conductor-oss/conductor · error · RuntimeException

No data found in SSE response: {sseBody}

Error message

No data found in SSE response: {sseBody}

What it means

Thrown by parseSseResponse when an SSE response body contains zero usable `data:` lines. It iterates lines, keeps data: payloads, skips empty and [DONE] markers, and if nothing remained it cannot produce JSON. Means the server sent an SSE stream with only comments, event: lines, ping/keep-alive, or was empty.

Source

Thrown at ai/src/main/java/org/conductoross/conductor/ai/mcp/MCPService.java:365

        log.debug("Parsing SSE response: {}", sseBody);

        // Find all "data:" lines and concatenate their content
        StringBuilder jsonData = new StringBuilder();
        String[] lines = sseBody.split("\n");

        for (String line : lines) {
            String trimmed = line.trim();
            if (trimmed.startsWith("data:")) {
                String data = trimmed.substring(5).trim();
                // Skip empty data or "[DONE]" markers
                if (!data.isEmpty() && !data.equals("[DONE]")) {
                    jsonData.append(data);
                }
            }
        }

        if (jsonData.length() == 0) {
            throw new RuntimeException("No data found in SSE response: " + sseBody);
        }

        try {
            return objectMapper.readTree(jsonData.toString());
        } catch (Exception e) {
            throw new RuntimeException("Failed to parse SSE data as JSON: " + jsonData, e);
        }
    }

    /** Executes one MCP request and follows redirects while protecting sensitive headers. */
    private ResponsePayload execute(Request initialRequest) throws Exception {
        Request request = initialRequest;
        for (int redirects = 0; redirects <= 5; redirects++) {
            try (Response response = httpClient.newCall(request).execute()) {
                if (!response.isRedirect()) {
                    return new ResponsePayload(
                            response.code(),
                            response.header("Content-Type", "application/json"),

View on GitHub (pinned to cf7c3e4a8a)

Solutions

1. Log the raw SSE body (it is in the exception message) to see what frames were actually sent.
2. Confirm the server emits `data:` lines for JSON-RPC responses per the MCP SSE transport spec.
3. If the server uses a different event field, use a compliant server or a custom SSE parser.
4. Check the connection wasn't closed/truncated before the result event arrived.

try {
    mcpService.listTools(serverUrl, headers);
} catch (RuntimeException e) {
    if (e.getMessage().contains("No data found in SSE response")) {
        // server sent an SSE stream with no data: lines; check transport compatibility
    }
    throw e;
}

When it happens

Trigger: Server's content-type was text/event-stream but the body was an empty stream, only `event:` headers, only `: comment` lines, or only `[DONE]` markers; the actual JSON-RPC result event was never delivered (server closed the stream early).

Common situations: Long-lived SSE endpoint where the response event hadn't arrived yet but the connection closed; server uses a non-standard field instead of `data:`; interceptor stripped data lines; the response was a heartbeat-only stream.

Related errors

• Failed to parse SSE data as JSON: {jsonData}
• Invalid JSON-RPC response: missing 'result' field
• Invalid response: 'tools' field is missing or not an array
• No data found in SSE response: {sseBody}
• HTTP %d error from MCP server: %s

AI-assisted analysis of conductor-oss/conductor@cf7c3e4a8a (2026-08-14). Data as JSON: /api/errors/3a9de34bb83b77aa. Report an issue: GitHub.