Start working on support for Real numbers.

src/ber.rs

@@ -0,0 +1,7 @@
+pub(crate) mod tag;
+pub(crate) mod length;
+pub(crate) mod value;
+
+pub use crate::ber::tag::*;
+pub use crate::ber::length::*;
+pub use crate::ber::value::*;

src/ber/length.rs

@@ -0,0 +1,200 @@
+use alloc::vec::Vec;
+use core::convert::TryFrom;
+use crate::ber::tag::Tag;
+use crate::ber::value::ValueReaderError;
+#[cfg(test)]
+use crate::ber::tag::{TagClass, TagForm, BasicTagType};
+use crate::number::Number;
+use crate::util::BufferReader;
+#[cfg(test)]
+use quickcheck::{quickcheck, Arbitrary, Gen};
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Length {
+    Short(usize),
+    Long(Number),
+    Indefinite,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum ConversionError {
+    ValueTooLarge,
+    Unconvertable,
+}
+
+impl From<ConversionError> for ValueReaderError {
+    fn from(x: ConversionError) -> ValueReaderError {
+        match x {
+            ConversionError::ValueTooLarge => ValueReaderError::LengthTooBig,
+            ConversionError::Unconvertable => ValueReaderError::LengthIncompatible,
+        }
+    }
+}
+
+impl<'a> TryFrom<&'a Length> for usize {
+    type Error = ConversionError;
+
+    fn try_from(x: &Length) -> Result<usize, Self::Error> {
+        match x {
+            Length::Short(x) => Ok(*x),
+            Length::Long(ref v) => usize::try_from(v),
+            Length::Indefinite => Err(ConversionError::Unconvertable),
+        }
+    }
+}
+
+impl From<usize> for Length {
+    fn from(x: usize) -> Self {
+        Length::Short(x)
+    }
+}
+
+#[cfg(test)]
+impl Arbitrary for Length {
+    fn arbitrary<G: Gen>(g: &mut G) -> Length {
+        match g.next_u32() % 3 {
+            0 => Length::Short(usize::arbitrary(g) % 128),
+            1 => Length::Long(Number::arbitrary(g)),
+            2 => Length::Indefinite,
+            _ => panic!("Mathematics broke."),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum LengthReaderError {
+    NotEnoughData,
+    IllegalConstructedFound,
+    IllegalLong,
+}
+
+#[derive(Debug, PartialEq)]
+pub enum LengthWriterError {
+    SizeTooLarge,
+}
+
+impl Length {
+    /// Read the next length value from the provided iterator, in the context of the provided tag.
+    /// (In some cases, the tag will allow or disallow certain forms of length field, hence the
+    /// need for the context.)
+    pub fn read<I: Iterator<Item = u8>>(tag: &Tag, it: &mut I) -> Result<Length, LengthReaderError> {
+        let constructed_form_allowed = !tag.has_primitive_form();
+
+        match it.next() {
+            None =>
+                Err(LengthReaderError::NotEnoughData),
+            Some(l) if l < 128 =>
+                Ok(Length::Short(l as usize)),
+            Some(l) if l == 0b1000_0000 && constructed_form_allowed =>
+                Ok(Length::Indefinite),
+            Some(l) if l == 0b1111_1111 =>
+                Err(LengthReaderError::IllegalLong),
+            Some(l) => {
+                let bytelen = (l & 0b0111_1111) as usize;
+                match bytelen.read_buffer(it) {
+                    None => Err(LengthReaderError::NotEnoughData),
+                    Some(bytes) => {
+                      let num = Number::from_bytes(&bytes);
+                      Ok(Length::Long(num))
+                    }
+                }
+            }
+        }
+    }
+
+    /// Write the start of a length value to the data stream. Unfortunately, for lengths, you may
+    /// also need to write something after the value, as well; for that, use `write_postfix` to
+    /// ensure you frame the length appropriately.
+    pub fn write(&self, buffer: &mut Vec<u8>) -> Result<(), LengthWriterError> {
+        match self {
+            Length::Short(s) if *s > 127 =>
+                Err(LengthWriterError::SizeTooLarge),
+            Length::Short(s) => {
+                buffer.push(*s as u8);
+                Ok(())
+            }
+            Length::Long(n) => {
+                let bytes = n.serialize();
+
+                if bytes.len() > 127 {
+                    return Err(LengthWriterError::SizeTooLarge);
+                }
+
+                buffer.push((bytes.len() as u8) | 0b1000_0000);
+                for x in bytes.iter() {
+                    buffer.push(*x);
+                }
+                Ok(())
+            }
+            Length::Indefinite => {
+                buffer.push(0b1000_0000);
+                Ok(())
+            }
+        }
+    }
+
+    /// Write, if required, the postfix bytes to the object. This is only relevant for a very
+    /// narrow set of types, but I suggest calling it no matter what; it will never do harm to call
+    /// it.
+    pub fn write_postfix(&self, buffer: &mut Vec<u8>) {
+        match self {
+            Length::Indefinite => {
+                buffer.push(0b0000_0000);
+                buffer.push(0b0000_0000);
+            }
+            _ => {}
+        }
+    }
+}
+
+impl BufferReader for Length {
+    fn read_buffer<I: Iterator<Item=u8>>(&self, it: &mut I) -> Option<Vec<u8>> {
+        match self {
+            Length::Indefinite => {
+                let mut res = Vec::new();
+                let mut successive_zeros = 0;
+
+                while successive_zeros < 2 {
+                    let next = it.next()?;
+
+                    if next == 0 {
+                        successive_zeros += 1;
+                    } else {
+                        successive_zeros = 0;
+                    }
+
+                    res.push(next);
+                }
+
+                res.truncate(res.len() - 2);
+                Some(res)
+            }
+            Length::Long(x) => match usize::try_from(x) {
+                Err(_) => None,
+                Ok(x) => x.read_buffer(it),
+            }
+            Length::Short(x) => x.read_buffer(it),
+        }
+    }
+}
+
+#[cfg(test)]
+quickcheck! {
+    fn length_bytes_length(l: Length) -> bool {
+        let form = if l == Length::Indefinite { TagForm::Constructed } else { TagForm::Primitive };
+        let tag = Tag::Simple(TagClass::Universal, form, BasicTagType::Boolean);
+        let mut output = Vec::new();
+        l.write(&mut output).unwrap();
+        let mut outiter = output.iter().map(|x| *x);
+        match Length::read(&tag, &mut outiter) {
+            Err(e) => {
+                println!("Error found: {:?}", e);
+                false
+            }
+            Ok(l2) => {
+                println!("Result: {:?}", l2);
+                l == l2
+            }
+        }
+    }
+}

