Add IDs and creation date to PDFs (#2374)

7 files changed, 147 insertions, 29 deletions

diff --git a/crates/typst-cli/src/compile.rs b/crates/typst-cli/src/compile.rs
index 6a5ca21e..b5cf0e54 100644
--- a/crates/typst-cli/src/compile.rs
+++ b/crates/typst-cli/src/compile.rs
@@ -1,12 +1,13 @@
 use std::fs;
 use std::path::{Path, PathBuf};
 
+use chrono::{Datelike, Timelike};
 use codespan_reporting::diagnostic::{Diagnostic, Label};
 use codespan_reporting::term::{self, termcolor};
 use termcolor::{ColorChoice, StandardStream};
 use typst::diag::{bail, Severity, SourceDiagnostic, StrResult};
 use typst::doc::Document;
-use typst::eval::{eco_format, Tracer};
+use typst::eval::{eco_format, Datetime, Tracer};
 use typst::geom::Color;
 use typst::syntax::{FileId, Source, Span};
 use typst::{World, WorldExt};
@@ -141,19 +142,37 @@ fn export(
         OutputFormat::Svg => {
             export_image(world, document, command, watching, ImageExportFormat::Svg)
         }
-        OutputFormat::Pdf => export_pdf(document, command),
+        OutputFormat::Pdf => export_pdf(document, command, world),
     }
 }
 
 /// Export to a PDF.
-fn export_pdf(document: &Document, command: &CompileCommand) -> StrResult<()> {
+fn export_pdf(
+    document: &Document,
+    command: &CompileCommand,
+    world: &SystemWorld,
+) -> StrResult<()> {
+    let ident = world.input().to_string_lossy();
+    let buffer = typst::export::pdf(document, Some(&ident), now());
     let output = command.output();
-    let buffer = typst::export::pdf(document);
     fs::write(output, buffer)
         .map_err(|err| eco_format!("failed to write PDF file ({err})"))?;
     Ok(())
 }
 
+/// Get the current date and time in UTC.
+fn now() -> Option<Datetime> {
+    let now = chrono::Local::now().naive_utc();
+    Datetime::from_ymd_hms(
+        now.year(),
+        now.month().try_into().ok()?,
+        now.day().try_into().ok()?,
+        now.hour().try_into().ok()?,
+        now.minute().try_into().ok()?,
+        now.second().try_into().ok()?,
+    )
+}
+
 /// An image format to export in.
 enum ImageExportFormat {
     Png,
diff --git a/crates/typst-cli/src/world.rs b/crates/typst-cli/src/world.rs
index 500b64e5..81480e62 100644
--- a/crates/typst-cli/src/world.rs
+++ b/crates/typst-cli/src/world.rs
@@ -25,6 +25,8 @@ use crate::package::prepare_package;
 pub struct SystemWorld {
     /// The working directory.
     workdir: Option<PathBuf>,
+    /// The canonical path to the input file.
+    input: PathBuf,
     /// The root relative to which absolute paths are resolved.
     root: PathBuf,
     /// The input path.
@@ -78,6 +80,7 @@ impl SystemWorld {
 
         Ok(Self {
             workdir: std::env::current_dir().ok(),
+            input,
             root,
             main: FileId::new(None, main_path),
             library: Prehashed::new(typst_library::build()),
@@ -123,6 +126,11 @@ impl SystemWorld {
         self.now.take();
     }
 
+    /// Return the canonical path to the input file.
+    pub fn input(&self) -> &PathBuf {
+        &self.input
+    }
+
     /// Lookup a source file by id.
     #[track_caller]
     pub fn lookup(&self, id: FileId) -> Source {
diff --git a/crates/typst-library/src/meta/document.rs b/crates/typst-library/src/meta/document.rs
index 57ce064c..55c365ac 100644
--- a/crates/typst-library/src/meta/document.rs
+++ b/crates/typst-library/src/meta/document.rs
@@ -34,9 +34,13 @@ pub struct DocumentElem {
 
     /// The document's creation date.
     ///
-    /// The year component must be at least zero in order to be embedded into
-    /// a PDF.
-    pub date: Option<Datetime>,
+    /// If this is `{auto}` (default), Typst uses the current date and time.
+    /// Setting it to `{none}` prevents Typst from embedding any creation date
+    /// into the PDF metadata.
+    ///
+    /// The year component must be at least zero in order to be embedded into a
+    /// PDF.
+    pub date: Smart<Option<Datetime>>,
 
