[Feature Request] Support `multipart/form-data`

[mattcoulter7]

Hey,

This is an awesome package btw.

I need to upload files as multipart/form-data.

Use Case

        "/api/files": {
            "post": {
                "tags": [
                    "files"
                ],
                "summary": "Create File",
                "description": "Upload a file",
                "operationId": "create_file_api_files_post",
                "requestBody": {
                    "required": true,
                    "content": {
                        "multipart/form-data": {
                            "schema": {
                                "$ref": "#/components/schemas/Body_create_file_api_files_post"
                            }
                        }
                    }
                },
            }
        }

I can see here, you are strictly not accepting anything other than application/json:

n8n-openapi-node/src/n8n/SchemaToINodeProperties.ts

Lines 171 to 175 in c08043b

	const regexp = /application\/json.*/
	const content = findKey(body.content, regexp)
	if (!content) {
	throw new Error(`No '${regexp}' content found`);
	}

---

Logs

Expected:

[04:01:59.227] WARN (6): Failed to parse request body
    operation: {
      "pattern": "/api/files",
      "method": "post",
      "operationId": "create_file_api_files_post"
    }
    error: "Error: No '/application\\/json.*/' content found"

And in the n8n UI, we will see a message like:

POST /api/files

There's no body available for request, kindly use HTTP Request node to send body

Unfortunately, I cannot use the HTTP Request Node, as my custom credential is not linked to it. But also, it feels a lot cleaner to use the custom node.

---

Implementation

Of course, there is no schema for the request to with form-data, so the way that n8n tends to support this is by specifying a Binary Data Input Field Name. See the HTTP Request V3.

https://docs.n8n.io/integrations/builtin/core-nodes/n8n-nodes-base.httprequest/#form-data

[mattcoulter7]

Update: I think we could support it like this one.

Essentially, the preSend hook allows us to inject the binary data into the request payload.

Snippet

https://github.com/n8n-io/n8n/blob/000cccb62700144fd41ed70e2177de1c3cb32c31/packages/nodes-base/nodes/Google/CloudStorage/ObjectDescription.ts#L161-L166

const binaryPropertyName = this.getNodeParameter(
	'createBinaryPropertyName',
) as string;
const binaryData = this.helpers.assertBinaryData(binaryPropertyName);
if (binaryData.id) {
	content = await this.helpers.getBinaryStream(binaryData.id);
	const binaryMetadata = await this.helpers.getBinaryMetadata(binaryData.id);
	contentType = binaryMetadata.mimeType ?? 'application/octet-stream';
	contentLength = binaryMetadata.fileSize;
}

Full Context

https://github.com/n8n-io/n8n/blob/000cccb62700144fd41ed70e2177de1c3cb32c31/packages/nodes-base/nodes/Google/CloudStorage/ObjectDescription.ts#L112-L190

---

IMO it would be nice if n8n supports this kind of configuration under the hook via routing. So we can map binary data to request.body as FormData somehow.

It is a very common pattern being used all over the place. Just do a search for "Input Binary Field" in the n8n code base!

Anyhow, I think this is the best approach for now.