fix: validate configuration before attempting to use

closes #38

Cargo.toml

@@ -36,7 +36,7 @@ derive-deftly = "0.14.2"
 dirs = "5.0.1"
 dns-lookup = "2.0.4"
 document-features = "0.2.10"
-engineering-repr = { version = "0.3.0", features = [ "serde" ] }
+engineering-repr = { version = "0.3.1", features = [ "serde" ] }
 expanduser = "1.2.2"
 figment = { version = "0.10.19" }
 futures-util = { version = "0.3.31", default-features = false }

src/cli/cli_main.rs

@@ -70,7 +70,8 @@ pub async fn cli() -> anyhow::Result<ExitCode> {
             err.into_iter().for_each(|e| eprintln!("{e}"));
             return Ok(ExitCode::FAILURE);
         }
-    };
+    }
+    .validate()?;
 
     setup_tracing(
         trace_level(&args.client_params),

src/config/structure.rs

@@ -5,7 +5,7 @@ use std::time::Duration;
 
 use anyhow::Result;
 use clap::Parser;
-use engineering_repr::EngineeringQuantity;
+use engineering_repr::{EngineeringQuantity, EngineeringRepr};
 use human_repr::{HumanCount as _, HumanDuration as _};
 use serde::{Deserialize, Serialize};
 use struct_field_names_as_array::FieldNamesAsSlice;
@@ -17,6 +17,10 @@ use crate::{
 
 use derive_deftly::Deftly;
 
+/// Minimum bandwidth we will accept in either direction.
+/// You have to have a limit somewhere; zero doesn't work. So I chose 1200 baud ...
+const MINIMUM_BANDWIDTH: u64 = 150;
+
 /// The set of configurable options supported by qcp.
 ///
 /// **Note:** The implementation of `default()` for this struct returns qcp's hard-wired configuration defaults.
@@ -285,6 +289,39 @@ impl Configuration {
             congestion = self.congestion,
         )
     }
+
+    /// Performs additional validation checks on the configuration.
+    pub fn validate(self) -> Result<Self> {
+        if self.rx() < MINIMUM_BANDWIDTH {
+            anyhow::bail!(
+                "The receive bandwidth (rx {}B) is too small; it must be at least {}",
+                self.rx.with_precision(0),
+                MINIMUM_BANDWIDTH.to_eng(3)
+            );
+        }
+        if self.tx() < MINIMUM_BANDWIDTH {
+            anyhow::bail!(
+                "The transmit bandwidth (rx {}B) is too small; it must be at least {}",
+                self.tx.with_precision(0),
+                MINIMUM_BANDWIDTH.to_eng(3)
+            );
+        }
+        if self.rx().checked_mul(self.rtt.into()).is_none() {
+            anyhow::bail!(
+                "The receive bandwidth delay product calculation (rx {}B x rtt {}ms) overflowed",
+                self.rx,
+                self.rtt
+            );
+        }
+        if self.tx().checked_mul(self.rtt.into()).is_none() {
+            anyhow::bail!(
+                "The transmit bandwidth delay product calculation (rx {}B x rtt {}ms) overflowed",
+                self.tx,
+                self.rtt
+            );
+        }
+        Ok(self)
+    }
 }
 
 impl Default for Configuration {