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Remove error handling from protobuf exercise (#2109)

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Nicole L 2024-06-07 09:13:11 -07:00 committed by GitHub
parent 511e5f0dbf
commit b69b68f5e2
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3 changed files with 63 additions and 99 deletions

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@ -42,7 +42,7 @@ a message into a series of calls to those callbacks.
What remains for you is to implement the `parse_field` function and the
`ProtoMessage` trait for `Person` and `PhoneNumber`.
<!-- compile_fail because `mdbook test` does not allow use of `thiserror` -->
<!-- compile_fail because the stubbed out code has type inference errors. -->
```rust,editable,compile_fail
{{#include exercise.rs:preliminaries }}
@ -62,3 +62,13 @@ What remains for you is to implement the `parse_field` function and the
{{#include exercise.rs:main }}
```
<details>
- In this exercise there are various cases where protobuf parsing might fail,
e.g. if you try to parse an `i32` when there are fewer than 4 bytes left in
the data buffer. In normal Rust code we'd handle this with the `Result` enum,
but for simplicity in this exercise we panic if any errors are encountered. On
day 4 we'll cover error handling in Rust in more detail.
</details>

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@ -14,25 +14,6 @@
// ANCHOR: solution
// ANCHOR: preliminaries
use std::convert::TryFrom;
use thiserror::Error;
#[derive(Debug, Error)]
enum Error {
#[error("Invalid varint")]
InvalidVarint,
#[error("Invalid wire-type")]
InvalidWireType,
#[error("Unexpected EOF")]
UnexpectedEOF,
#[error("Invalid length")]
InvalidSize(#[from] std::num::TryFromIntError),
#[error("Unexpected wire-type)")]
UnexpectedWireType,
#[error("Invalid string (not UTF-8)")]
InvalidString,
}
/// A wire type as seen on the wire.
enum WireType {
/// The Varint WireType indicates the value is a single VARINT.
@ -63,51 +44,57 @@ struct Field<'a> {
}
trait ProtoMessage<'a>: Default + 'a {
fn add_field(&mut self, field: Field<'a>) -> Result<(), Error>;
fn add_field(&mut self, field: Field<'a>);
}
impl TryFrom<u64> for WireType {
type Error = Error;
fn try_from(value: u64) -> Result<WireType, Error> {
Ok(match value {
impl From<u64> for WireType {
fn from(value: u64) -> Self {
match value {
0 => WireType::Varint,
//1 => WireType::I64, -- not needed for this exercise
2 => WireType::Len,
5 => WireType::I32,
_ => return Err(Error::InvalidWireType),
})
_ => panic!("Invalid wire type: {value}"),
}
}
}
impl<'a> FieldValue<'a> {
fn as_string(&self) -> Result<&'a str, Error> {
fn as_string(&self) -> &'a str {
let FieldValue::Len(data) = self else {
return Err(Error::UnexpectedWireType);
panic!("Expected string to be a `Len` field");
};
std::str::from_utf8(data).map_err(|_| Error::InvalidString)
std::str::from_utf8(data).expect("Invalid string")
}
fn as_bytes(&self) -> Result<&'a [u8], Error> {
fn as_bytes(&self) -> &'a [u8] {
let FieldValue::Len(data) = self else {
return Err(Error::UnexpectedWireType);
panic!("Expected bytes to be a `Len` field");
};
Ok(data)
data
}
fn as_u64(&self) -> Result<u64, Error> {
fn as_u64(&self) -> u64 {
let FieldValue::Varint(value) = self else {
return Err(Error::UnexpectedWireType);
panic!("Expected `u64` to be a `Varint` field");
};
Ok(*value)
*value
}
#[allow(dead_code)]
fn as_i32(&self) -> i32 {
let FieldValue::I32(value) = self else {
panic!("Expected `i32` to be an `I32` field");
};
*value
}
}
/// Parse a VARINT, returning the parsed value and the remaining bytes.
fn parse_varint(data: &[u8]) -> Result<(u64, &[u8]), Error> {
fn parse_varint(data: &[u8]) -> (u64, &[u8]) {
for i in 0..7 {
let Some(b) = data.get(i) else {
return Err(Error::InvalidVarint);
panic!("Not enough bytes for varint");
};
if b & 0x80 == 0 {
// This is the last byte of the VARINT, so convert it to
@ -116,45 +103,45 @@ fn parse_varint(data: &[u8]) -> Result<(u64, &[u8]), Error> {
for b in data[..=i].iter().rev() {
value = (value << 7) | (b & 0x7f) as u64;
}
return Ok((value, &data[i + 1..]));
return (value, &data[i + 1..]);
}
}
// More than 7 bytes is invalid.
Err(Error::InvalidVarint)
panic!("Too many bytes for varint");
}
/// Convert a tag into a field number and a WireType.
fn unpack_tag(tag: u64) -> Result<(u64, WireType), Error> {
