Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (googleapis#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764

Hedging previously covered only the stream open (#16344), so a connection
that stalled mid-download could not be raced. Once an attempt won the open
race, every subsequent Read() was a plain passthrough to that child for the
life of the download.

Make HedgedObjectReadSource stateful: track the stream position (offset,
direction, generation, size, transcoding) the same way RetryObjectReadSource
does when it resumes after a failure, so a hedge can be opened at the
stream's current offset rather than at the original request offset. Time each
read and re-race a read whose predecessor exceeded ReadHedgeDelayOption, with
the active child as the primary attempt. A hedge that wins replaces the
active child; once a read completes within the delay the stream returns to
direct reads.

ChildFactory now takes the position to open at, and
StorageConnectionImpl::ReadObject() applies the same request rewrite
RetryObjectReadSource uses on resume, so hedged and retried reads resume
through identical logic.

Racing is skipped where it cannot be correct or cannot help: under
decompressive transcoding, for reads above MaximumHedgeBufferOption, and once
the stream has reached the end of the requested data.

Also harden the race bookkeeping: resolve the race when every attempt fails,
prefer the primary's error over a hedge's, and fail fast on a permanent
primary error.

No new public options, and no behavior change when hedging is disabled.

TAG=agy
CONV=3c1752ee-1a2a-4f41-b047-1cc070877764