feat: wire EMF file output into NucleusEmitter publish flow by utsavvyas · Pull Request #22 · aws-greengrass/aws-greengrass-telemetry-nucleus-emitter

utsavvyas · 2026-04-02T22:26:37Z

Issue #, if available:

N/A — PR 4 of 4 in the extended metrics stacked series.

Description of changes:

Wire EMF file output into NucleusEmitter publish flow and update documentation:

Add DeviceConfiguration to constructor for thingName
Create/close EmfFileWriter in handleConfiguration() when outputMode or outputDirectory changes
Write metrics to EmfFileWriter in publishTelemetry() when isEmfEnabled()
Close EmfFileWriter on shutdown
README updated with all new config fields and extended metrics documentation

🤖 Assisted by AI

Why is this change necessary:

Completes the end-to-end flow: config (PR 1) → collect metrics (PR 2) → EMF writer (PR 3) → wire into publish loop (this PR). The emitter can now simultaneously publish via IPC/MQTT and write EMF files.

How was this change tested:

Unit tests for EMF wiring (emf-only, both, ipc-only modes)
config_emf.yaml test configuration
Deployed on EC2 with outputMode: both — PubSub and EMF files working simultaneously

Any additional information or context required to review the change:

Depends on PR #21. Final PR in the stack.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

MikeDombo · 2026-04-02T22:31:55Z

+public class EmfFileWriter implements Closeable {
+
+    private static final DateTimeFormatter HOUR_FORMAT =
+            DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH").withZone(ZoneOffset.UTC);


Recommendation generated by Amazon CodeGuru Reviewer. Leave feedback on this recommendation by replying to the comment or by reacting to the comment using emoji.

DateTimeFormatter.ofPattern

Note: “I18N doesn’t apply because this use case is internal” is a misconception. For formatting that isn’t user-facing: Set Locale to Locale.ROOT, set TimeZone to UTC, and check if your format is predefined in DateTimeFormatter.

Picture strings (for example, MM-dd-yyyy and HH:mm:ss) that you specify to represent the date won’t be appropriate for all locales, and should not be hardcoded. Different locales use different date and time formats, positioning, punctuation, and even numbers themselves. So, the developer or a translator has to adapt the string for each locale's specific needs. Otherwise, the results could look strange or wrong to users in another language or locale.

Also, DateTimeFormatter.ofPattern shouldn’t be used to fix issues with SimpleDateFormat, since the two produce similar results. The Internationalization channel on Broadcast has two videos on the challenges of using SimpleDateFormat for User-displayed customer experience (CX) and Application-internal timestamps and application-specific/application-defined values.

Suggested solutions:

For user-facing date and time:

[PREFERRED] MessageFormat supports "skeletons" that can automatically select the right pattern for the customer's locale. To learn more, see How to format dates and the MessageFormat Cheat Sheet.
MessageFormat fmt = new MessageFormat(pattern, locale); Object[] args = { new Date() }; return fmt.format(args);

If you want to get the string translated, create a resource file for the date and time pattern. Use Panther to get the date and time pattern string translated. MessageFormat is built into Panther. See the DateTimeFormatter.ofPattern wiki.

Consider using the ICU4J library DateFormat.getPatternInstance method (which uses a date skeleton string) instead of the stock Java DateFormat class. Skeleton-based date and time formats adapt to the locale automatically.
import com.ibm.icu.text.DateFormat; // note different import! DateFormat df = DateFormat.getPatternInstance("jmsz", pageLocale);

For application-internal timestamps:

Use a predefined ISO 8601 format like ISO_INSTANT (which looks like 2011-12-03T10:15:30Z) from DateTimeFormatter.

String now = DateTimeFormatter.ISO_INSTANT.format(new Date().toInstant());

If your format is not predefined in DateTimeFormatter and you must use a custom format:

Make sure you pass in the Locale (for non-user-facing, internal-processing usage, use Locale.ROOT )

Set the timezone (for example, UTC), if you want to ensure it is a certain timezone.

Example:

// your custom pattern goes here final String somePattern = "yyyy MM dd HH mm ss z"; // $NON-NLS-L$ Custom hard-coded pattern DateTimeFormatter myFormatter = DateTimeFormatter.ofPattern(somePattern, Locale.ROOT) // $NON-NLS-L$ custom pattern, invariant locale // only add this line if you want to ensure UTC (or some other time zone) .withZone(ZoneId.of("UTC")); // $NON-NLS-L$ forcing UTC myFormatter.format(/* some value */);

MikeDombo · 2026-04-02T22:31:55Z

+        if (config.isEmfEnabled()) {
+            String thingName = Coerce.toString(
+                    deviceConfiguration.getThingName());
+            this.emfFileWriter = new EmfFileWriter(


Recommendation generated by Amazon CodeGuru Reviewer. Leave feedback on this recommendation by replying to the comment or by reacting to the comment using emoji.

Problem
Analysis of this package determined that this line of code assigns a resource to a class field and there is no method that closes or returns this resource. This can result in a resource leak that slows down or crashes your system.

Fix
Create a method in this class that closes the following resource: emfFileWriter. After you use this resource, use this method to prevent a resource leak.

More info
View resource management guidelines at oracle.com (external link).

MikeDombo · 2026-04-02T22:31:55Z

+                        config.outputDirectory((String) entry.getValue());
+                        break;
+                    }
+                    logger.error(OUTPUT_DIRECTORY_CONFIG_PARSE_ERROR_LOG, entry.getValue());


Recommendation generated by Amazon CodeGuru Reviewer. Leave feedback on this recommendation by replying to the comment or by reacting to the comment using emoji.