src/ber/tag.rs

@@ -0,0 +1,456 @@
+use alloc::vec::Vec;
+use core::convert::TryFrom;
+use core::fmt;
+use crate::bitstring::BitString;
+use crate::lift_error;
+#[cfg(test)]
+use quickcheck::{quickcheck, Arbitrary, Gen};
+
+#[repr(u8)]
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum BasicTagType {
+    Boolean = 1,
+    Integer = 2,
+    BitString = 3,
+    OctetString = 4,
+    Null = 5,
+    ObjectIdentifier = 6,
+    ObjectDescriptor = 7,
+    External = 8,
+    Real = 9,
+    Enumerated = 10,
+    EmbeddedBDV = 11,
+    UTF8String = 12,
+    RelativeOID = 13,
+    Sequence = 16,
+    Set = 17,
+    NumericString = 18,
+    PrintableString = 19,
+    TeletexString = 20,
+    VideotexString = 21,
+    IA5String = 22,
+    UTCTime = 23,
+    GeneralizedTime = 24,
+    GraphicString = 25,
+    VisibleString = 26,
+    GeneralString = 27,
+    UniversalString = 28,
+    CharacterString = 29,
+    BMPString = 30,
+}
+
+#[cfg(test)]
+impl Arbitrary for BasicTagType {
+    fn arbitrary<G: Gen>(g: &mut G) -> BasicTagType {
+        let options = vec![
+            BasicTagType::Boolean,
+            BasicTagType::Integer,
+            BasicTagType::BitString,
+            BasicTagType::OctetString,
+            BasicTagType::Null,
+            BasicTagType::ObjectIdentifier,
+            BasicTagType::ObjectDescriptor,
+            BasicTagType::External,
+            BasicTagType::Real,
+            BasicTagType::Enumerated,
+            BasicTagType::EmbeddedBDV,
+            BasicTagType::UTF8String,
+            BasicTagType::RelativeOID,
+            BasicTagType::Sequence,
+            BasicTagType::Set,
+            BasicTagType::NumericString,
+            BasicTagType::PrintableString,
+            BasicTagType::TeletexString,
+            BasicTagType::VideotexString,
+            BasicTagType::IA5String,
+            BasicTagType::UTCTime,
+            BasicTagType::GeneralizedTime,
+            BasicTagType::GraphicString,
+            BasicTagType::VisibleString,
+            BasicTagType::GeneralString,
+            BasicTagType::UniversalString,
+            BasicTagType::CharacterString,
+            BasicTagType::BMPString,
+        ];
+        let index = usize::arbitrary(g) % options.len();
+        options[index]
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum TagTypeParseError {
+    UsedReservedSlot,
+    UsedSignalSlot,
+    ValueTooLarge,
+}
+
+impl fmt::Display for TagTypeParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TagTypeParseError::UsedReservedSlot => write!(
+                f,
+                "Tag type value was one marked reserved in our specification."
+            ),
+            TagTypeParseError::UsedSignalSlot => write!(
+                f,
+                "Tag type value was the one that signals a multi-byte tag."
+            ),
+            TagTypeParseError::ValueTooLarge => {
+                write!(f, "Tag type value was much too large for us.")
+            }
+        }
+    }
+}
+
+impl TryFrom<u8> for BasicTagType {
+    type Error = TagTypeParseError;
+
+    fn try_from(x: u8) -> Result<BasicTagType, TagTypeParseError> {
+        match x {
+            0 => Err(TagTypeParseError::UsedReservedSlot),
+            1 => Ok(BasicTagType::Boolean),
+            2 => Ok(BasicTagType::Integer),
+            3 => Ok(BasicTagType::BitString),
+            4 => Ok(BasicTagType::OctetString),
+            5 => Ok(BasicTagType::Null),
+            6 => Ok(BasicTagType::ObjectIdentifier),
+            7 => Ok(BasicTagType::ObjectDescriptor),
+            8 => Ok(BasicTagType::External),
+            9 => Ok(BasicTagType::Real),
+            10 => Ok(BasicTagType::Enumerated),
+            11 => Ok(BasicTagType::EmbeddedBDV),
+            12 => Ok(BasicTagType::UTF8String),
+            13 => Ok(BasicTagType::RelativeOID),
+            14 => Err(TagTypeParseError::UsedReservedSlot),
+            15 => Err(TagTypeParseError::UsedReservedSlot),
+            16 => Ok(BasicTagType::Sequence),
+            17 => Ok(BasicTagType::Set),
+            18 => Ok(BasicTagType::NumericString),
+            19 => Ok(BasicTagType::PrintableString),
+            20 => Ok(BasicTagType::TeletexString),
+            21 => Ok(BasicTagType::VideotexString),
+            22 => Ok(BasicTagType::IA5String),
+            23 => Ok(BasicTagType::UTCTime),
+            24 => Ok(BasicTagType::GeneralizedTime),
+            25 => Ok(BasicTagType::GraphicString),
+            26 => Ok(BasicTagType::VisibleString),
+            27 => Ok(BasicTagType::GeneralString),
+            28 => Ok(BasicTagType::UniversalString),
+            29 => Ok(BasicTagType::CharacterString),
+            30 => Ok(BasicTagType::BMPString),
+            31 => Err(TagTypeParseError::UsedSignalSlot),
+            _ => Err(TagTypeParseError::ValueTooLarge),
+        }
+    }
+}
+
+#[repr(u8)]
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum TagClass {
