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Add basic custom types for the 'meta' table
This adds types and the required impls that can represent the expected contents of the 'meta' table. This has to be handwritten, because the 'meta' table contains different payloads depending on the included tag for each record. I think having these as real types will provide a significantly better API though, and avoid us writing invalid data. The actual implementations for these types are very spartan; eventually I imagine having parsing & constructing code for the ScriptLangTag struct that ensures it conforms to the spec.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,29 +1,137 @@ | ||
| //! The [meta (Metadata)](https://docs.microsoft.com/en-us/typography/opentype/spec/meta) table | ||
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| use std::fmt::Display; | ||
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| include!("../../generated/generated_meta.rs"); | ||
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| impl DataMapRecord { | ||
| /// Required to append a variable length slice of bytes at the end of the | ||
| /// table, referenced by length and offset in this record. | ||
| fn compile_map_value(&self) -> MapValueAndLenWriter { | ||
| MapValueAndLenWriter(self.data.as_slice()) | ||
| pub const DLNG: Tag = Tag::new(b"dlng"); | ||
| pub const SLNG: Tag = Tag::new(b"slng"); | ||
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| /// Metadata in the `meta` table, associated with some tag. | ||
| #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)] | ||
| #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))] | ||
| pub enum Metadata { | ||
| /// For the 'dlng' and 'slng' tags | ||
| ScriptLangTags(Vec<ScriptLangTag>), | ||
| /// For other tags | ||
| Other(Vec<u8>), | ||
| } | ||
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| /// A ['ScriptLangTag'] value. | ||
| /// | ||
| /// This is currently just a string and we do not perform any validation, | ||
| /// but we should do that (TK open issue) | ||
| /// | ||
| /// [`ScriptLangTag`]: https://learn.microsoft.com/en-us/typography/opentype/spec/meta#scriptlangtag-values | ||
| #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)] | ||
| #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))] | ||
| pub struct ScriptLangTag(String); | ||
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| /// An error for if a [`ScriptLangTag`] does not conform to the specification. | ||
| #[derive(Clone, Debug)] | ||
| #[non_exhaustive] // so we can flesh this out later without breaking anything | ||
| pub struct InvalidScriptLangTag; | ||
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| impl ScriptLangTag { | ||
| pub fn new(raw: String) -> Result<Self, InvalidScriptLangTag> { | ||
| Ok(Self(raw)) | ||
| } | ||
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| pub fn as_str(&self) -> &str { | ||
| self.0.as_str() | ||
| } | ||
| } | ||
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| struct MapValueAndLenWriter<'a>(&'a [u8]); | ||
| impl Display for InvalidScriptLangTag { | ||
| fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { | ||
| f.write_str("ScriptLangTag was malformed") | ||
| } | ||
| } | ||
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| impl FontWrite for MapValueAndLenWriter<'_> { | ||
| fn write_into(&self, writer: &mut TableWriter) { | ||
| let length = u32::try_from(self.0.len()).expect("meta record data too long: exceeds u32"); | ||
| impl std::error::Error for InvalidScriptLangTag {} | ||
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| writer.write_offset(&self.0, 4); | ||
| length.write_into(writer); | ||
| impl DataMapRecord { | ||
| fn validate_data_type(&self, ctx: &mut ValidationCtx) { | ||
| if matches!( | ||
| (self.tag, self.data.as_ref()), | ||
| (SLNG | DLNG, Metadata::Other(_)) | ||
| ) { | ||
| ctx.report("'slng' or 'dlng' tags use ScriptLangTag data"); | ||
| } | ||
| } | ||
| } | ||
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| // TODO: is this necessary? | ||
| impl FontWrite for &[u8] { | ||
| impl FontWrite for Metadata { | ||
| fn write_into(&self, writer: &mut TableWriter) { | ||
| writer.write_slice(self); | ||
| let len = match self { | ||
| Metadata::ScriptLangTags(langs) => { | ||
| let mut len = 0; | ||
| for lang in langs { | ||
| if len > 0 { | ||
| b','.write_into(writer); | ||
| len += 1; | ||
| } | ||
| lang.0.as_bytes().write_into(writer); | ||
| len += lang.0.as_bytes().len(); | ||
| } | ||
| len | ||
| } | ||
| Metadata::Other(vec) => { | ||
| vec.write_into(writer); | ||
| vec.len() | ||
| } | ||
| }; | ||
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| let len: u32 = len.try_into().unwrap(); | ||
| len.write_into(writer); | ||
| } | ||
| } | ||
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| impl Validate for Metadata { | ||
| fn validate_impl(&self, _ctx: &mut ValidationCtx) {} | ||
| } | ||
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| impl FromObjRef<read_fonts::tables::meta::Metadata<'_>> for Metadata { | ||
| fn from_obj_ref(from: &read_fonts::tables::meta::Metadata<'_>, _: FontData) -> Self { | ||
| match from { | ||
| read_fonts::tables::meta::Metadata::ScriptLangTags(var_len_array) => { | ||
| Self::ScriptLangTags( | ||
| var_len_array | ||
| .iter() | ||
| .flat_map(|x| { | ||
| x.ok() | ||
| .and_then(|x| ScriptLangTag::new(x.as_str().into()).ok()) | ||
| }) | ||
| .collect(), | ||
| ) | ||
| } | ||
| read_fonts::tables::meta::Metadata::Other(bytes) => Self::Other(bytes.to_vec()), | ||
| } | ||
| } | ||
| } | ||
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| impl FromTableRef<read_fonts::tables::meta::Metadata<'_>> for Metadata {} | ||
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| // Note: This is required because of generated trait bounds, but we don't really | ||
| // want to use it because we want our metadata to match our tag... | ||
| impl Default for Metadata { | ||
| fn default() -> Self { | ||
| Metadata::ScriptLangTags(Vec::new()) | ||
| } | ||
| } | ||
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| impl FromObjRef<read_fonts::tables::meta::DataMapRecord> for DataMapRecord { | ||
| fn from_obj_ref(obj: &read_fonts::tables::meta::DataMapRecord, offset_data: FontData) -> Self { | ||
| let data = obj | ||
| .data(offset_data) | ||
| .map(|meta| meta.to_owned_table()) | ||
| .unwrap_or_else(|_| match obj.tag() { | ||
| DLNG | SLNG => Metadata::ScriptLangTags(Vec::new()), | ||
| _ => Metadata::Other(Vec::new()), | ||
| }); | ||
| DataMapRecord { | ||
| tag: obj.tag(), | ||
| data: OffsetMarker::new(data), | ||
| } | ||
| } | ||
| } |