blob: 49fbabdc3f4d6b6a4796878e1223e88c54f26191 [file] [log] [blame]
"Title": "Go 1.17 Release Notes",
"Path": "/doc/go1.17"
NOTE: In this document and others in this directory, the convention is to
set fixed-width phrases with non-fixed-width spaces, as in
<code>hello</code> <code>world</code>.
Do not send CLs removing the interior tags from such phrases.
main ul li { margin: 0.5em 0; }
<h2 id="introduction">DRAFT RELEASE NOTES — Introduction to Go 1.17</h2>
Go 1.17 is not yet released. These are work-in-progress
release notes. Go 1.17 is expected to be released in August 2021.
<h2 id="language">Changes to the language</h2>
Go 1.17 includes three small enhancements to the language.
<li><!-- CL 216424; issue 395 -->
<a href="/ref/spec#Conversions_from_slice_to_array_pointer">Conversions
from slice to array pointer</a>: An expression <code>s</code> of
type <code>[]T</code> may now be converted to array pointer type
<code>*[N]T</code>. If <code>a</code> is the result of such a
conversion, then corresponding indices that are in range refer to
the same underlying elements: <code>&amp;a[i] == &amp;s[i]</code>
for <code>0 &lt;= i &lt; N</code>. The conversion panics if
<code>len(s)</code> is less than <code>N</code>.
<li><!-- CL 312212; issue 40481 -->
<a href="/pkg/unsafe#Add"><code>unsafe.Add</code></a>:
<code>unsafe.Add(ptr, len)</code> adds <code>len</code>
to <code>ptr</code> and returns the updated pointer
<code>unsafe.Pointer(uintptr(ptr) + uintptr(len))</code>.
<li><!-- CL 312212; issue 19367 -->
<a href="/pkg/unsafe#Slice"><code>unsafe.Slice</code></a>:
For expression <code>ptr</code> of type <code>*T</code>,
<code>unsafe.Slice(ptr, len)</code> returns a slice of
type <code>[]T</code> whose underlying array starts
at <code>ptr</code> and whose length and capacity
are <code>len</code>.
These enhancements were added to simplify writing code that conforms
to <code>unsafe.Pointer</code>'s <a href="/pkg/unsafe/#Pointer">safety
rules</a>, but the rules remain unchanged. In particular, existing
programs that correctly use <code>unsafe.Pointer</code> remain
valid, and new programs must still follow the rules when
using <code>unsafe.Add</code> or <code>unsafe.Slice</code>.
Note that the new conversion from slice to array pointer is the
first case in which a type conversion can panic at run time.
Analysis tools that assume type conversions can never panic
should be updated to consider this possibility.
<h2 id="ports">Ports</h2>
<h3 id="darwin">Darwin</h3>
<p><!-- -->
As <a href="go1.16#darwin">announced</a> in the Go 1.16 release
notes, Go 1.17 requires macOS 10.13 High Sierra or later; support
for previous versions has been discontinued.
<h3 id="windows">Windows</h3>
<p><!-- -->
Go 1.17 adds support of 64-bit ARM architecture on Windows (the
<code>windows/arm64</code> port). This port supports cgo.
<h3 id="openbsd">OpenBSD</h3>
<p><!-- -->
The 64-bit MIPS architecture on OpenBSD (the <code>openbsd/mips64</code>
port) now supports cgo.
<p><!-- -->
In Go 1.16, on the 64-bit x86 and 64-bit ARM architectures on
OpenBSD (the <code>openbsd/amd64</code> and <code>openbsd/arm64</code>
ports) system calls are made through <code>libc</code>, instead
of directly using machine instructions. In Go 1.17, this is also
done on the 32-bit x86 and 32-bit ARM architectures on OpenBSD
(the <code>openbsd/386</code> and <code>openbsd/arm</code> ports).
This ensures forward-compatibility with future versions of
OpenBSD, in particular, with OpenBSD 6.9 onwards, which requires
system calls to be made through <code>libc</code> for non-static
Go binaries.
<h3 id="arm64">ARM64</h3>
<p><!-- CL 288814 -->
Go programs now maintain stack frame pointers on the 64-bit ARM
architecture on all operating systems. Previously it maintained
stack frame pointers only on Linux, macOS, and iOS.
<h2 id="tools">Tools</h2>
<h3 id="go-command">Go command</h3>
<h4 id="lazy-loading">Lazy module loading</h4>
<p><!-- -->
If a module specifies <code>go</code> <code>1.17</code> or higher in its
<code>go.mod</code> file, its transitive requirements are now loaded lazily,
avoiding the need to download or read <code>go.mod</code> files for
otherwise-irrelevant dependencies. To support lazy loading, in Go 1.17 modules
the <code>go</code> command maintains <em>explicit</em> requirements in
the <code>go.mod</code> file for every dependency that provides any package
transitively imported by any package or test within the module.
See <a href="">the design
document</a> for more detail.
