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} -</style> - -<h2 id="introduction">Introduction to Go 1.7</h2> - -<p> -The latest Go release, version 1.7, arrives six months after 1.6. -Most of its changes are in the implementation of the toolchain, runtime, and libraries. -There is one minor change to the language specification. -As always, the release maintains the Go 1 <a href="/doc/go1compat.html">promise of compatibility</a>. -We expect almost all Go programs to continue to compile and run as before. -</p> - -<p> -The release <a href="#ports">adds a port to IBM LinuxOne</a>; -<a href="#compiler">updates the x86-64 compiler back end</a> to generate more efficient code; -includes the <a href="#context">context package</a>, promoted from the -<a href="https://golang.org/x/net/context">x/net subrepository</a> -and now used in the standard library; -and <a href="#testing">adds support in the testing package</a> for -creating hierarchies of tests and benchmarks. -The release also <a href="#cmd_go">finalizes the vendoring support</a> -started in Go 1.5, making it a standard feature. -</p> - -<h2 id="language">Changes to the language</h2> - -<p> -There is one tiny language change in this release. -The section on <a href="/ref/spec#Terminating_statements">terminating statements</a> -clarifies that to determine whether a statement list ends in a terminating statement, -the “final non-empty statement” is considered the end, -matching the existing behavior of the gc and gccgo compiler toolchains. -In earlier releases the definition referred only to the “final statement,” -leaving the effect of trailing empty statements at the least unclear. -The <a href="/pkg/go/types/"><code>go/types</code></a> -package has been updated to match the gc and gccgo compiler toolchains -in this respect. -This change has no effect on the correctness of existing programs. -</p> - -<h2 id="ports">Ports</h2> - -<p> -Go 1.7 adds support for macOS 10.12 Sierra. -Binaries built with versions of Go before 1.7 will not work -correctly on Sierra. -</p> - -<p> -Go 1.7 adds an experimental port to <a href="https://en.wikipedia.org/wiki/Linux_on_z_Systems">Linux on z Systems</a> (<code>linux/s390x</code>) -and the beginning of a port to Plan 9 on ARM (<code>plan9/arm</code>). -</p> - -<p> -The experimental ports to Linux on 64-bit MIPS (<code>linux/mips64</code> and <code>linux/mips64le</code>) -added in Go 1.6 now have full support for cgo and external linking. -</p> - -<p> -The experimental port to Linux on little-endian 64-bit PowerPC (<code>linux/ppc64le</code>) -now requires the POWER8 architecture or later. -Big-endian 64-bit PowerPC (<code>linux/ppc64</code>) only requires the -POWER5 architecture. -</p> - -<p> -The OpenBSD port now requires OpenBSD 5.6 or later, for access to the <a href="https://man.openbsd.org/getentropy.2"><i>getentropy</i>(2)</a> system call. -</p> - -<h3 id="known_issues">Known Issues</h3> - -<p> -There are some instabilities on FreeBSD that are known but not understood. -These can lead to program crashes in rare cases. -See <a href="https://golang.org/issue/16136">issue 16136</a>, -<a href="https://golang.org/issue/15658">issue 15658</a>, -and <a href="https://golang.org/issue/16396">issue 16396</a>. -Any help in solving these FreeBSD-specific issues would be appreciated. -</p> - -<h2 id="tools">Tools</h2> - -<h3 id="cmd_asm">Assembler</h3> - -<p> -For 64-bit ARM systems, the vector register names have been -corrected to <code>V0</code> through <code>V31</code>; -previous releases incorrectly referred to them as <code>V32</code> through <code>V63</code>. -</p> - -<p> -For 64-bit x86 systems, the following instructions have been added: -<code>PCMPESTRI</code>, -<code>RORXL</code>, -<code>RORXQ</code>, -<code>VINSERTI128</code>, -<code>VPADDD</code>, -<code>VPADDQ</code>, -<code>VPALIGNR</code>, -<code>VPBLENDD</code>, -<code>VPERM2F128</code>, -<code>VPERM2I128</code>, -<code>VPOR</code>, -<code>VPSHUFB</code>, -<code>VPSHUFD</code>, -<code>VPSLLD</code>, -<code>VPSLLDQ</code>, -<code>VPSLLQ</code>, -<code>VPSRLD</code>, -<code>VPSRLDQ</code>, -and -<code>VPSRLQ</code>. -</p> - -<h3 id="compiler">Compiler Toolchain</h3> - -<p> -This release includes a new code generation back end for 64-bit x86 systems, -following a <a href="https://golang.org/s/go17ssa">proposal from 2015</a> -that has been under development since then. -The new back end, based on -<a href="https://en.wikipedia.org/wiki/Static_single_assignment_form">SSA</a>, -generates