vrs::FileDetailsCache Namespace Reference

Helper methods to read & write file details in a cache file. More...

Functions
int	write (const string &cacheFile, const set< StreamId > &streamIds, const map< string, string > &fileTags, const map< StreamId, StreamTags > &streamTags, const vector< IndexRecord::RecordInfo > &recordIndex, bool fileHasIndex)
int	read (const string &cacheFile, set< StreamId > &outStreamIds, map< string, string > &outFileTags, map< StreamId, StreamTags > &outStreamTags, vector< IndexRecord::RecordInfo > &outRecordIndex, bool &outFileHasIndex)

Detailed Description

Helper methods to read & write file details in a cache file.

File Format:

FileHeader: same struct as a regular VRS file, but with different magic numbers. descriptionRecordOffset: offset of the description record (same as for a VRS file). indexRecordOffset: offset of the index data, in its special case format. firstUserRecordOffset: offset past the index data, effectively the end of the file.

Description record: same as for a regular VRS file.

Index data: custom for this use case, stream IDs and the index itself. uint32_t recordableCount: count of StreamId structs, always present, value may be 0. DiskStreamId streamId[recordableCount]: one per stream ID instance uint32_t recordCount: count of DiskRecordInfo structs, always present, value may be 0. DiskRecordInfo recordInfo[recordCount]; // one per actual record, zstd-frames compressed.

The file header's "future4" is used to save some flags, which may not have been set in the past:

• bit 0, when set, means the original VRS file is known to NOT have an index.

Function Documentation

read()

int vrs::FileDetailsCache::read	(	const string &	cacheFile,
		set< StreamId > &	outStreamIds,
		map< string, string > &	outFileTags,
		map< StreamId, StreamTags > &	outStreamTags,
		vector< IndexRecord::RecordInfo > &	outRecordIndex,
		bool &	outFileHasIndex
	)

Read a VRS details file cache from a disk location.

Parameters

cacheFile	path to the cache file to read.
outStreamIds	stream Ids read.
outFileTags	file tags read.
outStreamTags	stream tags read.
outRecordIndex	VRS file index read.
outFileHasIndex	does the original VRS file have a proper index.

Returns

A status code, 0 for success.

write()

int vrs::FileDetailsCache::write	(	const string &	cacheFile,
		const set< StreamId > &	streamIds,
		const map< string, string > &	fileTags,
		const map< StreamId, StreamTags > &	streamTags,
		const vector< IndexRecord::RecordInfo > &	recordIndex,
		bool	fileHasIndex
	)

Create a VRS details file cache at a disk location, in one synchronous operation.

Parameters

cacheFile	path to the cache file to write.
streamIds	stream IDs to save.
fileTags	file tags to save.
streamTags	stream tags to save.
recordIndex	VRS file index to save.
fileHasIndex	does the original VRS file have a proper index.

Returns

A status code, 0 for success.