Details
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Bug
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Status: Resolved
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Major
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Resolution: Fixed
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1.9.0, 1.10.0, 1.9.1, 1.9.2, 1.11.0, 1.10.1, 1.10.2, 1.11.1
Description
The rust implementation of avro appears to behave according to an old specification when deserializing messages with a symbol in the writer's enum that is not in the reader's enum. The deserializer is returning an error even if the reader schema specifies a default. Starting in version 1.9.0, the default should be used in this situation according to this section of the documentation about schema resolution:
if both are enums: if the writer's symbol is not present in the reader's enum and the reader has a default value, then that value is used, otherwise an error is signalled.
This test currently in master expects the deserializer to error because it was written 5 years ago before spec 1.9.0 was released. (summary of the test: writer has symbol "clubs," the reader does not have the "clubs" symbol but does have a default, record gets made with symbol "clubs," the result is an error)
#[test]
fn test_enum_resolution() {
let writer_raw_schema = r#"
{
"type": "record",
"name": "test",
"fields": [
{"name": "a", "type": "long", "default": 42},
{"name": "b", "type": "string"},
{
"name": "c",
"type": {
"type": "enum",
"name": "suit",
"symbols": ["diamonds", "spades", "clubs", "hearts"]
},
"default": "spades"
}
]
}
"#;
let reader_raw_schema = r#"
{
"type": "record",
"name": "test",
"fields": [
{"name": "a", "type": "long", "default": 42},
{"name": "b", "type": "string"},
{
"name": "c",
"type": {
"type": "enum",
"name": "suit",
"symbols": ["diamonds", "spades", "ninja", "hearts"]
},
"default": "spades"
}
]
}
"#;
let writer_schema = Schema::parse_str(writer_raw_schema).unwrap();
let reader_schema = Schema::parse_str(reader_raw_schema).unwrap();
let mut writer = Writer::with_codec(&writer_schema, Vec::new(), Codec::Null);
let mut record = Record::new(writer.schema()).unwrap();
record.put("a", 27i64);
record.put("b", "foo");
record.put("c", "clubs");
writer.append(record).unwrap();
let input = writer.into_inner().unwrap();
let mut reader = Reader::with_schema(&reader_schema, &input[..]).unwrap();
assert!(reader.next().unwrap().is_err());
assert!(reader.next().is_none());
}
If the deserializer was correctly using the default, I would expect the last two lines to instead assert the first two values were as expected with c defaulting to "spades"
assert_eq!( reader.next().unwrap().unwrap(), Value::Record(vec![ ("a".to_string(), Value::Long(27)), ("b".to_string(), Value::String("foo".to_string())), ("c".to_string(), Value::Enum(1, "spades".to_string())), ]) ); assert!(reader.next().is_none());
The error returned is GetDefaultEnum, and it seems to be getting created here when we recognize that the symbol is not in the list of symbols that the reader has for the enum.
fn resolve_enum(self, symbols: &[String]) -> Result<Self, Error> { let validate_symbol = |symbol: String, symbols: &[String]| { if let Some(index) = symbols.iter().position(|item| item == &symbol) { Ok(Value::Enum(index as u32, symbol)) } else { Err(Error::GetEnumDefault { symbol, symbols: symbols.into(), }) } }; match self { Value::Enum(raw_index, s) => { let index = usize::try_from(raw_index) .map_err(|e| Error::ConvertU32ToUsize(e, raw_index))?; if (0..=symbols.len()).contains(&index) { validate_symbol(s, symbols) } else { Err(Error::GetEnumValue { index, nsymbols: symbols.len(), }) } } Value::String(s) => validate_symbol(s, symbols), other => Err(Error::GetEnum(other.into())), } }
To follow the specification, it seems that instead of always returning the GetEnumDefault error if the symbol doesn't exist in the reader enum, we should first check if there is a default to use and return it if possible. Or the caller should check for this error and use the default if available.
I'm relatively new to avro, so if I'm misunderstanding either the specification or the code behavior please let me know. Thanks!
(I'm also curious if there would be another issue if the record contained a symbol that exists in the writer enum and had an index greater than the len of the reader's symbols since it appears to be doing a check for that on line 859).
