Downloading files from skills example doesn't work with streaming

[uristdwarf]

Based on https://platform.claude.com/docs/en/build-with-claude/skills-guide#go

Maybe I misunderstood the documentation, but I can't find a way to extract FileID's without manually unmarshalling the output from the raw JSON when streaming.

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"os"

	"github.com/anthropics/anthropic-sdk-go"
)

func main() {
	client := anthropic.NewClient()
	stream := client.Beta.Messages.NewStreaming(context.TODO(), anthropic.BetaMessageNewParams{
		Model:     "claude-haiku-4-5",
		MaxTokens: 4096,
		Betas: []anthropic.AnthropicBeta{
			"code-execution-2025-08-25",
			anthropic.AnthropicBetaSkills2025_10_02,
		},
		Container: anthropic.BetaMessageNewParamsContainerUnion{
			OfContainers: &anthropic.BetaContainerParams{
				Skills: []anthropic.BetaSkillParams{
					{
						Type:    anthropic.BetaSkillParamsTypeAnthropic,
						SkillID: "pdf",
						Version: anthropic.String("latest"),
					},
				},
			},
		},
		Messages: []anthropic.BetaMessageParam{
			anthropic.NewBetaUserMessage(anthropic.NewBetaTextBlock("Create a blank PDF file")),
		},
		Tools: []anthropic.BetaToolUnionParam{
			{OfCodeExecutionTool20250825: &anthropic.BetaCodeExecutionTool20250825Param{}},
		},
	})


	response := anthropic.BetaMessage{}
	for stream.Next() {
		event := stream.Current()
		err := response.Accumulate(event)
		if err != nil {
			panic(err)
		}

		switch eventVariant := event.AsAny().(type) {
		case anthropic.BetaRawContentBlockDeltaEvent:
			switch deltaVariant := eventVariant.Delta.AsAny().(type) {
			case anthropic.BetaTextDelta:
				print(deltaVariant.Text)
			}

		}
	}
	fmt.Println()

	os.WriteFile("log.json", []byte(response.RawJSON()), 0600)
	// Step 2: Extract file IDs from the response
	fileIDs := extractFileIDsStreaming(&response)

	// Step 3: Download the file using Files API
	for _, fileID := range fileIDs {
		fileMetadata, err := client.Beta.Files.GetMetadata(context.TODO(), fileID, anthropic.BetaFileGetMetadataParams{
			Betas: []anthropic.AnthropicBeta{anthropic.AnthropicBetaFilesAPI2025_04_14},
		})
		if err != nil {
			log.Fatal(err)
		}

		fileContent, err := client.Beta.Files.Download(context.TODO(), fileID, anthropic.BetaFileDownloadParams{
			Betas: []anthropic.AnthropicBeta{anthropic.AnthropicBetaFilesAPI2025_04_14},
		})
		if err != nil {
			log.Fatal(err)
		}

		// Step 4: Save to disk
		out, err := os.Create(fileMetadata.Filename)
		if err != nil {
			log.Fatal(err)
		}
		io.Copy(out, fileContent.Body)
		out.Close()
		fileContent.Body.Close()
		fmt.Printf("Downloaded: %s\n", fileMetadata.Filename)
	}
}

type Content struct {
	Contents []ofContent `json:"OfContent"`
}

type ofContent struct {
	FileID string `json:"file_id"`
}

// Works
func extractFileIDsStreaming(response *anthropic.BetaMessage) []string {
	var fileIDs []string
	for _, item := range response.Content {
		switch v := item.AsAny().(type) {
		case anthropic.BetaBashCodeExecutionToolResultBlock:
			var content Content
			err := json.Unmarshal([]byte(v.Content.JSON.Content.Raw()), &content)
			if err != nil {
				panic(err)
			}
			for _, output := range content.Contents {
				if output.FileID != "" {
					fileIDs = append(fileIDs, output.FileID)
				}
			}
		}
	}
	return fileIDs
}

// Doesn't work (the example on https://platform.claude.com/docs/en/build-with-claude/skills-guide#go)
func extractFileIDs(response *anthropic.BetaMessage) []string {
	var fileIDs []string
	for _, item := range response.Content {
		switch v := item.AsAny().(type) {
		case anthropic.BetaBashCodeExecutionToolResultBlock:
			for _, output := range v.Content.Content {
				if output.FileID != "" {
					fileIDs = append(fileIDs, output.FileID)
				}
			}
		}
	}
	return fileIDs
}