midi_msg/

message.rs

use alloc::vec;
use alloc::vec::Vec;
use core::convert::TryFrom;

use super::{
    ChannelModeMsg, ChannelVoiceMsg, ParseError, ReceiverContext, SystemCommonMsg,
    SystemRealTimeMsg,
};

#[cfg(feature = "sysex")]
use super::SystemExclusiveMsg;

#[cfg(feature = "file")]
use super::Meta;

/// The primary interface of this library. Used to encode MIDI messages.
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, Clone, PartialEq)]
pub enum MidiMsg {
    /// Channel-level messages that act on a voice, such as turning notes on and off.
    ChannelVoice {
        channel: Channel,
        msg: ChannelVoiceMsg,
    },
    /// Like `ChannelVoice`, but with the first "status" byte of the message omitted.
    /// When these "running status" messages are sent, the receiver must treat them
    /// as implicitly referring to the previous "status" received.
    ///
    /// For instance, if a `ChannelVoiceMsg::NoteOn` message is received, and then
    /// the next message does not contain a status byte, it implicitly refers to a
    /// `ChannelVoiceMsg::NoteOn`.
    RunningChannelVoice {
        channel: Channel,
        msg: ChannelVoiceMsg,
    },
    /// Channel-level messages that should alter the mode of the receiver.
    ChannelMode {
        channel: Channel,
        msg: ChannelModeMsg,
    },
    /// Like `RunningChannelVoice` but for `ChannelMode`
    RunningChannelMode {
        channel: Channel,
        msg: ChannelModeMsg,
    },
    /// A fairly limited set of messages, generally for device synchronization.
    SystemCommon { msg: SystemCommonMsg },
    /// Another limited set of messages used for device synchronization.
    SystemRealTime { msg: SystemRealTimeMsg },
    /// The bulk of the MIDI spec lives here, in "Universal System Exclusive" messages.
    /// Also the home of manufacturer-specific messages.
    #[cfg(feature = "sysex")]
    SystemExclusive { msg: SystemExclusiveMsg },

    /// A Meta event, which occur within MIDI files.
    #[cfg(feature = "file")]
    Meta { msg: Meta },

    /// A message that was invalid.
    ///
    /// These can only occur in MIDI files, since only in MIDI files do we know the
    /// length of (some) messages before we parse them.
    #[cfg(feature = "file")]
    #[cfg_attr(feature = "serde", serde(skip))]
    Invalid { bytes: Vec<u8>, error: ParseError },
}

impl MidiMsg {
    /// Turn a `MidiMsg` into a series of bytes.
    pub fn to_midi(&self) -> Vec<u8> {
        let mut r: Vec<u8> = vec![];
        self.extend_midi(&mut r);
        r
    }

    /// Turn a series of bytes into a `MidiMsg`.
    ///
    /// Ok results return a MidiMsg and the number of bytes consumed from the input.
    pub fn from_midi(m: &[u8]) -> Result<(Self, usize), ParseError> {
        Self::from_midi_with_context(m, &mut ReceiverContext::default())
    }

    /// Turn a series of bytes into a `MidiMsg`, given a [`ReceiverContext`](crate::ReceiverContext).
    ///
    /// Consecutive messages that relate to each other will be collapsed into one
    /// `MidiMsg`. E.g. a `ChannelVoiceMsg::ControlChange` where the CC is the MSB and LSB
    /// of `ControlChange::Volume` will turn into a single `ControlChange::Volume` with both
    /// bytes turned into one. Use [`MidiMsg::from_midi_with_context_no_extensions`] to disable this
    /// behavior.
    ///
    /// The `ReceiverContext` is also used to track the current [`TimeCode`](crate::TimeCode)
    /// as sent through [`SystemCommonMsg::TimeCodeQuarterFrame`](crate::SystemCommonMsg::TimeCodeQuarterFrame1)
    /// messages, or [`UniversalRealTimeMsg::TimeCodeFull`](crate::UniversalRealTimeMsg::TimeCodeFull)
    /// messages.
    ///
    /// Ok results return a MidiMsg and the number of bytes consumed from the input.
    pub fn from_midi_with_context(
        m: &[u8],
        ctx: &mut ReceiverContext,
    ) -> Result<(Self, usize), ParseError> {
        Self::_from_midi_with_context(m, ctx, true)
    }