+    Universal = 0b00,
+    Application = 0b01,
+    ContextSpecific = 0b10,
+    Private = 0b11,
+}
+
+#[cfg(test)]
+impl Arbitrary for TagClass {
+    fn arbitrary<G: Gen>(g: &mut G) -> TagClass {
+        let options = vec![
+            TagClass::Universal,
+            TagClass::Application,
+            TagClass::ContextSpecific,
+            TagClass::Private,
+        ];
+        let index = usize::arbitrary(g) % options.len();
+        options[index]
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum TagClassParseError {
+    TagClassTooLarge,
+}
+
+impl fmt::Display for TagClassParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TagClassParseError::TagClassTooLarge => write!(f, "Tag class value is too big"),
+        }
+    }
+}
+
+impl TryFrom<u8> for TagClass {
+    type Error = TagClassParseError;
+
+    fn try_from(x: u8) -> Result<TagClass, TagClassParseError> {
+        match x {
+            0 => Ok(TagClass::Universal),
+            1 => Ok(TagClass::Application),
+            2 => Ok(TagClass::ContextSpecific),
+            3 => Ok(TagClass::Private),
+            _ => Err(TagClassParseError::TagClassTooLarge),
+        }
+    }
+}
+
+#[repr(u8)]
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum TagForm {
+    Primitive = 0,
+    Constructed = 1,
+}
+
+#[cfg(test)]
+impl Arbitrary for TagForm {
+    fn arbitrary<G: Gen>(g: &mut G) -> TagForm {
+        let options = vec![TagForm::Primitive, TagForm::Constructed];
+        let index = usize::arbitrary(g) % options.len();
+        options[index]
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum TagFormParseError {
+    TagFormTooLarge,
+}
+
+impl fmt::Display for TagFormParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TagFormParseError::TagFormTooLarge => write!(f, "Tag form value is more than one bit"),
+        }
+    }
+}
+
+impl TryFrom<u8> for TagForm {
+    type Error = TagFormParseError;
+
+    fn try_from(x: u8) -> Result<TagForm, TagFormParseError> {
+        match x {
+            0 => Ok(TagForm::Primitive),
+            1 => Ok(TagForm::Constructed),
+            _ => Err(TagFormParseError::TagFormTooLarge),
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Tag {
+    Simple(TagClass, TagForm, BasicTagType),
+    Extended(TagClass, TagForm, Vec<u8>),
+}
+
+#[cfg(test)]
+impl Arbitrary for Tag {
+    fn arbitrary<G: Gen>(g: &mut G) -> Tag {
+        if g.next_u32() & 1 == 0 {
+            Tag::Simple(
+                TagClass::arbitrary(g),
+                TagForm::arbitrary(g),
+                BasicTagType::arbitrary(g),
+            )
+        } else {
+            let mut basic_vec = Vec::<u8>::arbitrary(g);
+            basic_vec.push(u8::arbitrary(g)); // just to ensure there's at least one
+            Tag::Extended(TagClass::arbitrary(g), TagForm::arbitrary(g), basic_vec)
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum TagReaderError {
+    NotEnoughData,
+    InappropriateExtendedLength,
+    TagClassProblem(TagClassParseError),
+    TagFormProblem(TagFormParseError),
+    TagTypeProblem(TagTypeParseError),
+}
+
+lift_error!(TagClassParseError, TagClassProblem, TagReaderError);
+lift_error!(TagFormParseError, TagFormProblem, TagReaderError);
+lift_error!(TagTypeParseError, TagTypeProblem, TagReaderError);
+
+#[derive(Debug, PartialEq)]
+pub enum TagSerializationError {
+    NoExtendedTag,
+    ExtendedTagTooSmall,
+    InternalError,
+}
+
+impl Tag {
+    pub fn has_primitive_form(&self) -> bool {
+        match self {
+            Tag::Simple(_, TagForm::Primitive, _) => true,
+            Tag::Extended(_, TagForm::Primitive, _) => true,
+            _ => false,
+        }
+    }
+
+    pub fn read<I: Iterator<Item = u8>>(it: &mut I) -> Result<Tag, TagReaderError> {
+        match it.next() {
+            None => Err(TagReaderError::NotEnoughData),
+            Some(b) => {
+                let class = TagClass::try_from(b >> 6)?;
+                let form = TagForm::try_from((b >> 5) & 1)?;
+                let tag = b & 0b11111;
+
+                if tag == 31 {
+                    let mut bitstr = BitString::new();
+
+                    // OK, here's an example of what we have to do here.
+                    // Imagine that this tag was four bytes [67,33,30,42]:
+                    //
+                    //   01000011_00100001_00011110_00101010
+                    //
+                    // To encode them, we're going to pad the front, and then
+                    // group them into sevens:
+                    //
+                    //   0000100_0011001_0000100_0111100_0101010
+                    //      4       25      4       60      42
+                    //
+                    // We'll then set the high bits on the first 4, giving us
+                    // an input to this function of:
+                    //     132     153     132     188      42
