ic_host_tools/wasm/

mod.rs

//! Borrowed structural facts from core WebAssembly artifacts.
//!
//! `wasmparser` owns framing, section ordering, names and vector decoding.
//! Inspection checks the function/data/export structures it reports, but is not
//! instruction validation, type checking, feature admission, or IC install policy.
//! Facts borrow source bytes; no metadata or export names are copied.

use std::{collections::BTreeMap, fmt};
use wasmparser::{Encoding, ExternalKind, Parser, Payload};

#[cfg(test)]
mod tests;

/// Consumer-selected resource bounds; zero allows only an empty collection.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct InspectionLimits {
    /// Maximum complete module size in bytes.
    pub module_bytes: usize,
    /// Maximum number of top-level sections, including custom sections.
    pub sections: usize,
    /// Maximum number of export entries.
    pub exports: u32,
    /// Maximum number of custom sections retained as borrowed views.
    pub custom_sections: usize,
}

/// Which consumer-supplied bound rejected an artifact.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum InspectionResource {
    /// Complete source byte length.
    ModuleBytes,
    /// Number of top-level sections.
    Sections,
    /// Number of exported items.
    Exports,
    /// Number of custom metadata sections.
    CustomSections,
}

/// A structural inspection failed without yielding partial facts.
#[derive(Debug)]
pub enum InspectionError {
    /// A caller-supplied resource bound was exceeded.
    LimitExceeded {
        /// Resource being counted.
        resource: InspectionResource,
        /// Observed count or byte length.
        actual: u64,
        /// Caller-selected maximum.
        limit: u64,
    },
    /// A component was supplied instead of a core module.
    UnsupportedEncoding,
    /// Framing, section ordering, or an inspected vector is malformed.
    Parse(wasmparser::BinaryReaderError),
    /// Export names must be unique regardless of export kind.
    DuplicateExport {
        /// Offset of the duplicate entry in the original source.
        offset: usize,
    },
    /// An unknown core section cannot be interpreted as artifact evidence.
    UnknownSection {
        /// Binary section identifier.
        id: u8,
        /// Offset of the section payload.
        offset: usize,
    },
}

impl fmt::Display for InspectionError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::LimitExceeded {
                resource,
                actual,
                limit,
            } => write!(f, "Wasm {resource:?} count {actual} exceeds {limit}"),
            Self::UnsupportedEncoding => {
                f.write_str("expected a core Wasm module, received a component")
            }
            Self::Parse(source) => write!(f, "malformed Wasm structure: {source}"),
            Self::DuplicateExport { offset } => write!(f, "duplicate Wasm export at byte {offset}"),
            Self::UnknownSection { id, offset } => {
                write!(f, "unknown Wasm section {id} at byte {offset}")
            }
        }
    }
}
impl std::error::Error for InspectionError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            Self::Parse(source) => Some(source),
            _ => None,
        }
    }
}
impl From<wasmparser::BinaryReaderError> for InspectionError {
    fn from(source: wasmparser::BinaryReaderError) -> Self {
        Self::Parse(source)
    }
}

/// The exported item's core Wasm kind, independent of application method policy.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ExportKind {
    /// Function export.
    Function,
    /// Table export.
    Table,
    /// Linear memory export.
    Memory,
    /// Global export.
    Global,
    /// Exception tag export.
    Tag,
}

/// Export identity within its kind's index space.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Export {
    /// Item kind.
    pub kind: ExportKind,
    /// Index within that kind's index space; not type-validated here.
    pub index: u32,
}

/// Borrowed custom metadata, preserving duplicates and encounter order.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct CustomSection<'a> {
    /// Decoded UTF-8 section name.
    pub name: &'a str,
    /// Exact bytes after the name, with no normalization.
    pub data: &'a [u8],
}

/// Core Wasm facts for consumer reports and transform-contract comparisons.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct WasmFacts<'a> {
    /// Complete raw artifact byte length.
    pub raw_bytes: usize,
    /// Code section payload bytes, including its vector count and body lengths.
    pub code_section_bytes: usize,
    /// Data section payload bytes, including its vector count and framing.
    pub data_section_bytes: usize,
    /// Defined functions, excluding imports; function/code counts must agree.
    pub defined_functions: u32,
    /// Number of encoded data segments.
    pub data_segments: u32,
    /// All exports keyed by exact name; callers select IC/application methods.
    pub exports: BTreeMap<&'a str, Export>,
    /// All custom metadata; callers select Candid sections and acceptance rules.
    pub custom_sections: Vec<CustomSection<'a>>,
}

