feat(gossipsub)!: return typed error from config builder

Closes #4412.

Pull-Request: #4445.

protocols/gossipsub/CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 0.46.0 - unreleased
 
+- Return typed error from config builder.
+  See [PR 4445].
+
+[PR 4445]: https://github.com/libp2p/rust-libp2p/pull/4445
 
 ## 0.45.2
 
@@ -22,7 +26,7 @@
 
 ## 0.45.1
 
-- Add getter function to obtain `TopicScoreParams`.
+- Add getter function to o  btain `TopicScoreParams`.
   See [PR 4231].
 
 [PR 4231]: https://github.com/libp2p/rust-libp2p/pull/4231

protocols/gossipsub/src/config.rs

@@ -22,6 +22,7 @@ use std::borrow::Cow;
 use std::sync::Arc;
 use std::time::Duration;
 
+use crate::error::ConfigBuilderError;
 use crate::protocol::{ProtocolConfig, ProtocolId, FLOODSUB_PROTOCOL};
 use crate::types::{FastMessageId, Message, MessageId, PeerKind, RawMessage};
 
@@ -834,40 +835,34 @@ impl ConfigBuilder {
     }
 
     /// Constructs a [`Config`] from the given configuration and validates the settings.
-    pub fn build(&self) -> Result<Config, &'static str> {
+    pub fn build(&self) -> Result<Config, ConfigBuilderError> {
         // check all constraints on config
 
         if self.config.protocol.max_transmit_size < 100 {
-            return Err("The maximum transmission size must be greater than 100 to permit basic control messages");
+            return Err(ConfigBuilderError::MaxTransmissionSizeTooSmall);
         }
 
         if self.config.history_length < self.config.history_gossip {
-            return Err(
-                "The history_length must be greater than or equal to the history_gossip \
-                length",
-            );
+            return Err(ConfigBuilderError::HistoryLengthTooSmall);
         }
 
         if !(self.config.mesh_outbound_min <= self.config.mesh_n_low
             && self.config.mesh_n_low <= self.config.mesh_n
             && self.config.mesh_n <= self.config.mesh_n_high)
         {
-            return Err("The following inequality doesn't hold \
-                mesh_outbound_min <= mesh_n_low <= mesh_n <= mesh_n_high");
+            return Err(ConfigBuilderError::MeshParametersInvalid);
         }
 
         if self.config.mesh_outbound_min * 2 > self.config.mesh_n {
-            return Err(
-                "The following inequality doesn't hold mesh_outbound_min <= self.config.mesh_n / 2",
-            );
+            return Err(ConfigBuilderError::MeshOutboundInvalid);
         }
 
         if self.config.unsubscribe_backoff.as_millis() == 0 {
-            return Err("The unsubscribe_backoff parameter should be positive.");
+            return Err(ConfigBuilderError::UnsubscribeBackoffIsZero);
         }
 
         if self.invalid_protocol {
-            return Err("The provided protocol is invalid, it must start with a forward-slash");
+            return Err(ConfigBuilderError::InvalidProtocol);
         }
 
         Ok(self.config.clone())

protocols/gossipsub/src/error.rs

@@ -120,3 +120,37 @@ impl From<std::io::Error> for PublishError {
         PublishError::TransformFailed(error)
     }
 }
+
+/// Error associated with Config building.
+#[derive(Debug)]
+pub enum ConfigBuilderError {
+    /// Maximum transmission size is too small.
+    MaxTransmissionSizeTooSmall,
+    /// Histroy length less than history gossip length.
+    HistoryLengthTooSmall,
+    /// The ineauality doesn't hold mesh_outbound_min <= mesh_n_low <= mesh_n <= mesh_n_high
+    MeshParametersInvalid,
+    /// The inequality doesn't hold mesh_outbound_min <= self.config.mesh_n / 2
+    MeshOutboundInvalid,
+    /// unsubscribe_backoff is zero
+    UnsubscribeBackoffIsZero,
+    /// Invalid protocol
+    InvalidProtocol,
+}
+
+impl std::error::Error for ConfigBuilderError {}
+
+impl std::fmt::Display for ConfigBuilderError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            Self::MaxTransmissionSizeTooSmall => {
+                write!(f, "Maximum transmission size is too small")
+            }
+            Self::HistoryLengthTooSmall => write!(f, "Histroy length less than history gossip length"),
+            Self::MeshParametersInvalid => write!(f, "The ineauality doesn't hold mesh_outbound_min <= mesh_n_low <= mesh_n <= mesh_n_high"),
+            Self::MeshOutboundInvalid => write!(f, "The inequality doesn't hold mesh_outbound_min <= self.config.mesh_n / 2"),
+            Self::UnsubscribeBackoffIsZero => write!(f, "unsubscribe_backoff is zero"),
+            Self::InvalidProtocol => write!(f, "Invalid protocol"),
+        }
+    }
+}

protocols/gossipsub/src/lib.rs

@@ -158,7 +158,7 @@ mod types;
 
 pub use self::behaviour::{Behaviour, Event, MessageAuthenticity};
 pub use self::config::{Config, ConfigBuilder, ValidationMode, Version};
-pub use self::error::{PublishError, SubscriptionError, ValidationError};
+pub use self::error::{ConfigBuilderError, PublishError, SubscriptionError, ValidationError};
 pub use self::metrics::Config as MetricsConfig;
 pub use self::peer_score::{
     score_parameter_decay, score_parameter_decay_with_base, PeerScoreParams, PeerScoreThresholds,