<!-- TODO(bcmills): replace the design-doc link with proper documentation. -->
<p><!-- -->
Because the number of additional explicit requirements in the go.mod file may
be substantial, in a Go 1.17 module the newly-added requirements
on <em>indirect</em> dependencies are maintained in a
separate <code>require</code> block from the block containing direct
<p><!-- -->
To facilitate the upgrade to lazy loading, the
<code>go</code> <code>mod</code> <code>tidy</code> subcommand now supports
a <code>-go</code> flag to set or change the <code>go</code> version in
the <code>go.mod</code> file. To enable lazy loading for an existing module
without changing the selected versions of its dependencies, run:
go mod tidy -go=1.17
<p><!-- -->
By default, <code>go</code> <code>mod</code> <code>tidy</code> verifies that
the selected versions of dependencies relevant to the main module are the same
versions that would be used by the prior Go release (Go 1.16 for a module that
spsecifies <code>go</code> <code>1.17</code>), and preserves
the <code>go.sum</code> entries needed by that release even for dependencies
that are not normally needed by other commands.
The <code>-compat</code> flag allows that version to be overridden to support
older (or only newer) versions, up to the version specified by
the <code>go</code> directive in the <code>go.mod</code> file. To tidy
a <code>go</code> <code>1.17</code> module for Go 1.17 only, without saving
checksums for (or checking for consistency with) Go 1.16:
go mod tidy -compat=1.17
Note that even if the main module is tidied with <code>-compat=1.17</code>,
users who <code>require</code> the module from a
<code>go</code> <code>1.16</code> or earlier module will still be able to
use it, provided that the packages use only compatible language and library
<h4 id="module-deprecation-comments">Module deprecation comments</h4>
<p><!-- -->
Module authors may deprecate a module by adding a
<a href="/ref/mod#go-mod-file-module-deprecation"><code>// Deprecated:</code>
comment</a> to <code>go.mod</code>, then tagging a new version.
<code>go</code> <code>get</code> now prints a warning if a module needed to
build packages named on the command line is deprecated. <code>go</code>
<code>list</code> <code>-m</code> <code>-u</code> prints deprecations for all
dependencies (use <code>-f</code> or <code>-json</code> to show the full
message). The <code>go</code> command considers different major versions to
be distinct modules, so this mechanism may be used, for example, to provide
users with migration instructions for a new major version.
<h4 id="go-get"><code>go</code> <code>get</code></h4>
<p><!-- -->
The <code>go</code> <code>get</code> <code>-insecure</code> flag is
deprecated and has been removed. To permit the use of insecure schemes
when fetching dependencies, please use the <code>GOINSECURE</code>
environment variable. The <code>-insecure</code> flag also bypassed module
sum validation, use <code>GOPRIVATE</code> or <code>GONOSUMDB</code> if
you need that functionality. See <code>go</code> <code>help</code>
<code>environment</code> for details.
<h4 id="missing-go-directive"><code>go.mod</code> files missing <code>go</code> directives</h4>
<p><!-- -->
If the main module's <code>go.mod</code> file does not contain
a <a href="/doc/modules/gomod-ref#go"><code>go</code> directive</a> and
the <code>go</code> command cannot update the <code>go.mod</code> file, the
<code>go</code> command now assumes <code>go 1.11</code> instead of the
current release. (<code>go</code> <code>mod</code> <code>init</code> has added
<code>go</code> directives automatically <a href="/doc/go1.12#modules">since
Go 1.12</a>.)
<p><!-- -->
If a module dependency lacks an explicit <code>go.mod</code> file, or
its <code>go.mod</code> file does not contain
a <a href="/doc/modules/gomod-ref#go"><code>go</code> directive</a>,
the <code>go</code> command now assumes <code>go 1.16</code> for that
dependency instead of the current release. (Dependencies developed in GOPATH
mode may lack a <code>go.mod</code> file, and
the <code>vendor/modules.txt</code> has to date never recorded
the <code>go</code> versions indicated by dependencies' <code>go.mod</code>
<h4 id="vendor"><code>vendor</code> contents</h4>
<p><!-- -->
If the main module specifies <code>go</code> <code>1.17</code> or higher,
<code>go</code> <code>mod</code> <code>vendor</code> now annotates
<code>vendor/modules.txt</code> with the <code>go</code> version indicated by
each vendored module in its own <code>go.mod</code> file. The annotated
version is used when building the module's packages from vendored source code.
<p><!-- -->
If the main module specifies <code>go</code> <code>1.17</code> or higher,
<code>go</code> <code>mod</code> <code>vendor</code> now omits <code>go.mod</code>
and <code>go.sum</code> files for vendored dependencies, which can otherwise
interfere with the ability of the <code>go</code> command to identify the correct
module root when invoked within the <code>vendor</code> tree.
<h4 id="password-prompts">Password prompts</h4>
<p><!-- -->
The <code>go</code> command by default now suppresses SSH password prompts and
Git Credential Manager prompts when fetching Git repositories using SSH, as it
already did previously for other Git password prompts. Users authenticating to
private Git repos with password-protected SSH may configure
an <code>ssh-agent</code> to enable the <code>go</code> command to use
password-protected SSH keys.