+                    //
+                    // On the flip side, to parse, we need to first turn these
+                    // back into 8 bit quantities:
+                    //    00001000_01100100_00100011_11000101_010
+                    let mut ended_clean = false;
+
+                    while let Some(b) = it.next() {
+                        bitstr.push_bits(7, b);
+                        if b & 0b1000_0000 == 0 {
+                            ended_clean = true;
+                            break;
+                        }
+                    }
+
+                    if !ended_clean {
+                        return Err(TagReaderError::NotEnoughData);
+                    }
+                    //
+                    // which is off by three.
+                    let padding = bitstr.len() % 8;
+                    //
+                    // So if we pull three bits off the front we get back to:
+                    //    01000011_00100001_00011110_00101010
+                    //
+                    let mut bititer = bitstr.bits().skip(padding);
+                    let mut res = Vec::new();
+                    let mut work_byte = 0;
+                    let mut count = 0;
+
+                    while let Some(x) = bititer.next() {
+                        work_byte = (work_byte << 1) | (x & 1);
+                        count += 1;
+                        if count == 8 {
+                            res.push(work_byte);
+                            count = 0;
+                            work_byte = 0;
+                        }
+                    }
+
+                    if count != 0 {
+                        return Err(TagReaderError::InappropriateExtendedLength);
+                    }
+
+                    return Ok(Tag::Extended(class, form, res));
+                }
+
+                Ok(Tag::Simple(class, form, BasicTagType::try_from(tag)?))
+            }
+        }
+    }
+
+    pub fn write(&self, buffer: &mut Vec<u8>) -> Result<(), TagSerializationError> {
+        match self {
+            Tag::Simple(class, form, basic) => {
+                let class_val = (*class as u8) << 6;
+                let form_val = (*form as u8) << 5;
+                let basic_val = *basic as u8;
+
+                buffer.push(class_val | form_val | basic_val);
+                Ok(())
+            }
+            Tag::Extended(class, form, value) => {
+                let class_val = (*class as u8) << 6;
+                let form_val = (*form as u8) << 5;
+                let basic_val = 0b00011111;
+
+                if value.len() == 0 {
+                    return Err(TagSerializationError::NoExtendedTag);
+                }
+
+                buffer.push(class_val | form_val | basic_val);
+                let original_length = value.len() * 8;
+                let mut work_byte = 0;
+                let mut bits_added = if original_length % 7 == 0 {
+                    0
+                } else {
+                    7 - (original_length % 7)
+                };
+                let mut bitstream = BitString::from(value.iter().map(|x| *x)).bits().peekable();
+
+                while bitstream.peek().is_some() {
+                    while bits_added < 7 {
+                        match bitstream.next() {
+                            None => return Err(TagSerializationError::InternalError),
+                            Some(b) => {
+                                bits_added += 1;
+                                work_byte = (work_byte << 1) | b;
+                            }
+                        }
+                    }
+
+                    buffer.push(0b1000_0000 | work_byte);
+                    bits_added = 0;
+                    work_byte = 0;
+                }
+
+                let last_idx = buffer.len() - 1;
+                buffer[last_idx] &= 0b0111_1111;
+
+                Ok(())
+            }
+        }
+    }
+}
+
+macro_rules! item_u8_item {
+    ($name: ident, $type: ident) => {
+        #[cfg(test)]
+        quickcheck! {
+            fn $name(t: $type) -> bool {
+                let t8 = t as u8;
+                match $type::try_from(t8) {
+                    Err(_) => false,
+                    Ok(t2) => t == t2,
+                }
+            }
+        }
+    };
+}
+
+item_u8_item!(tag_u8_tag, BasicTagType);
+item_u8_item!(form_u8_form, TagForm);
+item_u8_item!(class_u8_class, TagClass);
+
+#[cfg(test)]
+quickcheck! {
+    fn tag_bytes_tag(t: Tag) -> bool {
+        let mut bytes = Vec::new();
+        let () = t.write(&mut bytes).unwrap();
+        let mut byteiter = bytes.iter().map(|x| *x);
+        match Tag::read(&mut byteiter) {
+            Err(e) => {
+                // println!("Error result: {:?}", e);
+                false
+            }
+            Ok(t2) => {
+                // println!("Result: {:?}", t2);
+                t == t2
+            }
+        }
+    }
+}

