Return structured server errors in FFI

bindings.h

@@ -5,6 +5,65 @@
 #include <cassert>
 
 
+struct FFIServerError {
+  uint16_t status;
+  const char *title;
+  const char *detail;
+};
+
+struct FFIError {
+  enum class Tag : uint8_t {
+    Server,
+    Network,
+  };
+
+  struct Server_Body {
+    FFIServerError _0;
+  };
+
+  struct Network_Body {
+    const char *_0;
+  };
+
+  Tag tag;
+  union {
+    Server_Body server;
+    Network_Body network;
+  };
+
+  static FFIError Server(const FFIServerError &_0) {
+    FFIError result;
+    ::new (&result.server._0) (FFIServerError)(_0);
+    result.tag = Tag::Server;
+    return result;
+  }
+
+  bool IsServer() const {
+    return tag == Tag::Server;
+  }
+
+  const FFIServerError& AsServer() const {
+    assert(IsServer());
+    return server._0;
+  }
+
+  static FFIError Network(const char *const &_0) {
+    FFIError result;
+    ::new (&result.network._0) (const char*)(_0);
+    result.tag = Tag::Network;
+    return result;
+  }
+
+  bool IsNetwork() const {
+    return tag == Tag::Network;
+  }
+
+  const char*const & AsNetwork() const {
+    assert(IsNetwork());
+    return network._0;
+  }
+};
+
 template<typename T>
 struct FFIResult {
   enum class Tag : uint8_t {
@@ -17,7 +76,7 @@ struct FFIResult {
   };
 
   struct Err_Body {
-    const char *_0;
+    FFIError _0;
   };
 
   Tag tag;
@@ -42,9 +101,9 @@ struct FFIResult {
     return ok._0;
   }
 
-  static FFIResult Err(const char *const &_0) {
+  static FFIResult Err(const FFIError &_0) {
     FFIResult result;
-    ::new (&result.err._0) (const char*)(_0);
+    ::new (&result.err._0) (FFIError)(_0);
     result.tag = Tag::Err;
     return result;
   }
@@ -53,7 +112,7 @@ struct FFIResult {
     return tag == Tag::Err;
   }
 
-  const char*const & AsErr() const {
+  const FFIError& AsErr() const {
     assert(IsErr());
     return err._0;
   }

src/cache.rs

@@ -83,29 +83,43 @@ pub fn update_file_caches(
 
 pub fn from_file_cache<T: for<'de> Deserialize<'de>>(cache_path: &Path) -> Result<T> {
     #[cfg(not(test))]
-    let file = File::open(cache_path).context(format!(
+    let file = File::open(cache_path).with_context(|| {
-        "Object not found in API or in cache: {}",
+        format!(
-        cache_path.file_name().unwrap_or_default().to_string_lossy()
+            "Object not found in API or in cache: {}",
-    ))?;
+            cache_path.file_name().unwrap_or_default().to_string_lossy()
+        )
+    })?;
     #[cfg(test)]
     let file = tempfile()?; // cache always reads from an empty temp file in cfg(test)
 
     let reader = BufReader::new(file);
     info!("returning value from cache: {:?}", cache_path);
-    Ok(bincode::deserialize_from(reader)?)
+    Ok(bincode::deserialize_from(reader).with_context(|| {
+        format!(
+            "Object not found in API or in cache: {}",
+            cache_path.file_name().unwrap_or_default().to_string_lossy(),
+        )
+    })?)
 }
 
 pub fn load_metadata_from_file_cache(cache_path: &Path) -> Result<Metadata> {
     #[cfg(not(test))]
-    let file = File::open(cache_path).context(format!(
+    let file = File::open(cache_path).with_context(|| {
-        "Object not found in API or in cache: {}",
+        format!(
-        cache_path.file_name().unwrap_or_default().to_string_lossy()
+            "Object not found in API or in cache: {}",
-    ))?;
+            cache_path.file_name().unwrap_or_default().to_string_lossy()
+        )
+    })?;
     #[cfg(test)]
     let file = tempfile()?; // cache always reads from an empty temp file in cfg(test)
 
     let reader = BufReader::new(file);
     info!("returning value from cache: {:?}", cache_path);
-    let metadata: Metadata = serde_json::from_reader(reader)?;
+    let metadata: Metadata = serde_json::from_reader(reader).with_context(|| {
+        format!(
+            "Object not found in API or in cache: {}",
+            cache_path.file_name().unwrap_or_default().to_string_lossy(),
+        )
+    })?;
     Ok(metadata)
 }

src/client.rs

@@ -10,7 +10,11 @@ use log::{error, info};
 #[cfg(test)]
 use std::{println as info, println as error};
 
