langchain - 💡(How to fix) Fix anthropic: base64 file blocks with non-PDF text mime types fail with media_type validation error

import base64
import os

from langchain_anthropic import ChatAnthropic
from langchain_core.messages import HumanMessage

assert os.environ.get("ANTHROPIC_API_KEY")

csv = "a,b,c\n1,2,3\n"
b64 = base64.b64encode(csv.encode()).decode()

model = ChatAnthropic(model="claude-sonnet-4-5")
model.invoke(
    [
        HumanMessage(
            content=[
                {"type": "text", "text": "summarize"},
                {
                    "type": "file",
                    "data": b64,
                    "mime_type": "text/csv",
                    "metadata": {"filename": "data.csv"},
                },
            ]
        )
    ]
)

---

anthropic.BadRequestError: Error code: 400 - {'type': 'error', 'error': {'type': 'invalid_request_error', 'message': "messages.0.content.1.document.source.base64.media_type: Input should be 'application/pdf'"}}

---

elif "base64" in block or block.get("source_type") == "base64":
    formatted_block = {
        "type": "document",
        "source": {
            "type": "base64",
            "media_type": block.get("mime_type") or "application/pdf",
            "data": block.get("base64") or block.get("data", ""),
        },
    }

---

elif "base64" in block or block.get("source_type") == "base64":
    mime_type = block.get("mime_type") or "application/pdf"
    data = block.get("base64") or block.get("data", "")
    if mime_type.startswith("text/") and mime_type != "application/pdf":
        try:
            text = base64.b64decode(data).decode("utf-8")
            formatted_block = {
                "type": "document",
                "source": {"type": "text", "media_type": "text/plain", "data": text},
            }
        except (binascii.Error, UnicodeDecodeError):
            formatted_block = {
                "type": "document",
                "source": {"type": "base64", "media_type": mime_type, "data": data},
            }
    else:
        formatted_block = {
            "type": "document",
            "source": {"type": "base64", "media_type": mime_type, "data": data},
        }

---

System Information
------------------
> OS:  Darwin
> OS Version:  Darwin Kernel Version 25.2.0: Tue Nov 18 21:09:45 PST 2025; root:xnu-12377.61.12~1/RELEASE_ARM64_T6030
> Python Version:  3.11.0 | packaged by conda-forge | (main, Jan 14 2023, 12:25:12) [Clang 14.0.6 ]

Package Information
-------------------
> langchain_core: 1.2.17
> langchain: 1.2.15
> langchain_anthropic: 1.3.4
> langchain_aws: 1.0.0
> langchain_classic: 1.0.1
> langsmith: 0.7.6
> langgraph: 1.1.6
> langgraph-checkpoint: 4.0.0