hidparser 1.0.3

HID report descriptor parsing library
Documentation 
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//! HID Report Descriptor Item Tokenization Support
//!
//! This module handles tokenizing a report descriptor given as a byte slice into report descriptor item structures as
//! described in HID spec 1.1 sections 6.2.2.1 through 6.2.2.3.
//!
//! ## License
//!
//! Copyright (C) Microsoft Corporation. All rights reserved.
//!
//! SPDX-License-Identifier: BSD-2-Clause-Patent
//!

/// Identifies the type for descriptor report items. See HID spec 1.1. section 6.2.2.2.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ReportItemType {
    Main,
    Global,
    Local,
    Reserved,
}

/// Parsed HID report descriptor item.
#[derive(Debug, PartialEq, Eq)]
pub struct ReportItem<'a> {
    pub item_type: ReportItemType,
    pub tag: u8,
    pub data: &'a [u8],
}

/// Item tokenizer - produces an iterator over a byte slice that returns ReportItems.
pub struct DescriptorItemTokenizer<'a> {
    descriptor: &'a [u8],
    position: usize,
}

impl<'a> DescriptorItemTokenizer<'a> {
    /// Instantiates a new HID Report Descriptor Item Tokenizer.
    pub fn new(descriptor: &'a [u8]) -> Self {
        DescriptorItemTokenizer { descriptor, position: 0 }
    }
}

impl<'a> Iterator for DescriptorItemTokenizer<'a> {
    type Item = ReportItem<'a>;
    fn next(&mut self) -> Option<Self::Item> {
        let item_header = self.descriptor.get(self.position)?;
        let mut size = item_header & 0x3;
        let item_type = match (item_header & 0xC) >> 2 {
            0 => ReportItemType::Main,
            1 => ReportItemType::Global,
            2 => ReportItemType::Local,
            3 => ReportItemType::Reserved,
            _ => unreachable!(),
        };
        let mut tag = (item_header & 0xF0) >> 4;

        if size == 3 {
            // short item size of 4 bytes is encoded as "3"
            size = 4;
        }

        self.position += 1;

        if (size == 2) && (tag == 0xF) && (item_type) == ReportItemType::Reserved {
            // long item type
            size = *self.descriptor.get(self.position)?;
            self.position += 1;
            tag = *self.descriptor.get(self.position)?;
            self.position += 1;
        }

        let data = self.descriptor.get(self.position..self.position + size as usize)?;

        self.position += size as usize;

        Some(ReportItem { item_type, tag, data })
    }
}

#[cfg(test)]
mod tests {
    use super::{DescriptorItemTokenizer, ReportItem, ReportItemType};
    use alloc::vec::Vec;