     /// The page runs.
     #[internal]
diff --git a/crates/typst/src/doc.rs b/crates/typst/src/doc.rs
index 890a94a5..1c23fd75 100644
--- a/crates/typst/src/doc.rs
+++ b/crates/typst/src/doc.rs
@@ -13,7 +13,8 @@ use crate::export::PdfPageLabel;
 use crate::font::Font;
 use crate::geom::{
     self, styled_rect, Abs, Axes, Color, Corners, Dir, Em, FixedAlign, FixedStroke,
-    Geometry, Length, Numeric, Paint, Path, Point, Rel, Shape, Sides, Size, Transform,
+    Geometry, Length, Numeric, Paint, Path, Point, Rel, Shape, Sides, Size, Smart,
+    Transform,
 };
 use crate::image::Image;
 use crate::model::{Content, Location, MetaElem, StyleChain};
@@ -31,7 +32,7 @@ pub struct Document {
     /// The document's keywords.
     pub keywords: Vec<EcoString>,
     /// The document's creation date.
-    pub date: Option<Datetime>,
+    pub date: Smart<Option<Datetime>>,
 }
 
 /// A finished layout with items at fixed positions.
diff --git a/crates/typst/src/export/pdf/mod.rs b/crates/typst/src/export/pdf/mod.rs
index c64b95b0..d18023cf 100644
--- a/crates/typst/src/export/pdf/mod.rs
+++ b/crates/typst/src/export/pdf/mod.rs
@@ -16,15 +16,17 @@ use std::collections::{BTreeMap, HashMap};
 use std::hash::Hash;
 use std::num::NonZeroUsize;
 
+use base64::Engine;
 use ecow::{eco_format, EcoString};
 use pdf_writer::types::Direction;
 use pdf_writer::writers::PageLabel;
 use pdf_writer::{Finish, Name, Pdf, Ref, TextStr};
-use xmp_writer::{LangId, RenditionClass, XmpWriter};
+use xmp_writer::{DateTime, LangId, RenditionClass, Timezone, XmpWriter};
 
 use self::gradient::PdfGradient;
 use self::page::Page;
 use crate::doc::{Document, Lang};
+use crate::eval::Datetime;
 use crate::font::Font;
 use crate::geom::{Abs, Dir, Em};
 use crate::image::Image;
@@ -35,8 +37,22 @@ use extg::ExtGState;
 /// Export a document into a PDF file.
 ///
 /// Returns the raw bytes making up the PDF file.
+///
+/// The `ident` parameter shall be a string that uniquely and stably identifies
+/// the document. It is used to write a PDF file identifier. It should not
+/// change between compilations of the same document. If it is `None`, a hash of
+/// the document is used instead (which means that it _will_ change across
+/// compilations).
+///
+/// The `timestamp`, if given, is expected to be the creation date of the
+/// document as a UTC datetime. It will be used as the PDFs creation date unless
+/// another date is given through `set document(date: ..)`.
 #[tracing::instrument(skip_all)]
-pub fn pdf(document: &Document) -> Vec<u8> {
+pub fn pdf(
+    document: &Document,
+    ident: Option<&str>,
+    timestamp: Option<Datetime>,
+) -> Vec<u8> {
     let mut ctx = PdfContext::new(document);
     page::construct_pages(&mut ctx, &document.pages);
     font::write_fonts(&mut ctx);
@@ -44,7 +60,7 @@ pub fn pdf(document: &Document) -> Vec<u8> {
     gradient::write_gradients(&mut ctx);
     extg::write_external_graphics_states(&mut ctx);
     page::write_page_tree(&mut ctx);
-    write_catalog(&mut ctx);
+    write_catalog(&mut ctx, ident, timestamp);
     ctx.pdf.finish()
 }
 
@@ -127,7 +143,7 @@ impl<'a> PdfContext<'a> {
 
 /// Write the document catalog.
 #[tracing::instrument(skip_all)]
-fn write_catalog(ctx: &mut PdfContext) {
+fn write_catalog(ctx: &mut PdfContext, ident: Option<&str>, timestamp: Option<Datetime>) {
     let lang = ctx
         .languages
         .iter()
@@ -171,21 +187,15 @@ fn write_catalog(ctx: &mut PdfContext) {
         xmp.pdf_keywords(&joined);
     }
 
-    if let Some(date) = ctx.document.date {
-        if let Some(year) = date.year().filter(|&y| y >= 0) {
-            let mut pdf_date = pdf_writer::Date::new(year as u16);
-            if let Some(month) = date.month() {
-                pdf_date = pdf_date.month(month);
-            }
-            if let Some(day) = date.day() {
-                pdf_date = pdf_date.day(day);
-            }
+    if let Some(date) = ctx.document.date.unwrap_or(timestamp) {
+        let tz = ctx.document.date.is_auto();
+        if let Some(pdf_date) = pdf_date(date, tz) {
             info.creation_date(pdf_date);
-
-            let mut xmp_date = xmp_writer::DateTime::year(year as u16);
-            xmp_date.month = date.month();
-            xmp_date.day = date.day();
+            info.modified_date(pdf_date);
+        }
+        if let Some(xmp_date) = xmp_date(date, tz) {
             xmp.create_date(xmp_date);
+            xmp.modify_date(xmp_date);
         }
     }
 