<h4 id="go-mod-download"><code>go</code> <code>mod</code> <code>download</code></h4>
<p><!-- -->
When <code>go</code> <code>mod</code> <code>download</code> is invoked without
arguments, it will no longer save sums for downloaded module content to
<code>go.sum</code>. It may still make changes to <code>go.mod</code> and
<code>go.sum</code> needed to load the build list. This is the same as the
behavior in Go 1.15. To save sums for all modules, use <code>go</code>
<code>mod</code> <code>download</code> <code>all</code>.
<h4 id="build-lines"><code>//go:build</code> lines</h4>
The <code>go</code> command now understands <code>//go:build</code> lines
and prefers them over <code>// +build</code> lines. The new syntax uses
boolean expressions, just like Go, and should be less error-prone.
As of this release, the new syntax is fully supported, and all Go files
should be updated to have both forms with the same meaning. To aid in
migration, <a href="#gofmt"><code>gofmt</code></a> now automatically
synchronizes the two forms. For more details on the syntax and migration plan,
<a href=""></a>.
<h3 id="gofmt"><code>gofmt</code></h3>
<code>gofmt</code> (and <code>go</code> <code>fmt</code>) now synchronizes
<code>//go:build</code> lines with <code>// +build</code> lines. If a file
only has <code>// +build</code> lines, they will be moved to the appropriate
location in the file, and matching <code>//go:build</code> lines will be
added. Otherwise, <code>// +build</code> lines will be overwritten based on
any existing <code>//go:build</code> lines. For more information, see
<a href=""></a>.
<h3 id="vet">Vet</h3>
<h4 id="vet-buildtags">New warning for mismatched <code>//go:build</code> and <code>// +build</code> lines</h4>
<p><!-- CL 240609 -->
The <code>vet</code> tool now verifies that <code>//go:build</code> and
<code>// +build</code> lines are in the correct part of the file and
synchronized with each other. If they aren't,
<a href="#gofmt"><code>gofmt</code></a> can be used to fix them. For more
information, see
<a href=""></a>.
<h4 id="vet-sigchanyzer">New warning for calling <code>signal.Notify</code> on unbuffered channels</h4>
<p><!-- CL 299532 -->
The vet tool now warns about calls to <a href="/pkg/os/signal/#Notify">signal.Notify</a>
with incoming signals being sent to an unbuffered channel. Using an unbuffered channel
risks missing signals sent on them as <code>signal.Notify</code> does not block when
sending to a channel. For example:
c := make(chan os.Signal)
// signals are sent on c before the channel is read from.
// This signal may be dropped as c is unbuffered.
signal.Notify(c, os.Interrupt)
Users of <code>signal.Notify</code> should use channels with sufficient buffer space to keep up with the
expected signal rate.
<h4 id="vet-error-stdmethods">New warnings for Is, As and Unwrap methods</h4>
<p><!-- CL 321389 -->
The vet tool now warns about methods named <code>As</code>, <code>Is</code> or <code>Unwrap</code>
on types implementing the <code>error</code> interface that have a different signature than the
one expected by the <code>errors</code> package. The <code>errors.{As,Is,Unwrap}</code> functions
expect such methods to implement either <code>Is(error)</code> <code>bool</code>,
<code>As(interface{})</code> <code>bool</code>, or <code>Unwrap()</code> <code>error</code>
respectively. The functions <code>errors.{As,Is,Unwrap}</code> will ignore methods with the same
names but a different signature. For example:
type MyError struct { hint string }
func (m MyError) Error() string { ... } // MyError implements error.
func (MyError) Is(target interface{}) bool { ... } // target is interface{} instead of error.
func Foo() bool {
x, y := MyError{"A"}, MyError{"B"}
return errors.Is(x, y) // returns false as x != y and MyError does not have an `Is(error) bool` function.
<h3 id="cover">Cover</h3>
<p><!-- CL 249759 -->
The <code>cover</code> tool now uses an optimized parser
from <code></code>, which may be noticeably faster
when parsing large coverage profiles.
<h2 id="compiler">Compiler</h2>
<p><!-- -->
Go 1.17 implements a new way of passing function arguments and results using
registers instead of the stack. This work is enabled for Linux, MacOS, and
Windows on the 64-bit x86 architecture (the <code>linux/amd64</code>,
<code>darwin/amd64</code>, <code>windows/amd64</code> ports). For a
representative set of Go packages and programs, benchmarking has shown
performance improvements of about 5%, and a typical reduction in binary size
of about 2%.
This change does not affect the functionality of any safe Go code. It can affect
code outside the <a href="/doc/go1compat">compatibility guidelines</a> with
minimal impact. To maintain compatibility with existing assembly functions,
adapter functions converting between the new register-based calling convention
and the previous stack-based calling convention (also known as ABI wrappers)
are sometimes used. This is mostly invisible to users, except for assembly
functions that have their addresses taken in Go. Using <code>reflect.ValueOf(fn).Pointer()</code>
(or similar approaches such as via <code>unsafe.Pointer</code>) to get the address
of an assembly function will now return the address of the ABI wrapper. This is
mostly harmless, except for special-purpose assembly code (such as accessing
thread-local storage or requiring a special stack alignment). Assembly functions
called indirectly from Go via <code>func</code> values will now be made through
ABI wrappers, which may cause a very small performance overhead. Also, calling
Go functions from assembly may now go through ABI wrappers, with a very small
performance overhead.
