This release includes quite a number of critical bug fixes and
performance/reliability enhancements.
#### Error when adding multiple files
The last release broke the simple command `ipfs add file1 file2`. It turns out
we simply lacked a test case for this. Both of these issues (the bug and the
lack of a test case) have now been fixed.
#### SECIO
As noted above, we've fixed a bug that could cause data to be dropped from a
SECIO connection on read. Specifically, this happens when:
1. The capacity of the read buffer is greater than the length.
2. The remote peer sent more than the length but less than the capacity in a
single secio "frame".
In this case, we'd fill the read buffer to it's capacity instead of its length.
#### Too many open files, too many peers, etc.
Go-ipfs automatically closes the least useful connections when it accumulates
too many connections. Unfortunately, some relayed connections were blocking in
`Close()`, halting the entire process.
#### Out of control CPU usage
Many users noted out of control CPU usage this release. This turned out to be a
long-standing issue with how the DHT handled provider records (records recording
which peers have what content):
1. It wasn't removing provider records for content until the set of providers
completely emptied.
2. It was loading every provider record into memory whenever we updated the set
of providers.
Combined, these two issues were trashing the provider record cache, forcing the
DHT to repeatedly load and discard provider records.
#### Improved Connection Management
Go-ipfs uses a service called the "connection manager" to rank connections them
by "usefulness" and close the least-useful ones when go-ipfs collects too many.
TODO: Fixed race condition between handling new connections and tagging them.
#### Improved Bitswap Connection Management
Bitswap now uses the connection manager to mark all peers downloading blocks as
important (while downloading). Previously, it only marked peers from which _it_
was downloading blocks.
#### Reduced Memory Usage
The most noticeable memory reduction in this release comes from fixing connection
closing. However, we've made a few additional improvements:
* Bitswap's "work queue" no longer remembers every peer it has seen
indefinitely.
* The peerstore now interns protocol names.
* The per-peer goroutine count has been reduced.
* The DHT now wastes less memory on idle peers by pooling buffered writers and
returning them to the pool when not actively using them.
#### Improved Address Freshness
TODO: Push new addresses when they change.
#### Increased File Descriptor Limit
The default file descriptor limit has been raised to 8192 (from 2048).
Unfortunately, go-ipfs behaves poorly when it runs out of file descriptors and
it uses a _lot_ of file descriptors.
Luckily, most modern kernels can handle thousands of file descriptors without
any difficulty.
### Commands
#### Fixed: `ipfs add` with multiple files
This release brings no new commands but does introduce a few changes, bugfixes,
and enhancements. This section is hardly complete but it lists the most
noticeable changes.
In version 0.4.20 a bug was introduced preventing `ipfs add fileA fileB` from working.
This was fixed in ([ipfs/go-ipfs#6255](https://github.com/ipfs/go-ipfs/pull/6255)).
Take note: this release also introduces a few breaking changes.
### New: TLS 1.3 handshake
#### [DEPRECATION] The URLStore Command Deprecated
Go-libp2p has gained ability to use TLS 1.3 for connection encryption and authentication.
Go-ipfs will accept TLS 1.3 handshakes but will still primarily use secio.
If you want to help testing the new handshake, you can enable [this experiment](https://github.com/ipfs/go-ipfs/blob/master/docs/experimental-features.md#tls-13-as-default-handshake-protocol).
The experimental `ipfs urlstore` command is now deprecated. Please use `ipfs add
--nocopy URL` instead.
### New: Build system `GOCC` variable
#### [BREAKING] The DHT Command Base64 Encodes Values
Build system now uses `GOCC` environment variable allowing for use of multiple
go versions during builds.
When responding to an `ipfs dht get` command, the daemon now encodes the
returned value using base64. The `ipfs` command will automatically decode this
value before returning it to the user so this change should only affect those
using the HTTP API directly.
Unfortunately, this change was necessary as DHT records are arbitrary binary
blobs which can't be directly stored in JSON strings.
#### [BREAKING] Base32 Encoded v1 CIDs By Default
Both js-ipfs and go-ipfs now encode CIDv1 CIDs using base32 by default, instead
of base58. Unfortunately, base58 is case-sensitive and doesn't play well with
browsers (see [#4143](https://github.com/ipfs/go-ipfs/issues/4143).
#### Human Readable Numbers
The `ipfs bitswap stat` and and `ipfs object stat` commands now support a
`--humanize` flag that formats numbers with human-readable units (GiB, MiB,
etc.).
#### Improved Errors
This release improves to types of errors:
1. Commands that take paths/multiaddrs now include the path/multiaddr in the
error message when it fails to parse.
2.`ipfs swarm connect` now returns a detailed error describing which addresses
were tried and why the dial failed.
#### Ping Improvements
The ping command has received some small improvements and fixes:
1. It now exits with a non-zero exit status on failure.
2. It no longer succeeds with zero successful pings if we have a zombie but
non-functional connection to the peer being pinged
