Hi, I was recently working on a project involving communication between a microcontroller and a host computer over UART. I used postcard on both sides to send extremely simple (less than 10 bytes) messages from the host computer to the microcontroller.
Here are enums equivalent to the messages I was sending:
The Parameter1 and Parameter2 enums were what caused issues. At first, the messages were failing to decode entirely; I was able to get them to decode after changing Parameter1 to a bool in Message. However, no matter which option I sent, postcard would always decode Parameter2 as Option1.
Eventually I was able to fix this by hand writing the Serialize and Deserialize implementations for Parameter2 to serialize and deserialize as a bool.
`Serialize` and `Deserialize` implementations for `Parameter2`
```rs
impl Serialize for Parameter2 {
fn serialize(&self, serializer: S) -> Result
where
S: serde::Serializer,
{
match self {
Parameter2::Option1 => serializer.serialize_bool(true),
Parameter2::Option2 => serializer.serialize_bool(false),
}
}
}
// Taken from serde::de
struct BoolVisitor;
impl<'de> Visitor<'de> for BoolVisitor {
type Value = bool;
fn expecting(&self, formatter: &mut core::fmt::Formatter) -> core::fmt::Result {
formatter.write_str("a boolean")
}
fn visit_bool(self, v: bool) -> Result
where
E: serde::de::Error,
{
Ok(v)
}
}
impl<'lt> Deserialize<'lt> for Parameter2 {
fn deserialize(deserializer: D) -> Result
where
D: serde::Deserializer<'lt>,
{
Ok(match deserializer.deserialize_bool(BoolVisitor)? {
true => Parameter2::Option1,
false => Parameter2::Option2,
})
}
}
```
Do you have any ideas what was causing this? Perhaps how serde was generating the Serialize and Deserialize implementations?
Additional notes:
I used postcard's COBS flavor to make communication easier. I have not yet tested this without COBS by sending the length of the message as the first byte.
If the cause of the issue isn't immediately clear, I can send message dumps of what the computer sends the microcontroller and vice versa.
I did not try using serde_repr's derive macros, but those probably would've fixed the issue.
If this is a real issue, a flavor that appends the hash of the structure/enum before encoding and then allows checking that hash vs the decoded structure/enum might be useful.
Hi, I was recently working on a project involving communication between a microcontroller and a host computer over UART. I used postcard on both sides to send extremely simple (less than 10 bytes) messages from the host computer to the microcontroller.
Here are enums equivalent to the messages I was sending:
The
Parameter1andParameter2enums were what caused issues. At first, the messages were failing to decode entirely; I was able to get them to decode after changingParameter1to aboolinMessage. However, no matter which option I sent, postcard would always decodeParameter2asOption1.Eventually I was able to fix this by hand writing the
SerializeandDeserializeimplementations forParameter2to serialize and deserialize as abool.`Serialize` and `Deserialize` implementations for `Parameter2`
```rs impl Serialize for Parameter2 { fn serialize(&self, serializer: S) -> Result
where
S: serde::Serializer,
{
match self {
Parameter2::Option1 => serializer.serialize_bool(true),
Parameter2::Option2 => serializer.serialize_bool(false),
}
}
}
// Taken from serde::de
struct BoolVisitor;
impl<'de> Visitor<'de> for BoolVisitor {
type Value = bool;
fn expecting(&self, formatter: &mut core::fmt::Formatter) -> core::fmt::Result {
formatter.write_str("a boolean")
}
fn visit_bool(self, v: bool) -> Result
where
E: serde::de::Error,
{
Ok(v)
}
}
impl<'lt> Deserialize<'lt> for Parameter2 {
fn deserialize(deserializer: D) -> Result
where
D: serde::Deserializer<'lt>,
{
Ok(match deserializer.deserialize_bool(BoolVisitor)? {
true => Parameter2::Option1,
false => Parameter2::Option2,
})
}
}
```
Do you have any ideas what was causing this? Perhaps how
serdewas generating theSerializeandDeserializeimplementations?Additional notes:
serde_repr's derive macros, but those probably would've fixed the issue.(also, unrelated but do you think you could checkout https://github.com/jamesmunns/cobs.rs/pull/20 and https://github.com/jamesmunns/cobs.rs/pull/22?)