decode() on bytes should support UTF-16

[sethhall]

It looks like the current implementation only supports ASCII and UTF-8 to decode into a string and the current library being used is strictly for UTF-8. In order to support anything with Windows roots, it would be nice to support UTF-16.

I poked around for a few minutes and found a potential small library that might work for the use case to decode UTF-16 into a string type.... https://github.com/nemtrif/utfcpp

[sethhall]

This still needs to be done (because the decode() method was clearly built with this in mind, but as a stop gap, I have a UTF-16 string reader (and it converts to utf-8 internally) implemented natively in spicy here: https://github.com/sethhall/spicy-parsers/blob/main/unicode/utf16.spicy

[Ethanholtking]

Hello I'd like to help solve this issue, however, I'm having difficulty trying to find where exactly the problem is. Could someone please help me locate where the decode() is?

[bbannier]

Hello I'd like to help solve this issue, however, I'm having difficulty trying to find where exactly the problem is. Could someone please help me locate where the decode() is?

Implementing the runtime part would go roughly like the following:

1. Adding a UTF16 Charset value here:

   spicy/hilti/runtime/include/types/bytes.h

   Line 42 in 943dea8

   HILTI_RT_ENUM(Charset, Undef, UTF8, ASCII);

2. Implementing handling of Charset::UTF16 in Bytes::decode here:

   spicy/hilti/runtime/src/types/bytes.cc

   Lines 105 to 132 in 943dea8

   	std::string Bytes::decode(bytes::Charset cs, bytes::DecodeErrorStrategy errors) const {
   	switch ( cs.value() ) {
   	case bytes::Charset::UTF8:
   	// Data is already in UTF-8, but let's validate it.
   	return Bytes(str(), cs, errors).str();
   	case bytes::Charset::ASCII: {
   	std::string s;
   	for ( auto c : str() ) {
   	if ( c >= 32 && c < 0x7f )
   	s += c;
   	else {
   	switch ( errors.value() ) {
   	case DecodeErrorStrategy::IGNORE: break;
   	case DecodeErrorStrategy::REPLACE: s += "?"; break;
   	case DecodeErrorStrategy::STRICT: throw RuntimeError("illegal ASCII character in string");
   	}
   	}
   	}
   	return s;
   	}
   	case bytes::Charset::Undef: throw RuntimeError("unknown character set for decoding");
   	}
   	cannot_be_reached();
   	}

   The C++ unit test for Bytes::decode should also be updated here:

   spicy/hilti/runtime/src/tests/bytes.cc

   Lines 64 to 83 in 943dea8

   	TEST_CASE("decode") {
   	CHECK_EQ("123"_b.decode(bytes::Charset::ASCII), "123");
   	CHECK_EQ("abc"_b.decode(bytes::Charset::ASCII), "abc");
   	CHECK_EQ("abc"_b.decode(bytes::Charset::UTF8), "abc");
   	CHECK_EQ("\xF0\x9F\x98\x85"_b.decode(bytes::Charset::UTF8), "\xF0\x9F\x98\x85");
   	CHECK_EQ("\xF0\x9F\x98\x85"_b.decode(bytes::Charset::ASCII), "????");
   	CHECK_EQ("€100"_b.decode(bytes::Charset::ASCII, bytes::DecodeErrorStrategy::REPLACE), "???100");
   	CHECK_EQ("€100"_b.decode(bytes::Charset::ASCII, bytes::DecodeErrorStrategy::IGNORE), "100");
   	CHECK_THROWS_WITH_AS("123ä4"_b.decode(bytes::Charset::ASCII, bytes::DecodeErrorStrategy::STRICT),
   	"illegal ASCII character in string", const RuntimeError&);
   	CHECK_EQ("\xc3\x28"_b.decode(bytes::Charset::UTF8, bytes::DecodeErrorStrategy::REPLACE), "\ufffd(");
   	CHECK_EQ("\xc3\x28"_b.decode(bytes::Charset::UTF8, bytes::DecodeErrorStrategy::IGNORE), "(");
   	CHECK_THROWS_WITH_AS("\xc3\x28"_b.decode(bytes::Charset::UTF8, bytes::DecodeErrorStrategy::STRICT),
   	"illegal UTF8 sequence in string", const RuntimeError&);
   	CHECK_THROWS_WITH_AS("123"_b.decode(bytes::Charset::Undef), "unknown character set for decoding",
   	const RuntimeError&);
   	}

To make this available in Spicy code it needs to be added to both HILTI as well as Spicy:

1. Add it to HILTI here:

   spicy/hilti/lib/hilti.hlt

   Line 14 in 943dea8

   public type Charset = enum { ASCII, UTF8 } &cxxname="hilti::rt::bytes::Charset";

   There should also be a new test case here: https://github.com/zeek/spicy/blob/943dea8d284c3b6fd65426e6e22abce1669ceeb1/tests/hilti/types/bytes/decode.hlt
2. Add it to Spicy here:

   spicy/spicy/lib/spicy.spicy

   Lines 33 to 37 in 943dea8

   	## Specifies the character set for bytes encoding/decoding.
   	public type Charset = enum {
   	ASCII,
   	UTF8
   	} &cxxname="hilti::rt::bytes::Charset";

   Adding a test case is not strictly needed since this just wraps HILTI functionality.