What causes "HTTP request error. Response code: %d" in hashicorp/packer?

Check the reported status code and fix the URL/path accordingly

HTTP request error. Response code: %d

Error message

HTTP request error. Response code: %d

What it means

After executing the HTTP request, the datasource treats any status outside 2xx as a failure and returns this error with the numeric status code. The response body is discarded, so you only get the code.

Source

Thrown at datasource/http/data.go:159

		fmt.Println("Error creating http request")
		return cty.NullVal(cty.EmptyObject), err
	}

	for name, value := range headers {
		req.Header.Set(name, value)
	}

	resp, err := client.Do(req)
	// TODO: How to make test case for this
	if err != nil {
		fmt.Println("Error making performing http request")
		return cty.NullVal(cty.EmptyObject), err
	}

	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return cty.NullVal(cty.EmptyObject), fmt.Errorf("HTTP request error. Response code: %d", resp.StatusCode)
	}

	contentType := resp.Header.Get("Content-Type")
	if contentType == "" || isContentTypeText(contentType) == false {
		fmt.Printf("Content-Type is not recognized as a text type, got %q\n",
			contentType)
		fmt.Println("If the content is binary data, Packer may not properly handle the contents of the response.")
	}

	bytes, err := io.ReadAll(resp.Body)
	// TODO: How to make test case for this?
	if err != nil {
		fmt.Println("Error processing response body of call")
		return cty.NullVal(cty.EmptyObject), err
	}

	responseHeaders := make(map[string]string)
	for k, v := range resp.Header {

View on GitHub (pinned to eb36e3c3e4)

Solutions

Check the reported status code and fix the URL/path accordingly
Add required authentication via `request_headers` (e.g. Authorization)
Test the URL with curl to confirm the expected 2xx response
If the server redirects, point `url` at the final destination directly

Example fix

// before
url = "https://api.example.com/v1/release" // 404
// after
url = "https://api.example.com/v2/release"

Defensive patterns

Strategy: try-catch

Validate before calling

// curl -I the URL in CI preflight and assert 200
curl -fsS -o /dev/null -w '%{http_code}' "$URL" | grep -q '^2'

Try / catch

// surface status code and body for diagnosis
if !strings.HasPrefix(resp.Status, "2") {
  body, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
  return fmt.Errorf("http %d from %s: %s", resp.StatusCode, url, body)
}

Prevention

Add auth headers via request_headers when the endpoint requires them
Monitor target endpoints for moves/404s
Test URLs with curl before embedding them in templates

When it happens

Trigger: The configured URL returns 404 (wrong path), 401/403 (auth required), 500 (server error), 301/302 not followed, etc. during Execute.

Common situations: Endpoint moved and returns 404; API requires a token not passed in headers; server-side outage returning 5xx; self-signed cert endpoints proxied behind an error page.

Related errors

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/29aadbcb6136e6e3. Report an issue: GitHub.