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fix: prevent parser poisoning from inline tool-call JSON patterns

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The streaming parser was incorrectly detecting tool call patterns that
appeared inline in prose (e.g., when explaining the format), causing
g3 to return control mid-task.

Fix: Modified find_first_tool_call_start() and find_last_tool_call_start()
to only recognize patterns that appear on their own line (at start of
buffer or after newline with only whitespace before the pattern).

Changes:
- Added is_on_own_line() helper to check line-boundary conditions
- Updated detection methods to skip inline patterns
- Removed sanitize_inline_tool_patterns() and LBRACE_HOMOGLYPH (no longer needed)
- Rewrote tests for new behavior
- Added streaming_repro tests that use process_chunk() to verify the exact bug scenario

28 tests covering: streaming repro, line boundaries, Unicode, code contexts, edge cases
This commit is contained in:
Dhanji R. Prasanna
2026-01-15 08:54:47 +05:30
parent 616e0898c7
commit 999ac6fe66
4 changed files with 390 additions and 240 deletions
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257
crates/g3-core/src/streaming_parser.rs
View File

@@ -2,6 +2,10 @@
//!
//! This module handles parsing of tool calls from streaming LLM responses,
//! supporting both native tool calls and JSON-based fallback parsing.
//!
//! **Important**: JSON tool calls are only recognized when they appear on their
//! own line (preceded by a newline or at the start of the buffer). This prevents
//! inline JSON examples in prose from being incorrectly parsed as tool calls.
use tracing::debug;
@@ -16,62 +20,6 @@ const TOOL_CALL_PATTERNS: [&str; 4] = [
r#"{ "tool" :"#,
];
/// Unicode homoglyph for left curly brace, used to sanitize inline tool-call-like patterns.
/// This is the "FULLWIDTH LEFT CURLY BRACKET" (U+FF5B).
pub const LBRACE_HOMOGLYPH: char = '｛';
/// Sanitize text content by replacing tool-call-like patterns that appear inline
/// (not on their own line) with homoglyphs to prevent parser poisoning.
///
/// Real tool calls from LLMs always appear on their own line. When we see patterns
/// like `{"tool":` embedded within other text (e.g., in code examples, inline code,
/// or prose), we replace the opening brace with a homoglyph to prevent the streaming
/// parser from incorrectly entering JSON parsing mode.
///
/// This function is called on each chunk of streamed content before it's added to
/// the text buffer.
pub fn sanitize_inline_tool_patterns(text: &str) -> String {
let mut result = String::with_capacity(text.len());
let lines: Vec<&str> = text.split('\n').collect();
for (i, line) in lines.iter().enumerate() {
if i > 0 {
result.push('\n');
}
// Check if this line starts with a tool call pattern (after trimming whitespace)
let trimmed = line.trim_start();
let is_standalone_tool_call = TOOL_CALL_PATTERNS.iter().any(|p| trimmed.starts_with(p));
if is_standalone_tool_call {
// This looks like a real tool call on its own line - leave it alone
result.push_str(line);
} else {
// Check if there are any tool call patterns embedded in this line
let mut line_result = line.to_string();
for pattern in &TOOL_CALL_PATTERNS {
// Find all occurrences of the pattern in this line
let mut search_start = 0;
while let Some(pos) = line_result[search_start..].find(pattern) {
let abs_pos = search_start + pos;
// Check if this pattern is at the start of the trimmed line
// (which we already handled above)
let before = &line_result[..abs_pos];
if !before.trim().is_empty() {
// There's non-whitespace before this pattern - it's inline, sanitize it
let replacement = format!("{}{}", LBRACE_HOMOGLYPH, &pattern[1..]);
line_result = format!("{}{}{}", &line_result[..abs_pos], replacement, &line_result[abs_pos + pattern.len()..]);
}
search_start = abs_pos + pattern.len();
}
}
result.push_str(&line_result);
}
}
result
}
/// Modern streaming tool parser that properly handles native tool calls and SSE chunks.
#[derive(Debug)]
pub struct StreamingToolParser {
@@ -105,34 +53,74 @@ impl StreamingToolParser {
}
}
/// Find the starting position of the last tool call pattern in the given text.
/// Returns None if no tool call pattern is found.
fn find_last_tool_call_start(text: &str) -> Option<usize> {
/// Find the starting position of the last tool call pattern in the given text,
/// but ONLY if it appears on its own line (preceded by newline or at start of text,
/// with only whitespace before the pattern on that line).
/// Returns None if no valid tool call pattern is found.
pub fn find_last_tool_call_start(text: &str) -> Option<usize> {
let mut best_start: Option<usize> = None;
for pattern in &TOOL_CALL_PATTERNS {
if let Some(pos) = text.rfind(pattern) {
if best_start.map_or(true, |best| pos > best) {
best_start = Some(pos);
let mut search_end = text.len();
while search_end > 0 {
