Convert smartrest_serializer to SmartrestPayload

Signed-off-by: Marcel Guzik <[email protected]>

crates/core/c8y_api/src/smartrest/message.rs

@@ -1,3 +1,6 @@
+use std::fmt::Display;
+
+use serde::Serialize;
 use tracing::error;
 
 // The actual limit defined by c8y is 16184 including header and body.
@@ -36,11 +39,23 @@ impl SmartrestPayload {
         let payload = super::csv::fields_to_csv_string(fields);
 
         if payload.len() > super::message::MAX_PAYLOAD_LIMIT_IN_BYTES {
-            return Err(SmartrestPayloadError(anyhow::anyhow!(
-                "Message is larger ({}) than size limit ({})",
-                payload.len(),
-                MAX_PAYLOAD_LIMIT_IN_BYTES
-            )));
+            return Err(SmartrestPayloadError::TooLarge(payload.len()));
+        }
+
+        Ok(Self(payload))
+    }
+
+    pub fn serialize<S: Serialize>(record: S) -> Result<Self, SmartrestPayloadError> {
+        let mut wtr = csv::Writer::from_writer(vec![]);
+        wtr.serialize(record)?;
+        let mut vec = wtr.into_inner().unwrap();
+        // remove newline character
+        vec.pop();
+        let payload = String::from_utf8(vec)
+            .expect("TODO: should SmartrestPayload wrap a string or a byte array?");
+
+        if payload.len() > super::message::MAX_PAYLOAD_LIMIT_IN_BYTES {
+            return Err(SmartrestPayloadError::TooLarge(payload.len()));
         }
 
         Ok(Self(payload))
@@ -59,8 +74,25 @@ impl SmartrestPayload {
 
 /// Errors that can occur when trying to create a SmartREST payload.
 #[derive(Debug, thiserror::Error)]
-#[error("Could not create SmartrestPayload: {0:#}")]
-pub struct SmartrestPayloadError(#[from] anyhow::Error);
+pub enum SmartrestPayloadError {
+    #[error("Payload size ({0}) would be bigger than the limit ({MAX_PAYLOAD_LIMIT_IN_BYTES})")]
+    TooLarge(usize),
+
+    #[error("Could not serialize the record")]
+    SerializeError(#[from] csv::Error),
+}
+
+impl From<SmartrestPayload> for Vec<u8> {
+    fn from(value: SmartrestPayload) -> Self {
+        value.0.into_bytes()
+    }
+}
+
+impl Display for SmartrestPayload {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&self.0)
+    }
+}
 
 /// Extract the Device ID from the SmartREST payload.
 ///