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Merge pull request #42 from karolz-ms/dev/karolz/activitypath
Improve activity path decoding
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src/Microsoft.Diagnostics.EventFlow.Inputs.EventSource/ActivityPathDecoder.cs
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| // ------------------------------------------------------------ | ||
| // Copyright (c) Microsoft Corporation. All rights reserved. | ||
| // Licensed under the MIT License (MIT). See License.txt in the repo root for license information. | ||
| // ------------------------------------------------------------ | ||
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| using System; | ||
| using System.Diagnostics; | ||
| using System.Text; | ||
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| namespace Microsoft.Diagnostics.EventFlow.Inputs | ||
| { | ||
| /// <summary> | ||
| /// A class to decode ETW Activity ID GUIDs into activity paths. | ||
| /// </summary> | ||
| internal static class ActivityPathDecoder | ||
| { | ||
| /// <summary> | ||
| /// The encoding for a list of numbers used to make Activity Guids. Basically | ||
| /// we operate on nibbles (which are nice because they show up as hex digits). The | ||
| /// list is ended with a end nibble (0) and depending on the nibble value (Below) | ||
| /// the value is either encoded into nibble itself or it can spill over into the | ||
| /// bytes that follow. | ||
| /// </summary> | ||
| private enum NumberListCodes : byte | ||
| { | ||
| End = 0x0, // ends the list. No valid value has this prefix. | ||
| LastImmediateValue = 0xA, | ||
| PrefixCode = 0xB, | ||
| MultiByte1 = 0xC, // 1 byte follows. If this Nibble is in the high bits, it the high bits of the number are stored in the low nibble. | ||
| // commented out because the code does not explicitly reference the names (but they are logically defined). | ||
| // MultiByte2 = 0xD, // 2 bytes follow (we don't bother with the nibble optimzation | ||
| // MultiByte3 = 0xE, // 3 bytes follow (we don't bother with the nibble optimzation | ||
| // MultiByte4 = 0xF, // 4 bytes follow (we don't bother with the nibble optimzation | ||
| } | ||
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| /// <summary> | ||
| /// Returns true if 'guid' follow the EventSource style activity ID for the process with ID processID. | ||
| /// You can pass a process ID of 0 to this routine and it will do the best it can, but the possibility | ||
| /// of error is significantly higher (but still under .1%). | ||
| /// </summary> | ||
| public static unsafe bool IsActivityPath(Guid guid, int processID) | ||
| { | ||
| uint* uintPtr = (uint*)&guid; | ||
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| uint sum = uintPtr[0] + uintPtr[1] + uintPtr[2] + 0x599D99AD; | ||
| if (processID == 0) | ||
| { | ||
| // We guess that the process ID is < 16 bits and because it was xored | ||
| // with the lower bits, the upper 16 bits should be independent of the | ||
| // particular process, so we can at least confirm that the upper bits | ||
| // match. | ||
| return (sum & 0xFFFF0000) == (uintPtr[3] & 0xFFFF0000); | ||
| } | ||
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| if ((sum ^ (uint)processID) == uintPtr[3]) | ||
| { | ||
| // This is the new style | ||
| return true; | ||
| } | ||
| return sum == uintPtr[3]; // THis is old style where we don't make the ID unique machine wide. | ||
| } | ||
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| /// <summary> | ||
| /// Returns a string representation for the activity path. If the GUID is not an activity path then it returns | ||
| /// the normal string representation for a GUID. | ||
| /// </summary> | ||
| public static unsafe string GetActivityPathString(Guid guid) | ||
| { | ||
| if (!IsActivityPath(guid, Process.GetCurrentProcess().Id)) | ||
| { | ||
| return guid.ToString(); | ||
| } | ||
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| var processID = ActivityPathProcessID(guid); | ||
| StringBuilder sb = StringBuilderCache.Acquire(); | ||
| if (processID != 0) | ||
| { | ||
