Add serde support to Blob type (#2647)

## Motivation and Context
This is a child PR of #2616

The changes that this PR introduces is same as the ones that were merged
to `unstable-serde-support` branch before.

Initially, we tried to make commit to unstable-serde-support branch and
merge changes one by one in small PRs. However, in order to make it up
to date with the main branch, we would need to go through a large PR of
over 700 files.

Thus, I decided to create individual PRs that commits directly to `main`
branch.

## Description
- Implements `serde` support to `Blob`

## Testing
- Test checks whether the serialized/de-serialized data matches with the
expected value

## Checklist
NA

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

---------

Co-authored-by: John DiSanti <johndisanti@gmail.com>

rust-runtime/aws-smithy-types/Cargo.toml

@@ -1,7 +1,10 @@
 [package]
 name = "aws-smithy-types"
 version = "0.0.0-smithy-rs-head"
-authors = ["AWS Rust SDK Team <aws-sdk-rust@amazon.com>", "Russell Cohen <rcoh@amazon.com>"]
+authors = [
+    "AWS Rust SDK Team <aws-sdk-rust@amazon.com>",
+    "Russell Cohen <rcoh@amazon.com>",
+]
 description = "Types for smithy-rs codegen."
 edition = "2021"
 license = "Apache-2.0"

rust-runtime/aws-smithy-types/additional-ci

@@ -5,8 +5,10 @@
 #
 
 # This script contains additional CI checks to run for this specific package
-
 set -e
 
 echo "### Checking for duplicate dependency versions in the normal dependency graph with all features enabled"
 cargo tree -d --edges normal --all-features
+
+echo "### Checking whether the features are properly feature-gated"
+! cargo tree -e no-dev | grep serde

rust-runtime/aws-smithy-types/src/blob.rs

@@ -30,3 +30,128 @@ impl AsRef<[u8]> for Blob {
         &self.inner
     }
 }
+
+#[cfg(all(aws_sdk_unstable, feature = "serde-serialize"))]
+mod serde_serialize {
+    use super::*;
+    use crate::base64;
+    use serde::Serialize;
+
+    impl Serialize for Blob {
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where
+            S: serde::Serializer,
+        {
+            if serializer.is_human_readable() {
+                serializer.serialize_str(&crate::base64::encode(&self.inner))
+            } else {
+                serializer.serialize_bytes(&self.inner)
+            }
+        }
+    }
+}
+
+#[cfg(all(aws_sdk_unstable, feature = "serde-deserialize"))]
+mod serde_deserialize {
+    use super::*;
+    use crate::base64;
+    use serde::{de::Visitor, Deserialize};
+
+    struct HumanReadableBlobVisitor;
+    impl<'de> Visitor<'de> for HumanReadableBlobVisitor {
+        type Value = Blob;
+        fn expecting(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            formatter.write_str("expected base64 encoded string")
+        }
+
+        fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+        where
+            E: serde::de::Error,
+        {
+            match base64::decode(v) {
+                Ok(inner) => Ok(Blob { inner }),
+                Err(e) => Err(E::custom(e)),
+            }
+        }
+    }
+
+    struct NotHumanReadableBlobVisitor;
+    impl<'de> Visitor<'de> for NotHumanReadableBlobVisitor {
+        type Value = Blob;
+        fn expecting(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            formatter.write_str("expected bytes")
+        }
+
+        fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+        where
+            E: serde::de::Error,
+        {
+            Ok(Blob { inner: v })
+        }
+    }
+
+    impl<'de> Deserialize<'de> for Blob {
+        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where
+            D: serde::Deserializer<'de>,
+        {
+            if deserializer.is_human_readable() {
+                deserializer.deserialize_str(HumanReadableBlobVisitor)
+            } else {
+                deserializer.deserialize_byte_buf(NotHumanReadableBlobVisitor)
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+#[cfg(all(
+    aws_sdk_unstable,
+    feature = "serde-serialize",
+    feature = "serde-deserialize"
+))]
+mod test_serde {
+    use crate::Blob;
+    use serde::{Deserialize, Serialize};
+    use std::collections::HashMap;
+
+    #[derive(Deserialize, Serialize, Debug, PartialEq)]
+    struct ForTest {
+        blob: Blob,
+    }
+
+    #[test]
+    fn human_readable_blob() {
+        let aws_in_base64 = r#"{"blob":"QVdT"}"#;
+        let for_test = ForTest {
+            blob: Blob {
+                inner: vec![b'A', b'W', b'S'],
+            },
+        };
+        assert_eq!(for_test, serde_json::from_str(aws_in_base64).unwrap());
+        assert_eq!(serde_json::to_string(&for_test).unwrap(), aws_in_base64);
+    }
+
+    #[test]
+    fn not_human_readable_blob() {
+        use std::ffi::CString;
+
+        let for_test = ForTest {
+            blob: Blob {
+                inner: vec![b'A', b'W', b'S'],
+            },
+        };
+        let mut buf = vec![];
+        let res = ciborium::ser::into_writer(&for_test, &mut buf);
+        assert!(res.is_ok());
+
+        // checks whether the bytes are deserialized properly
+        let n: HashMap<String, CString> =
+            ciborium::de::from_reader(std::io::Cursor::new(buf.clone())).unwrap();
+        assert!(n.get("blob").is_some());
+        assert!(n.get("blob") == CString::new([65, 87, 83]).ok().as_ref());
+
+        let de: ForTest = ciborium::de::from_reader(std::io::Cursor::new(buf)).unwrap();
+        assert_eq!(for_test, de);
+    }
+}