Unsupported document file format

[dan-jensen]

Problem

After getting past the "Does not match" error when using a file in messages, there is another error when using a file in messages: "Unsupported document file format: application/octet-stream. Only PDF and plaintext documents are supported." That is caused by this gem defaulting to content-type application/octet-stream when uploading files.

The workaround is to pass an Anthropic::FilePart object with an accurate content_type.

Additional details

The Anthropic API docs for uploading a file show a cURL example with no content-type, but that's because cURL automatically sets that header. The other examples (Python and TypeScript) show the content-type being set explicitly. In other words, an accurate content-type must be provided.

Proposal

Require that content_type is always passed as an argument:

• The Anthropic::FilePart should require a content_type argument.
• Either the files.upload() method should require a content_type argument as well, or it should only accept Anthropic::FilePart objects.

Example request

message = anthropic.messages.create(
  max_tokens: 1024,
  messages: [
    {
      role: "user",
      content: [
        {
          type: "text",
          text: "Hello Claude"
        },
        {
          type: "document",
          source: {
            type: "file",
            file_id: "file_011CSoYoHF8saWZ6CPh55555"
        }
      ]
    }
  ],
  model: :"claude-sonnet-4-20250514"
)

Example response

{
  "url": "https://api.anthropic.com/v1/messages",
  "status": 400,
  "body": {
    "type": "error",
    "error": {
      "type": "invalid_request_error",
      "message": "messages.0.content.1.source: Unsupported document file format: application/octet-stream. Only PDF and plaintext documents are supported."
    }
  }
}