commit f9cbad5a8ac4140a697f4dea5833c33c1eecf636
parent 439c9fddd6ea5a49bdb67f98714b593e6564957a
Author: Dylan ross <dylan.ssor@gmail.com>
Date: Fri, 29 Sep 2023 14:43:56 -0700
supports removal of manifests from pdf (#312)
* supports removal of manifests from pdf
* implements feedback - c2pa -> C2PA
---------
Co-authored-by: Dylan Ross <dyross@adobe.com>
Diffstat:
1 file changed, 161 insertions(+), 2 deletions(-)
diff --git a/sdk/src/asset_handlers/pdf.rs b/sdk/src/asset_handlers/pdf.rs
@@ -28,6 +28,7 @@ static C2PA_RELATIONSHIP: &[u8] = b"C2PA_Manifest";
static CONTENT_CREDS: &str = "Content Credentials";
static EMBEDDED_FILES_KEY: &[u8] = b"EmbeddedFiles";
static SUBTYPE_KEY: &[u8] = b"Subtype";
+static TYPE_KEY: &[u8] = b"Type";
static NAMES_KEY: &[u8] = b"Names";
/// Error representing failure scenarios while interacting with PDFs.
@@ -38,9 +39,18 @@ pub enum Error {
#[error(transparent)]
UnableToReadPdf(#[from] lopdf::Error),
+ /// No Manifest is present in the PDF.
+ #[error("No manifest is present in the PDF.")]
+ NoManifest,
+
/// Error occurred while adding a C2PA manifest as an `Annotation` to the PDF.
#[error("Unable to add C2PA manifest as an annotation to the PDF.")]
AddingAnnotation,
+
+ // The PDF has an `AFRelationship` set to C2PA, but we were unable to find
+ // the manifest bytes in the PDF's embedded files.
+ #[error("Unable to find C2PA manifest in the PDF's embedded files.")]
+ UnableToFindEmbeddedFileManifest,
}
const C2PA_MIME_TYPE: &str = "application/x-c2pa-manifest-store";
@@ -53,7 +63,7 @@ pub(crate) trait C2paPdf: Sized {
/// Returns `true` if the `PDF` is password protected, `false` otherwise.
fn is_password_protected(&self) -> bool;
- /// Returns `true` if this PDF has `c2pa` Manifests, `false` otherwise.
+ /// Returns `true` if this PDF has C2PA Manifests, `false` otherwise.
fn has_c2pa_manifest(&self) -> bool;
/// Writes provided `bytes` as a PDF `Embedded File`
@@ -66,6 +76,8 @@ pub(crate) trait C2paPdf: Sized {
#[allow(clippy::needless_lifetimes)] // required for automock::mockall
fn read_manifest_bytes<'a>(&'a self) -> Result<Option<Vec<&'a [u8]>>, Error>;
+ fn remove_manifest_bytes(&mut self) -> Result<(), Error>;
+
fn read_xmp(&self) -> Option<String>;
}
@@ -218,6 +230,45 @@ impl C2paPdf for Pdf {
]))
}
+ fn remove_manifest_bytes(&mut self) -> Result<(), Error> {
+ if !self.has_c2pa_manifest() {
+ return Err(Error::NoManifest);
+ }
+
+ // Find the File Spec, which contains the reference to the manifest.
+ let file_spec_ref = self
+ .document
+ .catalog()?
+ .get(ASSOCIATED_FILE_KEY)?
+ .as_reference()?;
+
+ // Find the manifest's file stream.
+ let file_stream_ref = self
+ .document
+ .get_object(file_spec_ref)?
+ .as_dict()?
+ .get(b"EF")?
+ .as_reference()?;
+
+ // Attempt to remove the manifest from the PDF's `Embedded Files`s. If the manifest
+ // isn't in the PDF's embedded files, remove the manifest from the PDF's annotations.
+ //
+ // We do the operation in this order because a PDF's annotations are attached to a page.
+ // It's possible we'd have to iterate over every page of the PDF before determining the
+ // manifest is referenced from an Embedded File instead.
+ self.remove_manifest_from_embedded_files()
+ .or_else(|_| self.remove_manifest_from_annotations())?;
+
+ // Remove the AF_Relationship from the catalog.
+ self.document.catalog_mut()?.remove(AF_RELATIONSHIP_KEY);
+
+ // Delete the manifest and its descriptor from the PDF
+ self.document.delete_object(file_stream_ref);
+ self.document.delete_object(file_spec_ref);
+
+ Ok(())
+ }
+
/// Reads the `Metadata` field referenced in the PDF document's `Catalog` entry. Will return
/// `None` if no Metadata is present.
fn read_xmp(&self) -> Option<String> {
@@ -327,7 +378,7 @@ impl Pdf {
"Desc" => Object::string_literal(CONTENT_CREDS),
"F" => Object::string_literal(CONTENT_CREDS),
"EF" => Reference(file_stream_ref),
- "Type" => Name("FileSpec".into()),
+ TYPE_KEY => Name("FileSpec".into()),
"UF" => Object::string_literal(CONTENT_CREDS),
};
@@ -347,6 +398,76 @@ impl Pdf {
self.document.add_object(stream)
}
+
+ /// Remove the C2PA Manifest `Annotation` from the PDF.
