Update thumbnail to be Vec<u8>, add serialization feature (#59)

* Update thumbnail to be `Vec<u8>`, add serialization feature
* Update README

README.md

@@ -50,7 +50,8 @@ c2pa = "0.5.0"
 
 * `async_signer` enables signing via asynchronous services which require `async` support.
 * `file_io` enables manifest generation, signing via OpenSSL, and embedding manifests in various file formats.
-* `xmp_write` enables updating XMP on embed with the dcterms:provenance field (requires xmp_toolkit)
+* `serialize_thumbnails` includes binary thumbnail data in the [Serde](https://serde.rs/) serialization output.
+* `xmp_write` enables updating XMP on embed with the `dcterms:provenance` field (requires [xmp_toolkit](https://crates.io/crates/xmp_toolkit)).
 
 ## Rust version requirements
 

sdk/Cargo.toml

@@ -14,6 +14,7 @@ rust-version = "1.58.0"
 [features]
 async_signer = ["async-trait"]
 file_io = ["openssl"]
+serialize_thumbnails = []
 xmp_write = ["xmp_toolkit"]
 
 # The diagnostics feature is unsupported and might be removed.

sdk/src/ingredient.rs

@@ -16,7 +16,6 @@
 use crate::{
     assertion::{get_thumbnail_image_type, Assertion, AssertionBase},
     assertions::{self, labels, Metadata, Relationship, Thumbnail},
-    cbor_types::BytesT,
     claim::Claim,
     error::{Error, Result},
     hashed_uri::HashedUri,
@@ -31,6 +30,12 @@ use crate::{error::wrap_io_err, validation_status::status_for_store, xmp_inmemor
 use log::{debug, error};
 use serde::{Deserialize, Serialize};
 
+/// Function that is used by serde to determine whether or not we should serialize
+/// thumbnail data based on the "serialize_thumbnails" flag (serialization is disabled by default)
+pub fn skip_serializing_thumbnails(_value: &Option<(String, Vec<u8>)>) -> bool {
+    !cfg!(feature = "serialize_thumbnails")
+}
+
 #[cfg(feature = "file_io")]
 use std::path::Path;
 #[derive(Debug, Deserialize, Serialize)]
@@ -56,8 +61,8 @@ pub struct Ingredient {
     /// A thumbnail image capturing the visual state at the time of import.
     ///
     /// A tuple of thumbnail MIME format (i.e. `image/jpeg`) and binary bits of the image.
-    #[serde(skip_serializing)]
-    thumbnail: Option<(String, BytesT)>,
+    #[serde(skip_serializing_if = "skip_serializing_thumbnails")]
+    thumbnail: Option<(String, Vec<u8>)>,
 
     /// An optional hash of the asset to prevent duplicates.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -236,7 +241,7 @@ impl Ingredient {
 
     /// Sets the thumbnail format and image data.
     pub fn set_thumbnail<S: Into<String>>(&mut self, format: S, thumbnail: Vec<u8>) -> &mut Self {
-        self.thumbnail = Some((format.into(), BytesT(thumbnail)));
+        self.thumbnail = Some((format.into(), thumbnail));
         self
     }