Update EIP-3540: Use exceptions with error messages in reference code (…

…ethereum#5663)

EIPS/eip-3540.md

@@ -312,45 +312,57 @@ S_DATA = 0x02
 def is_eof(code: bytes) -> bool:
     return code.startswith(MAGIC)
 
+class ValidationException(Exception):
+    pass
 
-# Validate EOF code.
+# Raises ValidationException on invalid code
 def validate_eof(code: bytes):
     # Check version
-    assert len(code) >= 3 and code[2] == VERSION
+    if len(code) < 3 or code[2] != VERSION:
+        raise ValidationException("invalid version")
 
     # Process section headers
     section_sizes = {S_CODE: 0, S_DATA: 0}
     pos = 3
     while True:
         # Terminator not found
-        assert pos < len(code)
+        if pos >= len(code):
+            raise ValidationException("no section terminator")            
+
         section_id = code[pos]
         pos += 1
         if section_id == S_TERMINATOR:
             break
 
         # Disallow unknown sections
-        assert section_id in section_sizes
+        if not section_id in section_sizes:
+            raise ValidationException("invalid section id")
 
         # Data section preceding code section
-        assert section_id != S_DATA or section_sizes[S_CODE] != 0
+        if section_id == S_DATA and section_sizes[S_CODE] == 0:
+            raise ValidationException("data section preceding code section")
 
         # Multiple sections with the same id
-        assert section_sizes[section_id] == 0
+        if section_sizes[section_id] != 0:
+            raise ValidationException("multiple sections with same id")
 
         # Truncated section size
-        assert (pos + 1) < len(code)
+        if (pos + 1) >= len(code):
+            raise ValidationException("truncated section size")
         section_sizes[section_id] = (code[pos] << 8) | code[pos + 1]
         pos += 2
 
         # Empty section
-        assert section_sizes[section_id] != 0
+        if section_sizes[section_id] == 0:
+            raise ValidationException("empty section")
 
     # Code section cannot be absent
-    assert section_sizes[S_CODE] != 0
+    if section_sizes[S_CODE] == 0:
+        raise ValidationException("no code section")
 
     # The entire container must be scanned
-    assert len(code) == (pos + section_sizes[S_CODE] + section_sizes[S_DATA])
+    if len(code) != (pos + section_sizes[S_CODE] + section_sizes[S_DATA]):
+        raise ValidationException("container size not equal to sum of section sizes")
 ```
 
 ## Security Considerations