    /// Like [`MidiMsg::from_midi_with_context`] but does not turn multiple related consecutive messages
    /// into one `MidiMsg`.
    pub fn from_midi_with_context_no_extensions(
        m: &[u8],
        ctx: &mut ReceiverContext,
    ) -> Result<(Self, usize), ParseError> {
        Self::_from_midi_with_context(m, ctx, false)
    }

    fn _from_midi_with_context(
        m: &[u8],
        ctx: &mut ReceiverContext,
        allow_extensions: bool,
    ) -> Result<(Self, usize), ParseError> {
        let (mut midi_msg, mut len) = match m.first() {
            Some(b) => match b >> 4 {
                0x8 | 0x9 | 0xA | 0xC | 0xD | 0xE => {
                    let (msg, len) = ChannelVoiceMsg::from_midi(m, ctx)?;
                    let channel = Channel::from_u8(b & 0x0F);
                    let midi_msg = Self::ChannelVoice { channel, msg };

                    ctx.previous_channel_message = Some(midi_msg.clone());
                    Ok((midi_msg, len))
                }
                0xB => {
                    // Could either be a Channel Mode or CC message
                    let channel = Channel::from_u8(b & 0x0F);
                    let (midi_msg, len) = if let Some(b2) = m.get(1) {
                        if b2 >= &120 {
                            let (msg, len) = ChannelModeMsg::from_midi(m)?;
                            (Self::ChannelMode { channel, msg }, len)
                        } else {
                            let (mut msg, len) = ChannelVoiceMsg::from_midi(m, ctx)?;

                            if allow_extensions {
                                // If we can interpret this message as an extension to the previous
                                // one, do it.
                                if let Some(Self::ChannelVoice {
                                    channel: prev_channel,
                                    msg: prev_msg,
                                }) = ctx.previous_channel_message
                                {
                                    if channel == prev_channel
                                        && prev_msg.is_extensible()
                                        && msg.is_extension()
                                    {
                                        if let Ok(updated_msg) = prev_msg.maybe_extend(&msg) {
                                            msg = updated_msg;
                                        }
                                    }
                                }
                            }
                            (Self::ChannelVoice { channel, msg }, len)
                        }
                    } else {
                        return Err(ParseError::UnexpectedEnd);
                    };

                    ctx.previous_channel_message = Some(midi_msg.clone());
                    Ok((midi_msg, len))
                }
                0xF => {
                    if b & 0b00001111 == 0 {
                        #[cfg(feature = "sysex")]
                        {
                            let (msg, len) = SystemExclusiveMsg::from_midi(m, ctx)?;
                            return Ok((Self::SystemExclusive { msg }, len));
                        }
                        #[cfg(not(feature = "sysex"))]
                        return Err(ParseError::SystemExclusiveDisabled);
                    } else if b & 0b00001111 == 0xF && ctx.parsing_smf {
                        #[cfg(feature = "file")]
                        {
                            let (msg, len) = Meta::from_midi(m)?;
                            return Ok((Self::Meta { msg }, len));
                        }
                        #[cfg(not(feature = "file"))]
                        return Err(ParseError::FileDisabled);
                    } else if b & 0b00001000 == 0 {
                        let (msg, len) = SystemCommonMsg::from_midi(m, ctx)?;
                        Ok((Self::SystemCommon { msg }, len))
                    } else {
                        let (msg, len) = SystemRealTimeMsg::from_midi(m)?;
                        Ok((Self::SystemRealTime { msg }, len))
                    }
                }
                _ => {
                    if let Some(p) = &ctx.previous_channel_message {
                        match p {
                            Self::ChannelVoice {
                                channel,
                                msg: prev_msg,
                            } => {
                                if m.len() < 2 {
                                    return Err(ParseError::UnexpectedEnd);
                                }
                                match prev_msg {
                                    // See A-2 of the MIDI spec
                                    ChannelVoiceMsg::ControlChange { .. } => {
                                        if m[0] >= 120 {
                                            let (msg, len) = ChannelModeMsg::from_midi_running(m)?;
                                            return Ok((
                                                Self::ChannelMode {
                                                    channel: *channel,
                                                    msg,
                                                },
                                                len,
                                            ));
                                        }
                                    }
                                    _ => (),
                                };
                                let (mut msg, len) =
                                    ChannelVoiceMsg::from_midi_running(m, prev_msg, ctx)?;