<p><!-- CL 304470 -->
The format of stack traces from the runtime (printed when an uncaught panic
occurs, or when <code>runtime.Stack</code> is called) is improved. Previously,
the function arguments were printed as hexadecimal words based on the memory
layout. Now each argument in the source code is printed separately, separated
by commas. Aggregate-typed (struct, array, string, slice, interface, and complex)
arguments are delimited by curly braces. A caveat is that the value of an
argument that only lives in a register and is not stored to memory may be
inaccurate. Results (which were usually inaccurate) are no longer printed.
<p><!-- CL 283112, -->
Functions containing closures can now be inlined. One effect of this change is
that a function with a closure may actually produce a distinct closure function
for each place that the function is inlined. Hence, this change could reveal
bugs where Go functions are compared (incorrectly) by pointer value. Go
functions are by definition not comparable.
<h2 id="library">Core library</h2>
<h3 id="runtime/cgo"><a href="/pkg/runtime/cgo">Cgo</a></h3>
The <a href="/pkg/runtime/cgo">runtime/cgo</a> package now provides a
new facility that allows to turn any Go values to a safe representation
that can be used to pass values between C and Go safely. See
<a href="/pkg/runtime/cgo#Handle">runtime/cgo.Handle</a> for more information.
<h3 id="minor_library_changes">Minor changes to the library</h3>
As always, there are various minor changes and updates to the library,
made with the Go 1 <a href="/doc/go1compat">promise of compatibility</a>
in mind.
<dl id="archive/zip"><dt><a href="/pkg/archive/zip/">archive/zip</a></dt>
<p><!-- CL 312310 -->
The new methods <a href="/pkg/archive/zip#File.OpenRaw"><code>File.OpenRaw</code></a>, <a href="/pkg/archive/zip#Writer.CreateRaw"><code>Writer.CreateRaw</code></a>, <a href="/pkg/archive/zip#Writer.Copy"><code>Writer.Copy</code></a> provide support for cases where performance is a primary concern.
</dl><!-- archive/zip -->
<dl id="bufio"><dt><a href="/pkg/bufio/">bufio</a></dt>
<p><!-- CL 280492 -->
The <a href="/pkg/bufio/#Writer.WriteRune"><code>Writer.WriteRune</code></a> method
now writes the replacement character U+FFFD for negative rune values,
as it does for other invalid runes.
</dl><!-- bufio -->
<dl id="bytes"><dt><a href="/pkg/bytes/">bytes</a></dt>
<p><!-- CL 280492 -->
The <a href="/pkg/bytes/#Buffer.WriteRune"><code>Buffer.WriteRune</code></a> method
now writes the replacement character U+FFFD for negative rune values,
as it does for other invalid runes.
</dl><!-- bytes -->
<dl id="compress/lzw"><dt><a href="/pkg/compress/lzw/">compress/lzw</a></dt>
<p><!-- CL 273667 -->
The <a href="/pkg/compress/lzw/#NewReader"><code>NewReader</code></a>
function is guaranteed to return a value of the new
type <a href="/pkg/compress/lzw/#Reader"><code>Reader</code></a>,
and similarly <a href="/pkg/compress/lzw/#NewWriter"><code>NewWriter</code></a>
is guaranteed to return a value of the new
type <a href="/pkg/compress/lzw/#Writer"><code>Writer</code></a>.
These new types both implement a <code>Reset</code> method
(<a href="/pkg/compress/lzw/#Reader.Reset"><code>Reader.Reset</code></a>,
<a href="/pkg/compress/lzw/#Writer.Reset"><code>Writer.Reset</code></a>)
that allows reuse of the <code>Reader</code> or <code>Writer</code>.
</dl><!-- compress/lzw -->
<dl id="crypto/ed25519"><dt><a href="/pkg/crypto/ed25519/">crypto/ed25519</a></dt>
<p><!-- CL 276272 -->
The <code>crypto/ed25519</code> package has been rewritten, and all
operations are now approximately twice as fast on amd64 and arm64.
The observable behavior has not otherwise changed.
</dl><!-- crypto/ed25519 -->
<dl id="crypto/elliptic"><dt><a href="/pkg/crypto/elliptic/">crypto/elliptic</a></dt>
<p><!-- CL 233939 -->
<a href="/pkg/crypto/elliptic#CurveParams"><code>CurveParams</code></a>
methods now automatically invoke faster and safer dedicated
implementations for known curves (P-224, P-256, and P-521) when
available. Note that this is a best-effort approach and applications
should avoid using the generic, not constant-time <code>CurveParams</code>
methods and instead use dedicated
<a href="/pkg/crypto/elliptic#Curve"><code>Curve</code></a> implementations
such as <a href="/pkg/crypto/elliptic#P256"><code>P256</code></a>.
