From cdb55a3a3537db22c39769ecf9476be2f6e055db Mon Sep 17 00:00:00 2001
From: Timothee Guerin <tiguerin@microsoft.com>
Date: Wed, 13 Dec 2023 14:15:44 -0800
Subject: [PATCH 1/3] Treat bytes array as many binary parts

---
 packages/openapi3/src/schema-emitter.ts  | 26 ++++++++++++++++--------
 packages/openapi3/test/multipart.test.ts | 21 +++++++++++++++++++
 2 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/packages/openapi3/src/schema-emitter.ts b/packages/openapi3/src/schema-emitter.ts
index 7e553e8d81..8d458b02c7 100644
--- a/packages/openapi3/src/schema-emitter.ts
+++ b/packages/openapi3/src/schema-emitter.ts
@@ -305,17 +305,27 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
     return props;
   }
 
+  #isBytesKeptRaw(type: Type) {
+    const program = this.emitter.getProgram();
+    return (
+      type.kind === "Scalar" && type.name === "bytes" && getEncode(program, type) === undefined
+    );
+  }
+
   modelPropertyLiteral(prop: ModelProperty): EmitterOutput<object> {
     const program = this.emitter.getProgram();
     const isMultipart = this.#getContentType().startsWith("multipart/");
-    if (
-      isMultipart &&
-      prop.type.kind === "Scalar" &&
-      prop.type.name === "bytes" &&
-      getEncode(program, prop.type) === undefined &&
-      getEncode(program, prop) === undefined
-    ) {
-      return { type: "string", format: "binary" };
+    if (isMultipart) {
+      if (this.#isBytesKeptRaw(prop.type) && getEncode(program, prop) === undefined) {
+        return { type: "string", format: "binary" };
+      }
+      if (
+        prop.type.kind === "Model" &&
+        isArrayModelType(program, prop.type) &&
+        this.#isBytesKeptRaw(prop.type.indexer.value)
+      ) {
+        return { type: "array", items: { type: "string", format: "binary" } };
+      }
     }
 
     const refSchema = this.emitter.emitTypeReference(prop.type, {
diff --git a/packages/openapi3/test/multipart.test.ts b/packages/openapi3/test/multipart.test.ts
index aaf66a0c88..a2d43c64fd 100644
--- a/packages/openapi3/test/multipart.test.ts
+++ b/packages/openapi3/test/multipart.test.ts
@@ -38,6 +38,27 @@ describe("typespec-autorest: multipart", () => {
     });
   });
 
+  it("part of type `bytes[]` produce `type: array, items: {type: string, format: binary}`", async () => {
+    const res = await openApiFor(
+      `
+      op upload(@header contentType: "multipart/form-data", profileImage: bytes): void;
+      `
+    );
+    const op = res.paths["/"].post;
+    deepStrictEqual(op.requestBody.content["multipart/form-data"], {
+      schema: {
+        type: "object",
+        properties: {
+          profileImage: {
+            type: "array",
+            items: { type: "string", format: "binary" },
+          },
+        },
+        required: ["profileImage"],
+      },
+    });
+  });
+
   it("part of type `string` produce `type: string`", async () => {
     const res = await openApiFor(
       `

From 34cefa09cc8baf572e30f256b7715d14b005a2aa Mon Sep 17 00:00:00 2001
From: Timothee Guerin <tiguerin@microsoft.com>
Date: Wed, 13 Dec 2023 14:16:46 -0800
Subject: [PATCH 2/3] changelog

---
 .../hotfix-multipart-bytes-array_2023-12-13-22-16.json | 10 ++++++++++
 1 file changed, 10 insertions(+)
 create mode 100644 common/changes/@typespec/openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json

diff --git a/common/changes/@typespec/openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json b/common/changes/@typespec/openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json
new file mode 100644
index 0000000000..d7f43d26d8
--- /dev/null
+++ b/common/changes/@typespec/openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@typespec/openapi3",
+      "comment": "Fix: Multipart part of type `bytes[]` is treated as multiple binary part",
+      "type": "none"
+    }
+  ],
+  "packageName": "@typespec/openapi3"
+}

From 551eb41579c4505b26ec32e994e4579678b6d578 Mon Sep 17 00:00:00 2001
From: Timothee Guerin <tiguerin@microsoft.com>
Date: Wed, 13 Dec 2023 14:40:17 -0800
Subject: [PATCH 3/3] fix

---
 .../openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json | 2 +-
 packages/openapi3/test/multipart.test.ts                        | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/common/changes/@typespec/openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json b/common/changes/@typespec/openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json
index d7f43d26d8..62d1503483 100644
--- a/common/changes/@typespec/openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json
+++ b/common/changes/@typespec/openapi3/hotfix-multipart-bytes-array_2023-12-13-22-16.json
@@ -2,7 +2,7 @@
   "changes": [
     {
       "packageName": "@typespec/openapi3",
-      "comment": "Fix: Multipart part of type `bytes[]` is treated as multiple binary part",
+      "comment": "Fix: Multipart part of type `bytes[]` is now treated as multiple binary part",
       "type": "none"
     }
   ],
diff --git a/packages/openapi3/test/multipart.test.ts b/packages/openapi3/test/multipart.test.ts
index a2d43c64fd..8138ef11f1 100644
--- a/packages/openapi3/test/multipart.test.ts
+++ b/packages/openapi3/test/multipart.test.ts
@@ -41,7 +41,7 @@ describe("typespec-autorest: multipart", () => {
   it("part of type `bytes[]` produce `type: array, items: {type: string, format: binary}`", async () => {
     const res = await openApiFor(
       `
-      op upload(@header contentType: "multipart/form-data", profileImage: bytes): void;
+      op upload(@header contentType: "multipart/form-data", profileImage: bytes[]): void;
       `
     );
     const op = res.paths["/"].post;