Add parsing example

README.md

@@ -5,3 +5,10 @@
 [![Matrix](https://img.shields.io/matrix/drogue-iot:matrix.org)](https://matrix.to/#/#drogue-iot:matrix.org)
 
 Rust mappings for APIs of *The Things Network*.
+
+## Parsing Messages on CLI
+
+There is an example application that can be used to test the parsing of TTN
+messages:
+
+    cargo run --example parse-v3 -- <path-to-message.json>

examples/parse-v3.rs

@@ -0,0 +1,24 @@
+use std::{env, fs};
+
+use drogue_ttn::v3 as ttn;
+use serde_json as json;
+
+fn main() -> Result<(), String> {
+    // Args
+    let args: Vec<String> = env::args().collect();
+    if args.len() < 2 {
+        return Err(format!("Usage: {} <jsonfile>", args[0]));
+    }
+
+    // Read from file
+    let buffer = fs::read(&args[1]).unwrap();
+
+    let ttn_msg = match json::from_slice::<ttn::Message>(&buffer) {
+        Ok(msg) => msg,
+        Err(e) => {
+            return Err(format!("Uplink message could not be parsed: {}", e));
+        }
+    };
+    println!("Parsed: {:#?}", ttn_msg);
+    Ok(())
+}