Initial raw lazy text reader (top-level nulls, bools, ints) #609

zslayton · 2023-07-24T20:56:40Z

This adds an initial implementation of a LazyRawTextReader that can yield LazyRawTextValues. At present it is limited to reading top-level nulls, bools, and ints of any radix. Support for other types, annotations, and containers will be added in follow-on PRs.

This implementation splits the parsing process for each value into two phases:

Matching finds a slice at the head of the input that corresponds to an element from the Ion grammar. It does not perform full semantic validation of the value.
Reading fully validates the previously matched input and turns it into a value.

This split makes it possible for the reader to avoid the cost of validation and materialization for values that the user simply skips over. To minimize rework done in the two phases, the matching phase records information it discovers along the way (subfield offsets, radix, etc) so it is available if and when the reading phase begins.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

codecov · 2023-07-24T20:58:55Z

Codecov Report

Patch coverage: 67.52% and project coverage change: -0.67% ⚠️

Comparison is base (42adf28) 82.39% compared to head (840be4d) 81.72%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #609      +/-   ##
==========================================
- Coverage   82.39%   81.72%   -0.67%     
==========================================
  Files         111      118       +7     
  Lines       20048    20969     +921     
  Branches    20048    20969     +921     
==========================================
+ Hits        16518    17137     +619     
- Misses       1912     2193     +281     
- Partials     1618     1639      +21

Files Changed	Coverage Δ
src/lazy/binary/raw/reader.rs	`76.31% <ø> (ø)`
src/lazy/binary/raw/sequence.rs	`60.93% <ø> (ø)`
src/lazy/binary/raw/struct.rs	`62.22% <ø> (ø)`
src/lazy/encoding.rs	`0.00% <0.00%> (ø)`
src/lazy/reader.rs	`66.66% <ø> (ø)`
src/lazy/sequence.rs	`73.07% <ø> (ø)`
src/lazy/struct.rs	`66.66% <ø> (ø)`
src/lazy/system_reader.rs	`77.15% <ø> (ø)`
src/lazy/value.rs	`74.61% <ø> (ø)`
src/result/decoding_error.rs	`42.85% <12.50%> (-40.48%)`	⬇️
... and 12 more

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zslayton

🗺️ PR tour

zslayton · 2023-07-25T12:17:08Z

Cargo.toml

@@ -66,7 +66,7 @@ num-bigint = "0.4.3"
 num-integer = "0.1.44"
 num-traits = "0.2"
 arrayvec = "0.7"
-smallvec = "1.9.0"
+smallvec = {version ="1.9.0", features = ["const_generics"]}


🗺️ The const_generics feature of the smallvec crate provides trait implementations for all sizes of backing array ([u8; N] in our case) rather than just 0-32 and several powers of two beyond. It's a feature because smallvec predates const generics and didn't want to force a breaking change.

zslayton · 2023-07-25T12:17:51Z

src/lazy/binary/encoding.rs

🗺️ This file was moved to the parent directory, not deleted. It appears again later in the diff.

zslayton · 2023-07-25T12:19:18Z

src/lazy/binary/raw/value.rs

@@ -35,7 +35,7 @@ impl<'a> Debug for LazyRawBinaryValue<'a> {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(
            f,
-            "LazyRawValue {{\n  val={:?},\n  buf={:?}\n}}\n",
+            "LazyRawBinaryValue {{\n  val={:?},\n  buf={:?}\n}}\n",


🗺️ LazyRawBinaryValue used to be the only kind of lazy value and was called LazyRawValue. Now LazyRawValue is the trait and this type is LazyRawBinaryValue.

zslayton · 2023-07-25T12:21:01Z

src/lazy/binary/raw/value.rs

@@ -54,6 +54,10 @@ impl<'data> LazyRawValue<'data, BinaryEncoding> for LazyRawBinaryValue<'data> {
        self.ion_type()
    }

+    fn is_null(&self) -> bool {
+        self.is_null()


🗺️is_null is a method on the LazyRawValue trait. This implementation delegates the call to the is_null method that lives on the LazyRawBinaryValue concrete type.

This arrangement produces a small amount of extra code (there are two fn is_nulls), but means that consumer code that works explicitly with LazyRawBinaryValue doesn't have to import a trait just to use its methods.

zslayton · 2023-07-25T12:24:44Z

src/lazy/encoding.rs

+impl<'data> LazyDecoder<'data> for BinaryEncoding {
+    type Reader = LazyRawBinaryReader<'data>;
+    type Value = LazyRawBinaryValue<'data>;
+    type Sequence = LazyRawBinarySequence<'data>;
+    type Struct = LazyRawBinaryStruct<'data>;
+    type AnnotationsIterator = RawBinaryAnnotationsIterator<'data>;
+}


🗺️ As mentioned earlier in the diff, encoding.rs was moved here from the binary directory. The BinaryEncoding struct and this impl existed before this PR, but appear as additions here because of the move. The TextEncoding struct and the content below this impl (line 33+) are new.

zslayton · 2023-07-25T14:12:55Z

src/lazy/text/as_utf8.rs

🗺️ This PR deals with two types that are effectively wrappers around a &[u8]: TextBufferView and SmallVec. Most of the time we don't need to view them as validated UTF-8 &strs--we can rely on the grammar to reject anything invalid--but sometimes we do. This trait defines an extension method that streamlines the "view these bytes as a &str or raise an IonError" task.

zslayton · 2023-07-25T14:15:19Z

src/lazy/text/buffer.rs

+        self.data.is_empty()
+    }
+
+    pub fn match_whitespace(self) -> IonMatchResult<'data> {


🗺️ Note that only a handful of the match_ parsing methods are pub. Most are helper-parsers.

