cmFilePathUuid: Add class to generate deterministic unique file names

The class generates a semi-unique (checksum based) pathless file name
from a full source file path.

3 files changed, 211 insertions, 0 deletions

diff --git a/Source/CMakeLists.txt b/Source/CMakeLists.txt
index a790994..cdc8fb1 100644
--- a/Source/CMakeLists.txt
+++ b/Source/CMakeLists.txt
@@ -238,6 +238,8 @@ set(SRCS
   cmFileLockPool.h
   cmFileLockResult.cxx
   cmFileLockResult.h
+  cmFilePathUuid.cxx
+  cmFilePathUuid.h
   cmFileTimeComparison.cxx
   cmFileTimeComparison.h
   cmFortranLexer.cxx
diff --git a/Source/cmFilePathUuid.cxx b/Source/cmFilePathUuid.cxx
new file mode 100644
index 0000000..2839b63
--- /dev/null
+++ b/Source/cmFilePathUuid.cxx
@@ -0,0 +1,132 @@
+/*============================================================================
+  CMake - Cross Platform Makefile Generator
+  Copyright 2016 Sebastian Holtermann (sebholt@xwmw.org)
+
+  Distributed under the OSI-approved BSD License (the "License");
+  see accompanying file Copyright.txt for details.
+
+  This software is distributed WITHOUT ANY WARRANTY; without even the
+  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the License for more information.
+============================================================================*/
+
+#include "cmFilePathUuid.h"
+
+#include "cmCryptoHash.h"
+#include "cmMakefile.h"
+#include "cmSystemTools.h"
+#include "cmsys/Base64.h"
+
+cmFilePathUuid::cmFilePathUuid(cmMakefile* makefile)
+{
+  initParentDirs(makefile->GetCurrentSourceDirectory(),
+                 makefile->GetCurrentBinaryDirectory(),
+                 makefile->GetHomeDirectory(),
+                 makefile->GetHomeOutputDirectory());
+}
+
+cmFilePathUuid::cmFilePathUuid(const std::string& currentSrcDir,
+                               const std::string& currentBinDir,
+                               const std::string& projectSrcDir,
+                               const std::string& projectBinDir)
+{
+  initParentDirs(currentSrcDir, currentBinDir, projectSrcDir, projectBinDir);
+}
+
+void cmFilePathUuid::initParentDirs(const std::string& currentSrcDir,
+                                    const std::string& currentBinDir,
+                                    const std::string& projectSrcDir,
+                                    const std::string& projectBinDir)
+{
+  parentDirs[0].first = cmsys::SystemTools::GetRealPath(currentSrcDir);
+  parentDirs[1].first = cmsys::SystemTools::GetRealPath(currentBinDir);
+  parentDirs[2].first = cmsys::SystemTools::GetRealPath(projectSrcDir);
+  parentDirs[3].first = cmsys::SystemTools::GetRealPath(projectBinDir);
+
+  parentDirs[0].second = "CurrentSource";
+  parentDirs[1].second = "CurrentBinary";
+  parentDirs[2].second = "ProjectSource";
+  parentDirs[3].second = "ProjectBinary";
+}
+
+std::string cmFilePathUuid::get(const std::string& filePath,
+                                const char* outputPrefix,
+                                const char* outputSuffix)
+{
+  std::string sourceFilename = cmsys::SystemTools::GetFilenameName(filePath);
+  std::string sourceBasename =
+    cmsys::SystemTools::GetFilenameWithoutLastExtension(sourceFilename);
+
+  // Acquire checksum string
+  std::string checksum;
+  {
+    std::string sourceRelPath;
+    std::string sourceRelSeed;
+    GetRelPathSeed(filePath, sourceRelPath, sourceRelSeed);
+    checksum = GetChecksumString(sourceFilename, sourceRelPath, sourceRelSeed);
+  }
+
+  // Compose the file name
+  std::string uuid;
+  if (outputPrefix) {
+    uuid += outputPrefix;
+  }
+  uuid += sourceBasename.substr(0, partLengthName);
+  uuid += "_";
+  uuid += checksum.substr(0, partLengthCheckSum);
+  if (outputSuffix) {
+    uuid += outputSuffix;
+  }
+  return uuid;
+}
+
+void cmFilePathUuid::GetRelPathSeed(const std::string& filePath,
+                                    std::string& sourceRelPath,
+                                    std::string& sourceRelSeed)
+{
+  const std::string sourceNameReal = cmsys::SystemTools::GetRealPath(filePath);
+  std::string parentDirectory;
+  // Find closest project parent directory
+  for (size_t ii = 0; ii != numParentDirs; ++ii) {
+    const std::string& pDir = parentDirs[ii].first;
+    if (!pDir.empty() &&
+        cmsys::SystemTools::IsSubDirectory(sourceNameReal, pDir)) {
+      sourceRelSeed = parentDirs[ii].second;
+      parentDirectory = pDir;
+      break;
+    }
+  }
+  // Check if the file path is below a known project directory
+  if (parentDirectory.empty()) {
