clean up InstanceCreate::user_data JSON schema

nexus/src/external_api/params.rs

@@ -12,7 +12,7 @@ use omicron_common::api::external::{
 use schemars::JsonSchema;
 use serde::{
     de::{self, Visitor},
-    Deserialize, Deserializer, Serialize,
+    Deserialize, Deserializer, Serialize, Serializer,
 };
 use std::net::IpAddr;
 use uuid::Uuid;
@@ -404,10 +404,15 @@ pub struct InstanceCreate {
     /// User data for instance initialization systems (such as cloud-init).
     /// Must be a Base64-encoded string, as specified in RFC 4648 § 4 (+ and /
     /// characters with padding). Maximum 32 KiB unencoded data.
-    // TODO: this should emit `"format": "byte"`, but progenitor doesn't
-    // understand that yet.
-    #[schemars(default, with = "String")]
-    #[serde(default, with = "serde_user_data")]
+    // While serde happily accepts #[serde(with = "<mod>")] as a shorthand for
+    // specifing `serialize_with` and `deserialize_with`, schemars requires the
+    // argument to `with` to be a type rather than merely a path prefix (i.e. a
+    // mod or type). It's admittedly a bit tricky for schemars to address;
+    // unlike `serialize` or `deserialize`, `JsonSchema` requires several
+    // functions working together. It's unfortunate that schemars has this
+    // built-in incompatibility, exacerbated by its glacial rate of progress
+    // and immunity to offers of help.
+    #[serde(default, with = "UserData")]
     pub user_data: Vec<u8>,
 
     /// The network interfaces to be created for this instance.
@@ -419,9 +424,8 @@ pub struct InstanceCreate {
     pub disks: Vec<InstanceDiskAttachment>,
 }
 
-mod serde_user_data {
-    use serde::{de::Error, Deserialize, Deserializer, Serialize, Serializer};
-
+struct UserData;
+impl UserData {
     pub fn serialize<S>(
         data: &Vec<u8>,
         serializer: S,
@@ -440,22 +444,43 @@ mod serde_user_data {
             Ok(buf) => {
                 // if you change this, also update the stress test in crate::cidata
                 if buf.len() > crate::cidata::MAX_USER_DATA_BYTES {
-                    Err(D::Error::invalid_length(
+                    Err(<D::Error as serde::de::Error>::invalid_length(
                         buf.len(),
                         &"less than 32 KiB",
                     ))
                 } else {
                     Ok(buf)
                 }
             }
-            Err(_) => Err(D::Error::invalid_value(
+            Err(_) => Err(<D::Error as serde::de::Error>::invalid_value(
                 serde::de::Unexpected::Other("invalid base64 string"),
                 &"a valid base64 string",
             )),
         }
     }
 }
 
+impl JsonSchema for UserData {
+    fn schema_name() -> String {
+        "String".to_string()
+    }
+
+    fn json_schema(
+        _: &mut schemars::gen::SchemaGenerator,
+    ) -> schemars::schema::Schema {
+        schemars::schema::SchemaObject {
+            instance_type: Some(schemars::schema::InstanceType::String.into()),
+            format: Some("byte".to_string()),
+            ..Default::default()
+        }
+        .into()
+    }
+
+    fn is_referenceable() -> bool {
+        false
+    }
+}
+
 /// Migration parameters for an [`Instance`](omicron_common::api::external::Instance)
 #[derive(Clone, Debug, Deserialize, Serialize, JsonSchema)]
 pub struct InstanceMigrate {

openapi/nexus.json

@@ -7830,7 +7830,8 @@
           "user_data": {
             "description": "User data for instance initialization systems (such as cloud-init). Must be a Base64-encoded string, as specified in RFC 4648 § 4 (+ and / characters with padding). Maximum 32 KiB unencoded data.",
             "default": "",
-            "type": "string"
+            "type": "string",
+            "format": "byte"
           }
         },
         "required": [