-use crate::{log_server_error, result::FFIResult};
+use crate::{
+    error::extract_error_from_response,
+    log_server_error,
+    result::{FFIError, FFIResult},
+};
 
 #[no_mangle]
 pub extern "C" fn init() -> bool {
@@ -33,34 +37,30 @@ pub extern "C" fn status_check(api_url: *const c_char) -> FFIResult<bool> {
     let api_url = unsafe { CStr::from_ptr(api_url) }.to_string_lossy();
     info!("status_check api_url: {:?}", api_url);
 
-    fn inner(api_url: &str) -> Result<Response> {
+    fn inner(api_url: &str) -> Result<()> {
         #[cfg(not(test))]
         let api_url = Url::parse(api_url)?.join("v1/status")?;
         #[cfg(test)]
         let api_url = Url::parse(&mockito::server_url())?.join("v1/status")?;
 
-        Ok(reqwest::blocking::get(api_url)?)
+        let resp = reqwest::blocking::get(api_url)?;
+        let status = resp.status();
+        let bytes = resp.bytes()?;
+        if status.is_success() {
+            Ok(())
+        } else {
+            Err(extract_error_from_response(status, &bytes))
+        }
     }
 
     match inner(&api_url) {
-        Ok(resp) if resp.status() == 200 => {
+        Ok(()) => {
             info!("status_check ok");
             FFIResult::Ok(true)
         }
-        Ok(resp) => {
-            error!("status_check failed. Server error");
-            log_server_error(resp);
-            let err_string = CString::new("API returned a non-200 status code".to_string())
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
-        }
         Err(err) => {
             error!("status_check failed. {}", err);
-            let err_string = CString::new(err.to_string())
+            FFIResult::Err(FFIError::from(err))
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -91,9 +91,17 @@ mod tests {
             FFIResult::Ok(success) => {
                 assert_eq!(success, true);
             }
-            FFIResult::Err(error) => panic!("status_check returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "status_check returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -109,12 +117,16 @@ mod tests {
         mock.assert();
         match result {
             FFIResult::Ok(success) => panic!("status_check returned Ok result: {:?}", success),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "API returned a non-200 status code"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("status_check did not return a server error"),
+            },
         }
     }
 }

src/error.rs

@@ -1,3 +1,4 @@
+use std::fmt;
 use std::str;
 
 use anyhow::{anyhow, Error};
@@ -10,27 +11,51 @@ use log::error;
 #[cfg(test)]
 use std::println as error;
 
-pub fn extract_error_from_response(status: StatusCode, bytes: &Bytes) -> Error {
+#[derive(Debug)]
-    match serde_json::from_slice::<HttpApiProblem>(bytes) {
+pub struct ServerError {
-        Ok(api_problem) => {
+    pub status: StatusCode,
-            let detail = api_problem.detail.unwrap_or("".to_string());
+    pub title: String,
-            error!(
+    pub detail: Option<String>,
-                "Server {}: {}. {}",
+}
-                status.as_u16(),
+
-                api_problem.title,
+impl fmt::Display for ServerError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if let Some(detail) = &self.detail {
+            write!(
+                f,
+                "Server {} {}: {}",
+                self.status.as_u16(),
+                self.title,
                 detail
-            );
+            )
-            anyhow!(format!(
+        } else {
-                "Server {}: {}. {}",
+            write!(f, "Server {} {}", self.status.as_u16(), self.title)
-                status.as_u16(),
+        }
-                api_problem.title,
+    }
-                detail
+}
-            ))
+
-        }
+pub fn extract_error_from_response(status: StatusCode, bytes: &Bytes) -> Error {
-        Err(_) => {
+    match serde_json::from_slice::<HttpApiProblem>(bytes) {
-            let detail = str::from_utf8(bytes).unwrap_or("unknown");
+        Ok(api_problem) => {
-            error!("Server {}: {}", status.as_u16(), detail);
+            let server_error = ServerError {
-            anyhow!(format!("Server {}: {}", status.as_u16(), detail))
+                status,
+                title: api_problem.title,
+                detail: api_problem.detail,
+            };
+            error!("{}", server_error);
+            anyhow!(server_error)
+        }
+        Err(_) => {
+            let title = str::from_utf8(bytes)
+                .unwrap_or_else(|_| &status.canonical_reason().unwrap_or("unknown"))
+                .to_string();
+            let server_error = ServerError {
+                status,
+                title,
+                detail: None,
+            };
+            error!("{}", server_error);
+            anyhow!(server_error)
         }
     }
 }

