BoundaryML/baml · error · StreamingError

Value was marked Done, but was incomplete in the stream

Error message

Value was marked Done, but was incomplete in the stream

What it means

StreamingError::IncompleteDoneValue indicates a value in the stream was marked Done (complete) but its content is not actually parseable as a complete value. The streaming state machine's Done marker disagrees with the actual data, so validation fails rather than silently returning truncated output.

Source

Thrown at engine/baml-lib/jsonish/src/deserializer/semantic_streaming.rs:24

use anyhow::{Context, Error};
use baml_types::{
    BamlMap, BamlValueWithMeta, Completion, CompletionState, ResponseCheck, TypeIR, TypeValue,
};
use indexmap::{IndexMap, IndexSet};
use internal_baml_core::ir::{
    ir_helpers::infer_type_with_meta,
    repr::{IntermediateRepr, Walker},
    Field, IRHelper, IRHelperExtended, IRSemanticStreamingHelper,
};
use thiserror;

use crate::{deserializer::coercer::ParsingError, BamlValueWithFlags, Flag};

#[derive(Debug, thiserror::Error)]
pub enum StreamingError {
    #[error("Expected to encounter a class")]
    ExpectedClass,
    #[error("Value was marked Done, but was incomplete in the stream")]
    IncompleteDoneValue,
    #[error("Class instance did not contain fields marked as needed: {fields:?}")]
    MissingNeededFields { fields: Vec<String> },
    #[error("Failed to distribute_type_with_meta: {0}")]
    DistributeTypeWithMetaFailure(#[from] anyhow::Error),
}

/// For a given baml value, traverse its nodes, comparing the completion state
/// of each node against the streaming behavior of the node's type.
pub fn validate_streaming_state(
    ir: &impl IRHelperExtended,
    baml_value: &BamlValueWithFlags,
    mode: baml_types::StreamingMode,
) -> Result<BamlValueWithMeta<Completion>, StreamingError> {
    let baml_value_with_meta_flags: BamlValueWithMeta<Vec<Flag>> = baml_value.clone().into();
    let typed_baml_value: BamlValueWithMeta<(Vec<Flag>, TypeIR)> =
        ir.distribute_type_with_meta(baml_value_with_meta_flags, baml_value.field_type().clone())?;
    let baml_value_with_streaming_state_and_behavior =

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Re-run the request with a higher max_tokens / output budget.
2. Enable partial streaming parsing and validate completeness before treating the value as final.
3. Check stop sequences and provider settings that may terminate generation early.
4. Retry the request; if reproducible, inspect whether your proxy/client truncates streams.

Example fix

// before: treating final chunk as complete
let value = parse_done(chunk)?;
// after: guard
match validate_streaming_state(&value) {
    Err(StreamingError::IncompleteDoneValue) => retry_or_request_continuation(),
    other => other?,
}

// before trusting a Done value
if let Err(StreamingError::IncompleteDoneValue) = validate_streaming_state(&value) {
    // do not use the value; request continuation or retry
}

fn is_complete(value: &BamlValueWithFlags) -> bool {
    validate_streaming_state(value).is_ok()
}

match validate_streaming_state(&value) {
    Err(StreamingError::IncompleteDoneValue) => retry_with_higher_budget().await?,
    Err(e) => return Err(e.into()),
    Ok(()) => commit(value),
}

When it happens

Trigger: validate_streaming_state traverses nodes and finds one whose completion state is Done while its parsed value is still incomplete — e.g. the stream terminated mid-object after the parser optimistically marked it done, or truncated JSON that matched a done heuristic.

Common situations: LLM hit max_tokens mid-JSON; network/proxy cut the stream; stop-sequences fired early; parser heuristics marking partial braces as complete in very long outputs.

Understand the failure class

Background: "Invalid JSON response" and "Failed to parse response" errors: when an API answers 200 but the body isn't the JSON your library expected — this error's family across 28 libraries.

Related errors

• Expected to encounter a class
• Class instance did not contain fields marked as needed: {fie
• Failed to distribute_type_with_meta: {0}
• Parsing failed due to: {s:?}
• Cannot stream expr function through this code path

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/686b8de17e9a39b2. Report an issue: GitHub.