<p><!-- CL 315271, CL 315274 -->
The <a href="/pkg/crypto/elliptic#P521"><code>P521</code></a> curve
implementation has been rewritten using code generated by the
<a href="">fiat-crypto project</a>,
which is based on a formally-verified model of the arithmetic
operations. It is now constant-time and three times faster on amd64 and
arm64. The observable behavior has not otherwise changed.
</dl><!-- crypto/elliptic -->
<dl id="crypto/rand"><dt><a href="/pkg/crypto/rand/">crypto/rand</a></dt>
<p><!-- CL 302489, CL 299134, CL 269999 -->
The <code>crypto/rand</code> package now uses the <code>getentropy</code>
syscall on macOS and the <code>getrandom</code> syscall on Solaris,
Illumos, and DragonFlyBSD.
</dl><!-- crypto/rand -->
<dl id="crypto/tls"><dt><a href="/pkg/crypto/tls/">crypto/tls</a></dt>
<p><!-- CL 295370 -->
The new <a href="/pkg/crypto/tls#Conn.HandshakeContext"><code>Conn.HandshakeContext</code></a>
method allows the user to control cancellation of an in-progress TLS
handshake. The provided context is accessible from various callbacks through the new
<a href="/pkg/crypto/tls#ClientHelloInfo.Context"><code>ClientHelloInfo.Context</code></a> and
<a href="/pkg/crypto/tls#CertificateRequestInfo.Context"><code>CertificateRequestInfo.Context</code></a>
methods. Canceling the context after the handshake has finished has no effect.
<p><!-- CL 289209 -->
When <a href="/pkg/crypto/tls#Config.NextProtos"><code>Config.NextProtos</code></a>
is set, servers now enforce that there is an overlap between the
configured protocols and the protocols advertised by the client, if any.
If there is no overlap the connection is closed with the
<code>no_application_protocol</code> alert, as required by RFC 7301.
<p><!-- CL 314609 -->
Cipher suite ordering is now handled entirely by the
<code>crypto/tls</code> package. Currently, cipher suites are sorted based
on their security, performance, and hardware support taking into account
both the local and peer's hardware. The order of the
<a href="/pkg/crypto/tls#Config.CipherSuites"><code>Config.CipherSuites</code></a>
field is now ignored, as well as the
<a href="/pkg/crypto/tls#Config.PreferServerCipherSuites"><code>Config.PreferServerCipherSuites</code></a>
field. Note that <code>Config.CipherSuites</code> still allows
applications to choose what TLS 1.0–1.2 cipher suites to enable.
The 3DES cipher suites have been moved to
<a href="/pkg/crypto/tls#InsecureCipherSuites"><code>InsecureCipherSuites</code></a>
due to <a href="">fundamental block size-related
weakness</a>. They are still enabled by default but only as a last resort,
thanks to the cipher suite ordering change above.
</dl><!-- crypto/tls -->
<dl id="crypto/x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
<p><!-- CL 224157 -->
<a href="/pkg/crypto/x509/#CreateCertificate"><code>CreateCertificate</code></a>
now returns an error if the provided private key doesn't match the
parent's public key, if any. The resulting certificate would have failed
to verify.
<p><!-- CL 315209 -->
The temporary <code>GODEBUG=x509ignoreCN=0</code> flag has been removed.
<p><!-- CL 274234 -->
<a href="/pkg/crypto/x509/#ParseCertificate"><code>ParseCertificate</code></a>
has been rewritten, and now consumes ~70% fewer resources. The observable
behavior has not otherwise changed, except for error messages.
<p><!-- CL 321190 -->
On BSD systems, <code>/etc/ssl/certs</code> is now searched for trusted
roots. This adds support for the new system trusted certificate store in
FreeBSD 12.2+.
</dl><!-- crypto/x509 -->
<dl id="database/sql"><dt><a href="/pkg/database/sql/">database/sql</a></dt>
<p><!-- CL 258360 -->
The <a href="/pkg/database/sql/#DB.Close"><code>DB.Close</code></a> method now closes
the <code>connector</code> field if the type in this field implements the
<a href="/pkg/io/#Closer"><code>io.Closer</code></a> interface.
<p><!-- CL 311572 -->
The new
<a href="/pkg/database/sql/#NullInt16"><code>NullInt16</code></a>
<a href="/pkg/database/sql/#NullByte"><code>NullByte</code></a>
structs represent the int16 and byte values that may be null. These can be used as
destinations of the <a href="/pkg/database/sql/#Scan"><code>Scan</code></a> method,
similar to NullString.
</dl><!-- database/sql -->
<dl id="debug/elf"><dt><a href="/pkg/debug/elf/">debug/elf</a></dt>
<p><!-- CL 239217 -->
The <a href="/pkg/debug/elf/#SHT_MIPS_ABIFLAGS"><code>SHT_MIPS_ABIFLAGS</code></a>
constant has been added.
