karatelabs/karate · info

[callSingle] disk cache skipped

Error message

[callSingle] disk cache skipped (not JSON-like at {}): {}

What it means

callSingle completed and produced a result, but the result was deemed not JSON-like, so Karate skipped writing it to the disk cache. Only JSON-compatible objects can be persisted; results like Java objects, binaries, or other non-map/list values are cached in memory only. This warning indicates reduced caching effectiveness, not a failure.

Solutions

1. Make the called feature return plain JSON: maps/lists of primitives instead of Java objects or binary data.
2. Convert non-JSON results explicitly (e.g. karate.toJson or build the response as JSON in the feature).
3. Accept the warning if the result is intentionally non-JSON — in-memory caching still applies.
4. If the result should be JSON, log/inspect the returned value to find which member is not serializable.

Example fix

// before (called feature ends with)
* def result = javaConfig.buildObject()
// after
* def result = { token: javaConfig.getToken(), expiry: javaConfig.getExpiry() }

// verify the callSingle result is JSON-like before caching expectations
if (!(result instanceof Map || result instanceof List)) skipDiskCache(result);

boolean isJsonLike(Object o) { return o instanceof Map || o instanceof List || o instanceof String || o instanceof Number || o instanceof Boolean; }

When it happens

Trigger: The callSingle result object fails the JSON-like check (notJsonLike non-zero) in ScenarioRuntime's disk-cache path, so the write branch is skipped.

Common situations: Called feature (or its configure/return) yields a Java object, byte array, or custom type; feature returns a variable set containing non-serializable values; version changes made the JSON-like detection stricter.

Understand the failure class

Background: "JSON serialization failed", "not JSON serializable", "Failed to serialize": why JSON marshaling errors happen and how to fix them — this error's family across 46 libraries.

Related errors

• [callSingle] disk cache read failed
• [callSingle] disk cache write failed
• <cached exception message>
• [callSingle] caching exception for
• callSingle failed

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/36f64b696d2eca02. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/core/ScenarioRuntime.java:788

                }

                long execTime = System.currentTimeMillis() - startExec;
                logger.info("[callSingle] << executed in {}ms: {}", execTime, path);

                // Write to disk cache if configured and result is JSON-like
                if (cacheMinutes > 0 && cacheFile != null) {
                    String notJsonLike = Json.isMapOrList(result) ? findNonJsonValue(result, "$") : "the result itself";
                    if (notJsonLike == null) {
                        try {
                            cacheFile.getParentFile().mkdirs();
                            String json = StringUtils.formatJson(result, false, false, false);
                            Files.writeString(cacheFile.toPath(), json);
                            logger.info("[callSingle] disk cache write: {}", cacheFile);
                        } catch (IOException e) {
                            logger.warn("[callSingle] disk cache write failed: {} - {}", cacheFile, e.getMessage());
                        }
                    } else {
                        logger.warn("[callSingle] disk cache skipped (not JSON-like at {}): {}", notJsonLike, path);
                    }
                }
            }

            // Cache in memory
            cache.put(path, result);
            logger.debug("[callSingle] memory cached: {}", path);

            return StepUtils.deepCopy(result);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Internal execution of callSingle - reads and evaluates the file.
     * Supports:
     * - ?suffix syntax for cache key differentiation (suffix is stripped for file read)

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