Struct StreamingParser 

pub struct StreamingParser<R: Read> { /* private fields */ }

Streaming HEDL parser.

Processes HEDL documents incrementally, yielding NodeEvent items as they are parsed without loading the entire document into memory.

Implementations

impl<R: Read> StreamingParser<R>

pub fn new(reader: R) -> StreamResult<Self>

Create a new streaming parser with default configuration.

The parser immediately reads and validates the HEDL header (version and schema directives). If the header is invalid, this function returns an error.

Parameters

• reader: Any type implementing Read (files, network streams, buffers, etc.)

Returns

• Ok(parser): Parser ready to yield events
• Err(e): Header parsing failed (missing version, invalid schema, etc.)

Examples

From a File

use hedl_stream::StreamingParser;
use std::fs::File;
use std::io::BufReader;

let file = File::open("data.hedl")?;
let reader = BufReader::new(file);
let parser = StreamingParser::new(reader)?;

From a String

use hedl_stream::StreamingParser;
use std::io::Cursor;

let data = r#"
%VERSION: 1.0
%STRUCT: User: [id, name]
---
users:@User
  | alice, Alice
"#;

let parser = StreamingParser::new(Cursor::new(data))?;

From Stdin

use hedl_stream::StreamingParser;
use std::io::stdin;

let parser = StreamingParser::new(stdin().lock())?;

Errors

• StreamError::MissingVersion: No %VERSION directive found
• StreamError::InvalidVersion: Invalid version format
• StreamError::Syntax: Malformed header directive
• StreamError::Io: I/O error reading input

pub fn with_config( reader: R, config: StreamingParserConfig, ) -> StreamResult<Self>

Create a streaming parser with custom configuration.

Use this when you need to control memory limits, buffer sizes, or enable timeout protection for untrusted input.

Parameters

• reader: Any type implementing Read
• config: Parser configuration options

Returns

• Ok(parser): Parser ready to yield events
• Err(e): Configuration invalid or header parsing failed

Examples

With Timeout Protection

use hedl_stream::{StreamingParser, StreamingParserConfig};
use std::time::Duration;
use std::io::Cursor;

let config = StreamingParserConfig {
    timeout: Some(Duration::from_secs(30)),
    ..Default::default()
};

let untrusted_input = "...";
let parser = StreamingParser::with_config(
    Cursor::new(untrusted_input),
    config
)?;

For Large Files

use hedl_stream::{StreamingParser, StreamingParserConfig};
use std::io::Cursor;

let config = StreamingParserConfig {
    buffer_size: 256 * 1024,      // 256KB read buffer
    max_line_length: 10_000_000,  // 10MB max line
    max_indent_depth: 1000,       // Deep nesting allowed
    timeout: None,
    ..Default::default()
};

let parser = StreamingParser::with_config(
    Cursor::new("..."),
    config
)?;

For Constrained Environments

use hedl_stream::{StreamingParser, StreamingParserConfig};
use std::time::Duration;
use std::io::Cursor;

let config = StreamingParserConfig {
    buffer_size: 8 * 1024,        // Small 8KB buffer
    max_line_length: 100_000,     // 100KB max line
    max_indent_depth: 50,         // Limited nesting
    timeout: Some(Duration::from_secs(10)),
    ..Default::default()
};

let parser = StreamingParser::with_config(
    Cursor::new("..."),
    config
)?;

Errors

Same as new(), plus:

• StreamError::Timeout: Header parsing exceeded configured timeout

pub fn header(&self) -> Option<&HeaderInfo>

Get the parsed header information.

Returns header metadata including version, schema definitions, aliases, and nesting rules. This is available immediately after parser creation.