+ fn remove_manifest_from_annotations(&mut self) -> Result<(), Error> {
+ for (_, page_id) in self.document.get_pages() {
+ self.document
+ .get_object_mut(page_id)?
+ .as_dict_mut()?
+ .get_mut(ANNOTATIONS_KEY)?
+ .as_array_mut()?
+ .retain(|obj| {
+ obj.as_dict()
+ .and_then(|annot| annot.get(TYPE_KEY))
+ .and_then(Object::as_name_str)
+ .map(|str| str != CONTENT_CREDS)
+ .unwrap_or(true)
+ });
+ }
+
+ Ok(())
+ }
+
+ /// Removes the manifest from the PDF's embedded files collection.
+ fn remove_manifest_from_embedded_files(&mut self) -> Result<(), Error> {
+ let Ok(names) = self.document.catalog_mut()?.get_mut(NAMES_KEY) else {
+ return Err(Error::NoManifest);
+ };
+
+ // Follows the reference to the /Names Dictionary.
+ let names_dictionary = match names.as_reference() {
+ Ok(object_id) => self.document.get_object_mut(object_id)?.as_dict_mut()?,
+ _ => names.as_dict_mut()?,
+ };
+
+ // Follows the reference to the /EmbeddedFiles Dictionary.
+ let embedded_files_object = names_dictionary.get_mut(EMBEDDED_FILES_KEY)?;
+ let embedded_files_dictionary = match embedded_files_object.as_reference() {
+ Ok(object_id) => self.document.get_object_mut(object_id)?.as_dict_mut()?,
+ _ => embedded_files_object.as_dict_mut()?,
+ };
+
+ // Gets the /Names array from the /EmbeddedFiles Dictionary. This will contain the reference
+ // to the C2PA manifest.
+ let names_vector_object = embedded_files_dictionary.get_mut(NAMES_KEY)?;
+ let names_vector = match names_vector_object.as_reference() {
+ Ok(object_id) => self.document.get_object_mut(object_id)?.as_array_mut()?,
+ _ => names_vector_object.as_array_mut()?,
+ };
+
+ // Find the "Content Credentials" marker name in the /Names Array.
+ let content_creds_marker_idx = names_vector
+ .iter()
+ .position(|value| {
+ value
+ .as_string()
+ .map(|value| value == CONTENT_CREDS)
+ .unwrap_or_default()
+ })
+ .ok_or_else(|| Error::UnableToFindEmbeddedFileManifest)?;
+
+ let content_creds_reference_idx = content_creds_marker_idx + 1;
+ if content_creds_reference_idx >= names_vector.len() {
+ return Err(Error::UnableToFindEmbeddedFileManifest);
+ }
+
+ // Delete the "Content Credentials" marker object and the reference to the C2PA
+ // manifest in the PDF's embedded files.
+ names_vector.drain(content_creds_marker_idx..=content_creds_reference_idx);
+
+ Ok(())
+ }
}
#[cfg(test)]
@@ -560,4 +681,42 @@ mod tests {
let pdf = Pdf::from_bytes(include_bytes!("../../tests/fixtures/basic.pdf")).unwrap();
assert!(pdf.read_xmp().is_some());
}
+
+ #[cfg_attr(not(target_arch = "wasm32"), test)]
+ #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+ fn test_remove_manifest_bytes_from_file_without_c2pa_returns_error() {
+ let mut pdf = Pdf::from_bytes(include_bytes!("../../tests/fixtures/basic.pdf")).unwrap();
+
+ assert!(matches!(
+ pdf.remove_manifest_bytes(),
+ Err(Error::NoManifest)
+ ));
+ }
+
+ #[cfg_attr(not(target_arch = "wasm32"), test)]
+ #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+ fn test_remove_manifest_from_file_with_annotation_based_manifest() {
+ let mut pdf = Pdf::from_bytes(include_bytes!("../../tests/fixtures/basic.pdf")).unwrap();
+ let manifest_bytes = vec![0u8, 1u8, 1u8, 2u8, 3u8];
+ pdf.write_manifest_as_annotation(manifest_bytes.clone())
+ .unwrap();
+
+ assert!(pdf.has_c2pa_manifest());
+ assert!(pdf.remove_manifest_bytes().is_ok());
+ assert!(!pdf.has_c2pa_manifest());
+ }
+
+ #[cfg_attr(not(target_arch = "wasm32"), test)]
+ #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+ fn test_remove_manifest_from_file_with_embedded_file_based_manifest() {
+ let mut pdf = Pdf::from_bytes(include_bytes!("../../tests/fixtures/basic.pdf")).unwrap();
+ let manifest_bytes = vec![0u8, 1u8, 1u8, 2u8, 3u8];
+
+ pdf.write_manifest_as_embedded_file(manifest_bytes.clone())
+ .unwrap();
+
+ assert!(pdf.has_c2pa_manifest());
+ assert!(pdf.remove_manifest_bytes().is_ok());
+ assert!(!pdf.has_c2pa_manifest());
+ }
}