    static TEST_REPORT_DESCRIPTOR: &[u8] = &[
        // Integrated Windows Pen TLC
        0x05, 0x0d, // USAGE_PAGE (Digitizers)
        0x09, 0x02, // USAGE (Pen)
        0xa1, 0x01, // COLLECTION (Application)
        0x85, 0x01, //   REPORT_ID (Pen)
        0x09, 0x20, //   USAGE (Stylus)
        0xa1, 0x00, //   COLLECTION (Physical)
        0x09, 0x42, //     USAGE (Tip Switch)
        0x09, 0x44, //     USAGE (Barrel Switch)
        0x09, 0x3c, //     USAGE (Invert)
        0x09, 0x45, //     USAGE (Eraser Switch)
        0x15, 0x00, //     LOGICAL_MINIMUM (0)
        0x25, 0x01, //     LOGICAL_MAXIMUM (1)
        0x75, 0x01, //     REPORT_SIZE (1)
        0x95, 0x04, //     REPORT_COUNT (4)
        0x81, 0x02, //     INPUT (Data,Var,Abs)
        0x95, 0x01, //     REPORT_COUNT (1)
        0x81, 0x03, //     INPUT (Cnst,Var,Abs)
        0x09, 0x32, //     USAGE (In Range)
        0x81, 0x02, //     INPUT (Data,Var,Abs)
        0x95, 0x02, //     REPORT_COUNT (2)
        0x81, 0x03, //     INPUT (Cnst,Var,Abs)
        0x05, 0x01, //     USAGE_PAGE (Generic Desktop)
        0x09, 0x30, //     USAGE (X)
        0x75, 0x10, //     REPORT_SIZE (16)
        0x95, 0x01, //     REPORT_COUNT (1)
        0xa4, //     PUSH
        0x55, 0x0d, //     UNIT_EXPONENT (-3)
        0x65, 0x13, //     UNIT (Inch,EngLinear)
        0x35, 0x00, //     PHYSICAL_MINIMUM (0)
        0x46, 0x3a, 0x20, //     PHYSICAL_MAXIMUM (8250)
        0x26, 0xf8, 0x52, //     LOGICAL_MAXIMUM (21240)
        0x81, 0x02, //     INPUT (Data,Var,Abs)
        0x09, 0x31, //     USAGE (Y)
        0x46, 0x2c, 0x18, //     PHYSICAL_MAXIMUM (6188)
        0x26, 0x6c, 0x3e, //     LOGICAL_MAXIMUM (15980)
        0x81, 0x02, //     INPUT (Data,Var,Abs)
        0xb4, //     POP
        0x05, 0x0d, //     USAGE_PAGE (Digitizers)
        0x09, 0x30, //     USAGE (Tip Pressure)
        0x26, 0xff, 0x00, //     LOGICAL_MAXIMUM (255)
        0x81, 0x02, //     INPUT (Data,Var,Abs)
        0x75, 0x08, //     REPORT_SIZE (8)
        0x09, 0x3d, //     USAGE (X Tilt)
        0x15, 0x81, //     LOGICAL_MINIMUM (-127)
        0x25, 0x7f, //     LOGICAL_MAXIMUM (127)
        0x81, 0x02, //     INPUT (Data,Var,Abs)
        0x09, 0x3e, //     USAGE (Y Tilt)
        0x15, 0x81, //     LOGICAL_MINIMUM (-127)
        0x25, 0x7f, //     LOGICAL_MAXIMUM (127)
        0x81, 0x02, //     INPUT (Data,Var,Abs)
        0xc0, //   END_COLLECTION
        0xc0, // END_COLLECTION
    ];