more compact, more efficient code -and provides a better platform for optimizations -such as bounds check elimination. -The new back end reduces the CPU time required by -<a href="https://golang.org/test/bench/go1/">our benchmark programs</a> by 5-35%. -</p> - -<p> -For this release, the new back end can be disabled by passing -<code>-ssa=0</code> to the compiler. -If you find that your program compiles or runs successfully -only with the new back end disabled, please -<a href="https://golang.org/issue/new">file a bug report</a>. -</p> - -<p> -The format of exported metadata written by the compiler in package archives has changed: -the old textual format has been replaced by a more compact binary format. -This results in somewhat smaller package archives and fixes a few -long-standing corner case bugs. -</p> - -<p> -For this release, the new export format can be disabled by passing -<code>-newexport=0</code> to the compiler. -If you find that your program compiles or runs successfully -only with the new export format disabled, please -<a href="https://golang.org/issue/new">file a bug report</a>. -</p> - -<p> -The linker's <code>-X</code> option no longer supports the unusual two-argument form -<code>-X</code> <code>name</code> <code>value</code>, -as <a href="/doc/go1.6#compiler">announced</a> in the Go 1.6 release -and in warnings printed by the linker. -Use <code>-X</code> <code>name=value</code> instead. -</p> - -<p> -The compiler and linker have been optimized and run significantly faster in this release than in Go 1.6, -although they are still slower than we would like and will continue to be optimized in future releases. -</p> - -<p> -Due to changes across the compiler toolchain and standard library, -binaries built with this release should typically be smaller than binaries -built with Go 1.6, -sometimes by as much as 20-30%. -</p> - -<p> -On x86-64 systems, Go programs now maintain stack frame pointers -as expected by profiling tools like Linux's perf and Intel's VTune, -making it easier to analyze and optimize Go programs using these tools. -The frame pointer maintenance has a small run-time overhead that varies -but averages around 2%. We hope to reduce this cost in future releases. -To build a toolchain that does not use frame pointers, set -<code>GOEXPERIMENT=noframepointer</code> when running -<code>make.bash</code>, <code>make.bat</code>, or <code>make.rc</code>. -</p> - -<h3 id="cmd_cgo">Cgo</h3> - -<p> -Packages using <a href="/cmd/cgo/">cgo</a> may now include -Fortran source files (in addition to C, C++, Objective C, and SWIG), -although the Go bindings must still use C language APIs. -</p> - -<p> -Go bindings may now use a new helper function <code>C.CBytes</code>. -In contrast to <code>C.CString</code>, which takes a Go <code>string</code> -and returns a <code>*C.byte</code> (a C <code>char*</code>), -<code>C.CBytes</code> takes a Go <code>[]byte</code> -and returns an <code>unsafe.Pointer</code> (a C <code>void*</code>). -</p> - -<p> -Packages and binaries built using <code>cgo</code> have in past releases -produced different output on each build, -due to the embedding of temporary directory names. -When using this release with -new enough versions of GCC or Clang -(those that support the <code>-fdebug-prefix-map</code> option), -those builds should finally be deterministic. -</p> - -<h3 id="gccgo">Gccgo</h3> - -<p> -Due to the alignment of Go's semiannual release schedule with GCC's annual release schedule, -GCC release 6 contains the Go 1.6.1 version of gccgo. -The next release, GCC 7, will likely have the Go 1.8 version of gccgo. -</p> - -<h3 id="cmd_go">Go command</h3> - -<p> -The <a href="/cmd/go/"><code>go</code></a> command's basic operation -is unchanged, but there are a number of changes worth noting. -</p> - -<p> -This release removes support for the <code>GO15VENDOREXPERIMENT</code> environment variable, -as <a href="/doc/go1.6#go_command">announced</a> in the Go 1.6 release. -<a href="https://golang.org/s/go15vendor">Vendoring support</a> -is now a standard feature of the <code>go</code> command and toolchain. -</p> - -<p> -The <code>Package</code> data structure made available to -“<code>go</code> <code>list</code>” now includes a -<code>StaleReason</code> field explaining why a particular package -is or is not considered stale (in need of rebuilding). -This field is available to the <code>-f</code> or <code>-json</code> -options