Initial attempt at no_std

Cargo.toml

@@ -16,7 +16,9 @@ exclude = [
 ]
 
 [features]
-default = []
+default = ["std"]
+alloc = []      # provides access to `Vec` without enabling `std` mode
+std = []        # std mode (enabled by default) - provides access to `std::io`, `Error` and `Vec`
 reference = []  # follows reference encoder implementation precisely, but may be slightly slower
 
 [dependencies]

src/decode.rs

@@ -1,3 +1,6 @@
+#[cfg(any(feature = "std", feature = "alloc"))]
+use alloc::{vec, vec::Vec};
+#[cfg(feature = "std")]
 use std::io::Read;
 
 // TODO: can be removed once https://github.com/rust-lang/rust/issues/74985 is stable
@@ -111,6 +114,7 @@ pub fn qoi_decode_to_buf(buf: impl AsMut<[u8]>, data: impl AsRef<[u8]>) -> Resul
     Ok(*decoder.header())
 }
 
+#[cfg(any(feature = "std", feature = "alloc"))]
 #[inline]
 pub fn qoi_decode_to_vec(data: impl AsRef<[u8]>) -> Result<(Header, Vec<u8>)> {
     let mut decoder = QoiDecoder::new(&data)?;
@@ -177,6 +181,7 @@ impl<'a> QoiDecoder<'a> {
         Ok(size)
     }
 
+    #[cfg(any(feature = "std", feature = "alloc"))]
     #[inline]
     pub fn decode_to_vec(&mut self) -> Result<Vec<u8>> {
         let mut out = vec![0; self.header.n_pixels() * self.channels.as_u8() as usize];
@@ -184,6 +189,7 @@ impl<'a> QoiDecoder<'a> {
     }
 }
 
+#[cfg(any(feature = "std"))]
 #[inline]
 fn qoi_decode_impl_stream<R: Read, const N: usize, const RGBA: bool>(
     data: &mut R, out: &mut [u8],
@@ -253,6 +259,7 @@ where
     Ok(())
 }
 
+#[cfg(feature = "std")]
 #[inline]
 fn qoi_decode_impl_stream_all<R: Read>(
     data: &mut R, out: &mut [u8], channels: u8, src_channels: u8,
@@ -269,12 +276,14 @@ fn qoi_decode_impl_stream_all<R: Read>(
     }
 }
 
+#[cfg(feature = "std")]
 pub struct QoiStreamDecoder<R> {
     reader: R,
     header: Header,
     channels: Channels,
 }
 
+#[cfg(feature = "std")]
 impl<R: Read> QoiStreamDecoder<R> {
     #[inline]
     pub fn new(mut reader: R) -> Result<Self> {

src/encode.rs

@@ -1,4 +1,7 @@
-use std::convert::TryFrom;
+#[cfg(any(feature = "std", feature = "alloc"))]
+use alloc::{vec, vec::Vec};
+use core::convert::TryFrom;
+#[cfg(feature = "std")]
 use std::io::Write;
 
 use crate::consts::{QOI_HEADER_SIZE, QOI_OP_INDEX, QOI_OP_RUN, QOI_PADDING, QOI_PADDING_SIZE};
@@ -6,7 +9,9 @@ use crate::error::{Error, Result};
 use crate::header::Header;
 use crate::pixel::{Pixel, SupportedChannels};
 use crate::types::{Channels, ColorSpace};
-use crate::utils::{unlikely, BytesMut, GenericWriter, Writer};
+#[cfg(feature = "std")]
+use crate::utils::GenericWriter;
+use crate::utils::{cold, unlikely, BytesMut, Writer};
 
 #[allow(clippy::cast_possible_truncation, unused_assignments)]
 fn qoi_encode_impl<W: Writer, const N: usize>(mut buf: W, data: &[u8]) -> Result<usize>
@@ -89,6 +94,7 @@ pub fn qoi_encode_to_buf(
     QoiEncoder::new(&data, width, height)?.encode_to_buf(buf)
 }
 
+#[cfg(any(feature = "alloc", feature = "std"))]
 #[inline]
 pub fn qoi_encode_to_vec(data: impl AsRef<[u8]>, width: u32, height: u32) -> Result<Vec<u8>> {
     QoiEncoder::new(&data, width, height)?.encode_to_vec()
@@ -149,6 +155,7 @@ impl<'a> QoiEncoder<'a> {
         Ok(QOI_HEADER_SIZE + n_written)
     }
 
+    #[cfg(any(feature = "alloc", feature = "std"))]
     #[inline]
     pub fn encode_to_vec(&self) -> Result<Vec<u8>> {
         let mut out = vec![0_u8; self.encoded_size_limit()];
@@ -157,6 +164,7 @@ impl<'a> QoiEncoder<'a> {
         Ok(out)
     }
 
+    #[cfg(feature = "std")]
     #[inline]
     pub fn encode_to_stream<W: Write>(&self, writer: &mut W) -> Result<usize> {
         writer.write_all(&self.header.encode())?;

src/error.rs

@@ -1,27 +1,47 @@
-use std::convert::Infallible;
-use std::error::Error as StdError;
-use std::fmt::{self, Display};
-use std::io;
-use std::result::Result as StdResult;
+use core::convert::Infallible;
+use core::fmt::{self, Display};
 
 use crate::consts::{QOI_MAGIC, QOI_PIXELS_MAX};
 