src/interior_ref_list.rs

@@ -11,9 +11,13 @@ use log::{error, info};
 use std::{println as info, println as error};
 
 use crate::{
-    cache::file_cache_dir, cache::from_file_cache, cache::load_metadata_from_file_cache,
+    cache::file_cache_dir,
-    cache::update_file_caches, error::extract_error_from_response, log_server_error,
+    cache::from_file_cache,
-    result::FFIResult,
+    cache::load_metadata_from_file_cache,
+    cache::update_file_caches,
+    error::extract_error_from_response,
+    log_server_error,
+    result::{FFIError, FFIResult},
 };
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -334,11 +338,7 @@ pub extern "C" fn create_interior_ref_list(
         Ok(interior_ref_list) => FFIResult::Ok(interior_ref_list.id),
         Err(err) => {
             error!("create_interior_ref_list failed. {}", err);
-            // TODO: also need to drop this CString once C++ is done reading it
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -419,11 +419,7 @@ pub extern "C" fn update_interior_ref_list(
         Ok(interior_ref_list) => FFIResult::Ok(interior_ref_list.id),
         Err(err) => {
             error!("update_interior_ref_list failed. {}", err);
-            // TODO: also need to drop this CString once C++ is done reading it
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -526,13 +522,8 @@ pub extern "C" fn get_interior_ref_list(
             })
         }
         Err(err) => {
-            error!("interior_ref_list failed. {}", err);
+            error!("get_interior_ref_list failed. {}", err);
-            // TODO: how to do error handling?
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            // TODO: also need to drop this CString once C++ is done reading it
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -633,12 +624,7 @@ pub extern "C" fn get_interior_ref_list_by_shop_id(
         }
         Err(err) => {
             error!("get_interior_ref_list_by_shop_id failed. {}", err);
-            // TODO: how to do error handling?
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            // TODO: also need to drop this CString once C++ is done reading it
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -742,11 +728,17 @@ mod tests {
             FFIResult::Ok(interior_ref_list_id) => {
                 assert_eq!(interior_ref_list_id, 1);
             }
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => panic!(
-                panic!("create_interior_ref_list returned error: {:?}", unsafe {
+                "create_interior_ref_list returned error: {:?}",
-                    CStr::from_ptr(error).to_string_lossy()
+                match error {
-                })
+                    FFIError::Server(server_error) =>
-            }
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -805,12 +797,16 @@ mod tests {
                 "create_interior_ref_list returned Ok result: {:?}",
                 interior_ref_list_id
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("create_interior_ref_list did not return a server error"),
+            },
         }
     }
 
@@ -905,11 +901,17 @@ mod tests {
             FFIResult::Ok(interior_ref_list_id) => {
                 assert_eq!(interior_ref_list_id, 1);
             }
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => panic!(
-                panic!("update_interior_ref_list returned error: {:?}", unsafe {
+                "update_interior_ref_list returned error: {:?}",
-                    CStr::from_ptr(error).to_string_lossy()
+                match error {
-                })
+                    FFIError::Server(server_error) =>
-            }
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -968,12 +970,16 @@ mod tests {
                 "update_interior_ref_list returned Ok result: {:?}",
                 interior_ref_list_id
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("update_interior_ref_list did not return a server error"),
+            },
         }
     }
 