src/ber/value.rs

@@ -0,0 +1,168 @@
+use crate::ber::length::{Length, LengthReaderError, LengthWriterError};
+use crate::ber::tag::{Tag, TagClass, TagForm, TagReaderError, TagSerializationError, BasicTagType};
+use crate::lift_error;
+use crate::number::Number;
+use crate::real::Real;
+use crate::util::BufferReader;
+
+pub enum Value {
+    Boolean(TagClass, TagForm, bool),
+    Integer(TagClass, TagForm, Number),
+    Null(TagClass, TagForm),
+    Real(TagClass, TagForm, Real),
+}
+
+pub enum ValueReaderError {
+    LengthIncompatible,
+    LengthTooBig,
+    NotEnoughData,
+    InvalidFormat(BasicTagType),
+    TagReaderProblem(TagReaderError),
+    LengthReaderError(LengthReaderError),
+}
+
+lift_error!(TagReaderError, TagReaderProblem, ValueReaderError);
+lift_error!(LengthReaderError, ValueReaderError);
+
+pub enum ValueWriterError {
+    Length(LengthWriterError),
+    Tag(TagSerializationError),
+}
+
+lift_error!(LengthWriterError, Length, ValueWriterError);
+lift_error!(TagSerializationError, Tag, ValueWriterError);
+
+impl Value {
+    /// Read a value from the provided iterator.
+    pub fn read<I: Iterator<Item = u8>>(it: &mut I) -> Result<Value, ValueReaderError> {
+        let tag = Tag::read(it)?;
+        let length = Length::read(&tag, it)?;
+        let mut bytes: Vec<u8> = match length.read_buffer(it) {
+            None => return Err(ValueReaderError::NotEnoughData),
+            Some(x) => x,
+        };
+
+        match tag {
+            Tag::Simple(c, f, BasicTagType::Boolean) => {
+                match it.next() {
+                    None => Err(ValueReaderError::NotEnoughData),
+                    Some(0) => Ok(Value::Boolean(c, f, false)),
+                    Some(_) => Ok(Value::Boolean(c, f, true)),
+                }
+            }
+
+            Tag::Simple(c, f, BasicTagType::Null) =>
+                Ok(Value::Null(c, f)),
+
+            Tag::Simple(c, f, BasicTagType::Integer) => {
+                let res = Number::from_bytes(&bytes);
+                Ok(Value::Integer(c, f, res))
+            }
+
+            Tag::Simple(c, f, BasicTagType::Real) => {
+                if bytes.len() == 0 {
+                    return Err(ValueReaderError::InvalidFormat(BasicTagType::Real));
+                }
+
+                let leader = bytes.remove(0); // has the handy side-effect of making bytes by the
+                                              // actual value.
+
+                if leader == 0b01000000 {
+                    return Ok(Value::Real(c, f, Real::PositiveInfinity));
+                }
+
+                if leader == 0b01000001 {
+                    return Ok(Value::Real(c, f, Real::NegativeInfinity));
+                }
+
+                if leader >> 6 == 0b00 {
+                    match String::from_utf8(bytes) {
+                        Err(_) => return Err(ValueReaderError::InvalidFormat(BasicTagType::Real)),
+                        Ok(v) => {
+                            let has_e = v.chars().any(|c| (c == 'e') || (c == 'E'));
+                            let has_p = v.chars().any(|c| (c == '.'));
+                            let nr = leader & 0b00111111;
+
+                            match nr {
+                                0b01 if !has_e && !has_p => return Ok(Value::Real(c, f, Real::ISO6093(v))),
+                                0b10 if !has_e &&  has_p => return Ok(Value::Real(c, f, Real::ISO6093(v))),
+                                0b11 if  has_e &&  has_p => return Ok(Value::Real(c, f, Real::ISO6093(v))),
+                                _ => return Err(ValueReaderError::InvalidFormat(BasicTagType::Real)),
+                            }
+                        }
+                    }
+                }
+
+                if (leader >> 7) == 0 {
+                    return Err(ValueReaderError::InvalidFormat(BasicTagType::Real));
+                }
+
+                let positive = (leader >> 6) & 1 == 0;
+                let mant_shift = ((leader >> 2) & 0b11) as usize;
+                let exp_shift = match (leader >> 4) & 0b11 {
+                    0b00 => 0,
+                    0b01 => 2,
+                    0b10 => 3,
+                    _ => return Err(ValueReaderError::InvalidFormat(BasicTagType::Real)),
+                } as usize;
+                let explen = match leader & 0b11 {
+                    0 => 1,
+                    1 => 2,
+                    2 => 3,
+                    3 => bytes.remove(0),
+                    _ => panic!("Mathematics has failed us.")
+                } as usize;
+
+                let mut exponent = Number::from_bytes(&bytes[0..explen]);
+                let mut mantissa = Number::from_bytes(&bytes[explen..]);
+
+                exponent <<= exp_shift;
+                mantissa <<= mant_shift;
+
+                if !positive {
+                    mantissa = -mantissa;
+                }
+
+                Ok(Value::Real(c, f, Real::new(exponent, mantissa)))
+            }
+
+            _ =>
+                unimplemented!("Cannot parse tag {:?}", tag)
+        }
+    }
+
+    /// Serialize the value to the given buffer. Note that this writes the full definiton of the
+    /// value: it's type, it's length, and the value itself.
+    pub fn write(&self, buffer: &mut Vec<u8>) -> Result<(), ValueWriterError> {
+        match self {
+            Value::Boolean(cl, form, v) => {
+                Length::from(1).write(buffer)?;
+                Tag::Simple(*cl, *form, BasicTagType::Boolean).write(buffer)?;
+                if *v {
+                    buffer.push(0b10101010);
+                } else {
+                    buffer.push(0b00000000);
+                }
+                Ok(())
+            }
+
+            Value::Integer(c, f, n) => {
+                let mut bytes = n.serialize();
+                Length::from(bytes.len()).write(buffer)?;
+                Tag::Simple(*c, *f, BasicTagType::Integer).write(buffer)?;
+                buffer.append(&mut bytes);
+                Ok(())
+            }
+
+            Value::Null(c, f) => {
+                Length::from(0).write(buffer)?;
+                Tag::Simple(*c, *f, BasicTagType::Null).write(buffer)?;
+                Ok(())
+            }
+
+            Value::Real(c, f, r) => {
+                unimplemented!() 
+            }
+        }
+    }
+}