zslayton · 2023-07-25T14:26:49Z

src/lazy/text/parse_result.rs

+// impl<'data> From<InvalidInputError<'data>> for IonError {
+//     fn from(value: InvalidInputError) -> Self {
+//         dbg!(&value.backtrace);
+//         let mut message = String::from(value.description().unwrap_or("invalid text Ion syntax"));
+//         if let Some(label) = value.label {
+//             message.push_str(" while ");
+//             message.push_str(label.as_ref());
+//         }
+//         let position = Position::with_offset(value.input.offset()).with_length(value.input.len());
+//         let decoding_error = DecodingError::new(message).with_position(position);
+//         IonError::Decoding(decoding_error)
+//     }
+// }


🗺️ I'll remove this obsolete code after the PR is reviewed. Pushing code as I write the PR tour comments causes some number of the comments to be discarded 😐.

zslayton · 2023-07-25T14:29:30Z

src/lazy/text/raw/reader.rs

+    use crate::IonType;
+
+    #[test]
+    fn test_top_level() -> IonResult<()> {


🗺️ This test demonstrates the total capability introduced in this PR. Namely, a LazyRawTextReader that can read top-level, unannotated nulls, bools, and ints in a text stream.

zslayton · 2023-07-25T14:30:43Z

src/lazy/text/value.rs

+/// If only part of the value is in the input buffer, calls to [`LazyRawTextValue::read`] (which examines
+/// bytes beyond the value's header) may return [`IonError::Incomplete`](crate::result::IonError::Incomplete).


🗺️ I have a lingering reference to "the value's header" that was a copy/paste error from this type's binary counterpart. I'll fix that before merging.

zslayton

🗺️ couple more PR tour comments

zslayton · 2023-07-25T19:37:19Z

src/lazy/text/parse_result.rs

🗺️ Much of this was copied over from the old text reader implementation's error handling code and then updated.

zslayton · 2023-07-25T19:40:50Z

src/lazy/text/parse_result.rs

+pub(crate) trait AddContext<'data, T> {
+    fn with_context(
+        self,
+        label: impl Into<Cow<'static, str>>,
+        input: TextBufferView<'data>,
+    ) -> IonResult<(TextBufferView<'data>, T)>;
+}


🗺️ I plan to add a doc comment to this trait before merging. I intentionally avoided providing an Into<IonError> impl for IonParseError because some of the nom error kinds that bubble up as IonParseError don't retain context. This trait is an easy way for methods that could surface without context to require more information before being passed on to the user.

For an example of its usage, see LazyRawTextReader::next():

desaikd · 2023-08-09T19:55:23Z

src/result/decoding_error.rs

@@ -6,12 +7,23 @@ use thiserror::Error;
 #[error("{description}")]
 pub struct DecodingError {
    description: Cow<'static, str>,
+    position: Option<Position>,


(Suggestion) Add comment regarding why position is optional here.

I'll add this in a follow-on PR to avoid needing to modify the queue.

desaikd · 2023-08-09T20:07:41Z

src/lazy/text/buffer.rs

+    }
+
+    /// Matches a single scalar value or the beginning of a container.
+    pub fn match_value(self) -> IonParseResult<'data, LazyRawTextValue<'data>> {


(Question) Should this be called read_value as it returns a parsed value? Same for match_top_level?

I was reserving the read_* names for methods that produce one of the RawValueRef::* variants. The LazyRawTextValue that this returns has its own read() method that serves that purpose.

Feedback from PRs: * #609 * #614 * #616 * #619 * #620 * #627 * #628 * #638 * #639

Top-level nulls, bools, ints

e0a83d8

zslayton added 2 commits July 25, 2023 08:36

Consolidate impls of AsUtf8 w/helper fn

89f79aa

Improved TextBufferView docs, removed DataSource

840be4d

zslayton commented Jul 25, 2023

View reviewed changes

zslayton requested review from jobarr-amzn, popematt and desaikd and removed request for jobarr-amzn July 25, 2023 14:45

zslayton marked this pull request as ready for review July 25, 2023 18:31

zslayton commented Jul 25, 2023

View reviewed changes

desaikd approved these changes Aug 9, 2023

View reviewed changes

zslayton mentioned this pull request Aug 10, 2023

Adds LazyRawTextReader support for structs #619

Merged

zslayton merged commit 31ec961 into main Aug 10, 2023

zslayton deleted the lazy-text-reader branch August 10, 2023 18:18

This was referenced Aug 10, 2023

Adds LazyRawTextReader support for reading IVMs #620

Merged

Initial impl of a LazyRawAnyReader #621

Merged

Adds lazy reader support for reading annotations #622

Merged

Adds lazy reader support for timestamps #623

Merged

zslayton self-assigned this Aug 29, 2023

zslayton added a commit that referenced this pull request Sep 7, 2023

Feedback from PR #609

98eae43

zslayton mentioned this pull request Sep 7, 2023

Incorporates pending feedback from lazy reader PRs #642

Merged

zslayton added a commit that referenced this pull request Sep 7, 2023

Incorporates pending feedback from lazy reader PRs (#642)

ec91888

Feedback from PRs: * #609 * #614 * #616 * #619 * #620 * #627 * #628 * #638 * #639

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Initial raw lazy text reader (top-level nulls, bools, ints) #609

Initial raw lazy text reader (top-level nulls, bools, ints) #609

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		/// If only part of the value is in the input buffer, calls to [`LazyRawTextValue::read`] (which examines
		/// bytes beyond the value's header) may return [`IonError::Incomplete`](crate::result::IonError::Incomplete).

Initial raw lazy text reader (top-level nulls, bools, ints) #609

Initial raw lazy text reader (top-level nulls, bools, ints) #609

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zslayton commented Jul 24, 2023 •

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