if let Some(pos) = text[..search_end].rfind(pattern) {
// Check if this pattern is on its own line
if Self::is_on_own_line(text, pos) {
if best_start.map_or(true, |best| pos > best) {
best_start = Some(pos);
}
break; // Found a valid one for this pattern
}
// Not on its own line, keep searching backwards
search_end = pos;
} else {
break;
}
}
}
best_start
}
/// Find the starting position of the FIRST tool call pattern in the given text.
/// Returns None if no tool call pattern is found.
fn find_first_tool_call_start(text: &str) -> Option<usize> {
/// Find the starting position of the FIRST tool call pattern in the given text,
/// but ONLY if it appears on its own line (preceded by newline or at start of text,
/// with only whitespace before the pattern on that line).
/// Returns None if no valid tool call pattern is found.
pub fn find_first_tool_call_start(text: &str) -> Option<usize> {
let mut best_start: Option<usize> = None;
for pattern in &TOOL_CALL_PATTERNS {
if let Some(pos) = text.find(pattern) {
if best_start.map_or(true, |best| pos < best) {
best_start = Some(pos);
let mut search_start = 0;
while search_start < text.len() {
if let Some(relative_pos) = text[search_start..].find(pattern) {
let pos = search_start + relative_pos;
// Check if this pattern is on its own line
if Self::is_on_own_line(text, pos) {
if best_start.map_or(true, |best| pos < best) {
best_start = Some(pos);
}
break; // Found a valid one for this pattern
}
// Not on its own line, keep searching forward
search_start = pos + 1;
} else {
break;
}
}
}
best_start
}
/// Check if a position in text is "on its own line" - meaning it's either
/// at the start of the text, or preceded by a newline with only whitespace
/// between the newline and the position.
pub fn is_on_own_line(text: &str, pos: usize) -> bool {
if pos == 0 {
return true;
}
// Find the start of the current line (position after the last newline before pos)
let line_start = text[..pos].rfind('\n').map(|p| p + 1).unwrap_or(0);
// Check if everything between line_start and pos is whitespace
text[line_start..pos].chars().all(|c| c.is_whitespace())
}
/// Detect malformed tool calls where LLM prose leaked into JSON keys.
///
/// When the LLM "stutters" or mixes formats, it sometimes emits JSON where
@@ -157,11 +145,9 @@ impl StreamingToolParser {
pub fn process_chunk(&mut self, chunk: &g3_providers::CompletionChunk) -> Vec<ToolCall> {
let mut completed_tools = Vec::new();
// Add text content to buffer after sanitizing inline tool-call patterns
// to prevent parser poisoning from examples/code blocks
// Add text content to buffer
if !chunk.content.is_empty() {
let sanitized = sanitize_inline_tool_patterns(&chunk.content);
self.text_buffer.push_str(&sanitized);
self.text_buffer.push_str(&chunk.content);
}
// Handle native tool calls - return them immediately when received.
@@ -520,97 +506,98 @@ Some text after"#;
#[test]
fn test_find_first_vs_last_tool_call() {
let text = r#"{"tool": "first"} and {"tool": "second"}"#;
// Both tool calls are on their own lines
let text = "{\"tool\": \"first\"}\n{\"tool\": \"second\"}";
let first_pos = StreamingToolParser::find_first_tool_call_start(text);
let last_pos = StreamingToolParser::find_last_tool_call_start(text);
assert!(first_pos.is_some());
assert!(last_pos.is_some());
assert!(first_pos.is_some(), "Should find first tool call");
assert!(last_pos.is_some(), "Should find last tool call");
assert!(first_pos.unwrap() < last_pos.unwrap(),
"First position ({:?}) should be less than last position ({:?})", first_pos, last_pos);
}
#[test]
fn test_sanitize_inline_tool_patterns_preserves_standalone() {
// Tool call on its own line should NOT be sanitized
let input = r#"{"tool": "shell", "args": {"command": "ls"}}"#;
let result = sanitize_inline_tool_patterns(input);
assert_eq!(result, input, "Standalone tool call should not be modified");
fn test_inline_tool_call_ignored() {
// Tool call pattern inline with other text should NOT be detected
let text = "Here is an example: {\"tool\": \"shell\"} in text";
assert!(StreamingToolParser::find_first_tool_call_start(text).is_none(),
"Inline tool call pattern should be ignored");
assert!(StreamingToolParser::find_last_tool_call_start(text).is_none(),
"Inline tool call pattern should be ignored");
}
#[test]
fn test_sanitize_inline_tool_patterns_preserves_indented_standalone() {
// Tool call with leading whitespace should NOT be sanitized
let input = r#" {"tool": "shell", "args": {"command": "ls"}}"#;
let result = sanitize_inline_tool_patterns(input);
assert_eq!(result, input, "Indented standalone tool call should not be modified");
fn test_standalone_tool_call_detected() {
// Tool call on its own line (at start of text) should be detected
let text = r#"{"tool": "shell", "args": {"command": "ls"}}"#;
assert!(StreamingToolParser::find_first_tool_call_start(text).is_some(),
"Standalone tool call should be detected");
}
#[test]