@@ -1080,9 +1086,17 @@ mod tests {
                 assert_eq!(raw_shelf.sort_on, std::ptr::null());
                 assert_eq!(raw_shelf.sort_asc, true);
             }
-            FFIResult::Err(error) => panic!("get_interior_ref_list returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "get_interior_ref_list returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -1102,12 +1116,15 @@ mod tests {
                 "get_interior_ref_list returned Ok result: {:#x?}",
                 raw_interior_ref_vec
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Network(network_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(
-                    "io error: failed to fill whole buffer" // empty tempfile
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() },
-                );
+                        "Object not found in API or in cache: interior_ref_list_1.bin",
-            }
+                    );
+                }
+                _ => panic!("get_interior_ref_list did not return a network error"),
+            },
         }
     }
 
@@ -1216,7 +1233,14 @@ mod tests {
             }
             FFIResult::Err(error) => panic!(
                 "get_interior_ref_list_by_shop_id returned error: {:?}",
-                unsafe { CStr::from_ptr(error).to_string_lossy() }
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
             ),
         }
     }
@@ -1237,12 +1261,15 @@ mod tests {
                 "get_interior_ref_list_by_shop_id returned Ok result: {:#x?}",
                 raw_interior_ref_vec
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Network(network_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(
-                    "io error: failed to fill whole buffer" // empty tempfile
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() },
-                );
+                        "Object not found in API or in cache: shop_1_interior_ref_list.bin",
-            }
+                    );
+                }
+                _ => panic!("get_interior_ref_list_by_shop_id did not return a network error"),
+            },
         }
     }
 }

src/merchandise_list.rs

@@ -13,7 +13,7 @@ use std::{println as info, println as error};
 use crate::{
     cache::file_cache_dir, cache::from_file_cache, cache::load_metadata_from_file_cache,
     cache::update_file_caches, error::extract_error_from_response, log_server_error,
-    result::FFIResult,
+    result::{FFIError, FFIResult},
 };
 
 #[derive(Serialize, Deserialize, Debug, Clone)]
@@ -207,12 +207,7 @@ pub extern "C" fn create_merchandise_list(
         }
         Err(err) => {
             error!("create_merchandise_list failed. {}", err);
-            // TODO: how to do error handling?
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            // TODO: also need to drop this CString once C++ is done reading it
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -312,12 +307,7 @@ pub extern "C" fn update_merchandise_list(
         }
         Err(err) => {
             error!("update_merchandise_list failed. {}", err);
-            // TODO: how to do error handling?
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            // TODO: also need to drop this CString once C++ is done reading it
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -428,13 +418,8 @@ pub extern "C" fn get_merchandise_list(
             FFIResult::Ok(RawMerchandiseVec { ptr, len, cap })
         }
         Err(err) => {
-            error!("merchandise_list failed. {}", err);
+            error!("get_merchandise_list failed. {}", err);
-            // TODO: how to do error handling?
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            // TODO: also need to drop this CString once C++ is done reading it
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -539,12 +524,7 @@ pub extern "C" fn get_merchandise_list_by_shop_id(
         }
         Err(err) => {
             error!("get_merchandise_list_by_shop_id failed. {}", err);
-            // TODO: how to do error handling?
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            // TODO: also need to drop this CString once C++ is done reading it
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -627,11 +607,17 @@ mod tests {
                 assert_eq!(raw_merchandise.is_food, false);
                 assert_eq!(raw_merchandise.price, 100);
             }
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => panic!(
-                panic!("create_merchandise_list returned error: {:?}", unsafe {
+                "create_merchandise_list returned error: {:?}",
-                    CStr::from_ptr(error).to_string_lossy()
+                match error {
-                })
+                    FFIError::Server(server_error) =>
-            }
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -666,12 +652,16 @@ mod tests {
                 "create_merchandise_list returned Ok result: {:#x?}",
                 raw_merchandise_vec
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("create_merchandise_list did not return a server error"),
+            },
         }
     }
 