</dl><!-- debug/elf -->
<dl id="encoding/binary"><dt><a href="/pkg/encoding/binary/">encoding/binary</a></dt>
<p><!-- CL 299531 -->
<code>binary.Uvarint</code> will stop reading after <code>10 bytes</code> to avoid
wasted computations. If more than <code>10 bytes</code> are needed, the byte count returned is <code>-11</code>.
<br />
Previous Go versions could return larger negative counts when reading incorrectly encoded varints.
</dl><!-- encoding/binary -->
<dl id="encoding/csv"><dt><a href="/pkg/encoding/csv/">encoding/csv</a></dt>
<p><!-- CL 291290 -->
The new
<a href="/pkg/encoding/csv/#Reader.FieldPos"><code>Reader.FieldPos</code></a>
method returns the line and column corresponding to the start of
a given field in the record most recently returned by
<a href="/pkg/encoding/csv/#Reader.Read"><code>Read</code></a>.
</dl><!-- encoding/csv -->
<dl id="flag"><dt><a href="/pkg/flag/">flag</a></dt>
<p><!-- CL 271788 -->
Flag declarations now panic if an invalid name is specified.
</dl><!-- flag -->
<dl id="go/build"><dt><a href="/pkg/go/build/">go/build</a></dt>
<p><!-- CL 310732 -->
The new
<a href="/pkg/go/build/#Context.ToolTags"><code>Context.ToolTags</code></a>
field holds the build tags appropriate to the current Go
toolchain configuration.
</dl><!-- go/build -->
<dl id="go/format"><dt><a href="/pkg/go/format/">go/format</a></dt>
The <a href="/pkg/go/format/#Source"><code>Source</code></a> and
<a href="/pkg/go/format/#Node"><code>Node</code></a> functions now
synchronize <code>//go:build</code> lines with <code>// +build</code>
lines. If a file only has <code>// +build</code> lines, they will be
moved to the appropriate location in the file, and matching
<code>//go:build</code> lines will be added. Otherwise,
<code>// +build</code> lines will be overwritten based on any existing
<code>//go:build</code> lines. For more information, see
<a href=""></a>.
</dl><!-- go/format -->
<dl id="io/fs"><dt><a href="/pkg/io/fs/">io/fs</a></dt>
<p><!-- CL 293649 -->
The new <a href="/pkg/io/fs/#FileInfoToDirEntry"><code>FileInfoToDirEntry</code></a> function converts a <code>FileInfo</code> to a <code>DirEntry</code>.
</dl><!-- io/fs -->
<dl id="math"><dt><a href="/pkg/math/">math</a></dt>
<p><!-- CL 247058 -->
The math package now defines three more constants: <code>MaxUint</code>, <code>MaxInt</code> and <code>MinInt</code>.
For 32-bit systems their values are <code>2^32 - 1</code>, <code>2^31 - 1</code> and <code>-2^31</code>, respectively.
For 64-bit systems their values are <code>2^64 - 1</code>, <code>2^63 - 1</code> and <code>-2^63</code>, respectively.
</dl><!-- math -->
<dl id="mime"><dt><a href="/pkg/mime/">mime</a></dt>
<p><!-- CL 305230 -->
On Unix systems, the table of MIME types is now read from the local system's
<a href="">Shared MIME-info Database</a>
when available.
</dl><!-- mime -->
<dl id="net"><dt><a href="/pkg/net/">net</a></dt>
<p><!-- CL 272668 -->
The new method <a href="/pkg/net/#IP.IsPrivate"><code>IP.IsPrivate</code></a> reports whether an address is
a private IPv4 address according to <a href="">RFC 1918</a>
or a local IPv6 address according <a href="">RFC 4193</a>.
<p><!-- CL 301709 -->
The Go DNS resolver now only sends one DNS query when resolving an address for an IPv4-only or IPv6-only network,
rather than querying for both address families.
<p><!-- CL 307030 -->
The <a href="/pkg/net/#ErrClosed"><code>ErrClosed</code></a> sentinel error and
<a href="/pkg/net/#ParseError"><code>ParseError</code></a> error type now implement
the <a href="/pkg/net/#Error"><code>net.Error</code></a> interface.
<p><!-- CL325829 -->
The <a href="/pkg/net/#ParseIP"><code>ParseIP</code></a> and <a href="/pkg/net/#ParseCIDR"><code>ParseCIDR</code></a>
functions now reject IPv4 addresses which contain decimal components with leading zeros.
These components were always interpreted as decimal, but some operating systems treat them as octal.
This mismatch could hypothetically lead to security issues if a Go application was used to validate IP addresses
which were then used in their original form with non-Go applications which interpreted components as octal. Generally,
it is advisable to always re-encoded values after validation, which avoids this class of parser misalignment issues.
</dl><!-- net -->
<dl id="net/http"><dt><a href="/pkg/net/http/">net/http</a></dt>
<p><!-- CL 295370 -->
The <a href="/pkg/net/http/"><code>net/http</code></a> package now uses the new
<a href="/pkg/crypto/tls#Conn.HandshakeContext"><code>(*tls.Conn).HandshakeContext</code></a>
with the <a href="/pkg/net/http/#Request"><code>Request</code></a> context
when performing TLS handshakes in the client or server.
