feat: add methods to create variants of the iroh-base::ticket::ParseError enum. (#3362)

## Description

Adds a `From` impl for `postcard::Error`, and adds
`ParseError::verification_failed` and `ParseError::wrong_prefix`
methods.

## Open Questions

Should we add a variant to `ParseError` for a more "open ended" error,
like we do for `protocol::AcceptError`? Something like
`ParseError::Custom`?

## Change checklist
<!-- Remove any that are not relevant. -->
- [x] Self-review.
- [x] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.

---------

Co-authored-by: “ramfox” <“kasey@n0.computer”>

Author: ramfox

iroh-base/src/ticket.rs

@@ -69,14 +69,14 @@ pub trait Ticket: Sized {
 #[snafu(visibility(pub(crate)))]
 #[non_exhaustive]
 pub enum ParseError {
-    /// Found a ticket of with the wrong prefix, indicating the wrong kind.
+    /// Found a ticket with the wrong prefix, indicating the wrong kind.
     #[snafu(display("wrong prefix, expected {expected}"))]
     Kind {
         /// The expected prefix.
         expected: &'static str,
     },
     /// This looks like a ticket, but postcard deserialization failed.
-    #[snafu(display("deserialization failed"))]
+    #[snafu(transparent)]
     Postcard { source: postcard::Error },
     /// This looks like a ticket, but base32 decoding failed.
     #[snafu(transparent)]
@@ -86,6 +86,22 @@ pub enum ParseError {
     Verify { message: &'static str },
 }
 
+impl ParseError {
+    /// Returns a [`ParseError`] that indicates the given ticket has the wrong
+    /// prefix.
+    ///
+    /// Indicate the expected prefix.
+    pub fn wrong_prefix(expected: &'static str) -> Self {
+        KindSnafu { expected }.build()
+    }
+
+    /// Return a `ParseError` variant that indicates verification of the
+    /// deserialized bytes failed.
+    pub fn verification_failed(message: &'static str) -> Self {
+        VerifySnafu { message }.build()
+    }
+}
+
 #[derive(Serialize, Deserialize)]
 struct Variant0NodeAddr {
     node_id: NodeId,

iroh-base/src/ticket/node.rs

@@ -3,7 +3,6 @@
 use std::str::FromStr;
 
 use serde::{Deserialize, Serialize};
-use snafu::ResultExt;
 
 use super::{Variant0AddrInfo, Variant0NodeAddr};
 use crate::{
@@ -63,7 +62,7 @@ impl Ticket for NodeTicket {
     }
 
     fn from_bytes(bytes: &[u8]) -> Result<Self, ParseError> {
-        let res: TicketWireFormat = postcard::from_bytes(bytes).context(ticket::PostcardSnafu)?;
+        let res: TicketWireFormat = postcard::from_bytes(bytes)?;
         let TicketWireFormat::Variant0(Variant0NodeTicket { node }) = res;
         Ok(Self {
             node: NodeAddr {