@@ -745,11 +735,17 @@ mod tests {
                 assert_eq!(raw_merchandise.is_food, false);
                 assert_eq!(raw_merchandise.price, 100);
             }
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => panic!(
-                panic!("update_merchandise_list returned error: {:?}", unsafe {
+                "update_merchandise_list returned error: {:?}",
-                    CStr::from_ptr(error).to_string_lossy()
+                match error {
-                })
+                    FFIError::Server(server_error) =>
-            }
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -784,12 +780,16 @@ mod tests {
                 "update_merchandise_list returned Ok result: {:#x?}",
                 raw_merchandise_vec
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("update_merchandise_list did not return a server error"),
+            },
         }
     }
     #[test]
@@ -857,9 +857,17 @@ mod tests {
                     "VendorItemWeapon".to_string(),
                 );
             }
-            FFIResult::Err(error) => panic!("get_merchandise_list returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "get_merchandise_list returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -879,12 +887,15 @@ mod tests {
                 "get_merchandise_list returned Ok result: {:#x?}",
                 raw_merchandise_vec
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Network(network_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(
-                    "io error: failed to fill whole buffer" // empty tempfile
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() },
-                );
+                        "Object not found in API or in cache: merchandise_list_1.bin",
-            }
+                    );
+                }
+                _ => panic!("get_merchandise_list did not return a network error"),
+            },
         }
     }
 
@@ -955,7 +966,14 @@ mod tests {
             }
             FFIResult::Err(error) => panic!(
                 "get_merchandise_list_by_shop_id returned error: {:?}",
-                unsafe { CStr::from_ptr(error).to_string_lossy() }
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
             ),
         }
     }
@@ -976,12 +994,15 @@ mod tests {
                 "get_merchandise_list_by_shop_id returned Ok result: {:#x?}",
                 raw_merchandise_vec
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Network(network_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(
-                    "io error: failed to fill whole buffer" // empty tempfile
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() },
-                );
+                        "Object not found in API or in cache: shop_1_merchandise_list.bin",
-            }
+                    );
+                }
+                _ => panic!("get_merchandise_list_by_shop_id did not return a network error"),
+            },
         }
     }
 }

src/owner.rs

@@ -11,8 +11,10 @@ use log::{error, info};
 use std::{println as info, println as error};
 
 use crate::{
-    cache::file_cache_dir, cache::update_file_caches, error::extract_error_from_response,
+    cache::file_cache_dir,
-    result::FFIResult,
+    cache::update_file_caches,
+    error::extract_error_from_response,
+    result::{FFIError, FFIResult},
 };
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -112,11 +114,7 @@ pub extern "C" fn create_owner(
         }
         Err(err) => {
             error!("create_owner failed. {}", err);
-            // TODO: also need to drop this CString once C++ is done reading it
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -182,11 +180,7 @@ pub extern "C" fn update_owner(
         }
         Err(err) => {
             error!("update_owner failed. {}", err);
-            // TODO: also need to drop this CString once C++ is done reading it
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -229,9 +223,17 @@ mod tests {
                 );
                 assert_eq!(raw_owner.mod_version, 1);
             }
-            FFIResult::Err(error) => panic!("create_owner returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "create_owner returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -252,12 +254,16 @@ mod tests {
             FFIResult::Ok(raw_owner) => {
                 panic!("create_owner returned Ok result: {:#x?}", raw_owner)
             }
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("create_owner did not return a server error"),
+            },
         }
     }
 
@@ -291,9 +297,17 @@ mod tests {
                 );
                 assert_eq!(raw_owner.mod_version, 1);
             }
-            FFIResult::Err(error) => panic!("update_owner returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "update_owner returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -314,12 +328,16 @@ mod tests {
             FFIResult::Ok(raw_owner) => {
                 panic!("update_owner returned Ok result: {:#x?}", raw_owner)
             }
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("update_owner did not return a server error"),
+            },
         }
     }
 }

