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Swap MD5 hash to CRC32 for checksum calculation #39

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Merged
merged 4 commits into from
Jan 28, 2025
Merged

Swap MD5 hash to CRC32 for checksum calculation #39

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d68056f
Swap cryptographic MD5 hash for NCHF CRC32 for checksum calculation
pirgeo Jan 17, 2025
e2b1c18
use null to differentiate from zero (a valid CRC32 output)
pirgeo Jan 21, 2025
0d67f5c
spotless
pirgeo Jan 21, 2025
7dbdb16
ensure no NullPointerException
pirgeo Jan 21, 2025
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24 changes: 14 additions & 10 deletions lib/src/main/java/com/dynatrace/file/util/PollBasedFilePoller.java
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
import java.nio.file.Files;
import java.nio.file.Path;
import java.time.Duration;
import java.util.Objects;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.logging.Logger;
Expand All @@ -32,7 +33,7 @@ class PollBasedFilePoller extends FilePoller {
private final ScheduledExecutorService executorService;

private final CRC32 crc32 = new CRC32();
private long prevChecksumValue = 0;
private Long prevChecksumValue = null;

protected PollBasedFilePoller(Path filePath, Duration pollInterval) {
super(filePath);
Expand Down Expand Up @@ -64,27 +65,30 @@ public boolean fileContentsUpdated() {
}

private synchronized void poll() {
long latestChecksumValue = getChecksumValue();
if (latestChecksumValue != prevChecksumValue) {
prevChecksumValue = latestChecksumValue;
Long latestChecksumValue = getChecksumValue();

// If the latest checksum value is a value other than zero, it means that the file is not
// empty.
// The if check above ensures that it is also different from the previous checksum, so the
// file contents must have been updated.
if (latestChecksumValue != 0) {
// | latest | previous | outcome |
// | ------ | -------- | ----------------------- |
// | null | null | do nothing |
// | null | !null | do nothing |
// | !null | null | update (no file before) |
// | !null | !null | update if changed |
if (latestChecksumValue != null) {
if (!prevChecksumValue.equals(latestChecksumValue)) {
changedSinceLastInquiry.set(true);
}
prevChecksumValue = latestChecksumValue;
}
}

private synchronized long getChecksumValue() {
private synchronized Long getChecksumValue() {
crc32.reset();
try {
byte[] fileBytes = Files.readAllBytes(absoluteFilePath);
crc32.update(fileBytes, 0, fileBytes.length);
} catch (IOException e) {
LOGGER.warning(() -> String.format(LOG_MESSAGE_FAILED_FILE_READ, absoluteFilePath, e));
return null;
}
return crc32.getValue();
}
Expand Down
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