Returns

• Some(&HeaderInfo): Header was successfully parsed
• None: Should never happen after successful parser creation

Examples

Inspecting Schema Definitions

use hedl_stream::StreamingParser;
use std::io::Cursor;

let input = r#"
%VERSION: 1.0
%STRUCT: User: [id, name, email]
%STRUCT: Order: [id, user_id, amount]
%ALIAS: active = "Active"
%NEST: User > Order
---
"#;

let parser = StreamingParser::new(Cursor::new(input))?;
let header = parser.header().unwrap();

// Check version
assert_eq!(header.version, (1, 0));

// Get schema
let user_schema = header.get_schema("User").unwrap();
assert_eq!(user_schema, &vec!["id", "name", "email"]);

// Check aliases
assert_eq!(header.aliases.get("active"), Some(&"Active".to_string()));

// Check nesting rules
assert!(header.get_child_types("User").map_or(false, |v| v.contains(&"Order".to_string())));

Validating Before Processing

use hedl_stream::StreamingParser;
use std::io::Cursor;

let input = r#"
%VERSION: 1.0
%STRUCT: User: [id, name]
---
users:@User
  | alice, Alice
"#;

let parser = StreamingParser::new(Cursor::new(input))?;

// Validate we have the expected schema before processing
if let Some(header) = parser.header() {
    if header.version.0 != 1 {
        eprintln!("Warning: Unexpected major version");
    }

    if !header.structs.contains_key("User") {
        return Err("Missing User schema".into());
    }
}

// Proceed with parsing...

impl StreamingParser<CompressionReader<File>>

pub fn open<P: AsRef<Path>>(path: P) -> StreamResult<Self>

Open a file with automatic compression detection.

Detects compression format from the file extension (.gz, .zst, .lz4) and automatically decompresses the content.

Examples

use hedl_stream::StreamingParser;

// Open a GZIP-compressed HEDL file
let parser = StreamingParser::open("data.hedl.gz")?;

for event in parser {
    println!("{:?}", event?);
}

Errors

• StreamError::Io: File not found or cannot be opened
• StreamError::Compression: Decompression initialization failed
• StreamError::MissingVersion: Invalid HEDL header

pub fn open_with_config<P: AsRef<Path>>( path: P, config: StreamingParserConfig, ) -> StreamResult<Self>

Open a file with automatic compression detection and custom configuration.

Combines automatic compression detection with custom parser settings.

Examples

use hedl_stream::{StreamingParser, StreamingParserConfig};
use std::time::Duration;

let config = StreamingParserConfig {
    timeout: Some(Duration::from_secs(30)),
    ..Default::default()
};

let parser = StreamingParser::open_with_config("data.hedl.zst", config)?;

pub fn open_with_compression<P: AsRef<Path>>( path: P, format: CompressionFormat, ) -> StreamResult<Self>

Open a file with explicit compression format.

Use this when the file extension doesn’t match the actual compression format, or when you want to force a specific decompression algorithm.

Examples

use hedl_stream::StreamingParser;
use hedl_stream::compression::CompressionFormat;

// File has no extension but is GZIP compressed
let parser = StreamingParser::open_with_compression(
    "data.hedl",
    CompressionFormat::Gzip,
)?;

Trait Implementations

impl<R: Read> Iterator for StreamingParser<R>

type Item = Result<NodeEvent, StreamError>

The type of the elements being iterated over.

fn next(&mut self) -> Option<Self::Item>

Advances the iterator and returns the next value.

fn next_chunk<const N: usize>( &mut self, ) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>

where Self: Sized,

🔬This is a nightly-only experimental API. (iter_next_chunk)

Advances the iterator and returns an array containing the next N values.

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the iterator.

fn count(self) -> usize

where Self: Sized,

Consumes the iterator, counting the number of iterations and returning it.

fn last(self) -> Option<Self::Item>

where Self: Sized,

Consumes the iterator, returning the last element.

fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>

🔬This is a nightly-only experimental API. (iter_advance_by)

Advances the iterator by n elements.

fn nth(&mut self, n: usize) -> Option<Self::Item>

Returns the nth element of the iterator.

fn step_by(self, step: usize) -> StepBy<Self>

where Self: Sized,

Creates an iterator starting at the same point, but stepping by the given amount at each iteration.

fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter>

where Self: Sized, U: IntoIterator<Item = Self::Item>,

Takes two iterators and creates a new iterator over both in sequence.

fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter>

where Self: Sized, U: IntoIterator,

‘Zips up’ two iterators into a single iterator of pairs.

fn intersperse(self, separator: Self::Item) -> Intersperse<Self>

where Self: Sized, Self::Item: Clone,

🔬This is a nightly-only experimental API. (iter_intersperse)

Creates a new iterator which places a copy of separator between adjacent items of the original iterator.

fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G>

where Self: Sized, G: FnMut() -> Self::Item,

🔬This is a nightly-only experimental API. (iter_intersperse)

Creates a new iterator which places an item generated by separator between adjacent items of the original iterator.

fn map<B, F>(self, f: F) -> Map<Self, F>

where Self: Sized, F: FnMut(Self::Item) -> B,

Takes a closure and creates an iterator which calls that closure on each element.

fn for_each<F>(self, f: F)

where Self: Sized, F: FnMut(Self::Item),

Calls a closure on each element of an iterator.

fn filter<P>(self, predicate: P) -> Filter<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator which uses a closure to determine if an element should be yielded.

fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>

where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both filters and maps.

fn enumerate(self) -> Enumerate<Self>

where Self: Sized,

Creates an iterator which gives the current iteration count as well as the next value.

fn peekable(self) -> Peekable<Self>

where Self: Sized,

Creates an iterator which can use the peek and peek_mut methods to look at the next element of the iterator without consuming it. See their documentation for more information.

fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that skips elements based on a predicate.

fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that yields elements based on a predicate.

fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P>

where Self: Sized, P: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both yields elements based on a predicate and maps.

fn skip(self, n: usize) -> Skip<Self>

where Self: Sized,

Creates an iterator that skips the first n elements.

fn take(self, n: usize) -> Take<Self>

where Self: Sized,

Creates an iterator that yields the first n elements, or fewer if the underlying iterator ends sooner.

fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>

where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>,

An iterator adapter which, like fold, holds internal state, but unlike fold, produces a new iterator.

fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>

where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U,

Creates an iterator that works like map, but flattens nested structure.

fn flatten(self) -> Flatten<Self>

where Self: Sized, Self::Item: IntoIterator,

Creates an iterator that flattens nested structure.

fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N>

where Self: Sized, F: FnMut(&[Self::Item; N]) -> R,

🔬This is a nightly-only experimental API. (iter_map_windows)

Calls the given function f for each contiguous window of size N over self and returns an iterator over the outputs of f. Like slice::windows(), the windows during mapping overlap as well.

fn fuse(self) -> Fuse<Self>

where Self: Sized,

Creates an iterator which ends after the first None.

fn inspect<F>(self, f: F) -> Inspect<Self, F>

where Self: Sized, F: FnMut(&Self::Item),

Does something with each element of an iterator, passing the value on.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Iterator.

fn collect<B>(self) -> B

where B: FromIterator<Self::Item>, Self: Sized,

Transforms an iterator into a collection.

fn try_collect<B>( &mut self, ) -> <<Self::Item as Try>::Residual as Residual<B>>::TryType

where Self: Sized, Self::Item: Try, <Self::Item as Try>::Residual: Residual<B>, B: FromIterator<<Self::Item as Try>::Output>,

🔬This is a nightly-only experimental API. (iterator_try_collect)

Fallibly transforms an iterator into a collection, short circuiting if a failure is encountered.

fn collect_into<E>(self, collection: &mut E) -> &mut E

where E: Extend<Self::Item>, Self: Sized,

🔬This is a nightly-only experimental API. (iter_collect_into)

Collects all the items from an iterator into a collection.

fn partition<B, F>(self, f: F) -> (B, B)

where Self: Sized, B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool,

Consumes an iterator, creating two collections from it.

fn is_partitioned<P>(self, predicate: P) -> bool

where Self: Sized, P: FnMut(Self::Item) -> bool,

🔬This is a nightly-only experimental API. (iter_is_partitioned)

Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return true precede all those that return false.

fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R

where Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Output = B>,

An iterator method that applies a function as long as it returns successfully, producing a single, final value.

fn try_for_each<F, R>(&mut self, f: F) -> R

where Self: Sized, F: FnMut(Self::Item) -> R, R: Try<Output = ()>,

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error.

fn fold<B, F>(self, init: B, f: F) -> B

where Self: Sized, F: FnMut(B, Self::Item) -> B,

Folds every element into an accumulator by applying an operation, returning the final result.

fn reduce<F>(self, f: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(Self::Item, Self::Item) -> Self::Item,

Reduces the elements to a single one, by repeatedly applying a reducing operation.