                                if allow_extensions {
                                    // If we can interpret this message as an extension to the previous
                                    // one, do it.
                                    if prev_msg.is_extensible() && msg.is_extension() {
                                        if let Ok(updated_msg) = prev_msg.maybe_extend(&msg) {
                                            msg = updated_msg;
                                        }
                                    }
                                }
                                Ok((
                                    Self::ChannelVoice {
                                        channel: *channel,
                                        msg,
                                    },
                                    len,
                                ))
                            }

                            Self::ChannelMode { channel, .. } => {
                                if m.len() < 2 {
                                    return Err(ParseError::UnexpectedEnd);
                                }
                                // See A-2 of the MIDI spec
                                if m[0] >= 120 {
                                    let (msg, len) = ChannelModeMsg::from_midi_running(m)?;
                                    Ok((
                                        Self::ChannelMode {
                                            channel: *channel,
                                            msg,
                                        },
                                        len,
                                    ))
                                } else {
                                    let control = crate::ControlChange::from_midi(m, ctx)?;
                                    Ok((
                                        Self::ChannelVoice {
                                            channel: *channel,
                                            msg: ChannelVoiceMsg::ControlChange { control },
                                        },
                                        2,
                                    ))
                                }
                            }
                            _ => Err(ParseError::Invalid(
                                "ReceiverContext::previous_channel_message may only be a ChannelMode or ChannelVoice message.",
                            )),
                        }
                    } else {
                        Err(ParseError::ContextlessRunningStatus)
                    }
                }
            },
            None => Err(ParseError::UnexpectedEnd),
        }?;

        if allow_extensions {
            // TODO: this loop could be written as a `while let` loop
            // for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#while_let_loop

            // If this is an extensible message, try to extend it
            loop {
                if let Self::ChannelVoice { channel, msg } = midi_msg {
                    if msg.is_extensible() {
                        // Shadow the context;
                        let mut ctx = ctx.clone();
                        // Try to extend an extensible message
                        match Self::_from_midi_with_context(&m[len..], &mut ctx, false) {
                            Ok((
                                Self::ChannelVoice {
                                    channel: next_channel,
                                    msg: next_msg,
                                },
                                next_len,
                            )) => {
                                if channel == next_channel && next_msg.is_extension() {
                                    match msg.maybe_extend(&next_msg) {
                                        Ok(updated_msg) => {
                                            midi_msg = Self::ChannelVoice {
                                                channel,
                                                msg: updated_msg,
                                            };
                                            len += next_len;
                                        }
                                        _ => break,
                                    }
                                } else {
                                    break;
                                }
                            }
                            _ => break,
                        }
                    } else {
                        break;
                    }
                } else {
                    break;
                }
            }
        }

        Ok((midi_msg, len))
    }

    /// Turn a set of `MidiMsg`s into a series of bytes, with fewer allocations than
    /// repeatedly concatenating the results of `to_midi`.
    pub fn messages_to_midi(msgs: &[Self]) -> Vec<u8> {
        let mut r: Vec<u8> = vec![];
        for m in msgs.iter() {
            m.extend_midi(&mut r);
        }
        r
    }

