_char, serde_bytes::ByteBuf));
+            struct _ExtStruct((i8, serde_bytes::ByteBuf));
 
             match serde::Deserialize::deserialize(deserializer)? {
                 _ExtStruct((ffi::MP_DECIMAL, bytes)) => {
@@ -1142,7 +1142,7 @@ mod standalone_decimal {
             S: serde::Serializer,
         {
             #[derive(serde::Serialize)]
-            struct _ExtStruct((std::os::raw::c_char, serde_bytes::ByteBuf));
+            struct _ExtStruct((i8, serde_bytes::ByteBuf));
 
             let data = {
                 let mut data = vec![];
@@ -1162,7 +1162,7 @@ mod standalone_decimal {
         {
             use serde::de::Error;
             #[derive(serde::Deserialize)]
-            struct _ExtStruct((std::os::raw::c_char, serde_bytes::ByteBuf));
+            struct _ExtStruct((i8, serde_bytes::ByteBuf));
 
             match serde::Deserialize::deserialize(deserializer)? {
                 _ExtStruct((ffi::MP_DECIMAL, bytes)) => {

tarantool/src/ffi/datetime.rs

@@ -1,4 +1,4 @@
-pub const MP_DATETIME: std::os::raw::c_char = 4;
+pub const MP_DATETIME: i8 = 4;
 
 #[repr(C)]
 #[derive(Debug, Copy, Clone)]

tarantool/src/ffi/decimal.rs

@@ -28,7 +28,7 @@ impl Hash for decNumber {
 pub const DECDPUN: usize = 3;
 pub const DECNUMUNITS: u32 = 13;
 pub const DECIMAL_MAX_DIGITS: u32 = 38;
-pub const MP_DECIMAL: c_char = 1;
+pub const MP_DECIMAL: i8 = 1;
 
 crate::define_dlsym_reloc! {
     /// Return decimal precision,

tarantool/src/ffi/uuid.rs

@@ -1,4 +1,4 @@
-pub const MP_UUID: std::os::raw::c_char = 2;
+pub const MP_UUID: i8 = 2;
 
 #[repr(C)]
 #[derive(Copy, Clone)]

tarantool/src/uuid.rs

@@ -1,5 +1,4 @@
 use crate::ffi::uuid as ffi;
-use std::os::raw::c_char;
 
 pub use ::uuid::{adapter, Error};
 use serde::{Deserialize, Serialize};
@@ -217,7 +216,7 @@ impl serde::Serialize for Uuid {
         S: serde::Serializer,
     {
         #[derive(Serialize)]
-        struct _ExtStruct((c_char, serde_bytes::ByteBuf));
+        struct _ExtStruct((i8, serde_bytes::ByteBuf));
 
         let data = self.as_bytes();
         _ExtStruct((ffi::MP_UUID, serde_bytes::ByteBuf::from(data as &[_]))).serialize(serializer)
@@ -230,7 +229,7 @@ impl<'de> serde::Deserialize<'de> for Uuid {
         D: serde::Deserializer<'de>,
     {
         #[derive(Deserialize)]
-        struct _ExtStruct((c_char, serde_bytes::ByteBuf));
+        struct _ExtStruct((i8, serde_bytes::ByteBuf));
 
         let _ExtStruct((kind, bytes)) = serde::Deserialize::deserialize(deserializer)?;