move wasi-c2 into wasi-common

crates/wasi-common/src/string_array.rs

@@ -0,0 +1,74 @@
+use crate::{Error, ErrorExt};
+use wiggle::GuestPtr;
+
+pub struct StringArray {
+    elems: Vec<String>,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum StringArrayError {
+    #[error("Number of elements exceeds 2^32")]
+    NumberElements,
+    #[error("Element size exceeds 2^32")]
+    ElementSize,
+    #[error("Cumulative size exceeds 2^32")]
+    CumulativeSize,
+}
+
+impl StringArray {
+    pub fn new() -> Self {
+        StringArray { elems: Vec::new() }
+    }
+
+    pub fn push(&mut self, elem: String) -> Result<(), StringArrayError> {
+        if self.elems.len() + 1 > std::u32::MAX as usize {
+            return Err(StringArrayError::NumberElements);
+        }
+        if elem.as_bytes().len() + 1 > std::u32::MAX as usize {
+            return Err(StringArrayError::ElementSize);
+        }
+        if self.cumulative_size() as usize + elem.as_bytes().len() + 1 > std::u32::MAX as usize {
+            return Err(StringArrayError::CumulativeSize);
+        }
+        self.elems.push(elem);
+        Ok(())
+    }
+
+    pub fn number_elements(&self) -> u32 {
+        self.elems.len() as u32
+    }
+
+    pub fn cumulative_size(&self) -> u32 {
+        self.elems
+            .iter()
+            .map(|e| e.as_bytes().len() + 1)
+            .sum::<usize>() as u32
+    }
+
+    pub fn write_to_guest<'a>(
+        &self,
+        buffer: &GuestPtr<'a, u8>,
+        element_heads: &GuestPtr<'a, GuestPtr<'a, u8>>,
+    ) -> Result<(), Error> {
+        let element_heads = element_heads.as_array(self.number_elements());
+        let buffer = buffer.as_array(self.cumulative_size());
+        let mut cursor = 0;
+        for (elem, head) in self.elems.iter().zip(element_heads.iter()) {
+            let bytes = elem.as_bytes();
+            let len = bytes.len() as u32;
+            {
+                let elem_buffer = buffer
+                    .get_range(cursor..(cursor + len))
+                    .ok_or(Error::invalid_argument())?; // Elements don't fit in buffer provided
+                elem_buffer.copy_from_slice(bytes)?;
+            }
+            buffer
+                .get(cursor + len)
+                .ok_or(Error::invalid_argument())?
+                .write(0)?; // 0 terminate
+            head?.write(buffer.get(cursor).expect("already validated"))?;
+            cursor += len + 1;
+        }
+        Ok(())
+    }
+}