    /// Given a `Vec<u8>`, append this `MidiMsg` to it.
    pub fn extend_midi(&self, v: &mut Vec<u8>) {
        match self {
            MidiMsg::ChannelVoice { channel, msg } => {
                let p = v.len();
                msg.extend_midi(v);
                v[p] += *channel as u8;
                match msg {
                    ChannelVoiceMsg::HighResNoteOff { .. }
                    | ChannelVoiceMsg::HighResNoteOn { .. } => {
                        v[p + 3] += *channel as u8;
                    }
                    _ => (),
                }
            }
            MidiMsg::RunningChannelVoice { msg, .. } => msg.extend_midi_running(v),
            MidiMsg::ChannelMode { channel, msg } => {
                let p = v.len();
                msg.extend_midi(v);
                v[p] += *channel as u8;
            }
            MidiMsg::RunningChannelMode { msg, .. } => msg.extend_midi_running(v),
            MidiMsg::SystemCommon { msg } => msg.extend_midi(v),
            MidiMsg::SystemRealTime { msg } => msg.extend_midi(v),
            #[cfg(feature = "sysex")]
            MidiMsg::SystemExclusive { msg } => msg.extend_midi(v, true),
            #[cfg(feature = "file")]
            MidiMsg::Meta { msg } => msg.extend_midi(v),
            #[cfg(feature = "file")]
            MidiMsg::Invalid { .. } => {
                // Do nothing
            }
        }
    }

    /// Returns true if this message is a channel voice message.
    pub fn is_channel_voice(&self) -> bool {
        matches!(
            self,
            Self::ChannelVoice { .. } | Self::RunningChannelVoice { .. }
        )
    }

    pub fn is_note_on(&self) -> bool {
        matches!(
            self,
            Self::ChannelVoice {
                msg: ChannelVoiceMsg::NoteOn { .. } | ChannelVoiceMsg::HighResNoteOn { .. },
                ..
            } | Self::RunningChannelVoice {
                msg: ChannelVoiceMsg::NoteOn { .. } | ChannelVoiceMsg::HighResNoteOn { .. },
                ..
            }
        )
    }

    pub fn is_note_off(&self) -> bool {
        matches!(
            self,
            Self::ChannelVoice {
                msg: ChannelVoiceMsg::NoteOff { .. } | ChannelVoiceMsg::HighResNoteOff { .. },
                ..
            } | Self::RunningChannelVoice {
                msg: ChannelVoiceMsg::NoteOff { .. } | ChannelVoiceMsg::HighResNoteOff { .. },
                ..
            }
        )
    }

    /// Returns true if this message is a note (on or off) message.
    pub fn is_note(&self) -> bool {
        matches!(
            self,
            Self::ChannelVoice {
                msg: ChannelVoiceMsg::NoteOn { .. }
                    | ChannelVoiceMsg::NoteOff { .. }
                    | ChannelVoiceMsg::HighResNoteOn { .. }
                    | ChannelVoiceMsg::HighResNoteOff { .. },
                ..
            } | Self::RunningChannelVoice {
                msg: ChannelVoiceMsg::NoteOn { .. }
                    | ChannelVoiceMsg::NoteOff { .. }
                    | ChannelVoiceMsg::HighResNoteOn { .. }
                    | ChannelVoiceMsg::HighResNoteOff { .. },
                ..
            }
        )
    }

    /// Returns true if this message is a control change message.
    pub fn is_cc(&self) -> bool {
        matches!(
            self,
            Self::ChannelVoice {
                msg: ChannelVoiceMsg::ControlChange { .. },
                ..
            } | Self::RunningChannelVoice {
                msg: ChannelVoiceMsg::ControlChange { .. },
                ..
            }
        )
    }

    /// Returns true if this message is a channel mode message.
    pub fn is_channel_mode(&self) -> bool {
        matches!(
            self,
            Self::ChannelMode { .. } | Self::RunningChannelMode { .. }
        )
    }

    /// Returns true if this message is a system common message.
    pub fn is_system_common(&self) -> bool {
        matches!(self, Self::SystemCommon { .. })
    }

    /// Returns true if this message is a system real-time message.
    pub fn is_system_real_time(&self) -> bool {
        matches!(self, Self::SystemRealTime { .. })
    }

    #[cfg(feature = "sysex")]
    /// Returns true if this message is a system exclusive message.
    pub fn is_system_exclusive(&self) -> bool {
        matches!(self, Self::SystemExclusive { .. })
    }