and is useful for understanding why a target is being rebuilt. -</p> - -<p> -The “<code>go</code> <code>get</code>” command now supports -import paths referring to <code>git.openstack.org</code>. -</p> - -<p> -This release adds experimental, minimal support for building programs using -<a href="/pkg/go/build#hdr-Binary_Only_Packages">binary-only packages</a>, -packages distributed in binary form -without the corresponding source code. -This feature is needed in some commercial settings -but is not intended to be fully integrated into the rest of the toolchain. -For example, tools that assume access to complete source code -will not work with such packages, and there are no plans to support -such packages in the “<code>go</code> <code>get</code>” command. -</p> - -<h3 id="cmd_doc">Go doc</h3> - -<p> -The “<code>go</code> <code>doc</code>” command -now groups constructors with the type they construct, -following <a href="/cmd/godoc/"><code>godoc</code></a>. -</p> - -<h3 id="cmd_vet">Go vet</h3> - -<p> -The “<code>go</code> <code>vet</code>” command -has more accurate analysis in its <code>-copylock</code> and <code>-printf</code> checks, -and a new <code>-tests</code> check that checks the name and signature of likely test functions. -To avoid confusion with the new <code>-tests</code> check, the old, unadvertised -<code>-test</code> option has been removed; it was equivalent to <code>-all</code> <code>-shadow</code>. -</p> - -<p id="vet_lostcancel"> -The <code>vet</code> command also has a new check, -<code>-lostcancel</code>, which detects failure to call the -cancelation function returned by the <code>WithCancel</code>, -<code>WithTimeout</code>, and <code>WithDeadline</code> functions in -Go 1.7's new <code>context</code> package (see <a -href='#context'>below</a>). -Failure to call the function prevents the new <code>Context</code> -from being reclaimed until its parent is cancelled. -(The background context is never cancelled.) -</p> - -<h3 id="cmd_dist">Go tool dist</h3> - -<p> -The new subcommand “<code>go</code> <code>tool</code> <code>dist</code> <code>list</code>” -prints all supported operating system/architecture pairs. -</p> - -<h3 id="cmd_trace">Go tool trace</h3> - -<p> -The “<code>go</code> <code>tool</code> <code>trace</code>” command, -<a href="/doc/go1.5#trace_command">introduced in Go 1.5</a>, -has been refined in various ways. -</p> - -<p> -First, collecting traces is significantly more efficient than in past releases. -In this release, the typical execution-time overhead of collecting a trace is about 25%; -in past releases it was at least 400%. -Second, trace files now include file and line number information, -making them more self-contained and making the -original executable optional when running the trace tool. -Third, the trace tool now breaks up large traces to avoid limits -in the browser-based viewer. -</p> - -<p> -Although the trace file format has changed in this release, -the Go 1.7 tools can still read traces from earlier releases. -</p> - -<h2 id="performance">Performance</h2> - -<p> -As always, the changes are so general and varied that precise statements -about performance are difficult to make. -Most programs should run a bit faster, -due to speedups in the garbage collector and -optimizations in the core library. -On x86-64 systems, many programs will run significantly faster, -due to improvements in generated code brought by the -new compiler back end. -As noted above, in our own benchmarks, -the code generation changes alone typically reduce program CPU time by 5-35%. -</p> - -<p> -<!-- git log -''-grep '-[0-9][0-9]\.[0-9][0-9]%' go1.6.. --> -There have been significant optimizations bringing more than 10% improvements -to implementations in the -<a href="/pkg/crypto/sha1/"><code>crypto/sha1</code></a>, -<a href="/pkg/crypto/sha256/"><code>crypto/sha256</code></a>, -<a href="/pkg/encoding/binary/"><code>encoding/binary</code></a>, -<a href="/pkg/fmt/"><code>fmt</code></a>, -<a href="/pkg/hash/adler32/"><code>hash/adler32</code></a>, -<a href="/pkg/hash/crc32/"><code>hash/crc32</code></a>, -<a href="/pkg/hash/crc64/"><code>hash/crc64</code></a>, -<a href="/pkg/image/color/"><code>image/color</code></a>, -<a href="/pkg/math/big/"><code>math/big</code></a>, -<a href="/pkg/strconv/"><code>strconv</code></a>, -<a href="/pkg/strings/"><code>strings</code></a>, -<a href="/pkg/unicode/"><code>unicode</code></a>, -and -<a