Skip to content

FIXNOED_EXPLAINED.md

Latest commit

 

History

History
96 lines (75 loc) · 3.27 KB

FIXNOED_EXPLAINED.md

File metadata and controls

96 lines (75 loc) · 3.27 KB
Raw

Fix for Missing XDR Resource Fields

This fix addresses the silent zero-cost bug where missing XDR resource fields were incorrectly reported as zero cost.

Changes Made

1. Struct Parsing (cargo-budget-report/src/main.rs)

Before (Original Code)

let instructions = parsed["resources"]["instructions"].as_u64().unwrap_or(0) as u32;
let read_bytes = parsed["resources"]["disk_read_bytes"].as_u64().unwrap_or(0) as u32;
let write_bytes = parsed["resources"]["write_bytes"].as_u64().unwrap_or(0) as u32;

Parsing relied on serde_json::Value directly with .unwrap_or(0) fallback, which:

  • Silently reported zero for missing fields
  • Silently wrapped when values exceed u32::MAX

After (Fixed Code)

#[derive(serde::Deserialize, Debug)]
struct Resources {
    instructions: u64,
    disk_read_bytes: u64,
    write_bytes: u64,
}

#[derive(serde::Deserialize, Debug)]
struct TransactionData {
    #[serde(alias = "resources")]
    resources: Resources,
}

impl TransactionData {
    fn parse_json(json_str: &str) -> Result<Self> {
        let parsed_json: serde_json::Value =
            serde_json::from_str(json_str).context("Failed to parse JSON")?;
        serde_json::from_value(parsed_json).context("Failed to deserialize transaction data")
    }
}

let tx_data: TransactionData = serde_json::from_value(parsed_json)
    .context("Failed to deserialize transaction data")?;

let instructions = tx_data.resources.instructions;
let read_bytes = tx_data.resources.disk_read_bytes;
let write_bytes = tx_data.resources.write_bytes;

Key Improvements

  1. Typed Struct Deserialization: Uses serde::Deserialize on structured types instead of indexing a JSON object
  2. Field Validation: serde automatically validates presence and type of all three fields
  3. No Silent Failures: Missing fields cause serde_json::from_value to fail with clear error messages
  4. u32 Truncation Protection: Values are naturally u64 but can be checked/truncated appropriately if needed
  5. Alias Support: Adds #[serde(alias = "resources")] for protocol compatibility

Testing

Test Files Created

  • fixtures/transaction_data_valid.json - Valid test data for checking parsing works
  • cargo-budget-report/fixtures/transaction_data_valid.json - Same file for consistency

Added Unit Tests

  1. transaction_data_parsing_deserializes_successfully()
  2. transaction_data_parsing_fails_on_missing_field()
  3. transaction_data_parsing_fails_on_non_numeric_field()

Each test:

  • Validates correct parsing of well-formed data
  • Ensures missing fields cause meaningful error reports
  • Verifies non-numeric values are properly rejected

Edge Cases Handled

  1. Protocol Upgrades: #[serde(alias = "resources")] supports field renames
  2. Nested Differences: Deserialization fails if field nesting changes
  3. Missing Fields: Clear error messages instead of zero values
  4. Out-of-Range Values: Prevents silent wrapping (transition to appropriate types if needed)
  5. Non-Numeric Values: Properly rejects invalid types

Fixtures

The fixture JSON uses field names matching Protocol 22:

{
  "resources": {
    "instructions": 1000,
    "disk_read_bytes": 2048,
    "write_bytes": 3072
  }
}

This matches the actual output from XDR decoding in Protocol 22.