 #[derive(Debug)]
 pub enum Error {
-    InvalidChannels { channels: u8 },
-    EmptyImage { width: u32, height: u32 },
-    ImageTooLarge { width: u32, height: u32 },
-    InvalidImageLength { size: usize, width: u32, height: u32 },
-    InputBufferTooSmall { size: usize, required: usize },
-    OutputBufferTooSmall { size: usize, required: usize },
-    InvalidMagic { magic: u32 },
+    InvalidChannels {
+        channels: u8,
+    },
+    EmptyImage {
+        width: u32,
+        height: u32,
+    },
+    ImageTooLarge {
+        width: u32,
+        height: u32,
+    },
+    InvalidImageLength {
+        size: usize,
+        width: u32,
+        height: u32,
+    },
+    InputBufferTooSmall {
+        size: usize,
+        required: usize,
+    },
+    OutputBufferTooSmall {
+        size: usize,
+        required: usize,
+    },
+    InvalidMagic {
+        magic: u32,
+    },
     UnexpectedBufferEnd,
-    InvalidColorSpace { colorspace: u8 },
+    InvalidColorSpace {
+        colorspace: u8,
+    },
     InvalidPadding,
-    IoError(io::Error),
+    #[cfg(feature = "std")]
+    IoError(std::io::Error),
 }
 
-pub type Result<T> = StdResult<T, Error>;
+pub type Result<T> = core::result::Result<T, Error>;
 
 impl Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -57,6 +77,7 @@ impl Display for Error {
             Self::InvalidPadding => {
                 write!(f, "invalid padding (stream end marker)")
             }
+            #[cfg(feature = "std")]
             Self::IoError(ref err) => {
                 write!(f, "i/o error: {}", err)
             }
@@ -64,7 +85,8 @@ impl Display for Error {
     }
 }
 
-impl StdError for Error {}
+#[cfg(feature = "std")]
+impl std::error::Error for Error {}
 
 impl From<Infallible> for Error {
     fn from(_: Infallible) -> Self {
@@ -72,8 +94,9 @@ impl From<Infallible> for Error {
     }
 }
 
-impl From<io::Error> for Error {
-    fn from(err: io::Error) -> Self {
+#[cfg(feature = "std")]
+impl From<std::io::Error> for Error {
+    fn from(err: std::io::Error) -> Self {
         Self::IoError(err)
     }
 }

src/header.rs

@@ -1,4 +1,4 @@
-use std::convert::TryInto;
+use core::convert::TryInto;
 
 use bytemuck::cast_slice;
 

src/lib.rs

@@ -8,6 +8,11 @@
     clippy::module_name_repetitions,
     clippy::cargo_common_metadata
 )]
+#![cfg_attr(not(any(feature = "std", test)), no_std)]
+#[cfg(all(feature = "alloc", not(any(feature = "std", test))))]
+extern crate alloc;
+#[cfg(any(feature = "std", test))]
+extern crate std as alloc;
 
 mod decode;
 mod encode;
@@ -20,10 +25,15 @@ mod utils;
 #[doc(hidden)]
 pub mod consts;
 
-pub use crate::decode::{
-    qoi_decode_header, qoi_decode_to_buf, qoi_decode_to_vec, QoiDecoder, QoiStreamDecoder,
-};
-pub use crate::encode::{encoded_size_limit, qoi_encode_to_buf, qoi_encode_to_vec, QoiEncoder};
+#[cfg(any(feature = "alloc", feature = "std"))]
+pub use crate::decode::qoi_decode_to_vec;
+#[cfg(feature = "std")]
+pub use crate::decode::QoiStreamDecoder;
+pub use crate::decode::{qoi_decode_header, qoi_decode_to_buf, QoiDecoder};
+
+#[cfg(any(feature = "alloc", feature = "std"))]
+pub use crate::encode::qoi_encode_to_vec;
+pub use crate::encode::{encoded_size_limit, qoi_encode_to_buf, QoiEncoder};
 pub use crate::error::{Error, Result};
 pub use crate::header::Header;
 pub use crate::types::{Channels, ColorSpace};

src/types.rs

@@ -1,4 +1,4 @@
-use std::convert::TryFrom;
+use core::convert::TryFrom;
 
 use crate::error::{Error, Result};
 use crate::utils::unlikely;

src/utils.rs

@@ -1,3 +1,4 @@
+#[cfg(feature = "std")]
 use std::io::Write;
 
 use crate::error::Result;
@@ -29,17 +30,20 @@ pub trait Writer: Sized {
     fn capacity(&self) -> usize;
 }
 
+#[cfg(feature = "std")]
 pub struct GenericWriter<W> {
     writer: W,
     n_written: usize,
 }
 
+#[cfg(feature = "std")]
 impl<W: Write> GenericWriter<W> {
     pub fn new(writer: W) -> Self {
         Self { writer, n_written: 0 }
     }
 }
 
+#[cfg(feature = "std")]
 impl<W: Write> Writer for GenericWriter<W> {
     fn write_one(mut self, v: u8) -> Result<Self> {
         self.n_written += 1;