Add function to get NULL-terminated strings from memory

Fixes wasmerio#1086.

Signed-off-by: Stephan Renatus <[email protected]>

lib/runtime-core/src/memory/ptr.rs

@@ -10,7 +10,7 @@ use crate::{
     memory::Memory,
     types::{ValueType, WasmExternType},
 };
-use std::{cell::Cell, fmt, marker::PhantomData, mem};
+use std::{cell::Cell, ffi::CStr, fmt, marker::PhantomData, mem};
 
 /// Array.
 pub struct Array;
@@ -137,6 +137,14 @@ impl<T: Copy + ValueType> WasmPtr<T, Array> {
         let slice: &[u8] = unsafe { std::slice::from_raw_parts(ptr, str_len as usize) };
         std::str::from_utf8(slice).ok()
     }
+
+    /// Get a UTF-8 string representation of this `WasmPtr`, where the string is NULL-terminated.
+    /// Note that this does not account for UTF-8 strings that _contain_ NULL themselves,
+    /// [`get_utf8_string`] has to be used for those.
+    pub fn get_utf8_string_null_terminated<'a>(self, memory: &'a Memory) -> Option<&'a str> {
+        let c_str = unsafe { CStr::from_ptr(memory.view::<u8>().as_ptr().add(self.offset as usize) as *const i8) };
+        c_str.to_str().ok()
+    }
 }
 
 unsafe impl<T: Copy, Ty> WasmExternType for WasmPtr<T, Ty> {