{"record":{"id":"84f9a765a9f80660","repo":"jstedfast/MailKit","slug":"error-deflating","errorCode":null,"errorMessage":"Error deflating: ","messagePattern":"Error deflating: ","errorType":"exception","errorClass":"IOException","httpStatus":null,"severity":"error","filePath":"MailKit/CompressedStream.cs","lineNumber":325,"sourceCode":"\t\tpublic override void Write (byte[] buffer, int offset, int count)\n\t\t{\n\t\t\tCheckDisposed ();\n\n\t\t\tValidateArguments (buffer, offset, count);\n\n\t\t\tif (count == 0)\n\t\t\t\treturn;\n\n\t\t\tzOut.next_in = buffer;\n\t\t\tzOut.next_in_index = offset;\n\t\t\tzOut.avail_in = count;\n\n\t\t\tdo {\n\t\t\t\tzOut.avail_out = zOut.next_out.Length;\n\t\t\t\tzOut.next_out_index = 0;\n\n\t\t\t\tif (zOut.deflate (JZlib.Z_FULL_FLUSH) != JZlib.Z_OK)\n\t\t\t\t\tthrow new IOException (\"Error deflating: \" + zOut.msg);\n\n\t\t\t\tInnerStream.Write (zOut.next_out, 0, zOut.next_out.Length - zOut.avail_out);\n\t\t\t} while (zOut.avail_in > 0 || zOut.avail_out == 0);\n\t\t}\n\n\t\t/// <summary>\n\t\t/// Writes a sequence of bytes to the stream and advances the current\n\t\t/// position within this stream by the number of bytes written.\n\t\t/// </summary>\n\t\t/// <returns>A task that represents the asynchronous write operation.</returns>\n\t\t/// <param name=\"buffer\">The buffer to write.</param>\n\t\t/// <param name=\"offset\">The offset of the first byte to write.</param>\n\t\t/// <param name=\"count\">The number of bytes to write.</param>\n\t\t/// <param name=\"cancellationToken\">The cancellation token.</param>\n\t\t/// <exception cref=\"System.ArgumentNullException\">\n\t\t/// <paramref name=\"buffer\"/> is <see langword=\"null\" />.\n\t\t/// </exception>\n\t\t/// <exception cref=\"System.ArgumentOutOfRangeException\">","sourceCodeStart":307,"sourceCodeEnd":343,"githubUrl":"https://github.com/jstedfast/MailKit/blob/9d3859a7855e3e17582c07fd01972b8e262bf176/MailKit/CompressedStream.cs#L307-L343","documentation":"Write() throws IOException(\"Error deflating: \" + zOut.msg) when JZlib's deflate(Z_FULL_FLUSH) returns a status other than Z_OK. This means zlib itself rejected the compression step, typically due to exhausted/inconsistent internal state rather than bad input bytes.","triggerScenarios":"Calling CompressedStream.Write after the stream or zlib state is invalid (e.g. writing after disposal mid-state, corrupted zOut state, zlib-level failure such as Z_STREAM_ERROR from bad parameters).","commonSituations":"Concurrent unsynchronized writes corrupting the zlib state, writing to a stream whose underlying transport already failed mid-flush, resource exhaustion inside the deflate window.","solutions":["Check zOut.msg in the exception message for the specific zlib error code/cause.","Discard the stream and create a new CompressedStream; a failed deflate state is not recoverable.","Ensure all writes are single-threaded or serialized - concurrent Write calls corrupt the zlib state machine.","Verify the underlying stream is writable and healthy before writing."],"exampleFix":"// before\nstream.Write(data, 0, data.Length); // IOException: Error deflating\n// after\ntry {\n    stream.Write(data, 0, data.Length);\n} catch (IOException ex) when (ex.Message.Contains(\"Error deflating\")) {\n    stream.Dispose();\n    stream = new CompressedStream(innerStream); // fresh deflate state\n}","handlingStrategy":"try-catch","validationCode":"if (!stream.CanWrite)\n    throw new InvalidOperationException(\"Cannot write: inner stream is not writable.\");\n// and ensure writes are serialized (no concurrent callers)","typeGuard":"static bool IsSafeToWrite(CompressedStream s, object writeLock) =>\n    s.CanWrite && !Monitor.IsEntered(writeLock) == false; // inside the lock => safe","tryCatchPattern":"try {\n    stream.Write(data, 0, data.Length);\n} catch (IOException ex) when (ex.Message.Contains(\"Error deflating\")) {\n    stream.Dispose();\n    stream = new CompressedStream(innerStream); // recreate; state is unrecoverable\n}","preventionTips":["Guard all writes with a lock or SemaphoreSlim - concurrent writes corrupt zlib state","Treat any deflate failure as fatal to the stream; do not retry on the same instance","Check CanWrite before the first write","Keep deflate window-bits settings consistent with the peer's inflate settings","Flush explicitly and handle IO errors on the inner stream promptly"],"tags":["io","zlib","compression","write"],"backgroundTag":"zlib-deflate-failed","analyzedSha":"9d3859a7855e3e17582c07fd01972b8e262bf176","analyzedAt":"2026-09-15T15:46:11.592Z","contentChangedAt":"2026-09-15T15:46:11.592Z","schemaVersion":2},"datasetVersion":"2026-09-16T04:17:20.429Z"}