    #[rustfmt::skip]
  static EXPECTED_ITEMS: &[ReportItem] = &[
    ReportItem {item_type: ReportItemType::Global, tag: 0x00, data: &[0x0d]}, // USAGE_PAGE (Digitizers)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x02]}, // USAGE (Pen)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x0a, data: &[0x01]}, // COLLECTION (Application)
    ReportItem {item_type: ReportItemType::Global, tag: 0x08, data: &[0x01]}, //   REPORT_ID (Pen)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x20]}, //   USAGE (Stylus)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x0a, data: &[0x00]}, //   COLLECTION (Physical)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x42]}, //     USAGE (Tip Switch)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x44]}, //     USAGE (Barrel Switch)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x3c]}, //     USAGE (Invert)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x45]}, //     USAGE (Eraser Switch)
    ReportItem {item_type: ReportItemType::Global, tag: 0x01, data: &[0x00]}, //     LOGICAL_MINIMUM (0)
    ReportItem {item_type: ReportItemType::Global, tag: 0x02, data: &[0x01]}, //     LOGICAL_MAXIMUM (1)
    ReportItem {item_type: ReportItemType::Global, tag: 0x07, data: &[0x01]}, //     REPORT_SIZE (1)
    ReportItem {item_type: ReportItemType::Global, tag: 0x09, data: &[0x04]}, //     REPORT_COUNT (4)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x02]}, //     INPUT (Data,Var,Abs)
    ReportItem {item_type: ReportItemType::Global, tag: 0x09, data: &[0x01]}, //     REPORT_COUNT (1)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x03]}, //     INPUT (Cnst,Var,Abs)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x32]}, //     USAGE (In Range)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x02]}, //     INPUT (Data,Var,Abs)
    ReportItem {item_type: ReportItemType::Global, tag: 0x09, data: &[0x02]}, //     REPORT_COUNT (2)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x03]}, //     INPUT (Cnst,Var,Abs)
    ReportItem {item_type: ReportItemType::Global, tag: 0x00, data: &[0x01]}, //     USAGE_PAGE (Generic Desktop)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x30]}, //     USAGE (X)
    ReportItem {item_type: ReportItemType::Global, tag: 0x07, data: &[0x10]}, //     REPORT_SIZE (16)
    ReportItem {item_type: ReportItemType::Global, tag: 0x09, data: &[0x01]}, //     REPORT_COUNT (1)
    ReportItem {item_type: ReportItemType::Global, tag: 0x0a, data: &[]},     //     PUSH
    ReportItem {item_type: ReportItemType::Global, tag: 0x05, data: &[0x0d]}, //     UNIT_EXPONENT (-3)
    ReportItem {item_type: ReportItemType::Global, tag: 0x06, data: &[0x13]}, //     UNIT (Inch,EngLinear)
    ReportItem {item_type: ReportItemType::Global, tag: 0x03, data: &[0x00]}, //     PHYSICAL_MINIMUM (0)
    ReportItem {item_type: ReportItemType::Global, tag: 0x04, data: &[0x3a, 0x20]}, //     PHYSICAL_MAXIMUM (8250)
    ReportItem {item_type: ReportItemType::Global, tag: 0x02, data: &[0xf8, 0x52]}, //     LOGICAL_MAXIMUM (21240)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x02]}, //     INPUT (Data,Var,Abs)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x31]}, //     USAGE (Y)
    ReportItem {item_type: ReportItemType::Global, tag: 0x04, data: &[0x2c, 0x18]}, //     PHYSICAL_MAXIMUM (6188)
    ReportItem {item_type: ReportItemType::Global, tag: 0x02, data: &[0x6c, 0x3e]}, //     LOGICAL_MAXIMUM (15980)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x02]}, //     INPUT (Data,Var,Abs)
    ReportItem {item_type: ReportItemType::Global, tag: 0x0b, data: &[]},     //     POP
    ReportItem {item_type: ReportItemType::Global, tag: 0x00, data: &[0x0d]}, //     USAGE_PAGE (Digitizers)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x30]}, //     USAGE (Tip Pressure)
    ReportItem {item_type: ReportItemType::Global, tag: 0x02, data: &[0xff, 0x00]}, //     LOGICAL_MAXIMUM (255)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x02]}, //     INPUT (Data,Var,Abs)
    ReportItem {item_type: ReportItemType::Global, tag: 0x07, data: &[0x08]}, //     REPORT_SIZE (8)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x3d]}, //     USAGE (X Tilt)
    ReportItem {item_type: ReportItemType::Global, tag: 0x01, data: &[0x81]}, //     LOGICAL_MINIMUM (-127)
    ReportItem {item_type: ReportItemType::Global, tag: 0x02, data: &[0x7f]}, //     LOGICAL_MAXIMUM (127)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x02]}, //     INPUT (Data,Var,Abs)
    ReportItem {item_type: ReportItemType::Local,  tag: 0x00, data: &[0x3e]}, //     USAGE (Y Tilt)
    ReportItem {item_type: ReportItemType::Global, tag: 0x01, data: &[0x81]}, //     LOGICAL_MINIMUM (-127)
    ReportItem {item_type: ReportItemType::Global, tag: 0x02, data: &[0x7f]}, //     LOGICAL_MAXIMUM (127)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x08, data: &[0x02]}, //     INPUT (Data,Var,Abs)
    ReportItem {item_type: ReportItemType::Main,   tag: 0x0c, data: &[]},     //   END_COLLECTION
    ReportItem {item_type: ReportItemType::Main,   tag: 0x0c, data: &[]},     // END_COLLECTION
  ];

    #[test]
    fn item_tokenizer_should_tokenize_items() {
        let tokenizer = DescriptorItemTokenizer::new(TEST_REPORT_DESCRIPTOR);

        let items: Vec<_> = tokenizer.collect();

        assert_eq!(items.len(), EXPECTED_ITEMS.len(), "tokenizer did not produce the correct number of items");

        for (index, (item, expected_item)) in items.iter().zip(EXPECTED_ITEMS.iter()).enumerate() {
            assert_eq!(item, expected_item, "invalid tokenization of item at index {index:?}");
        }
    }
}