Potential log injection detected. Ensure all untrusted input is properly sanitized before logging. Use parameterized logging or validate input against a allow list to prevent log injection vulnerabilities. Consider using a dedicated logging library's built-in sanitization features when available. Learn more - https://cwe.mitre.org/data/definitions/117.html

MikeDombo · 2026-04-02T22:31:56Z

+                            break;
+                        }
+                    }
+                    logger.error(OUTPUT_MODE_CONFIG_PARSE_ERROR_LOG, entry.getValue());


Recommendation generated by Amazon CodeGuru Reviewer. Leave feedback on this recommendation by replying to the comment or by reacting to the comment using emoji.

Potential log injection detected. Ensure all untrusted input is properly sanitized before logging. Use parameterized logging or validate input against a allow list to prevent log injection vulnerabilities. Consider using a dedicated logging library's built-in sanitization features when available. Learn more - https://cwe.mitre.org/data/definitions/117.html

MikeDombo · 2026-04-02T22:31:56Z

+                            break;
+                        }
+                    }
+                    logger.error(METRICS_LEVEL_CONFIG_PARSE_ERROR_LOG, entry.getValue());


Recommendation generated by Amazon CodeGuru Reviewer. Leave feedback on this recommendation by replying to the comment or by reacting to the comment using emoji.

Potential log injection detected. Ensure all untrusted input is properly sanitized before logging. Use parameterized logging or validate input against a allow list to prevent log injection vulnerabilities. Consider using a dedicated logging library's built-in sanitization features when available. Learn more - https://cwe.mitre.org/data/definitions/117.html

zhaotong-a · 2026-04-08T17:16:28Z

+        close();
+        Files.createDirectories(outputDirectory);
+        Path file = outputDirectory.resolve(fileName);
+        writer = Files.newBufferedWriter(file, StandardOpenOption.CREATE, StandardOpenOption.APPEND);


Since we are checking writer != null in line 96, we also need to make sure in here when we create this writer is not null for whatever reason so next check it will go to the line 96 check correctly.

zhaotong-a · 2026-04-08T17:18:37Z

+            for (String line : context.serialize()) {
+                writer.write(line);
+                writer.newLine();


Do we know if context.serialize() already contains the newline?

zhaotong-a · 2026-04-08T17:27:34Z

+            assertTrue(pubsubLog.await(30, TimeUnit.SECONDS), "Pub/sub publish log detected.");
+
+            // Poll for EMF file creation (publish fires immediately with initialDelay=0)
+            Path emfDir = Paths.get("/tmp/greengrass/telemetry");


will this tmp file get cleanup after the test?

MikeDombo · 2026-04-30T21:00:04Z

+        if (outputModeChanged || outputDirectoryChanged) {
+            if (newConfiguration.isEmfEnabled()) {
+                this.emfFileWriter = new EmfFileWriter(getThingName(),
+                        Paths.get(newConfiguration.getOutputDirectory()));


Recommendation generated by Amazon CodeGuru Reviewer. Leave feedback on this recommendation by replying to the comment or by reacting to the comment using emoji.

Path traversal vulnerability detected. User-controlled input in file paths
can allow attackers to access files outside intended directories using
../ sequences. Secure your code by using framework functions like
getCanonicalPath(), normalize(), or validating paths with
.startsWith() checks. Learn more:
https://cwe.mitre.org/data/definitions/22.html

utsavvyas force-pushed the cr4/ipc-payload branch from d915fbc to 31ea09a Compare April 2, 2026 22:31

MikeDombo reviewed Apr 2, 2026

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utsavvyas force-pushed the cr4/ipc-payload branch 12 times, most recently from 6b22832 to 9571992 Compare April 7, 2026 01:30

utsavvyas marked this pull request as ready for review April 7, 2026 02:16

utsavvyas force-pushed the cr4/ipc-payload branch 3 times, most recently from bb89013 to 4817f2d Compare April 8, 2026 16:22

zhaotong-a reviewed Apr 8, 2026

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utsavvyas force-pushed the cr4/ipc-payload branch from 4817f2d to 6e289fb Compare April 9, 2026 01:36

utsavvyas mentioned this pull request Apr 14, 2026

chore: bump logging dependency to 2.4.0-SNAPSHOT aws-greengrass/aws-greengrass-nucleus#1780

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utsavvyas force-pushed the cr4/ipc-payload branch from 6e289fb to d24c6b4 Compare April 30, 2026 20:50

MikeDombo reviewed Apr 30, 2026

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utsavvyas force-pushed the cr4/ipc-payload branch 3 times, most recently from be86d0c to 242ec95 Compare April 30, 2026 23:40

Utsav Vyas added 2 commits May 7, 2026 12:06

feat: add EMF file writer using aws-embedded-metrics library

78088f5

feat: wire EmfFileWriter into NucleusEmitter publish loop

843d5a2

utsavvyas force-pushed the cr4/ipc-payload branch from 242ec95 to 843d5a2 Compare May 7, 2026 19:06

utsavvyas marked this pull request as draft May 7, 2026 19:09

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utsavvyas commented Apr 2, 2026

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DateTimeFormatter.ofPattern

Note: “I18N doesn’t apply because this use case is internal” is a misconception. For formatting that isn’t user-facing: Set Locale to Locale.ROOT, set TimeZone to UTC, and check if your format is predefined in DateTimeFormatter.

Suggested solutions:

For user-facing date and time:

For application-internal timestamps:

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