    #[cfg(feature = "file")]
    /// Returns true if this message is a meta message.
    pub fn is_meta(&self) -> bool {
        matches!(self, Self::Meta { .. })
    }

    #[cfg(feature = "file")]
    /// Returns true if this message is an invalid message.
    pub fn is_invalid(&self) -> bool {
        matches!(self, Self::Invalid { .. })
    }
}

impl From<&MidiMsg> for Vec<u8> {
    fn from(m: &MidiMsg) -> Vec<u8> {
        m.to_midi()
    }
}

/// Find the index of the next message in a MIDI byte sequence. This is useful for
/// being able to skip over messages, which may be necessary when a message is
/// unable to be deserialized.
///
/// This *will* skip any running status messages, since we're not parsing the byte stream,
/// we're just looking for a "status byte" -- a byte with the upper bit set.
pub fn next_message(m: &[u8]) -> Option<usize> {
    if m.is_empty() {
        return None;
    }
    // If the first byte has the upper bit set, it's the start of the message we're skipping over.
    // If not, we're somewhere in the middle of a message, and we need to find the next one.
    let start = if upper_bit_set(m[0]) { 1 } else { 0 };

    (start..m.len()).find(|&i| upper_bit_set(m[i]))
}

fn upper_bit_set(x: u8) -> bool {
    x & 0b10000000 != 0
}

#[cfg(feature = "std")]
use strum::{EnumIter, EnumString};

/// The MIDI channel, 1-16. Used by [`MidiMsg`] and elsewhere.
#[cfg_attr(feature = "std", derive(EnumIter, EnumString))]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
pub enum Channel {
    Ch1,
    Ch2,
    Ch3,
    Ch4,
    Ch5,
    Ch6,
    Ch7,
    Ch8,
    Ch9,
    Ch10,
    Ch11,
    Ch12,
    Ch13,
    Ch14,
    Ch15,
    Ch16,
}

impl core::fmt::Display for Channel {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "Ch{}", *self as u8 + 1)
    }
}

impl Channel {
    pub fn from_u8(x: u8) -> Self {
        match x {
            0 => Self::Ch1,
            1 => Self::Ch2,
            2 => Self::Ch3,
            3 => Self::Ch4,
            4 => Self::Ch5,
            5 => Self::Ch6,
            6 => Self::Ch7,
            7 => Self::Ch8,
            8 => Self::Ch9,
            9 => Self::Ch10,
            10 => Self::Ch11,
            11 => Self::Ch12,
            12 => Self::Ch13,
            13 => Self::Ch14,
            14 => Self::Ch15,
            _ => Self::Ch16,
        }
    }
}

impl TryFrom<u8> for Channel {
    type Error = &'static str;

    fn try_from(value: u8) -> Result<Self, Self::Error> {
        if value > 15 {
            return Err("Invalid channel value");
        }
        Ok(Self::from_u8(value))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::Channel::*;

    #[test]
    fn test_ch() {
        assert_eq!(Ch1, Channel::from_u8(0));
        assert_eq!(Ch2, Channel::from_u8(1));
        assert_eq!(Ch16, Channel::from_u8(255));
    }

    #[test]
    fn test_ch_try_from() {
        assert_eq!(Ch1, Channel::try_from(0).unwrap());
        assert_eq!(Ch2, Channel::try_from(1).unwrap());
        assert_eq!(Ch16, Channel::try_from(15).unwrap());
        assert!(Channel::try_from(16).is_err());
    }

    #[test]
    fn test_running_status() {
        let noteon = MidiMsg::ChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::NoteOn {
                note: 0x42,
                velocity: 0x60,
            },
        };
        let running_noteon = MidiMsg::RunningChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::NoteOn {
                note: 0x42,
                velocity: 0x60,
            },
        };
        let reset = MidiMsg::ChannelMode {
            channel: Channel::Ch1,
            msg: ChannelModeMsg::ResetAllControllers,
        };
        let running_reset = MidiMsg::RunningChannelMode {
            channel: Channel::Ch1,
            msg: ChannelModeMsg::ResetAllControllers,
        };
        let cc = MidiMsg::ChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::ControlChange {
                control: crate::ControlChange::Volume(0x7F),
            },
        };
        let running_cc = MidiMsg::RunningChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::ControlChange {
                control: crate::ControlChange::Volume(0x7F),
            },
        };

