Initial working version (but lots of temp stuff)

src/error.rs

@@ -0,0 +1,42 @@
+use std::error::Error as StdError;
+use std::fmt::{self, Display};
+use std::result::Result as StdResult;
+
+use crate::consts::{QOI_HEADER_SIZE, QOI_MAGIC, QOI_PADDING};
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum Error {
+    InvalidChannels { channels: u8 },
+    EmptyImage { width: u32, height: u32 },
+    BadEncodingDataSize { size: usize, expected: usize },
+    BadDecodingDataSize { size: usize },
+    InvalidMagic { magic: [u8; 4] },
+    // TODO: invalid colorspace
+}
+
+pub type Result<T> = StdResult<T, Error>;
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Self::InvalidChannels { channels } => {
+                write!(f, "invalid number of channels: {}", channels)
+            }
+            Self::EmptyImage { width, height } => {
+                write!(f, "image contains no pixels: {}x{}", width, height)
+            }
+            Self::BadEncodingDataSize { size, expected } => {
+                write!(f, "bad data size when encoding: {} (expected: {})", size, expected)
+            }
+            Self::BadDecodingDataSize { size } => {
+                let min_size = QOI_HEADER_SIZE + QOI_PADDING;
+                write!(f, "bad data size when decoding: {} (minimum required: {})", size, min_size)
+            }
+            Self::InvalidMagic { magic } => {
+                write!(f, "invalid magic: expected {:?}, got {:?}", QOI_MAGIC, magic)
+            }
+        }
+    }
+}
+
+impl StdError for Error {}