fn test_sanitize_inline_tool_patterns_sanitizes_inline() {
// Tool call pattern embedded in text should be sanitized
let input = "Here is an example: {\"tool\": \"shell\"} in text";
let result = sanitize_inline_tool_patterns(input);
assert!(!result.contains("{\"tool\":"), "Inline pattern should be sanitized");
assert!(result.contains(LBRACE_HOMOGLYPH), "Should contain homoglyph");
fn test_indented_tool_call_detected() {
// Tool call with leading whitespace should be detected
let text = r#" {"tool": "shell", "args": {"command": "ls"}}"#;
assert!(StreamingToolParser::find_first_tool_call_start(text).is_some(),
"Indented tool call should be detected");
}
#[test]
fn test_sanitize_inline_tool_patterns_sanitizes_in_code_block() {
// Tool call pattern in inline code should be sanitized
let input = "Use `{\"tool\": \"shell\"}` to run commands";
let result = sanitize_inline_tool_patterns(input);
assert!(!result.contains("{\"tool\":"), "Pattern in code should be sanitized");
assert!(result.contains(LBRACE_HOMOGLYPH), "Should contain homoglyph");
fn test_tool_call_after_newline_detected() {
// Tool call after a newline should be detected
let text = "Some prose here\n{\"tool\": \"shell\", \"args\": {}}";
let pos = StreamingToolParser::find_first_tool_call_start(text);
assert!(pos.is_some(), "Tool call after newline should be detected");
assert_eq!(pos.unwrap(), 16, "Should find tool call at position after newline");
}
#[test]
fn test_sanitize_inline_tool_patterns_multiline() {
// Mixed: standalone on one line, inline on another
let input = "Some text with {\"tool\": \"inline\"} here\n{\"tool\": \"standalone\", \"args\": {}}\nMore text";
let result = sanitize_inline_tool_patterns(input);
fn test_inline_ignored_but_standalone_detected() {
// Mixed: inline on first line (ignored), standalone on second line (detected)
let text = "Some text with {\"tool\": \"inline\"} here\n{\"tool\": \"standalone\", \"args\": {}}";
let pos = StreamingToolParser::find_first_tool_call_start(text);
assert!(pos.is_some(), "Should find the standalone tool call");
// The standalone one starts after the newline
assert!(pos.unwrap() > 30, "Should skip the inline pattern and find the standalone one");
}
#[test]
fn test_multiple_inline_patterns_all_ignored() {
// Multiple inline patterns on same line - all should be ignored
let text = "Compare {\"tool\": \"a\"} with {\"tool\": \"b\"}";
assert!(StreamingToolParser::find_first_tool_call_start(text).is_none(),
"All inline patterns should be ignored");
}
#[test]
fn test_is_on_own_line() {
// Test the is_on_own_line helper directly
let text = "prefix {\"tool\":\n {\"tool\":";
// The inline one should be sanitized
let lines: Vec<&str> = result.lines().collect();
assert!(lines[0].contains(LBRACE_HOMOGLYPH), "First line should have homoglyph");
// Position 0 is always on its own line
assert!(StreamingToolParser::is_on_own_line(text, 0));
// The standalone one should NOT be sanitized
assert!(lines[1].starts_with("{\"tool\":"), "Second line should be unchanged");
}
#[test]
fn test_sanitize_inline_tool_patterns_multiple_inline() {
// Multiple inline patterns on same line
let input = "Compare {\"tool\": \"a\"} with {\"tool\": \"b\"}";
let result = sanitize_inline_tool_patterns(input);
// Position 7 (after "prefix ") is NOT on its own line
assert!(!StreamingToolParser::is_on_own_line(text, 7));
// Both should be sanitized
assert!(!result.contains("{\"tool\":"), "All inline patterns should be sanitized");
// Count homoglyphs - should be 2
let homoglyph_count = result.matches(LBRACE_HOMOGLYPH).count();
assert_eq!(homoglyph_count, 2, "Should have 2 homoglyphs, got {}", homoglyph_count);
// Position after newline with only whitespace before pattern IS on its own line
let newline_pos = text.find('\n').unwrap();
assert!(StreamingToolParser::is_on_own_line(text, newline_pos + 11)); // 10 spaces before {
}
#[test]
fn test_sanitize_inline_tool_patterns_no_false_positives() {
// Regular JSON that doesn't match tool patterns should be unchanged
let input = "Some {\"key\": \"value\"} json";
let result = sanitize_inline_tool_patterns(input);
assert_eq!(result, input, "Non-tool JSON should not be modified");
}
#[test]
fn test_sanitize_inline_tool_patterns_all_pattern_variants() {
// Test all whitespace variants are caught
let inputs = [
"text { \"tool\":\"x\"} more",
"text {\"tool\" :\"x\"} more",
"text { \"tool\" :\"x\"} more",
fn test_all_pattern_variants_require_own_line() {
// All whitespace variants should require their own line
let patterns = [
"text { \"tool\":\"x\"}",
"text {\"tool\" :\"x\"}",
"text { \"tool\" :\"x\"}",
];
for input in inputs {
let result = sanitize_inline_tool_patterns(input);
assert!(result.contains(LBRACE_HOMOGLYPH), "Pattern in '{}' should be sanitized", input);
for pattern in patterns {
assert!(StreamingToolParser::find_first_tool_call_start(pattern).is_none(),
"Inline pattern '{}' should be ignored", pattern);
}
}
}