src/bitstring.rs

@@ -0,0 +1,139 @@
+pub struct BitString {
+    current_bit: usize,
+    work_byte: u8,
+    contents: Vec<u8>,
+}
+
+pub struct BitIter {
+    current_bit: usize,
+    contents: BitString,
+}
+
+impl BitString {
+    /// Create a new, empty bit string
+    pub fn new() -> BitString {
+        BitString {
+            current_bit: 7,
+            work_byte: 0,
+            contents: vec![],
+        }
+    }
+
+    /// Create an iterator over the bits in the BitString
+    pub fn bits(self) -> BitIter {
+        BitIter {
+            current_bit: 0,
+            contents: self,
+        }
+    }
+
+    /// Add a bit to the end of the bitstring
+    pub fn push_bit(&mut self, x: bool) {
+        let bitval = if x { 1 } else { 0 };
+        self.work_byte |= bitval << self.current_bit;
+
+        if self.current_bit == 0 {
+            self.contents.push(self.work_byte);
+            self.work_byte = 0;
+            self.current_bit = 7;
+        } else {
+            self.current_bit -= 1;
+        }
+    }
+
+    /// Add the low `n` bits of the provided byte to the BitString
+    pub fn push_bits(&mut self, mut n: usize, x: u8) {
+        while n > 0 {
+            let bit = (x >> (n - 1)) & 1 == 1;
+            self.push_bit(bit);
+            n -= 1;
+        }
+    }
+
+    /// Get the length of this bitstring, in bits
+    pub fn len(&self) -> usize {
+        (self.contents.len() * 8) + (7 - self.current_bit)
+    }
+}
+
+impl<I: Iterator<Item = u8>> From<I> for BitString {
+    fn from(x: I) -> BitString {
+        let contents: Vec<u8> = x.collect();
+        BitString {
+            current_bit: contents.len() * 8,
+            work_byte: 0,
+            contents,
+        }
+    }
+}
+
+impl Iterator for BitIter {
+    type Item = u8;
+
+    fn next(&mut self) -> Option<u8> {
+        let byte_idx = self.current_bit / 8;
+        let bit_idx = self.current_bit % 8;
+        let shift_amt = 7 - bit_idx;
+
+        // if we're still in the main body of the thing, then we just compute
+        // the offset and shift and be done with it.
+        if byte_idx < self.contents.contents.len() {
+            let byte = self.contents.contents[byte_idx];
+            let retval = byte >> shift_amt;
+            self.current_bit += 1;
+            return Some(retval & 1);
+        }
+
+        // just a sanity check; this should reallly never happen.
+        if byte_idx > self.contents.contents.len() {
+            return None;
+        }
+
+        // in this case, we're processing in the work_byte area of our parent
+        // BitString.
+        if shift_amt <= self.contents.current_bit {
+            return None;
+        }
+
+        self.current_bit += 1;
+        return Some((self.contents.work_byte >> shift_amt) & 1);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn nullary_test() {
+        let bitstr = BitString::new();
+        let bits: Vec<u8> = bitstr.bits().collect();
+        assert_eq!(bits.len(), 0);
+    }
+
+    #[test]
+    fn add_bit() {
+        let mut bitstr = BitString::new();
+
+        bitstr.push_bit(false);
+        bitstr.push_bit(true);
+        bitstr.push_bit(false);
+        bitstr.push_bit(false);
+        bitstr.push_bit(true);
+        bitstr.push_bit(true);
+        bitstr.push_bit(true);
+        bitstr.push_bit(false);
+        bitstr.push_bit(false);
+        let bits: Vec<u8> = bitstr.bits().collect();
+        assert_eq!(bits, vec![0, 1, 0, 0, 1, 1, 1, 0, 0]);
+    }
+
+    #[test]
+    fn add_bits() {
+        let mut bitstr = BitString::new();
+
+        bitstr.push_bits(5, 0b11111111);
+        let bits: Vec<u8> = bitstr.bits().collect();
+        assert_eq!(bits, vec![1, 1, 1, 1, 1]);
+    }
+}