+    // Use file syste root as fallback parent directory
+    sourceRelSeed = "FileSystemRoot";
+    cmsys::SystemTools::SplitPathRootComponent(sourceNameReal,
+                                               &parentDirectory);
+  }
+  sourceRelPath = cmsys::SystemTools::RelativePath(
+    parentDirectory, cmsys::SystemTools::GetParentDirectory(sourceNameReal));
+}
+
+std::string cmFilePathUuid::GetChecksumString(
+  const std::string& sourceFilename, const std::string& sourceRelPath,
+  const std::string& sourceRelSeed)
+{
+  std::string checksumBase64;
+  {
+    // Calculate the file ( seed + relative path + name ) checksum
+    std::vector<unsigned char> hashBytes =
+      cmCryptoHash::New("SHA256")->ByteHashString(
+        (sourceRelSeed + sourceRelPath + sourceFilename).c_str());
+    // Convert hash bytes to Base64 text string
+    std::vector<unsigned char> base64Bytes(hashBytes.size() * 2, 0);
+    cmsysBase64_Encode(&hashBytes[0], hashBytes.size(), &base64Bytes[0], 0);
+    checksumBase64 = reinterpret_cast<const char*>(&base64Bytes[0]);
+  }
+  // Base64 allows '/', '+' and '=' characters which are problematic
+  // when used in file names. Replace them with safer alternatives.
+  std::replace(checksumBase64.begin(), checksumBase64.end(), '/', '-');
+  std::replace(checksumBase64.begin(), checksumBase64.end(), '+', '_');
+  std::replace(checksumBase64.begin(), checksumBase64.end(), '=', '_');
+
+  return checksumBase64;
+}
diff --git a/Source/cmFilePathUuid.h b/Source/cmFilePathUuid.h
new file mode 100644
index 0000000..42e89b1
--- /dev/null
+++ b/Source/cmFilePathUuid.h
@@ -0,0 +1,77 @@
+/*============================================================================
+  CMake - Cross Platform Makefile Generator
+  Copyright 2016 Sebastian Holtermann (sebholt@xwmw.org)
+
+  Distributed under the OSI-approved BSD License (the "License");
+  see accompanying file Copyright.txt for details.
+
+  This software is distributed WITHOUT ANY WARRANTY; without even the
+  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the License for more information.
+============================================================================*/
+
+#ifndef cmFilePathUuid_h
+#define cmFilePathUuid_h
+
+#include "cmStandardIncludes.h"
+
+#include <string>
+#include <utility>
+
+class cmMakefile;
+
+/** \class cmFilePathUuid
+ * @brief Generates a unique pathless file name with a checksum component
+ *        calculated from the file path.
+ *
+ * The checksum is calculated from the relative file path to the
+ * closest known project directory. This guarantees reproducibility
+ * when source and build directory differ e.g. for different project
+ * build directories.
+ */
+class cmFilePathUuid
+{
+public:
+  /// Maximum number of characters to use from the file name
+  static const size_t partLengthName = 14;
+  /// Maximum number of characters to use from the path checksum
+  static const size_t partLengthCheckSum = 14;
+
+  /// @brief Initilizes the parent directories from a makefile
+  cmFilePathUuid(cmMakefile* makefile);
+
+  /// @brief Initilizes the parent directories manually
+  cmFilePathUuid(const std::string& currentSrcDir,
+                 const std::string& currentBinDir,
+                 const std::string& projectSrcDir,
+                 const std::string& projectBinDir);
+
+  /* @brief Calculates and returns the uuid for a file path
+   *
+   * @arg outputPrefix optional string to prepend to the result
+   * @arg outputSuffix optional string to append to the result
+   */
+  std::string get(const std::string& filePath, const char* outputPrefix = NULL,
+                  const char* outputSuffix = NULL);
+
+private:
+  void initParentDirs(const std::string& currentSrcDir,
+                      const std::string& currentBinDir,
+                      const std::string& projectSrcDir,
+                      const std::string& projectBinDir);
+
+  /// Returns the relative path and the parent directory key string (seed)
+  void GetRelPathSeed(const std::string& filePath, std::string& sourceRelPath,
+                      std::string& sourceRelSeed);
+
+  std::string GetChecksumString(const std::string& sourceFilename,
+                                const std::string& sourceRelPath,
+                                const std::string& sourceRelSeed);
+
+  /// Size of the parent directory list
+  static const size_t numParentDirs = 4;
+  /// List of (directory name, seed name) pairs
+  std::pair<std::string, std::string> parentDirs[numParentDirs];
+};
+
+#endif