github/copilot-sdk · error

failed to parse package.json

Error message

failed to parse package.json: %w

What it means

After a successful 200 fetch, the body is JSON-decoded into a struct expecting a `copilotCliVersion` field. Malformed JSON is wrapped as 'failed to parse package.json'. This means the fetched file exists but its contents are not valid JSON in the expected shape.

Solutions

1. curl the printed URL and inspect what was actually returned (often HTML instead of JSON)
2. Fix proxy/captive-portal issues so the raw JSON file is served
3. Retry if the body was truncated by a transient network error
4. Pin a released SDK version whose package.json is valid

Example fix

// before: failed to parse package.json: invalid character '<' looking for beginning of value
// after: bypass proxy / retry so raw package.json is fetched and parses cleanly

body, _ := io.ReadAll(resp.Body)
if !bytes.HasPrefix(bytes.TrimSpace(body), []byte("{")) {
    return fmt.Errorf("expected JSON, got: %.80s", body)
}
var pkg struct{ CopilotCLIVersion string `json:"copilotCliVersion"` }
if err := json.Unmarshal(body, &pkg); err != nil {
    return fmt.Errorf("bad package.json: %v", err)
}

if err := json.NewDecoder(resp.Body).Decode(&pkg); err != nil {
    var jsonErr *json.SyntaxError
    if errors.As(err, &jsonErr) {
        // log offset jsonErr.Offset, capture body for diagnostics, retry or fail loudly
    }
}

When it happens

Trigger: The URL returns HTML (e.g. a 200 error page or rate-limit interstitial), a truncated body, or the package.json at that ref has invalid/differently-encoded JSON.

Common situations: Proxy or captive portal returning an HTML 200 page; an SDK ref where package.json was corrupted or moved; extremely rare — transient network truncation mid-body.

Understand the failure class

Background: JSON parse error: "Unexpected token" / "not valid JSON" / "failed to parse" — what JSON parsers are really complaining about — this error's family across 45 libraries.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• failed to parse legacy package-lock.json
• Unexpected trailing content at position
• Unescaped control character at position <pos-1>
• Unterminated string escape at position
• Invalid escape sequence \

AI-assisted analysis of github/copilot-sdk@cd8cf15dc3 (2026-09-09). Data as JSON: /api/errors/940785bfc41cc840. Report an issue: GitHub.

Appendix: source

Thrown at go/cmd/bundler/main.go:338

	url := fmt.Sprintf(packageJSONURLFmt, gitRef)
	fmt.Printf("Fetching %s...\n", url)

	resp, err := http.Get(url)
	if err != nil {
		return "", fmt.Errorf("failed to fetch: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("failed to fetch package.json: %s", resp.Status)
	}

	var packageJSON struct {
		CopilotCLIVersion string `json:"copilotCliVersion"`
	}

	if err := json.NewDecoder(resp.Body).Decode(&packageJSON); err != nil {
		return "", fmt.Errorf("failed to parse package.json: %w", err)
	}

	if packageJSON.CopilotCLIVersion == "" {
		return fetchLegacyCLIVersionFromRepo(gitRef)
	}

	return packageJSON.CopilotCLIVersion, nil
}

func fetchLegacyCLIVersionFromRepo(gitRef string) (string, error) {
	url := fmt.Sprintf(packageLockURLFmt, gitRef)
	fmt.Printf("Falling back to %s...\n", url)

	resp, err := http.Get(url)
	if err != nil {
		return "", fmt.Errorf("failed to fetch legacy package-lock.json: %w", err)
	}
	defer resp.Body.Close()

View on GitHub (pinned to cd8cf15dc3)