Add manifest_rewriter class

1 files changed, 144 insertions, 0 deletions

diff --git a/libbutl/manifest-rewriter.cxx b/libbutl/manifest-rewriter.cxx
new file mode 100644
index 0000000..1e1c3d5
--- /dev/null
+++ b/libbutl/manifest-rewriter.cxx
@@ -0,0 +1,144 @@
+// file      : libbutl/manifest-rewriter.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2018 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef __cpp_modules
+#include <libbutl/manifest-rewriter.mxx>
+#endif
+
+#include <cassert>
+
+// C includes.
+
+#ifndef __cpp_lib_modules
+#include <string>
+#include <cstdint> // uint64_t
+#endif
+
+// Other includes.
+
+#ifdef __cpp_modules
+module butl.manifest_rewriter;
+
+// Only imports additional to interface.
+#ifdef __clang__
+#ifdef __cpp_lib_modules
+import std.core;
+#endif
+import butl.path;
+import butl.fdstream;
+import butl.manifest_types;
+#endif
+
+import butl.manifest_serializer;
+#else
+#include <libbutl/manifest-serializer.mxx>
+#endif
+
+using namespace std;
+
+namespace butl
+{
+  manifest_rewriter::
+  manifest_rewriter (path p)
+      : path_ (move (p)),
+        fd_ (fdopen (path_,
+                     fdopen_mode::in  |
+                     fdopen_mode::out |
+                     fdopen_mode::exclusive))
+  {
+  }
+
+  // Seek the file descriptor to the specified logical position and truncate
+  // the file. Return the file suffix (cached prior to truncating) starting
+  // from the specified position.
+  //
+  static string
+  truncate (auto_fd& fd, uint64_t pos, uint64_t suffix_pos)
+  {
+    string r;
+    {
+      // Temporary move the descriptor into the stream.
+      //
+      ifdstream is (move (fd));
+      fdbuf& buf (static_cast<fdbuf&> (*is.rdbuf ()));
+
+      // Read suffix.
+      //
+      buf.seekg (suffix_pos);
+      r = is.read_text ();
+
+      // Seek to the specified position and move the file descriptor back.
+      //
+      buf.seekg (pos);
+      fd = is.release ();
+    }
+
+    // Truncate the file starting from the current position. Note that we need
+    // to use the physical position rather than logical.
+    //
+    fdtruncate (fd.get (), fdseek (fd.get (), 0, fdseek_mode::cur));
+    return r;
+  }
+
+  void manifest_rewriter::
+  replace (const manifest_name_value& nv)
+  {
+    assert (nv.colon_pos != 0); // Sanity check.
+
+    // Truncate right after the value colon.
+    //
+    string suffix (truncate (fd_, nv.colon_pos + 1, nv.end_pos));
+
+    // Temporary move the descriptor into the stream.
+    //
+    ofdstream os (move (fd_));
+
+    if (!nv.value.empty ())
+    {
+      os << ' ';
+
+      manifest_serializer s (os, path_.string ());
+      s.write_value (nv.value, nv.colon_pos - nv.start_pos + 2);
+    }
+
+    os << suffix;
+
+    // Move the file descriptor back.
+    //
+    fd_ = os.release (); // Note: flushes the buffer.
+  }
+
+  void manifest_rewriter::
+  insert (const manifest_name_value& pos, const manifest_name_value& nv)
+  {
+    assert (pos.end_pos != 0); // Sanity check.
+
+    // We could have just started writing over the suffix but the truncation
+    // doesn't hurt.
+    //
+    string suffix (truncate (fd_, pos.end_pos, pos.end_pos));
+
+    // Temporary move the descriptor into the stream.
+    //
+    ofdstream os (move (fd_));
+    os << '\n';
+
+    manifest_serializer s (os, path_.string ());
+    s.write_name (nv.name);
+
+    os << ':';
+
+    if (!nv.value.empty ())
+    {
+      os << ' ';
+      s.write_value (nv.value, nv.colon_pos - nv.start_pos + 2);
+    }
+
+    os << suffix;
+
+    // Move the file descriptor back.
+    //
+    fd_ = os.release (); // Note: flushes the buffer.
+  }
+}