Struct ResourceLimits 

pub struct ResourceLimits {
    pub max_memory_size: Option<usize>,
    pub max_table_elements: Option<usize>,
}

Configure limits on the resources a single waPC WebAssembly instance is allowed to consume, leveraging wasmtime’s ResourceLimiter facility (via wasmtime::StoreLimits).

This can be used to prevent a malicious, or misbehaving, WebAssembly module from exhausting the host’s memory, for example by growing its linear memory in an unbounded loop.

When a limit is exceeded, the corresponding memory.grow/table.grow wasm instruction fails and returns -1 to the guest, following the WebAssembly specification. Most language toolchains (Rust, TinyGo, AssemblyScript, …) treat a failed growth as a fatal allocation failure and abort the guest, which is reported back to the host as a trap. The memory/table cap itself is always enforced by the host regardless of how the guest reacts to the failed growth.

Fields

max_memory_size: Option<usize>

Maximum size, in bytes, that each of the module’s linear memories is allowed to grow to. This limit is applied to each linear memory individually.

None (the default) means no limit is enforced.

max_table_elements: Option<usize>

Maximum number of elements each of the module’s tables is allowed to grow to. This limit is applied to each table individually.

WebAssembly tables are used to hold indirect function references (e.g. Rust trait objects, Go interfaces, C function pointers) and each element costs roughly the size of a pointer of host memory. Most modules never grow their tables at runtime, so this is a secondary, defense-in-depth limit compared to ResourceLimits::max_memory_size. A generous value such as 100_000 (~0.8 MB on a 64-bit host) is unlikely to affect legitimate modules.

None (the default) means no limit is enforced.

Trait Implementations

impl Clone for ResourceLimits

fn clone(&self) -> ResourceLimits

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for ResourceLimits

impl Debug for ResourceLimits

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ResourceLimits

fn default() -> ResourceLimits

Returns the “default value” for a type.