runtime.rs

			0 => Vec::new(),
			_ => read_sandbox_memory_as(ctx, topics_ptr, topics_len)?,
		};

		// If there are more than `max_event_topics`, then trap.
		if topics.len() > ctx.schedule.max_event_topics as usize {
			return Err(sp_sandbox::HostError);
		}

		// Check for duplicate topics. If there are any, then trap.
		if has_duplicates(&mut topics) {
			return Err(sp_sandbox::HostError);
		}

		let event_data = read_sandbox_memory(ctx, data_ptr, data_len)?;

		charge_gas(
			ctx.gas_meter,
			ctx.schedule,
			&mut ctx.trap_reason,
			RuntimeToken::DepositEvent(topics.len() as u32, data_len)
		)?;
		ctx.ext.deposit_event(topics, event_data);

		Ok(())
	},

	// Set rent allowance of the contract
	//
	// - value_ptr: a pointer to the buffer with value, how much to allow for rent
	//   Should be decodable as a `T::Balance`. Traps otherwise.
	// - value_len: length of the value buffer.
	ext_set_rent_allowance(ctx, value_ptr: u32, value_len: u32) => {
		let value: BalanceOf<<E as Ext>::T> =
			read_sandbox_memory_as(ctx, value_ptr, value_len)?;
		ctx.ext.set_rent_allowance(value);

		Ok(())
	},

	// Stores the rent allowance into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// The data is encoded as T::Balance.
	ext_rent_allowance(ctx, out_ptr: u32, out_len_ptr: u32) => {
		write_sandbox_output(ctx, out_ptr, out_len_ptr, &ctx.ext.rent_allowance().encode(), false)
	},

	// Prints utf8 encoded string from the data buffer.
	// Only available on `--dev` chains.
	// This function may be removed at any time, superseded by a more general contract debugging feature.
	ext_println(ctx, str_ptr: u32, str_len: u32) => {
		let data = read_sandbox_memory(ctx, str_ptr, str_len)?;
		if let Ok(utf8) = core::str::from_utf8(&data) {
			sp_runtime::print(utf8);
		}
		Ok(())
	},

	// Stores the current block number of the current contract into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	ext_block_number(ctx, out_ptr: u32, out_len_ptr: u32) => {
		write_sandbox_output(ctx, out_ptr, out_len_ptr, &ctx.ext.block_number().encode(), false)
	},

	// Computes the SHA2 256-bit hash on the given input buffer.
	//
	// Returns the result directly into the given output buffer.
	//
	// # Note
	//
	// - The `input` and `output` buffer may overlap.
	// - The output buffer is expected to hold at least 32 bytes (256 bits).
	// - It is the callers responsibility to provide an output buffer that
	//   is large enough to hold the expected amount of bytes returned by the
	//   chosen hash function.
	//
	// # Parameters
	//
	// - `input_ptr`: the pointer into the linear memory where the input
	//                data is placed.
	// - `input_len`: the length of the input data in bytes.
	// - `output_ptr`: the pointer into the linear memory where the output
	//                 data is placed. The function will write the result
	//                 directly into this buffer.
	ext_hash_sha2_256(ctx, input_ptr: u32, input_len: u32, output_ptr: u32) => {
		compute_hash_on_intermediate_buffer(ctx, sha2_256, input_ptr, input_len, output_ptr)
	},

	// Computes the KECCAK 256-bit hash on the given input buffer.
	//
	// Returns the result directly into the given output buffer.
	//
	// # Note
	//
	// - The `input` and `output` buffer may overlap.
	// - The output buffer is expected to hold at least 32 bytes (256 bits).
	// - It is the callers responsibility to provide an output buffer that
	//   is large enough to hold the expected amount of bytes returned by the
	//   chosen hash function.
	//
	// # Parameters
	//
	// - `input_ptr`: the pointer into the linear memory where the input
	//                data is placed.
	// - `input_len`: the length of the input data in bytes.
	// - `output_ptr`: the pointer into the linear memory where the output
	//                 data is placed. The function will write the result
	//                 directly into this buffer.
	ext_hash_keccak_256(ctx, input_ptr: u32, input_len: u32, output_ptr: u32) => {
		compute_hash_on_intermediate_buffer(ctx, keccak_256, input_ptr, input_len, output_ptr)
	},