/// Inspect bounded core Wasm framing and the vectors used by artifact reports.
///
/// Preserves input bytes and borrows names/metadata. Storage is bounded by the
/// explicit export/custom-section limits; traversal is bounded by module bytes.
/// Unreported core section contents and function instructions are not validated.
/// Run the consumer's Wasm validator before admitting a deployable artifact.
///
/// # Errors
/// Rejects resource overflow, unsupported encoding, malformed framing or
/// inspected vectors, duplicate exports, unknown sections, and unequal function
/// and code counts. No partial facts are returned.
pub fn inspect(bytes: &[u8], limits: InspectionLimits) -> Result<WasmFacts<'_>, InspectionError> {
    enforce(
        InspectionResource::ModuleBytes,
        bytes.len() as u64,
        limits.module_bytes as u64,
    )?;
    let mut facts = WasmFacts {
        raw_bytes: bytes.len(),
        code_section_bytes: 0,
        data_section_bytes: 0,
        defined_functions: 0,
        data_segments: 0,
        exports: BTreeMap::new(),
        custom_sections: Vec::new(),
    };
    let mut sections = 0;
    for payload in Parser::new(0).parse_all(bytes) {
        let payload = payload?;
        if payload.as_section().is_some() {
            sections += 1;
            enforce(
                InspectionResource::Sections,
                sections,
                limits.sections as u64,
            )?;
        }
        match payload {
            Payload::Version { encoding, .. } if encoding != Encoding::Module => {
                return Err(InspectionError::UnsupportedEncoding);
            }
            Payload::FunctionSection(reader) => {
                facts.defined_functions = reader.count();
                // Exhaust the iterator to reject count/payload mismatch, rather
                // than trusting the count prefix as the hand-written readers did.
                for index in reader {
                    index?;
                }
            }
            Payload::CodeSectionStart { range, .. } => {
                facts.code_section_bytes = range.len();
            }
            Payload::DataSection(reader) => {
                facts.data_section_bytes = reader.range().len();
                facts.data_segments = reader.count();
                for segment in reader {
                    segment?;
                }
            }
            Payload::ExportSection(reader) => {
                enforce(
                    InspectionResource::Exports,
                    u64::from(reader.count()),
                    u64::from(limits.exports),
                )?;
                for entry in reader.into_iter_with_offsets() {
                    let (offset, entry) = entry?;
                    let kind = match entry.kind {
                        ExternalKind::Func | ExternalKind::FuncExact => ExportKind::Function,
                        ExternalKind::Table => ExportKind::Table,
                        ExternalKind::Memory => ExportKind::Memory,
                        ExternalKind::Global => ExportKind::Global,
                        ExternalKind::Tag => ExportKind::Tag,
                    };
                    if facts
                        .exports
                        .insert(
                            entry.name,
                            Export {
                                kind,
                                index: entry.index,
                            },
                        )
                        .is_some()
                    {
                        return Err(InspectionError::DuplicateExport { offset });
                    }
                }
            }
            Payload::CustomSection(reader) => {
                enforce(
                    InspectionResource::CustomSections,
                    facts.custom_sections.len() as u64 + 1,
                    limits.custom_sections as u64,
                )?;
                facts.custom_sections.push(CustomSection {
                    name: reader.name(),
                    data: reader.data(),
                });
            }
            Payload::UnknownSection { id, range, .. } => {
                return Err(InspectionError::UnknownSection {
                    id,
                    offset: range.start,
                });
            }
            _ => {}
        }
    }
    Ok(facts)
}

const fn enforce(
    resource: InspectionResource,
    actual: u64,
    limit: u64,
) -> Result<(), InspectionError> {
    if actual > limit {
        return Err(InspectionError::LimitExceeded {
            resource,
            actual,
            limit,
        });
    }
    Ok(())
}