src/lib.rs

@@ -26,6 +26,13 @@
 //!
 //! Please send any bug reports, patches, and curses to the GitHub repository
 //! at <code>https://github.com/acw/simple_asn1</code>.
+extern crate alloc;
+mod ber;
+mod bitstring;
+mod number;
+mod real;
+mod util;
+
 use chrono::{DateTime, TimeZone, Utc};
 pub use num_bigint::{BigInt, BigUint};
 use num_traits::{FromPrimitive, One, ToPrimitive, Zero};

src/number.rs

@@ -0,0 +1,201 @@
+use core::convert::TryFrom;
+use core::ops::{Neg, ShlAssign};
+use crate::ber::length::ConversionError;
+#[cfg(test)]
+use quickcheck::{quickcheck, Arbitrary, Gen};
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Number {
+    value: Vec<u64>,
+    bits: usize,
+}
+
+#[cfg(test)]
+impl Arbitrary for Number {
+    fn arbitrary<G: Gen>(g: &mut G) -> Number {
+        let bytes = u8::arbitrary(g) as usize;
+        let digits = (bytes + 7) / 8;
+        let bits = bytes * 8;
+
+        let mut value = Vec::with_capacity(digits);
+        for _ in 0..digits {
+            value.push(g.next_u64());
+        }
+
+        if digits > 0 {
+            let spare_bits = (digits * 64) - bits;
+            let mask = 0xFFFFFFFFFFFFFFFFu64 >> spare_bits;
+            value[digits - 1] &= mask;
+        }
+
+        Number {
+            value,
+            bits,
+        }
+    }
+}
+
+impl Number {
+    pub fn new() -> Number {
+        Number {
+            value: Vec::new(),
+            bits: 0
+        }
+    }
+
+    pub fn serialize(&self) -> Vec<u8> {
+        let serialized_bytes = (self.bits + 7) / 8;
+        let mut res = Vec::with_capacity(serialized_bytes);
+
+        for idx in 0..serialized_bytes {
+            let byte_off = serialized_bytes - idx - 1;
+            let val64_off = byte_off / 8;
+            let internal_bit_off = (byte_off % 8) * 8;
+            let val = (self.value[val64_off] >> internal_bit_off) & 0xff;
+
+            res.push(val as u8);
+        }
+
+        res
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Number {
+        let bits = bytes.len() * 8;
+        let digit_len = (bytes.len() + 7) / 8;
+        let mut value = Vec::with_capacity(digit_len);
+        let mut bytes_added = 0;
+        let mut next = 0u64;
+
+        for x in bytes.iter().rev() {
+            next += (*x as u64) << (bytes_added * 8);
+            bytes_added += 1;
+            if bytes_added == 8 {
+                value.push(next);
+                next = 0;
+                bytes_added = 0;
+            }
+        }
+
+        if bytes_added != 0 {
+            value.push(next);
+        }
+
+        Number { value, bits }
+    }
+}
+
+#[cfg(test)]
+#[test]
+fn basic_serialization() {
+    assert_eq!(Number::new().serialize(), vec![]);
+    //
+    let one = Number {
+        value: vec![1],
+        bits: 8,
+    };
+    let onevec = vec![1];
+    assert_eq!(one.serialize(), onevec);
+    assert_eq!(Number::from_bytes(&onevec), one);
+    //
+    let one_oh_oh_one = Number {
+        value: vec![0x1001],
+        bits: 16,
+    };
+    let one_oh_oh_one_vec = vec![0x10,0x01];
+    assert_eq!(one_oh_oh_one.serialize(), one_oh_oh_one_vec);
+    assert_eq!(Number::from_bytes(&one_oh_oh_one_vec), one_oh_oh_one);
+    //
+    let one_to_nine = Number {
+        value: vec![0x0807060504030201, 0x09],
+        bits: 72,
+    };
+    let one_to_nine_vec = vec![0x09, 0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01];
