micro/go-micro · error

failed to marshal request: %w

Error message

failed to marshal request: %w

What it means

Returned by Provider.callAPI when json.Marshal fails to serialize the request map to JSON. In practice this is nearly impossible for map[string]any built from strings/ints, so it usually indicates a non-serializable value (channel, func, cyclic structure) was placed into the request map.

Source

Thrown at ai/anthropic/anthropic.go:356

func (s *streamReader) Close() error {
	if s.closed {
		return nil
	}
	s.closed = true
	return s.body.Close()
}

func usage(input, output int) ai.Usage {
	return ai.Usage{InputTokens: input, OutputTokens: output, TotalTokens: input + output}
}

// callAPI makes an HTTP request to the Anthropic API
func (p *Provider) callAPI(ctx context.Context, req map[string]any) (*ai.Response, any, error) {
	// Marshal request
	reqBody, err := json.Marshal(req)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to marshal request: %w", err)
	}

	// Build HTTP request
	apiURL := strings.TrimRight(p.opts.BaseURL, "/") + "/v1/messages"
	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, apiURL, bytes.NewReader(reqBody))
	if err != nil {
		return nil, nil, fmt.Errorf("failed to create request: %w", err)
	}

	// Set headers
	httpReq.Header.Set("Content-Type", "application/json")
	httpReq.Header.Set("x-api-key", p.opts.APIKey)
	httpReq.Header.Set("anthropic-version", "2023-06-01")

	// Make request
	httpResp, err := http.DefaultClient.Do(httpReq)
	if err != nil {
		return nil, nil, fmt.Errorf("API request failed: %w", err)

View on GitHub (pinned to 24529f1404)

Solutions

1. Inspect the wrapped error: json.UnsupportedTypeError names the offending Go type.
2. Remove or replace non-serializable values (func, channel, complex) from request options/metadata before calling Generate.
3. Marshal the request yourself in a test (json.Marshal(req)) to reproduce and isolate the bad value.
4. Ensure metadata values are plain strings/numbers/bools/maps/slices.

func assertJSONSafe(v map[string]any) error {
	_, err := json.Marshal(v)
	return err
}

resp, err := provider.Generate(ctx, prompt)
if err != nil {
	var typeErr *json.UnsupportedTypeError
	if errors.As(err, &typeErr) {
		log.Printf("non-serializable type in request: %v", typeErr.Type)
	}
}

When it happens

Trigger: A caller-supplied option or metadata value placed into the req map is not JSON-encodable (e.g. a func, channel, or a value with a custom Marshaler returning an error), or json.Marshal returns an UnsupportedTypeError/UnsupportedValueError.

Common situations: Passing custom option structs into provider options where a nested value can't serialize; rarely hit in normal use since the request map holds plain scalars.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• failed to parse stream chunk: %w
• failed to parse response: %w
• failed to marshal stream request: %w
• failed to marshal request: %w
• failed to marshal request: %w

AI-assisted analysis of micro/go-micro@24529f1404 (2026-09-01). Data as JSON: /api/errors/592e0fe8e1a02648. Report an issue: GitHub.