<p><!-- CL 235437 -->
Setting the <a href="/pkg/net/http/#Server"><code>Server</code></a>
<code>ReadTimeout</code> or <code>WriteTimeout</code> fields to a negative value now indicates no timeout
rather than an immediate timeout.
<p><!-- CL 308952 -->
The <a href="/pkg/net/http/#ReadRequest"><code>ReadRequest</code></a> function
now returns an error when the request has multiple Host headers.
</dl><!-- net/http -->
<dl id="net/http/httptest"><dt><a href="/pkg/net/http/httptest/">net/http/httptest</a></dt>
<p><!-- CL 308950 -->
<a href="/pkg/net/http/httptest/#ResponseRecorder.WriteHeader"><code>ResponseRecorder.WriteHeader></code></a>
now panics when the provided code is not a valid three-digit HTTP status code.
This matches the behavior of <a href="/pkg/net/http/#ResponseWriter"><code>ResponseWriter></code></a>
implementations in the <a href="/pkg/net/http/"><code>net/http</code></a> package.
</dl><!-- net/http/httptest -->
<dl id="net/url"><dt><a href="/pkg/net/url/">net/url</a></dt>
<p><!-- CL 314850 -->
The new method <a href="/pkg/net/url/#Values.Has"><code>Values.Has</code></a>
reports whether a query parameter is set.
</dl><!-- net/url -->
<dl id="os"><dt><a href="/pkg/os/">os</a></dt>
<p><!-- CL 268020 -->
The <a href="/pkg/os/#File.WriteString"><code>File.WriteString</code></a> method
has been optimized to no longer make a copy of the input string.
</dl><!-- os -->
<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
<p><!-- CL 266197 -->
The new
<a href="/pkg/reflect/#StructField.IsExported"><code>StructField.IsExported</code></a>
<a href="/pkg/reflect/#Method.IsExported"><code>Method.IsExported</code></a>
methods report whether a struct field or type method is exported.
They provide a more readable alternative to checking whether <code>PkgPath</code>
is empty.
<p><!-- CL 281233 -->
The new <a href="/pkg/reflect/#VisibleFields"><code>VisibleFields</code></a> function
returns all the visible fields in a struct type, including fields inside anonymous struct members.
<p><!-- CL 284136 -->
The <a href="/pkg/reflect/#ArrayOf"><code>ArrayOf</code></a> function now panics when
called with a negative length.
</dl><!-- reflect -->
<dl id="runtime/metrics"><dt><a href="/pkg/runtime/metrics">runtime/metrics</a></dt>
<p><!-- CL 308933, CL 312431, CL 312909 -->
New metrics were added that track total bytes and objects allocated and freed.
A new metric tracking the distribution of goroutine scheduling latencies was
also added.
</dl><!-- runtime/metrics -->
<dl id="runtime/pprof"><dt><a href="/pkg/runtime/pprof">runtime/pprof</a></dt>
<p><!-- CL 299991 -->
Block profiles are no longer biased to favor infrequent long events over
frequent short events.
</dl><!-- runtime/pprof -->
<dl id="strconv"><dt><a href="/pkg/strconv/">strconv</a></dt>
<p><!-- CL 170079, CL 170080 -->
The <code>strconv</code> package now uses Ulf Adams's Ryū algorithm for formatting floating-point numbers.
This algorithm improves performance on most inputs, and is more than 99% faster on worst-case inputs.
<p><!-- CL 314775 -->
The new <a href="/pkg/strconv/#QuotedPrefix"><code>QuotedPrefix</code></a> function
returns the quoted string (as understood by
<a href="/pkg/strconv/#Unquote"><code>Unquote</code></a>)
at the start of input.
</dl><!-- strconv -->
<dl id="strings"><dt><a href="/pkg/strings/">strings</a></dt>
<p><!-- CL 280492 -->
The <a href="/pkg/strings/#Builder.WriteRune"><code>Builder.WriteRune</code></a> method
now writes the replacement character U+FFFD for negative rune values,
as it does for other invalid runes.
</dl><!-- strings -->
<dl id="sync/atomic"><dt><a href="/pkg/sync/atomic/">sync/atomic</a></dt>
<p><!-- CL 241678 -->
<code>atomic.Value</code> now has <a href="/pkg/sync/atomic/#Value.Swap"><code>Swap</code></a> and
<a href="/pkg/sync/atomic/#Value.CompareAndSwap"><code>CompareAndSwap</code></a> methods that provide
additional atomic operations.
</dl><!-- sync/atomic -->
<dl id="syscall"><dt><a href="/pkg/syscall/">syscall</a></dt>
<p><!-- CL 295371 -->
The <a href="/pkg/syscall/#GetQueuedCompletionStatus"><code>GetQueuedCompletionStatus</code></a> and
<a href="/pkg/syscall/#PostQueuedCompletionStatus"><code>PostQueuedCompletionStatus</code></a>
functions are now deprecated. These functions have incorrect signatures and are superseded by
equivalents in the <a href=""><code></code></a> package.