+    assert_eq!(one_to_nine.serialize(), one_to_nine_vec);
+    assert_eq!(Number::from_bytes(&one_to_nine_vec), one_to_nine);
+}
+
+#[cfg(test)]
+#[derive(Clone, Debug)]
+struct SmallByteArray {
+    a: Vec<u8>
+}
+
+#[cfg(test)]
+impl Arbitrary for SmallByteArray {
+    fn arbitrary<G: Gen>(g: &mut G) -> SmallByteArray {
+        let len = u8::arbitrary(g);
+        let mut a = Vec::with_capacity(len as usize);
+        for _ in 0..len {
+            a.push(u8::arbitrary(g));
+        }
+        SmallByteArray{ a }
+    }
+}
+
+#[cfg(test)]
+quickcheck! {
+    fn bytes_num_bytes(x: SmallByteArray) -> bool {
+        let num = Number::from_bytes(&x.a);
+        let y = num.serialize();
+        println!("x.a: {:?}", x.a);
+        println!("y:   {:?}", y);
+        &x.a == &y
+    }
+
+    fn num_bytes_num(x: Number) -> bool {
+        let bytes = x.serialize();
+        let y = Number::from_bytes(&bytes);
+        println!("x: {:?}", x);
+        println!("b: {:?}", bytes);
+        println!("y: {:?}", y);
+        x == y
+    }
+}
+
+impl From<u8> for Number {
+    fn from(x: u8) -> Number {
+        Number {
+            value: vec![x as u64],
+            bits: 8,
+        }
+    }
+}
+
+impl<'a> TryFrom<&'a Number> for usize {
+    type Error = ConversionError;
+
+    fn try_from(x: &Number) -> Result<Self, Self::Error> {
+        if x.value.iter().skip(1).all(|v| *v == 0) {
+            if x.value.len() == 0 {
+                return Ok(0);
+            }
+
+            let mut value = x.value[0];
+
+            if x.bits < 64 {
+                value &= 0xFFFFFFFFFFFFFFFFu64 >> (64 - x.bits);
+            }
+
+            match usize::try_from(value) {
+                Err(_) => Err(ConversionError::ValueTooLarge),
+                Ok(v) => Ok(v)
+            }
+        } else {
+            Err(ConversionError::ValueTooLarge)
+        }
+    }
+}
+
+impl ShlAssign<usize> for Number {
+    fn shl_assign(&mut self, amt: usize) {
+        unimplemented!()
+    }
+}
+
+impl Neg for Number {
+    type Output = Number;
+
+    fn neg(self) -> Number {
+        unimplemented!()
+    }
+}

src/real.rs

@@ -0,0 +1,23 @@
+use crate::number::Number;
+
+pub enum Real {
+    PositiveInfinity,
+    NegativeInfinity,
+    ISO6093(String),
+    Binary(RealNumber),
+}
+
+impl Real {
+    pub fn new(exponent: Number, mantissa: Number) -> Real {
+        Real::Binary(RealNumber{
+            exponent,
+            mantissa,
+        })
+    }
+}
+
+pub struct RealNumber {
+    exponent: Number,
+    mantissa: Number,
+}
+

src/util.rs

@@ -0,0 +1,33 @@
+use alloc::vec::Vec;
+
+pub trait BufferReader {
+    fn read_buffer<I: Iterator<Item=u8>>(&self, it: &mut I) -> Option<Vec<u8>>;
+}
+
+impl BufferReader for usize {
+    fn read_buffer<I: Iterator<Item=u8>>(&self, it: &mut I) -> Option<Vec<u8>> {
+        let me = *self;
+        let mut res = Vec::with_capacity(me);
+
+        while res.len() < me {
+            let n = it.next()?;
+            res.push(n);
+        }
+
+        Some(res)
+    }
+}
+
+#[macro_export]
+macro_rules! lift_error {
+    ($fromt: ident, $tot: ident) => {
+        lift_error!($fromt, $fromt, $tot);
+    };
+    ($fromt: ident, $const: ident, $tot: ident) => {
+        impl From<$fromt> for $tot {
+            fn from(x: $fromt) -> $tot {
+                $tot::$const(x)
+            }
+        }
+    }
+}