@@ -193,6 +203,25 @@ fn write_catalog(ctx: &mut PdfContext) {
     xmp.num_pages(ctx.document.pages.len() as u32);
     xmp.format("application/pdf");
     xmp.language(ctx.languages.keys().map(|lang| LangId(lang.as_str())));
+
+    // A unique ID for this instance of the document. Changes if anything
+    // changes in the frames.
+    let instance_id =
+        hash_base64(&(&ctx.document, ctx.document.date.unwrap_or(timestamp)));
+
+    if let Some(ident) = ident {
+        // A unique ID for the document that stays stable across compilations.
+        let doc_id = hash_base64(&("PDF-1.7", ident));
+        xmp.document_id(&doc_id);
+        xmp.instance_id(&instance_id);
+        ctx.pdf
+            .set_file_id((doc_id.clone().into_bytes(), instance_id.into_bytes()));
+    } else {
+        // This is not spec-compliant, but some PDF readers really want an ID.
+        let bytes = instance_id.into_bytes();
+        ctx.pdf.set_file_id((bytes.clone(), bytes));
+    }
+
     xmp.rendition_class(RenditionClass::Proof);
     xmp.pdf_version("1.7");
 
@@ -207,7 +236,7 @@ fn write_catalog(ctx: &mut PdfContext) {
     let mut catalog = ctx.pdf.catalog(ctx.alloc.bump());
     catalog.pages(ctx.page_tree_ref);
     catalog.viewer_preferences().direction(dir);
-    catalog.pair(Name(b"Metadata"), meta_ref);
+    catalog.metadata(meta_ref);
 
     // Insert the page labels.
     if !page_labels.is_empty() {
@@ -283,6 +312,59 @@ fn deflate(data: &[u8]) -> Vec<u8> {
     miniz_oxide::deflate::compress_to_vec_zlib(data, COMPRESSION_LEVEL)
 }
 
+/// Create a base64-encoded hash of the value.
+fn hash_base64<T: Hash>(value: &T) -> String {
+    base64::engine::general_purpose::STANDARD
+        .encode(crate::util::hash128(value).to_be_bytes())
+}
+
+/// Converts a datetime to a pdf-writer date.
+fn pdf_date(datetime: Datetime, tz: bool) -> Option<pdf_writer::Date> {
+    let year = datetime.year().filter(|&y| y >= 0)? as u16;
+
+    let mut pdf_date = pdf_writer::Date::new(year);
+
+    if let Some(month) = datetime.month() {
+        pdf_date = pdf_date.month(month);
+    }
+
+    if let Some(day) = datetime.day() {
+        pdf_date = pdf_date.day(day);
+    }
+
+    if let Some(h) = datetime.hour() {
+        pdf_date = pdf_date.hour(h);
+    }
+
+    if let Some(m) = datetime.minute() {
+        pdf_date = pdf_date.minute(m);
+    }
+
+    if let Some(s) = datetime.second() {
+        pdf_date = pdf_date.second(s);
+    }
+
+    if tz {
+        pdf_date = pdf_date.utc_offset_hour(0).utc_offset_minute(0);
+    }
+
+    Some(pdf_date)
+}
+
+/// Converts a datetime to an xmp-writer datetime.
+fn xmp_date(datetime: Datetime, tz: bool) -> Option<xmp_writer::DateTime> {
+    let year = datetime.year().filter(|&y| y >= 0)? as u16;
+    Some(DateTime {
+        year,
+        month: datetime.month(),
+        day: datetime.day(),
+        hour: datetime.hour(),
+        minute: datetime.minute(),
+        second: datetime.second(),
+        timezone: if tz { Some(Timezone::Utc) } else { None },
+    })
+}
+
 /// Assigns new, consecutive PDF-internal indices to items.
 struct Remapper<T> {
     /// Forwards from the items to the pdf indices.
diff --git a/tests/src/tests.rs b/tests/src/tests.rs
index 1aed32d7..d974b731 100644
--- a/tests/src/tests.rs
+++ b/tests/src/tests.rs
@@ -420,7 +420,11 @@ fn test(
     let document = Document { pages: frames, ..Default::default() };
     if compare_ever {
         if let Some(pdf_path) = pdf_path {
-            let pdf_data = typst::export::pdf(&document);
+            let pdf_data = typst::export::pdf(
+                &document,
+                Some(&format!("typst-test: {}", name.display())),
+                world.today(Some(0)),
+            );
             fs::create_dir_all(pdf_path.parent().unwrap()).unwrap();
             fs::write(pdf_path, pdf_data).unwrap();
         }
diff --git a/tests/typ/meta/document.typ b/tests/typ/meta/document.typ
index 814d547d..43e4ca39 100644
--- a/tests/typ/meta/document.typ
+++ b/tests/typ/meta/document.typ
@@ -11,7 +11,7 @@ What's up?
 #set document(author: ("A", "B"), date: datetime.today())
 
 ---
-// Error: 21-28 expected datetime or none, found string
+// Error: 21-28 expected datetime, none, or auto, found string
 #set document(date: "today")
 
 ---