Class ObjectReadStream (2.32.0-rc)

Attempts to use this stream will result in failures.

When downloading an object a limited amount of information about the object's metadata is returned as part of the download.

Some of this information is important for applications performing multiple downloads (maybe of different ranges) of the same object. Such applications may want to use the generation number to guarantee all the downloads are actually referencing the same object. One could do this by first querying the metadata before the first download, but this is less efficient as it requires one additional server round trip.

Note that all these attributes are absl::optional<>, as the attributes may not be known (or exist) if there is an error during the download. If the attribute is needed for the application's correctness the application should fetch the object metadata when the attribute is not available.

When downloading an object a limited amount of information about the object's metadata is returned as part of the download.

Some of this information is important for applications performing multiple downloads (maybe of different ranges) of the same object. Such applications may want to use the generation number to guarantee all the downloads are actually referencing the same object. One could do this by first querying the metadata before the first download, but this is less efficient as it requires one additional server round trip.

Note that all these attributes are absl::optional<>, as the attributes may not be known (or exist) if there is an error during the download. If the attribute is needed for the application's correctness the application should fetch the object metadata when the attribute is not available.

When downloading an object a limited amount of information about the object's metadata is returned as part of the download.

Some of this information is important for applications performing multiple downloads (maybe of different ranges) of the same object. Such applications may want to use the generation number to guarantee all the downloads are actually referencing the same object. One could do this by first querying the metadata before the first download, but this is less efficient as it requires one additional server round trip.

Note that all these attributes are absl::optional<>, as the attributes may not be known (or exist) if there is an error during the download. If the attribute is needed for the application's correctness the application should fetch the object metadata when the attribute is not available.

If you are using object transcoding this represents the stored size of the object, the number of downloaded bytes (after decompression) may be larger.

Note that errors may go undetected until the download completes.

When the download is finalized (via Close() or the end of file) the GCS server reports the CRC32C checksum and, except for composite objects, the MD5 hash of the data. This class compares the locally computed and received hashes so applications can detect data download errors.

The values are reported as comma separated tag=value pairs, e.g. crc32c=AAAAAA==,md5=1B2M2Y8AsgTpgAmY7PhCfg==. The format of this string is subject to change without notice, they are provided for informational purposes only.

See Also

https://cloud.google.com/storage/docs/hashes-etags for more information on checksums and hashes in GCS.

This object computes the CRC32C checksum and MD5 hash of the downloaded data. Note that there are several cases where these values may be empty or irrelevant, for example:

• When reading only a portion of a blob the hash of that portion is irrelevant, note that GCS only reports the hashes for the full blob.
• The application may disable the CRC32C and/or the MD5 hash computation.

The string has the same format as the value returned by received_hash(). Note that the format of this string is also subject to change without notice.

See Also

https://cloud.google.com/storage/docs/hashes-etags for more information on checksums and hashes in GCS.

For debugging only.