src/result.rs

@@ -1,8 +1,62 @@
+use anyhow::Error;
+
+use std::convert::From;
+use std::ffi::CString;
 use std::os::raw::c_char;
+use std::ptr::null;
+
+use crate::error::ServerError;
+
+#[derive(Debug, PartialEq)]
+#[repr(C)]
+pub struct FFIServerError {
+    pub status: u16,
+    pub title: *const c_char,
+    pub detail: *const c_char,
+}
+
+impl From<&ServerError> for FFIServerError {
+    fn from(server_error: &ServerError) -> Self {
+        FFIServerError {
+            status: server_error.status.as_u16(),
+            // TODO: may need to drop these CStrings once C++ is done reading them
+            title: CString::new(server_error.title.clone())
+                .expect("could not create CString")
+                .into_raw(),
+            detail: match &server_error.detail {
+                Some(detail) => CString::new(detail.clone())
+                    .expect("could not create CString")
+                    .into_raw(),
+                None => null(),
+            },
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+#[repr(C, u8)]
+pub enum FFIError {
+    Server(FFIServerError),
+    Network(*const c_char),
+}
+
+impl From<Error> for FFIError {
+    fn from(error: Error) -> Self {
+        if let Some(server_error) = error.downcast_ref::<ServerError>() {
+            FFIError::Server(FFIServerError::from(server_error))
+        } else {
+            // TODO: also need to drop this CString once C++ is done reading it
+            let err_string = CString::new(error.to_string())
+                .expect("could not create CString")
+                .into_raw();
+            FFIError::Network(err_string)
+        }
+    }
+}
 
 #[derive(Debug, PartialEq)]
 #[repr(C, u8)]
 pub enum FFIResult<T> {
     Ok(T),
-    Err(*const c_char),
+    Err(FFIError),
 }

src/shop.rs

@@ -11,9 +11,13 @@ use log::{error, info};
 use std::{println as info, println as error};
 
 use crate::{
-    cache::file_cache_dir, cache::from_file_cache, cache::load_metadata_from_file_cache,
+    cache::file_cache_dir,
-    cache::update_file_caches, error::extract_error_from_response, log_server_error,
+    cache::from_file_cache,
-    result::FFIResult,
+    cache::load_metadata_from_file_cache,
+    cache::update_file_caches,
+    error::extract_error_from_response,
+    log_server_error,
+    result::{FFIError, FFIResult},
 };
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -155,11 +159,7 @@ pub extern "C" fn create_shop(
         }
         Err(err) => {
             error!("create_shop failed. {}", err);
-            // TODO: also need to drop this CString once C++ is done reading it
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -272,11 +272,7 @@ pub extern "C" fn update_shop(
         }
         Err(err) => {
             error!("update_shop failed. {}", err);
-            // TODO: also need to drop this CString once C++ is done reading it
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -346,12 +342,8 @@ pub extern "C" fn get_shop(
             FFIResult::Ok(RawShop::from(shop))
         }
         Err(err) => {
-            error!("get_shop_list failed. {}", err);
+            error!("get_shop failed. {}", err);
-            let err_string = CString::new(err.to_string())
+            FFIResult::Err(FFIError::from(err))
-                .expect("could not create CString")
-                .into_raw();
-            // TODO: also need to drop this CString once C++ is done reading it
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -419,11 +411,7 @@ pub extern "C" fn list_shops(
         }
         Err(err) => {
             error!("list_shops failed. {}", err);
-            let err_string = CString::new(err.to_string())
+            FFIResult::Err(FFIError::from(err))
-                .expect("could not create CString")
-                .into_raw();
-            // TODO: also need to drop this CString once C++ is done reading it
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -490,9 +478,17 @@ mod tests {
                 );
                 assert_eq!(raw_shop.vendor_keywords_exclude, true);
             }
-            FFIResult::Err(error) => panic!("create_shop returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "create_shop returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -511,12 +507,16 @@ mod tests {
         mock.assert();
         match result {
             FFIResult::Ok(raw_shop) => panic!("create_shop returned Ok result: {:#x?}", raw_shop),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("create_shop did not return a server error"),
+            },
         }
     }
 
@@ -589,9 +589,17 @@ mod tests {
                 );
                 assert_eq!(raw_shop.vendor_keywords_exclude, true);
             }
-            FFIResult::Err(error) => panic!("update_shop returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "update_shop returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -625,12 +633,16 @@ mod tests {
         mock.assert();
         match result {
             FFIResult::Ok(raw_shop) => panic!("update_shop returned Ok result: {:#x?}", raw_shop),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("update_shop did not return a server error"),
+            },
         }
     }
 
