Add LEN as a const associated to AtatCmd

atat/src/traits.rs

@@ -45,8 +45,10 @@ pub trait AtatUrc {
 ///
 /// impl<'a> AtatCmd for SetGreetingText<'a> {
 ///     type Response = NoResponse;
+///     const LEN: usize = 64;
 ///
 ///     fn write(&self, mut buf: &mut [u8]) -> usize {
+///         assert!(buf.len() >= Self::LEN);
 ///         let buf_len = buf.len();
 ///         use embedded_io::Write;
 ///         write!(buf, "AT+CSGT={}", self.text);
@@ -62,6 +64,9 @@ pub trait AtatCmd {
     /// The type of the response. Must implement the `AtatResp` trait.
     type Response: AtatResp;
 
+    /// The size of the buffer required to write the request.
+    const LEN: usize;
+
     /// Whether or not this command can be aborted.
     const CAN_ABORT: bool = false;
 
@@ -94,6 +99,7 @@ impl<const L: usize> AtatResp for String<L> {}
 
 impl<const L: usize> AtatCmd for String<L> {
     type Response = String<256>;
+    const LEN: usize = L;
 
     fn write(&self, buf: &mut [u8]) -> usize {
         let bytes = self.as_bytes();

atat_derive/src/cmd.rs

@@ -69,6 +69,14 @@ pub fn atat_cmd(input: TokenStream) -> TokenStream {
         None => quote! {},
     };
 
+    let mut cmd_len = cmd_prefix.len() + cmd.len() + termination.len();
+    if value_sep {
+        cmd_len += 1;
+    }
+    if quote_escape_strings {
+        cmd_len += 2;
+    }
+
     let (field_names, field_names_str): (Vec<_>, Vec<_>) = variants
         .iter()
         .map(|f| {
@@ -93,6 +101,8 @@ pub fn atat_cmd(input: TokenStream) -> TokenStream {
         impl #impl_generics atat::AtatCmd for #ident #ty_generics #where_clause {
             type Response = #resp;
 
+            const LEN: usize = { #ident_len + #cmd_len };
+
             #timeout
 
             #abortable