| sb.Append("/#"); // Use /# to mark the fact that the first number is a process ID. | ||
| sb.Append(processID); | ||
| } | ||
| else | ||
| { | ||
| sb.Append('/'); // Use // to start to make it easy to anchor | ||
| } | ||
| byte* bytePtr = (byte*)&guid; | ||
| byte* endPtr = bytePtr + 12; | ||
| char separator = '/'; | ||
| while (bytePtr < endPtr) | ||
| { | ||
| uint nibble = (uint)(*bytePtr >> 4); | ||
| bool secondNibble = false; // are we reading the second nibble (low order bits) of the byte. | ||
| NextNibble: | ||
| if (nibble == (uint)NumberListCodes.End) | ||
| { | ||
| break; | ||
| } | ||
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| if (nibble <= (uint)NumberListCodes.LastImmediateValue) | ||
| { | ||
| sb.Append('/').Append(nibble); | ||
| if (!secondNibble) | ||
| { | ||
| nibble = (uint)(*bytePtr & 0xF); | ||
| secondNibble = true; | ||
| goto NextNibble; | ||
| } | ||
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| // We read the second nibble so we move on to the next byte. | ||
| bytePtr++; | ||
| continue; | ||
| } | ||
| else if (nibble == (uint)NumberListCodes.PrefixCode) | ||
| { | ||
| // This are the prefix codes. If the next nibble is MultiByte, then this is an overflow ID. | ||
| // we we denote with a $ instead of a / separator. | ||
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| // Read the next nibble. | ||
| if (!secondNibble) | ||
| { | ||
| nibble = (uint)(*bytePtr & 0xF); | ||
| } | ||
| else | ||
| { | ||
| bytePtr++; | ||
| if (endPtr <= bytePtr) | ||
| { | ||
| break; | ||
| } | ||
| nibble = (uint)(*bytePtr >> 4); | ||
| } | ||
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| if (nibble < (uint)NumberListCodes.MultiByte1) | ||
| { | ||
| // If the nibble is less than MultiByte we have not defined what that means | ||
| // For now we simply give up, and stop parsing. We could add more cases here... | ||
| return guid.ToString(); | ||
| } | ||
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| // If we get here we have a overflow ID, which is just like a normal ID but the separator is $ | ||
| separator = '$'; | ||
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| // Fall into the Multi-byte decode case. | ||
| } | ||
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| Debug.Assert((uint)NumberListCodes.MultiByte1 <= nibble, "Single-byte number should be fully handled by the code above"); | ||
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| // At this point we are decoding a multi-byte number. | ||
| // We are fetching the number as a stream of bytes. | ||
| uint numBytes = nibble - (uint)NumberListCodes.MultiByte1; | ||
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| uint value = 0; | ||
| if (!secondNibble) | ||
| { | ||
| value = (uint)(*bytePtr & 0xF); | ||
| } | ||
| bytePtr++; // Adance to the value bytes | ||
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| numBytes++; // Now numBytes is 1-4 and reprsents the number of bytes to read. | ||
| if (endPtr < bytePtr + numBytes) | ||
| { | ||
| break; | ||
| } | ||
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| // Compute the number (little endian) (thus backwards). | ||
| for (int i = (int)numBytes - 1; i >= 0; --i) | ||
| { | ||
| value = (value << 8) + bytePtr[i]; | ||
| } | ||
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| // Print the value | ||
| sb.Append(separator).Append(value); | ||
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| bytePtr += numBytes; // Advance past the bytes. | ||
| } | ||
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| sb.Append('/'); | ||
| return StringBuilderCache.GetStringAndRelease(sb); | ||
| } | ||
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| /// <summary> | ||
| /// Assuming guid is an Activity Path, extract the process ID from it. | ||
| /// </summary> | ||
| private static unsafe int ActivityPathProcessID(Guid guid) | ||
| { | ||
| uint* uintPtr = (uint*)&guid; | ||
| uint sum = uintPtr[0] + uintPtr[1] + uintPtr[2] + 0x599D99AD; | ||
| return (int)(sum ^ uintPtr[3]); | ||
| } | ||
| } | ||
| } |
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