@@ -686,9 +698,17 @@ mod tests {
                 );
                 assert_eq!(raw_shop.vendor_keywords_exclude, true);
             }
-            FFIResult::Err(error) => panic!("get_shop returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "get_shop returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -705,12 +725,15 @@ mod tests {
         mock.assert();
         match result {
             FFIResult::Ok(raw_shop) => panic!("get_shop returned Ok result: {:#x?}", raw_shop),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Network(network_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(
-                    "io error: failed to fill whole buffer" // empty tempfile
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() },
-                );
+                        "Object not found in API or in cache: shop_1.bin",
-            }
+                    );
+                }
+                _ => panic!("get_shop did not return a network error"),
+            },
         }
     }
 
@@ -771,9 +794,17 @@ mod tests {
                 );
                 assert_eq!(raw_shop.vendor_keywords_exclude, true);
             }
-            FFIResult::Err(error) => panic!("list_shops returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "list_shops returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -790,12 +821,15 @@ mod tests {
         mock.assert();
         match result {
             FFIResult::Ok(raw_shop) => panic!("list_shops returned Ok result: {:#x?}", raw_shop),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Network(network_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(
-                    "io error: failed to fill whole buffer" // empty tempfile
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() },
-                );
+                        "Object not found in API or in cache: shops.bin",
-            }
+                    );
+                }
+                _ => panic!("list_shops did not return a network error"),
+            },
         }
     }
 }

src/transaction.rs

@@ -11,8 +11,10 @@ use log::{error, info};
 use std::{println as info, println as error};
 
 use crate::{
-    cache::file_cache_dir, cache::update_file_caches, error::extract_error_from_response,
+    cache::file_cache_dir,
-    result::FFIResult,
+    cache::update_file_caches,
+    error::extract_error_from_response,
+    result::{FFIError, FFIResult},
 };
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -193,11 +195,7 @@ pub extern "C" fn create_transaction(
         Ok(transaction) => FFIResult::Ok(RawTransaction::from(transaction)),
         Err(err) => {
             error!("create_transaction failed. {}", err);
-            // TODO: also need to drop this CString once C++ is done reading it
+            FFIResult::Err(FFIError::from(err))
-            let err_string = CString::new(err.to_string())
-                .expect("could not create CString")
-                .into_raw();
-            FFIResult::Err(err_string)
         }
     }
 }
@@ -294,9 +292,17 @@ mod tests {
                     vec!["VendorItemMisc".to_string()]
                 );
             }
-            FFIResult::Err(error) => panic!("create_transaction returned error: {:?}", unsafe {
+            FFIResult::Err(error) => panic!(
-                CStr::from_ptr(error).to_string_lossy()
+                "create_transaction returned error: {:?}",
-            }),
+                match error {
+                    FFIError::Server(server_error) =>
+                        format!("{} {}", server_error.status, unsafe {
+                            CStr::from_ptr(server_error.title).to_string_lossy()
+                        }),
+                    FFIError::Network(network_error) =>
+                        unsafe { CStr::from_ptr(network_error).to_string_lossy() }.to_string(),
+                }
+            ),
         }
     }
 
@@ -344,12 +350,16 @@ mod tests {
                 "create_transaction returned Ok result: {:#?}",
                 raw_transaction
             ),
-            FFIResult::Err(error) => {
+            FFIResult::Err(error) => match error {
-                assert_eq!(
+                FFIError::Server(server_error) => {
-                    unsafe { CStr::from_ptr(error).to_string_lossy() },
+                    assert_eq!(server_error.status, 500);
-                    "Server 500: Internal Server Error. Some error detail"
+                    assert_eq!(
-                );
+                        unsafe { CStr::from_ptr(server_error.title).to_string_lossy() },
-            }
+                        "Internal Server Error"
+                    );
+                }
+                _ => panic!("create_transaction did not return a server error"),
+            },
         }
     }
 }