fix(s3): allow UTF-8 in PostObject form field values (fix #1489) (#1492)

PostObject (presigned POST) returns `400 InvalidHeaderValue` when the upload involves a non-ASCII filename. The same key uploads fine vie PUT, as the issue #1489 noted.

The problem was that `handle_post_object` stores the form field values in an `http::HeaderMap`. values go in through `HeaderValue::from_str` but are read back with the strict `HeaderValue::to_str()` (ASCII-only) which fails on any UTF-8 value.

This is the same problem fixed in eab2b81b for `x-amz-meta-*` headers, and the fix is the same:
`std::str::from_utf8(value.as_bytes())` instead of `to_str()`. The `key` field in `post_object.rs` and the standard headers (`content-disposition` etc.) in `extract_metadata_headers`.

Added integration tests for PostObject (there were none): UTF-8 key, `${filename}` substitution, and UTF-8 `Content-Disposition` metadata. The substitution test passes even without the fix, proving that the filename path was never broken, only the form-params round-trip.

Co-authored-by: Mathew Storm <mathew@stormdevelopments.ca>
Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/1492
Reviewed-by: trinity-1686a <trinity-1686a@noreply.localhost>

src/api/s3/post_object.rs

@@ -83,10 +83,12 @@ pub async fn handle_post_object(
 	};
 
 	// Current part is file. Do some checks before handling to PutObject code
-	let key = params
-		.get("key")
-		.ok_or_bad_request("No key was provided")?
-		.to_str()?;
+	let key = std::str::from_utf8(
+		params
+			.get("key")
+			.ok_or_bad_request("No key was provided")?
+			.as_bytes(),
+	)?;
 	let policy = params
 		.get("policy")
 		.ok_or_bad_request("No policy was provided")?

src/api/s3/put.rs

@@ -679,7 +679,10 @@ pub(crate) fn extract_metadata_headers(
 	];
 	for name in standard_header.iter() {
 		if let Some(value) = headers.get(name) {
-			ret.push((name.to_string(), value.to_str()?.to_string()));
+			ret.push((
+				name.to_string(),
+				std::str::from_utf8(value.as_bytes())?.to_string(),
+			));
 		}
 	}