OwnedStringView: Add a method to extract a substring

luna/include/luna/CString.h

@@ -7,12 +7,16 @@ extern "C"
     void* memset(void* buf, int c, usize n);
     int memcmp(const void* a, const void* b, usize n);
     void* memmove(void* dest, const void* src, usize n);
+
     usize strlen(const char* str);
+    usize strnlen(const char* str, usize max);
+
     int strcmp(const char* a, const char* b);
 
     usize wcslen(const wchar_t* str);
 
     char* strdup(const char* str);
+    char* strndup(const char* str, usize max);
 
     // Copies len bytes from src into dest and adds a null terminator.
     // FIXME: Replace this invented function with strlcpy().

luna/include/luna/OwnedStringView.h

@@ -5,6 +5,7 @@ class OwnedStringView
 {
   public:
     OwnedStringView(char* c_str);
+    OwnedStringView(char* c_str, usize length);
     OwnedStringView();
     OwnedStringView(OwnedStringView&&);
     OwnedStringView(const OwnedStringView&) = delete;
@@ -12,6 +13,8 @@ class OwnedStringView
 
     Result<OwnedStringView> clone() const;
 
+    Result<OwnedStringView> substring(usize begin, usize size) const;
+
     static Result<OwnedStringView> from_string_literal(const char* str);
 
     const char* chars() const

luna/src/CString.cpp

@@ -46,6 +46,14 @@ extern "C"
         return (usize)(i - str);
     }
 
+    usize strnlen(const char* str, usize max)
+    {
+        const char* i = str;
+        for (; max, *i; ++i, --max)
+            ;
+        return (usize)(i - str);
+    }
+
     int strcmp(const char* a, const char* b)
     {
         while (*a && (*a == *b))
@@ -68,10 +76,22 @@ extern "C"
     {
         const usize len = strlen(str);
 
-        char* dest = (char*)malloc_impl(len + 1).value_or(nullptr);
+        char* dest = (char*)calloc_impl(len + 1, 1).value_or(nullptr);
         if (!dest) return nullptr;
 
-        memcpy(dest, str, len + 1);
+        memcpy(dest, str, len);
+
+        return dest;
+    }
+
+    char* strndup(const char* str, usize max)
+    {
+        const usize len = strnlen(str, max);
+
+        char* dest = (char*)calloc_impl(len + 1, 1).value_or(nullptr);
+        if (!dest) return nullptr;
+
+        memcpy(dest, str, len);
 
         return dest;
     }

luna/src/OwnedStringView.cpp

@@ -21,6 +21,12 @@ OwnedStringView::OwnedStringView(char* c_str)
     if (m_string) { m_length = strlen(m_string); }
 }
 
+OwnedStringView::OwnedStringView(char* c_str, usize length)
+{
+    m_string = c_str;
+    m_length = length;
+}
+
 OwnedStringView::~OwnedStringView()
 {
     if (m_string) free_impl(m_string);
@@ -31,6 +37,14 @@ Result<OwnedStringView> OwnedStringView::clone() const
     return from_string_literal(m_string);
 }
 
+Result<OwnedStringView> OwnedStringView::substring(usize begin, usize size) const
+{
+    if (begin + size >= size) return err(EINVAL);
+    char* const dup = strndup(m_string + begin, size);
+    if (!dup) return err(ENOMEM);
+    return OwnedStringView { dup, size };
+}
+
 const char& OwnedStringView::operator[](usize index) const
 {
     expect(index < m_length, "index out of range");