fn try_reduce<R>( &mut self, f: impl FnMut(Self::Item, Self::Item) -> R, ) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType

where Self: Sized, R: Try<Output = Self::Item>, <R as Try>::Residual: Residual<Option<Self::Item>>,

🔬This is a nightly-only experimental API. (iterator_try_reduce)

Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately.

fn all<F>(&mut self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if every element of the iterator matches a predicate.

fn any<F>(&mut self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if any element of the iterator matches a predicate.

fn find<P>(&mut self, predicate: P) -> Option<Self::Item>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator that satisfies a predicate.

fn find_map<B, F>(&mut self, f: F) -> Option<B>

where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Applies function to the elements of iterator and returns the first non-none result.

fn try_find<R>( &mut self, f: impl FnMut(&Self::Item) -> R, ) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType

where Self: Sized, R: Try<Output = bool>, <R as Try>::Residual: Residual<Option<Self::Item>>,

🔬This is a nightly-only experimental API. (try_find)

Applies function to the elements of iterator and returns the first true result or the first error.

fn position<P>(&mut self, predicate: P) -> Option<usize>

where Self: Sized, P: FnMut(Self::Item) -> bool,

Searches for an element in an iterator, returning its index.

fn max(self) -> Option<Self::Item>

where Self: Sized, Self::Item: Ord,

Returns the maximum element of an iterator.

fn min(self) -> Option<Self::Item>

where Self: Sized, Self::Item: Ord,

Returns the minimum element of an iterator.

fn max_by_key<B, F>(self, f: F) -> Option<Self::Item>

where B: Ord, Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the maximum value from the specified function.

fn max_by<F>(self, compare: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the maximum value with respect to the specified comparison function.

fn min_by_key<B, F>(self, f: F) -> Option<Self::Item>

where B: Ord, Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the minimum value from the specified function.

fn min_by<F>(self, compare: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the minimum value with respect to the specified comparison function.

fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)

where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Sized + Iterator<Item = (A, B)>,

Converts an iterator of pairs into a pair of containers.

fn copied<'a, T>(self) -> Copied<Self>

where T: Copy + 'a, Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which copies all of its elements.

fn cloned<'a, T>(self) -> Cloned<Self>

where T: Clone + 'a, Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which clones all of its elements.

fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>

where Self: Sized,

🔬This is a nightly-only experimental API. (iter_array_chunks)

Returns an iterator over N elements of the iterator at a time.

fn sum<S>(self) -> S

where Self: Sized, S: Sum<Self::Item>,

Sums the elements of an iterator.

fn product<P>(self) -> P

where Self: Sized, P: Product<Self::Item>,

Iterates over the entire iterator, multiplying all the elements

fn cmp<I>(self, other: I) -> Ordering

where I: IntoIterator<Item = Self::Item>, Self::Item: Ord, Self: Sized,

Lexicographically compares the elements of this Iterator with those of another.

fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering,

🔬This is a nightly-only experimental API. (iter_order_by)

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.

fn partial_cmp<I>(self, other: I) -> Option<Ordering>

where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Lexicographically compares the PartialOrd elements of this Iterator with those of another. The comparison works like short-circuit evaluation, returning a result without comparing the remaining elements. As soon as an order can be determined, the evaluation stops and a result is returned.

fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,

🔬This is a nightly-only experimental API. (iter_order_by)

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.

fn eq<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialEq<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are equal to those of another.

fn eq_by<I, F>(self, other: I, eq: F) -> bool

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool,

🔬This is a nightly-only experimental API. (iter_order_by)

Determines if the elements of this Iterator are equal to those of another with respect to the specified equality function.

fn ne<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialEq<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are not equal to those of another.

fn lt<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically less than those of another.

fn le<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically less or equal to those of another.

fn gt<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically greater than those of another.

fn ge<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically greater than or equal to those of another.

fn is_sorted(self) -> bool

where Self: Sized, Self::Item: PartialOrd,

Checks if the elements of this iterator are sorted.

fn is_sorted_by<F>(self, compare: F) -> bool

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> bool,

Checks if the elements of this iterator are sorted using the given comparator function.

fn is_sorted_by_key<F, K>(self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> K, K: PartialOrd,

Checks if the elements of this iterator are sorted using the given key extraction function.