Reading from a ProtoBuffer file

help
1

I am trying to read a ProtoBuffer file. I am using Prost and trying to use the prost::Message::decode_length_delimited function .

If I pass the Vector I get an error saying the Buf trait is not implemented. Passing the Cursor also results in the same error ( cannot infer type )

I understand that it does not make sense to read the entire file at once and this will be a kind of server . But I am trying to initially play around before moving to a different approach
Any help appreciated.
But I always get the following error

cargo run
   Compiling dnstap v0.1.0 (/home/hvram/projects/dnstap)
warning: unused import: `prost::Message`
 --> src/main.rs:6:5
  |
6 | use prost::Message;
  |     ^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error[E0283]: type annotations needed
  --> src/main.rs:30:5
   |
30 |     prost::Message::decode_length_delimited(&mut buffer);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type
   |
   = note: cannot satisfy `_: prost::Message`
   = note: required by `decode_length_delimited`

error: aborting due to previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0283`.
error: could not compile `dnstap`

To learn more, run the command again with --verbose.
fn main() -> Result<(), Box> { 
println!("Hello, world!");
let mut f = File::open("dnstap.log")?;
let mut reader = BufReader::new(f);
let capacity = reader.capacity();
let mut buffer = reader.fill_buf()?;
//let mut buffer = Vec::new();
// read the whole file
//let msg = f.read_to_end(&mut buffer)?;
//let mut cursor: Cursor<Vec<u8>> = Cursor::new(buffer);
//println!("Finished Reading! {}",buffer.len());
prost::Message::decode_length_delimited(&mut buffer);
//println!("Finished Reading! {}",m1);
Ok(())

}
2

I believe you need something like

let message: SomeType = prost::Message::decode_length_delimited(&mut buffer)?;

Where SomeType implements the prost::Message trait. (There are many such types, and Rust has no way to infer which one you meant.)

3

Thanks @quinedot .It works I tried

// Include the dnstap module, which is generated from dnstap.proto.
pub mod dnstap {
include!(concat!(env!("OUT_DIR"), "/dnstap.rs"));
}
....
....
let dnstap_message:dnstap::Message = prost::Message::decode_length_delimited(&mut cursor)?;

where the dnstap.rs is from dnstap.proto Github using the protobuild

and that works.
Thanks for the hep

4

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