        // Push 10 messages
        let mut midi = vec![];
        noteon.extend_midi(&mut midi);
        running_noteon.extend_midi(&mut midi);
        // Ensure that channel mode messages can follow one another
        reset.extend_midi(&mut midi);
        running_reset.extend_midi(&mut midi);
        // Ensure that control changes can follow one another
        cc.extend_midi(&mut midi);
        running_cc.extend_midi(&mut midi);
        //   Ensure that control changes and channel mode messages can follow one another
        reset.extend_midi(&mut midi);
        running_cc.extend_midi(&mut midi);
        cc.extend_midi(&mut midi);
        running_reset.extend_midi(&mut midi);

        // Read back ten messages
        let mut offset = 0;
        let mut ctx = ReceiverContext::new().complex_cc();
        let (msg1, len) = MidiMsg::from_midi_with_context(&midi, &mut ctx).expect("Not an error");
        offset += len;
        let (msg2, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg3, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg4, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg5, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg6, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg7, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg8, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg9, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg10, _) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");

        // The expected messages are not running status messages, since we never deserialize into them
        assert_eq!(msg1, noteon);
        assert_eq!(msg2, noteon);
        assert_eq!(msg3, reset);
        assert_eq!(msg4, reset);
        assert_eq!(msg5, cc);
        assert_eq!(msg6, cc);
        assert_eq!(msg7, reset);
        assert_eq!(msg8, cc);
        assert_eq!(msg9, cc);
        assert_eq!(msg10, reset);
    }

    #[test]
    fn test_simple_cc_running_status() {
        let cc = MidiMsg::ChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::ControlChange {
                control: crate::ControlChange::Volume(0x7F),
            },
        };
        let running_cc = MidiMsg::RunningChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::ControlChange {
                control: crate::ControlChange::Volume(0x7F),
            },
        };
        let simple_cc_msb = MidiMsg::ChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::ControlChange {
                control: crate::ControlChange::CC {
                    control: 7,
                    value: 0,
                },
            },
        };
        let simple_cc_lsb = MidiMsg::ChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::ControlChange {
                control: crate::ControlChange::CC {
                    control: 7 + 32,
                    value: 0x7F,
                },
            },
        };

        // Push two messages
        let mut midi = vec![];
        cc.extend_midi(&mut midi);
        running_cc.extend_midi(&mut midi);

        // Read back 4 messages (two are running status messages)
        let mut offset = 0;
        let mut ctx = ReceiverContext::new();
        let (msg1, len) = MidiMsg::from_midi_with_context(&midi, &mut ctx).expect("Not an error");
        offset += len;
        let (msg2, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg3, len) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");
        offset += len;
        let (msg4, _) =
            MidiMsg::from_midi_with_context(&midi[offset..], &mut ctx).expect("Not an error");

        // The expected messages are not running status messages, since we never deserialize into them
        assert_eq!(msg1, simple_cc_msb);
        assert_eq!(msg2, simple_cc_lsb);
        assert_eq!(msg3, simple_cc_msb);
        assert_eq!(msg4, simple_cc_lsb);
    }

    #[test]
    fn test_next_message() {
        let mut midi = vec![];
        MidiMsg::ChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::NoteOn {
                note: 0x42,
                velocity: 0x60,
            },
        }
        .extend_midi(&mut midi);
        let first_message_len = midi.len();
        MidiMsg::ChannelVoice {
            channel: Channel::Ch1,
            msg: ChannelVoiceMsg::NoteOn {
                note: 0x42,
                velocity: 0x60,
            },
        }
        .extend_midi(&mut midi);

        assert_eq!(next_message(&midi), Some(first_message_len));
        // Offset by a byte, so we're in the middle of a message
        assert_eq!(next_message(&midi[1..]), Some(first_message_len - 1));
        assert_eq!(next_message(&midi[first_message_len..]), None);
    }
}