Add manifest_rewriter class

1 files changed, 75 insertions, 0 deletions

diff --git a/libbutl/manifest-rewriter.mxx b/libbutl/manifest-rewriter.mxx
new file mode 100644
index 0000000..3261ef2
--- /dev/null
+++ b/libbutl/manifest-rewriter.mxx
@@ -0,0 +1,75 @@
+// file      : libbutl/manifest-rewriter.mxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2018 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef __cpp_modules
+#pragma once
+#endif
+
+// C includes.
+
+#ifndef __cpp_lib_modules
+#endif
+
+// Other includes.
+
+#ifdef __cpp_modules
+export module butl.manifest_rewriter;
+#ifdef __cpp_lib_modules
+#endif
+import butl.path;
+import butl.fdstream;
+import butl.manifest_types;
+#else
+#include <libbutl/path.mxx>
+#include <libbutl/fdstream.mxx>
+#include <libbutl/manifest-types.mxx>
+#endif
+
+#include <libbutl/export.hxx>
+
+LIBBUTL_MODEXPORT namespace butl
+{
+  // Rewrite a hand-written manifest file preserving formatting, comments,
+  // etc., of the unaffected parts. The general workflow is as follows:
+  //
+  // 1. Parse the manifest file using manifest_parser into a sequence of
+  //    name/value pairs and their positions.
+  //
+  // 2. Create an instance of manifest_rewriter for the manifest file. This
+  //    opens the file in read/write mode with exclusive access.
+  //
+  // 3. Iterate over this sequence in reverse and apply changes to the desired
+  //    name/value pairs using the below API. Doing this in reverse makes sure
+  //    the positions obtained on step 1 remain valid.
+  //
+  // Note that if an exception is thrown by replace() or insert(), then the
+  // writer is no longer usable and there is no guarantees that the file is
+  // left in a consistent state.
+  //
+  class LIBBUTL_SYMEXPORT manifest_rewriter
+  {
+  public:
+    manifest_rewriter (path);
+
+    // Replace the existing value at the specified position (specifically,
+    // between colon_pos and end_pos) with the specified new value. The new
+    // value is serialized as if by manifest_serializer.
+    //
+    void
+    replace (const manifest_name_value&);
+
+    // Insert a new name/value after the specified position (specifically,
+    // after end_pos). To insert before the first value, use the special
+    // start-of-manifest value as position. The new name/value is serialized
+    // as if by manifest_serializer. Throw manifest_serialization exception
+    // on error.
+    //
+    void
+    insert (const manifest_name_value& pos, const manifest_name_value&);
+
+  private:
+    path path_;
+    auto_fd fd_;
+  };
+}