Stop circumventing the std definition of FromUtf8Error

By already taking the `Vec<u8>` out of this error we leave
users no choice to bubble up the error with typical `?` or
`anyhow::Context::context()`, because `vec<u8>` does not implement
`std::error::Error` (it's not an error after all).

Instead of trying to outsmart the standard library and annoying the
user, return the original `FromUtf8Error` *as it is*, leaving the
caller to deal with it however they please (i.e. bubble it up, or
call `into_bytes()` themselves if they wish to continue parsing it
otherwise).

Author: MarijnS95

src/lib.rs

@@ -750,11 +750,10 @@ impl Socket {
 
     /// Receive a `String` from the socket.
     ///
-    /// If the received message is not valid UTF-8, it is returned as the original
-    /// Vec in the `Err` part of the inner result.
-    pub fn recv_string(&self, flags: i32) -> Result<result::Result<String, Vec<u8>>> {
-        self.recv_bytes(flags)
-            .map(|bytes| String::from_utf8(bytes).map_err(FromUtf8Error::into_bytes))
+    /// If the received message is not valid UTF-8, a [`FromUtf8Error`] is returned and the original
+    /// bytes can be retrieved via [`FromUtf8Error::into_bytes()`].
+    pub fn recv_string(&self, flags: i32) -> Result<result::Result<String, FromUtf8Error>> {
+        self.recv_bytes(flags).map(String::from_utf8)
     }
 
     /// Receive a multipart message from the socket.
@@ -885,7 +884,7 @@ impl Socket {
         sockopt::get_bytes(self.sock, zmq_sys::ZMQ_ROUTING_ID as c_int, 255)
     }
 
-    pub fn get_socks_proxy(&self) -> Result<result::Result<String, Vec<u8>>> {
+    pub fn get_socks_proxy(&self) -> Result<result::Result<String, FromUtf8Error>> {
         // 255 = longest allowable domain name is 253 so this should
         // be a reasonable size.
         sockopt::get_string(self.sock, zmq_sys::ZMQ_SOCKS_PROXY as c_int, 255, true)
@@ -901,17 +900,17 @@ impl Socket {
         })
     }
 
-    pub fn get_plain_username(&self) -> Result<result::Result<String, Vec<u8>>> {
+    pub fn get_plain_username(&self) -> Result<result::Result<String, FromUtf8Error>> {
         // 255 = arbitrary size
         sockopt::get_string(self.sock, zmq_sys::ZMQ_PLAIN_USERNAME as c_int, 255, true)
     }
 
-    pub fn get_plain_password(&self) -> Result<result::Result<String, Vec<u8>>> {
+    pub fn get_plain_password(&self) -> Result<result::Result<String, FromUtf8Error>> {
         // 256 = arbitrary size based on std crypto key size
         sockopt::get_string(self.sock, zmq_sys::ZMQ_PLAIN_PASSWORD as c_int, 256, true)
     }
 
-    pub fn get_zap_domain(&self) -> Result<result::Result<String, Vec<u8>>> {
+    pub fn get_zap_domain(&self) -> Result<result::Result<String, FromUtf8Error>> {
         // 255 = arbitrary size
         sockopt::get_string(self.sock, zmq_sys::ZMQ_ZAP_DOMAIN as c_int, 255, true)
     }
@@ -924,7 +923,7 @@ impl Socket {
     /// used with the wildcard address (`"*"`), in the address
     /// returned, the wildcard will be expanded into the any address
     /// (i.e. `0.0.0.0` with IPv4).
-    pub fn get_last_endpoint(&self) -> Result<result::Result<String, Vec<u8>>> {
+    pub fn get_last_endpoint(&self) -> Result<result::Result<String, FromUtf8Error>> {
         // 256 + 9 + 1 = maximum inproc name size (= 256) + "inproc://".len() (= 9), plus null byte
         sockopt::get_string(
             self.sock,
@@ -962,12 +961,12 @@ impl Socket {
         sockopt::get_bytes(self.sock, zmq_sys::ZMQ_CURVE_SERVERKEY as c_int, 32)
     }
 
-    pub fn get_gssapi_principal(&self) -> Result<result::Result<String, Vec<u8>>> {
+    pub fn get_gssapi_principal(&self) -> Result<result::Result<String, FromUtf8Error>> {
         // 260 = best guess of max length based on docs.
         sockopt::get_string(self.sock, zmq_sys::ZMQ_GSSAPI_PRINCIPAL as c_int, 260, true)
     }
 
-    pub fn get_gssapi_service_principal(&self) -> Result<result::Result<String, Vec<u8>>> {
+    pub fn get_gssapi_service_principal(&self) -> Result<result::Result<String, FromUtf8Error>> {
         // 260 = best guess of max length based on docs.
         sockopt::get_string(
             self.sock,

src/sockopt.rs

@@ -63,13 +63,13 @@ pub fn get_string(
     opt: c_int,
     size: size_t,
     remove_nulbyte: bool,
-) -> Result<result::Result<String, Vec<u8>>> {
+) -> Result<result::Result<String, FromUtf8Error>> {
     let mut value = get_bytes(sock, opt, size)?;
 
     if remove_nulbyte {
         value.pop();
     }
-    Ok(String::from_utf8(value).map_err(FromUtf8Error::into_bytes))
+    Ok(String::from_utf8(value))
 }
 
 macro_rules! setsockopt_num(

tests/test.rs

@@ -3,6 +3,7 @@ mod common;
 
 use std::io;
 use std::net::TcpStream;
+use std::string::FromUtf8Error;
 use zmq::*;
 
 fn version_ge_4_2() -> bool {
@@ -64,7 +65,10 @@ test!(test_exchanging_strings, {
     // non-UTF8 strings -> get an Err with bytes when receiving
     receiver.send(b"\xff\xb7".as_ref(), 0).unwrap();
     let result = sender.recv_string(0).unwrap();
-    assert_eq!(result, Err(vec![0xff, 0xb7]));
+    assert_eq!(
+        result.map_err(FromUtf8Error::into_bytes),
+        Err(vec![0xff, 0xb7])
+    );
 });
 
 test!(test_exchanging_multipart, {