	// Computes the BLAKE2 256-bit hash on the given input buffer.
	//
	// Returns the result directly into the given output buffer.
	//
	// # Note
	//
	// - The `input` and `output` buffer may overlap.
	// - The output buffer is expected to hold at least 32 bytes (256 bits).
	// - It is the callers responsibility to provide an output buffer that
	//   is large enough to hold the expected amount of bytes returned by the
	//   chosen hash function.
	//
	// # Parameters
	//
	// - `input_ptr`: the pointer into the linear memory where the input
	//                data is placed.
	// - `input_len`: the length of the input data in bytes.
	// - `output_ptr`: the pointer into the linear memory where the output
	//                 data is placed. The function will write the result
	//                 directly into this buffer.
	ext_hash_blake2_256(ctx, input_ptr: u32, input_len: u32, output_ptr: u32) => {
		compute_hash_on_intermediate_buffer(ctx, blake2_256, input_ptr, input_len, output_ptr)
	},

	// Computes the BLAKE2 128-bit hash on the given input buffer.
	//
	// Returns the result directly into the given output buffer.
	//
	// # Note
	//
	// - The `input` and `output` buffer may overlap.
	// - The output buffer is expected to hold at least 16 bytes (128 bits).
	// - It is the callers responsibility to provide an output buffer that
	//   is large enough to hold the expected amount of bytes returned by the
	//   chosen hash function.
	//
	// # Parameters
	//
	// - `input_ptr`: the pointer into the linear memory where the input
	//                data is placed.
	// - `input_len`: the length of the input data in bytes.
	// - `output_ptr`: the pointer into the linear memory where the output
	//                 data is placed. The function will write the result
	//                 directly into this buffer.
	ext_hash_blake2_128(ctx, input_ptr: u32, input_len: u32, output_ptr: u32) => {
		compute_hash_on_intermediate_buffer(ctx, blake2_128, input_ptr, input_len, output_ptr)
	},
);

/// Computes the given hash function on the supplied input.
///
/// Reads from the sandboxed input buffer into an intermediate buffer.
/// Returns the result directly to the output buffer of the sandboxed memory.
///
/// It is the callers responsibility to provide an output buffer that
/// is large enough to hold the expected amount of bytes returned by the
/// chosen hash function.
///
/// # Note
///
/// The `input` and `output` buffers may overlap.
fn compute_hash_on_intermediate_buffer<E, F, R>(
	ctx: &mut Runtime<E>,
	hash_fn: F,
	input_ptr: u32,
	input_len: u32,
	output_ptr: u32,
) -> Result<(), sp_sandbox::HostError>
where
	E: Ext,
	F: FnOnce(&[u8]) -> R,
	R: AsRef<[u8]>,
{
	// Copy input into supervisor memory.
	let input = read_sandbox_memory(ctx, input_ptr, input_len)?;
	// Compute the hash on the input buffer using the given hash function.
	let hash = hash_fn(&input);
	// Write the resulting hash back into the sandboxed output buffer.
	write_sandbox_memory(
		ctx,
		output_ptr,
		hash.as_ref(),
	)?;
	Ok(())
}

/// Finds duplicates in a given vector.
///
/// This function has complexity of O(n log n) and no additional memory is required, although
/// the order of items is not preserved.
fn has_duplicates<T: PartialEq + AsRef<[u8]>>(items: &mut Vec<T>) -> bool {
	// Sort the vector
	items.sort_by(|a, b| {
		Ord::cmp(a.as_ref(), b.as_ref())
	});
	// And then find any two consecutive equal elements.
	items.windows(2).any(|w| {
		match w {
			&[ref a, ref b] => a == b,
			_ => false,
		}
	})
}