<p><!-- CL 313653 -->
On Unix-like systems, the process group of a child process is now set with signals blocked.
This avoids sending a <code>SIGTTOU</code> to the child when the parent is in a background process group.
<p><!-- CL 288298, CL 288300 -->
The Windows version of
<a href="/pkg/syscall/#SysProcAttr"><code>SysProcAttr</code></a>
has two new fields. <code>AdditionalInheritedHandles</code> is
a list of additional handles to be inherited by the new child
process. <code>ParentProcess</code> permits specifying the
parent process of the new process.
<p><!-- CL 311570 -->
The constant <code>MSG_CMSG_CLOEXEC</code> is now defined on
DragonFly and all OpenBSD systems (it was already defined on
some OpenBSD systems and all FreeBSD, NetBSD, and Linux systems).
<p><!-- CL 315281 -->
The constants <code>SYS_WAIT6</code> and <code>WEXITED</code>
are now defined on NetBSD systems (<code>SYS_WAIT6</code> was
already defined on DragonFly and FreeBSD systems;
<code>WEXITED</code> was already defined on Darwin, DragonFly,
FreeBSD, Linux, and Solaris systems).
</dl><!-- syscall -->
<dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
<p><!-- CL 310033 -->
Added a new <a href="/cmd/go/#hdr-Testing_flags">testing flag</a> <code>-shuffle</code> which controls the execution order of tests and benchmarks.
<p><!-- CL 260577 -->
The new
<a href="/pkg/testing/#T.Setenv"><code>T.Setenv</code></a>
and <a href="/pkg/testing/#B.Setenv"><code>B.Setenv</code></a>
methods support setting an environment variable for the duration
of the test or benchmark.
</dl><!-- testing -->
<dl id="text/template/parse"><dt><a href="/pkg/text/template/parse/">text/template/parse</a></dt>
<p><!-- CL 301493 -->
The new <a href="/pkg/text/template/parse/#Mode"><code>SkipFuncCheck</code></a> <a href=><code>Mode</code></a>
value changes the template parser to not verify that functions are defined.
</dl><!-- text/template/parse -->
<dl id="time"><dt><a href="/pkg/time/">time</a></dt>
<p><!-- CL 260858 -->
The <a href="/pkg/time/#Time"><code>Time</code></a> type now has a
<a href="/pkg/time/#Time.GoString"><code>GoString</code></a> method that
will return a more useful value for times when printed with the
<code>%#v</code> format specifier in the <code>fmt</code> package.
<p><!-- CL 264077 -->
The new <a href="/pkg/time/#Time.IsDST"><code>Time.IsDST</code></a> method can be used to check whether the time
is in Daylight Savings Time in its configured location.
<p><!-- CL 293349 -->
The new <a href="/pkg/time/#Time.UnixMilli"><code>Time.UnixMilli</code></a> and
<a href="/pkg/time/#Time.UnixMicro"><code>Time.UnixMicro</code></a> methods return the number of milliseconds and
microseconds elapsed since January 1, 1970 UTC respectively.<br>
The new <code>UnixMilli</code> and <code>UnixMicro</code> functions return local Time corresponding to given
Unix time.
<p><!-- CL 300996 -->
The package now accepts comma "," as a separator for fractional seconds when parsing and formatting time.
The following time formats are now accepted:
<li>2006-01-02 14:06:03,999999999 -0700 MST</li>
<li>Mon Jan _2 14:06:03,120007 2006</li>
<li>Mon Jan 2 14:06:03,120007 2006</li>
<p><!-- CL 320252 -->
The new constant <a href="/pkg/time/#Layout"><code>Layout</code></a>
defines the reference time.
</dl><!-- time -->
<dl id="unicode"><dt><a href="/pkg/unicode/">unicode</a></dt>
<p><!-- CL 280493 -->
The <a href="/pkg/unicode/#Is"><code>Is</code></a>,
<a href="/pkg/unicode/#IsGraphic"><code>IsGraphic</code></a>,
<a href="/pkg/unicode/#IsLetter"><code>IsLetter</code></a>,
<a href="/pkg/unicode/#IsLower"><code>IsLower</code></a>,
<a href="/pkg/unicode/#IsMark"><code>IsMark</code></a>,
<a href="/pkg/unicode/#IsNumber"><code>IsNumber</code></a>,
<a href="/pkg/unicode/#IsPrint"><code>IsPrint</code></a>,
<a href="/pkg/unicode/#IsPunct"><code>IsPunct</code></a>,
<a href="/pkg/unicode/#IsSpace"><code>IsSpace</code></a>,
<a href="/pkg/unicode/#IsSymbol"><code>IsSymbol</code></a>, and
<a href="/pkg/unicode/#IsUpper"><code>IsUpper</code></a> functions
now return <code>false</code> on negative rune values, as they do for other invalid runes.
</dl><!-- unicode -->