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Miscellaneous API

value_return(value_len: u64, value_ptr: u64)

Sets the blob of data as the return value of the contract.

Panics​
  • If value_len + value_ptr exceeds the memory container or points to an unused register it panics with MemoryAccessViolation;
panic()

Terminates the execution of the program with panic GuestPanic("explicit guest panic").

panic_utf8(len: u64, ptr: u64)

Terminates the execution of the program with panic GuestPanic(s), where s is the given UTF-8 encoded string.

Normal behavior​

If len == u64::MAX then treats the string as null-terminated with character '\0';

Panics​
  • If string extends outside the memory of the guest with MemoryAccessViolation;
  • If string is not UTF-8 returns BadUtf8.
  • If string length without null-termination symbol is larger than config.max_log_len returns BadUtf8.
log_utf8(len: u64, ptr: u64)

Logs the UTF-8 encoded string.

Normal behavior​

If len == u64::MAX then treats the string as null-terminated with character '\0';

Panics​
  • If string extends outside the memory of the guest with MemoryAccessViolation;
  • If string is not UTF-8 returns BadUtf8.
  • If string length without null-termination symbol is larger than config.max_log_len returns BadUtf8.
log_utf16(len: u64, ptr: u64)

Logs the UTF-16 encoded string. len is the number of bytes in the string. See https://stackoverflow.com/a/5923961 that explains that null termination is not defined through encoding.

Normal behavior​

If len == u64::MAX then treats the string as null-terminated with two-byte sequence of 0x00 0x00.

Panics​
  • If string extends outside the memory of the guest with MemoryAccessViolation;
abort(msg_ptr: u32, filename_ptr: u32, line: u32, col: u32)

Special import kept for compatibility with AssemblyScript contracts. Not called by smart contracts directly, but instead called by the code generated by AssemblyScript.

Future Improvements

In the future we can have some of the registers to be on the guest. For instance a guest can tell the host that it has some pre-allocated memory that it wants to be used for the register, e.g.

set_guest_register(register_id: u64, register_ptr: u64, max_register_size: u64)

will assign register_id to a span of memory on the guest. Host then would also know the size of that buffer on guest and can throw a panic if there is an attempted copying that exceeds the guest register size.