fn unpack_tag(tag: u64) -> (u64, WireType) {
let field_num = tag >> 3;
let wire_type = WireType::try_from(tag & 0x7)?;
Ok((field_num, wire_type))
let wire_type = WireType::from(tag & 0x7);
(field_num, wire_type)
}
// ANCHOR_END: preliminaries
// ANCHOR: parse_field
/// Parse a field, returning the remaining bytes
fn parse_field(data: &[u8]) -> Result<(Field, &[u8]), Error> {
let (tag, remainder) = parse_varint(data)?;
let (field_num, wire_type) = unpack_tag(tag)?;
fn parse_field(data: &[u8]) -> (Field, &[u8]) {
let (tag, remainder) = parse_varint(data);
let (field_num, wire_type) = unpack_tag(tag);
let (fieldvalue, remainder) = match wire_type {
// ANCHOR_END: parse_field
WireType::Varint => {
let (value, remainder) = parse_varint(remainder)?;
let (value, remainder) = parse_varint(remainder);
(FieldValue::Varint(value), remainder)
}
WireType::Len => {
let (len, remainder) = parse_varint(remainder)?;
let len: usize = len.try_into()?;
let (len, remainder) = parse_varint(remainder);
let len: usize = len.try_into().expect("len not a valid `usize`");
if remainder.len() < len {
return Err(Error::UnexpectedEOF);
panic!("Unexpected EOF");
}
let (value, remainder) = remainder.split_at(len);
(FieldValue::Len(value), remainder)
}
WireType::I32 => {
if remainder.len() < 4 {
return Err(Error::UnexpectedEOF);
panic!("Unexpected EOF");
}
let (value, remainder) = remainder.split_at(4);
// Unwrap error because `value` is definitely 4 bytes long.
@ -162,7 +149,7 @@ fn parse_field(data: &[u8]) -> Result<(Field, &[u8]), Error> {
(FieldValue::I32(value), remainder)
}
};
Ok((Field { field_num, value: fieldvalue }, remainder))
(Field { field_num, value: fieldvalue }, remainder)
}
// ANCHOR: parse_message
@ -170,14 +157,14 @@ fn parse_field(data: &[u8]) -> Result<(Field, &[u8]), Error> {
/// the message.
///
/// The entire input is consumed.
fn parse_message<'a, T: ProtoMessage<'a>>(mut data: &'a [u8]) -> Result<T, Error> {
fn parse_message<'a, T: ProtoMessage<'a>>(mut data: &'a [u8]) -> T {
let mut result = T::default();
while !data.is_empty() {
let parsed = parse_field(data)?;
result.add_field(parsed.0)?;
let parsed = parse_field(data);
result.add_field(parsed.0);
data = parsed.1;
}
Ok(result)
result
}
// ANCHOR_END: parse_message
@ -197,25 +184,23 @@ struct Person<'a> {
// ANCHOR_END: message_types
impl<'a> ProtoMessage<'a> for Person<'a> {
fn add_field(&mut self, field: Field<'a>) -> Result<(), Error> {
fn add_field(&mut self, field: Field<'a>) {
match field.field_num {
1 => self.name = field.value.as_string()?,
2 => self.id = field.value.as_u64()?,
3 => self.phone.push(parse_message(field.value.as_bytes()?)?),
1 => self.name = field.value.as_string(),
2 => self.id = field.value.as_u64(),
3 => self.phone.push(parse_message(field.value.as_bytes())),
_ => {} // skip everything else
}
Ok(())
}
}
impl<'a> ProtoMessage<'a> for PhoneNumber<'a> {
fn add_field(&mut self, field: Field<'a>) -> Result<(), Error> {
fn add_field(&mut self, field: Field<'a>) {
match field.field_num {
1 => self.number = field.value.as_string()?,
2 => self.type_ = field.value.as_string()?,
1 => self.number = field.value.as_string(),
2 => self.type_ = field.value.as_string(),
_ => {} // skip everything else
}
Ok(())
}
}
@ -228,36 +213,7 @@ fn main() {
0x18, 0x0a, 0x0e, 0x2b, 0x31, 0x38, 0x30, 0x30, 0x2d, 0x38, 0x36, 0x37,
0x2d, 0x35, 0x33, 0x30, 0x38, 0x12, 0x06, 0x6d, 0x6f, 0x62, 0x69, 0x6c,
0x65,
])
.unwrap();
]);
println!("{:#?}", person);
}
// ANCHOR_END: main
// ANCHOR: tests
#[cfg(test)]
mod test {
use super::*;
#[test]
fn as_string() {
assert!(FieldValue::Varint(10).as_string().is_err());
assert!(FieldValue::I32(10).as_string().is_err());
assert_eq!(FieldValue::Len(b"hello").as_string().unwrap(), "hello");
}
#[test]
fn as_bytes() {
assert!(FieldValue::Varint(10).as_bytes().is_err());
assert!(FieldValue::I32(10).as_bytes().is_err());
assert_eq!(FieldValue::Len(b"hello").as_bytes().unwrap(), b"hello");
}
#[test]
fn as_u64() {
assert_eq!(FieldValue::Varint(10).as_u64().unwrap(), 10u64);
assert!(FieldValue::I32(10).as_u64().is_err());
assert!(FieldValue::Len(b"hello").as_u64().is_err());
}
}
// ANCHOR_END: tests

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@ -1,7 +1,5 @@
# Solution
<!-- compile_fail because `mdbook test` does not allow use of `thiserror` -->
```rust,editable,compile_fail
```rust,editable
{{#include exercise.rs:solution}}
```