{"record":{"id":"9cc87155b78f8c51","repo":"apache/hadoop","slug":"premature-eof-reading-from-channel","errorCode":null,"errorMessage":"Premature EOF reading from ${channel}","messagePattern":"Premature EOF reading from (.+?)","errorType":"exception","errorClass":"IOException","httpStatus":null,"severity":"error","filePath":"hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/datatransfer/PacketReceiver.java","lineNumber":268,"sourceCode":"\n    // Slice the data.\n    curPacketBuf.position(lenThroughChecksums);\n    curPacketBuf.limit(lenThroughData);\n    curDataSlice = curPacketBuf.slice();\n\n    // Reset buffer to point to the entirety of the packet (including\n    // length prefixes)\n    curPacketBuf.position(0);\n    curPacketBuf.limit(lenThroughData);\n  }\n\n\n  private static void readChannelFully(ReadableByteChannel ch, ByteBuffer buf)\n      throws IOException {\n    while (buf.remaining() > 0) {\n      int n = ch.read(buf);\n      if (n < 0) {\n        throw new IOException(\"Premature EOF reading from \" + ch);\n      }\n    }\n  }\n\n  private void reallocPacketBuf(int atLeastCapacity) {\n    // Realloc the buffer if this packet is longer than the previous\n    // one.\n    if (curPacketBuf == null ||\n        curPacketBuf.capacity() < atLeastCapacity) {\n      ByteBuffer newBuf;\n      if (useDirectBuffers) {\n        newBuf = bufferPool.getBuffer(atLeastCapacity);\n      } else {\n        newBuf = ByteBuffer.allocate(atLeastCapacity);\n      }\n      // If reallocing an existing buffer, copy the old packet length\n      // prefixes over\n      if (curPacketBuf != null) {","sourceCodeStart":250,"sourceCodeEnd":286,"githubUrl":"https://github.com/apache/hadoop/blob/2add9630210752f88ceb1bb74eb65e37bf41da8e/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/datatransfer/PacketReceiver.java#L250-L286","documentation":"PacketReceiver.readChannelFully() loops until the target buffer is full; if the channel's read() returns -1 before that, the peer closed the connection mid-packet and 'Premature EOF reading from <channel>' is thrown. The reader (client block reader or DataNode mirror) expected more packet bytes than the sender delivered.","triggerScenarios":"DataNode process death or restart during a block read; pipeline abort where an upstream node closes on error; idle timeout or firewall/LB killing the data connection mid-transfer; client disconnect during mirrored writes.","commonSituations":"DataNode OOM/crash under load, aggressive TCP idle timeouts on stateful firewalls between client and DataNode, nodes dropping during rolling restarts, long-running reads that outlive connection limits.","solutions":["Retry the read at the application level (with a fresh block reader) — DFSClient internally tries other replicas, so surface occurrences usually mean all replicas failed or repeated drops.","Check DataNode health/logs at the failure time (OOM, disk failure, restart).","Increase or remove idle timeouts for the data-transfer ports on firewalls/load balancers.","For writes, enable/verify pipeline recovery and keep dfs.client... retry windows sane."],"exampleFix":null,"handlingStrategy":"retry","validationCode":null,"typeGuard":null,"tryCatchPattern":"try {\n  in = blockReader.read(...);\n} catch (IOException e) {\n  if (e.getMessage().contains(\"Premature EOF\")) {\n    // peer closed mid-packet: rebuild reader against another replica and resume from offset\n    reopenAt(offsetSoFar);\n  } else { throw e; }\n}","preventionTips":["Design readers to be resumable by offset so a dropped connection costs one retry, not a job failure.","Raise firewall/LB idle timeouts for DataNode data ports (default 9866) for long, slow transfers.","Watch DataNode liveness/OOM metrics; nodes that die mid-transfer are the top source of premature EOF."],"tags":["hdfs","data-transfer","connection-reset","eof","network"],"backgroundTag":"connection-closed-remotely","analyzedSha":"2add9630210752f88ceb1bb74eb65e37bf41da8e","analyzedAt":"2026-08-22T19:55:07.957Z","schemaVersion":2},"datasetVersion":"2026-08-22T20:17:22.307Z"}