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Improve the FileSystemObjectSink interface

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More invariants are enforced in the type, and less state needs to be
stored in the main sink itself. The method here is roughly that known as
"session types".

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
This commit is contained in:
John Ericson 2023-12-20 14:47:05 -05:00
parent 966d6fcd01
commit 6365bbfa81
9 changed files with 357 additions and 219 deletions
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61
src/libutil/fs-sink.hh
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@ -9,18 +9,13 @@
namespace nix {
/**
* \todo Fix this API, it sucks.
* Actions on an open regular file in the process of creating it.
*
* See `FileSystemObjectSink::createRegularFile`.
*/
struct FileSystemObjectSink
struct CreateRegularFileSink : Sink
{
virtual void createDirectory(const Path & path) = 0;
virtual void createRegularFile(const Path & path) = 0;
virtual void receiveContents(std::string_view data) = 0;
virtual void isExecutable() = 0;
virtual void closeRegularFile() = 0;
virtual void createSymlink(const Path & path, const std::string & target) = 0;
/**
* An optimization. By default, do nothing.
@ -28,8 +23,24 @@ struct FileSystemObjectSink
virtual void preallocateContents(uint64_t size) { };
};
struct FileSystemObjectSink
{
virtual void createDirectory(const Path & path) = 0;
/**
* This function in general is no re-entrant. Only one file can be
* written at a time.
*/
virtual void createRegularFile(
const Path & path,
std::function<void(CreateRegularFileSink &)>) = 0;
virtual void createSymlink(const Path & path, const std::string & target) = 0;
};
/**
* Recusively copy file system objects from the source into the sink.
* Recursively copy file system objects from the source into the sink.
*/
void copyRecursive(
SourceAccessor & accessor, const CanonPath & sourcePath,
@ -41,11 +52,10 @@ void copyRecursive(
struct NullFileSystemObjectSink : FileSystemObjectSink
{
void createDirectory(const Path & path) override { }
void receiveContents(std::string_view data) override { }
void createSymlink(const Path & path, const std::string & target) override { }
void createRegularFile(const Path & path) override { }
void closeRegularFile() override { }
void isExecutable() override { }
void createRegularFile(
const Path & path,
std::function<void(CreateRegularFileSink &)>) override;
};
/**
@ -57,17 +67,11 @@ struct RestoreSink : FileSystemObjectSink
void createDirectory(const Path & path) override;
void createRegularFile(const Path & path) override;
void receiveContents(std::string_view data) override;
void isExecutable() override;
void closeRegularFile() override;
void createRegularFile(
const Path & path,
std::function<void(CreateRegularFileSink &)>) override;
void createSymlink(const Path & path, const std::string & target) override;
void preallocateContents(uint64_t size) override;
private:
AutoCloseFD fd;
};
/**
@ -87,19 +91,14 @@ struct RegularFileSink : FileSystemObjectSink
regular = false;
}
void receiveContents(std::string_view data) override
{
sink(data);
}
void createSymlink(const Path & path, const std::string & target) override
{
regular = false;
}
void createRegularFile(const Path & path) override { }
void closeRegularFile() override { }
void isExecutable() override { }
void createRegularFile(
const Path & path,
std::function<void(CreateRegularFileSink &)>) override;
};
}