improve error handling and utility (#100)

* improve error handling and utility

* non-exhaustive

* fix warning

* clean up test utility and properly classify EOF errors

* address comments

src/helpers.rs

@@ -25,11 +25,8 @@ pub const fn u32_bit_length(v: u32) -> u8 {
 }
 
 #[cold]
-pub fn err_exit_code<T>(_error_code: ExitCode, message: &str) -> anyhow::Result<T> {
-    return Err(anyhow::Error::new(LeptonError {
-        exit_code: _error_code,
-        message: message.to_string(),
-    }));
+pub fn err_exit_code<T>(error_code: ExitCode, message: &str) -> anyhow::Result<T> {
+    return Err(anyhow::Error::new(LeptonError::new(error_code, message)));
 }
 
 pub fn buffer_prefix_matches_marker<const BS: usize, const MS: usize>(

src/lepton_error.rs

@@ -4,16 +4,16 @@
  *  This software incorporates material from third parties. See NOTICE.txt for details.
  *--------------------------------------------------------------------------------------------*/
 
-use std::fmt::Display;
+use std::{fmt::Display, io::ErrorKind};
 
 #[derive(Debug, Clone, Copy, PartialEq)]
 #[allow(dead_code)]
-
+#[non_exhaustive]
 /// Well-defined errors for bad things that are expected to happen as part of compression/decompression
 pub enum ExitCode {
     //AssertionFailure = 1,
     //CodingError = 2,
-    //ShortRead = 3,
+    ShortRead = 3,
     Unsupported4Colors = 4,
     CoefficientOutOfRange = 6,
     StreamInconsistent = 7,
@@ -23,10 +23,13 @@ pub enum ExitCode {
     //ThreadingPartialMcu = 12,
     VersionUnsupported = 13,
     //OnlyGarbageNoJpeg = 14,
-    //OsError = 33,
+    OsError = 33,
     //HeaderTooLarge = 34,
     //BlockOffsetOOM = 37,
     UnsupportedJpeg = 42,
+    UnsupportedJpegWithZeroIdct0 = 43,
+    InvalidResetCode = 44,
+    InvalidPadding = 45,
     //WrapperOutputWriteFailed = 101,
     BadLeptonFile = 102,
 
@@ -48,13 +51,13 @@ impl Display for ExitCode {
 }
 
 /// Standard error returned by Lepton library
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct LeptonError {
     /// standard error code
-    pub exit_code: ExitCode,
+    exit_code: ExitCode,
 
     /// diagnostic message including location. Content should not be relied on.
-    pub message: String,
+    message: String,
 }
 
 impl Display for LeptonError {
@@ -63,4 +66,122 @@ impl Display for LeptonError {
     }
 }
 
+impl LeptonError {
+    pub fn new(exit_code: ExitCode, message: &str) -> LeptonError {
+        LeptonError {
+            exit_code,
+            message: message.to_owned(),
+        }
+    }
+
+    pub fn exit_code(&self) -> ExitCode {
+        self.exit_code
+    }
+
+    pub fn message(&self) -> &str {
+        &self.message
+    }
+}
+
 impl std::error::Error for LeptonError {}
+
+impl From<anyhow::Error> for LeptonError {
+    fn from(mut error: anyhow::Error) -> Self {
+        // first see if there is a LeptonError already inside
+        match error.downcast::<LeptonError>() {
+            Ok(le) => {
+                return le;
+            }
+            Err(old_error) => {
+                error = old_error;
+            }
+        }
+
+        // capture the original error string before we lose it due
+        // to downcasting to look for stashed LeptonErrors
+        let original_string = error.to_string();
+
+        // see if there is a LeptonError hiding inside an io error
+        // which happens if we cross an API boundary that returns an std::io:Error
+        // like Read or Write
+        match error.downcast::<std::io::Error>() {
+            Ok(ioe) => match ioe.downcast::<LeptonError>() {
+                Ok(le) => {
+                    return le;
+                }
+                Err(e) => {
+                    return LeptonError {
+                        exit_code: get_io_error_exit_code(&e),
+                        message: format!("{} {}", e, original_string),
+                    };
+                }
+            },
+            Err(_) => {}
+        }
+
+        // don't know what we got, so treat it as a general failure
+        return LeptonError {
+            exit_code: ExitCode::GeneralFailure,
+            message: original_string,
+        };
+    }
+}
+
+fn get_io_error_exit_code(e: &std::io::Error) -> ExitCode {
+    if e.kind() == ErrorKind::UnexpectedEof {
+        ExitCode::ShortRead
+    } else {
+        ExitCode::OsError
+    }
+}
+
+/// translates std::io::Error into LeptonError
+impl From<std::io::Error> for LeptonError {
+    #[track_caller]
+    fn from(e: std::io::Error) -> Self {
+        match e.downcast::<LeptonError>() {
+            Ok(le) => {
+                return le;
+            }
+            Err(e) => {
+                let caller = std::panic::Location::caller();
+                return LeptonError {
+                    exit_code: get_io_error_exit_code(&e),
+                    message: format!("error {} at {}", e.to_string(), caller.to_string()),
+                };
+            }
+        }
+    }
+}
+
+/// translates LeptonError into std::io::Error, which involves putting into a Box and using Other
+impl From<LeptonError> for std::io::Error {
+    fn from(e: LeptonError) -> Self {
+        return std::io::Error::new(std::io::ErrorKind::Other, e);
+    }
+}
+
+#[test]
+fn test_error_translation() {
+    // test wrapping inside an io error
+    fn my_std_error() -> Result<(), std::io::Error> {
+        Err(LeptonError::new(ExitCode::SyntaxError, "test error").into())
+    }
+
+    let e: LeptonError = my_std_error().unwrap_err().into();
+    assert_eq!(e.exit_code, ExitCode::SyntaxError);
+    assert_eq!(e.message, "test error");
+
+    // wrapping inside anyhow
+    fn my_anyhow() -> Result<(), anyhow::Error> {
+        Err(LeptonError::new(ExitCode::SyntaxError, "test error").into())
+    }
+
+    let e: LeptonError = my_anyhow().unwrap_err().into();
+    assert_eq!(e.exit_code, ExitCode::SyntaxError);
+    assert_eq!(e.message, "test error");
+
+    // an IO error should be translated into an OsError
+    let e: LeptonError = std::io::Error::new(std::io::ErrorKind::NotFound, "file not found").into();
+    assert_eq!(e.exit_code, ExitCode::OsError);
+}