href="/pkg/unicode/utf16/"><code>unicode/utf16</code></a> -packages. -</p> - -<p> -Garbage collection pauses should be significantly shorter than they -were in Go 1.6 for programs with large numbers of idle goroutines, -substantial stack size fluctuation, or large package-level variables. -</p> - -<h2 id="library">Core library</h2> - -<h3 id="context">Context</h3> - -<p> -Go 1.7 moves the <code>golang.org/x/net/context</code> package -into the standard library as <a href="/pkg/context/"><code>context</code></a>. -This allows the use of contexts for cancelation, timeouts, and passing -request-scoped data in other standard library packages, -including -<a href="#net">net</a>, -<a href="#net_http">net/http</a>, -and -<a href="#os_exec">os/exec</a>, -as noted below. -</p> - -<p> -For more information about contexts, see the -<a href="/pkg/context/">package documentation</a> -and the Go blog post -“<a href="https://blog.golang.org/context">Go Concurrent Patterns: Context</a>.” -</p> - -<h3 id="httptrace">HTTP Tracing</h3> - -<p> -Go 1.7 introduces <a href="/pkg/net/http/httptrace/"><code>net/http/httptrace</code></a>, -a package that provides mechanisms for tracing events within HTTP requests. -</p> - -<h3 id="testing">Testing</h3> - -<p> -The <code>testing</code> package now supports the definition -of tests with subtests and benchmarks with sub-benchmarks. -This support makes it easy to write table-driven benchmarks -and to create hierarchical tests. -It also provides a way to share common setup and tear-down code. -See the <a href="/pkg/testing/#hdr-Subtests_and_Sub_benchmarks">package documentation</a> for details. -</p> - -<h3 id="runtime">Runtime</h3> - -<p> -All panics started by the runtime now use panic values -that implement both the -builtin <a href="/ref/spec#Errors"><code>error</code></a>, -and -<a href="/pkg/runtime/#Error"><code>runtime.Error</code></a>, -as -<a href="/ref/spec#Run_time_panics">required by the language specification</a>. -</p> - -<p> -During panics, if a signal's name is known, it will be printed in the stack trace. -Otherwise, the signal's number will be used, as it was before Go1.7. -</p> - -<p> -The new function -<a href="/pkg/runtime/#KeepAlive"><code>KeepAlive</code></a> -provides an explicit mechanism for declaring -that an allocated object must be considered reachable -at a particular point in a program, -typically to delay the execution of an associated finalizer. -</p> - -<p> -The new function -<a href="/pkg/runtime/#CallersFrames"><code>CallersFrames</code></a> -translates a PC slice obtained from -<a href="/pkg/runtime/#Callers"><code>Callers</code></a> -into a sequence of frames corresponding to the call stack. -This new API should be preferred instead of direct use of -<a href="/pkg/runtime/#FuncForPC"><code>FuncForPC</code></a>, -because the frame sequence can more accurately describe -call stacks with inlined function calls. -</p> - -<p> -The new function -<a href="/pkg/runtime/#SetCgoTraceback"><code>SetCgoTraceback</code></a> -facilitates tighter integration between Go and C code executing -in the same process called using cgo. -</p> - -<p> -On 32-bit systems, the runtime can now use memory allocated -by the operating system anywhere in the address space, -eliminating the -“memory allocated by OS not in usable range” failure -common in some environments. -</p> - -<p> -The runtime can now return unused memory to the operating system on -all architectures. -In Go 1.6 and earlier, the runtime could not -release memory on ARM64, 64-bit PowerPC, or MIPS. -</p> - -<p> -On Windows, Go programs in Go 1.5 and earlier forced -the global Windows timer resolution to 1ms at startup -by calling <code>timeBeginPeriod(1)</code>. -Changing the global timer resolution caused problems on some systems, -and testing suggested that the call was not needed for good scheduler performance, -so Go 1.6 removed the call. -Go 1.7 brings the call back: under some workloads the call -is still needed for good scheduler performance. -</p> - - -<h3 id="minor_library_changes">Minor changes to the library</h3> - -<p> -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. -</p> - -<dl id="bufio"><dt><a href="/pkg/bufio/">bufio</a></dt> - -<dd> -<p> -In previous releases of Go, if -<a href="/pkg/bufio/#Reader"><code>Reader</code></a>'s -<a href="/pkg/bufio/#Reader.Peek"><code>Peek</code></a> method -were asked for more bytes than fit in the underlying buffer, -it would return an empty slice and the error <code>ErrBufferFull</code>. -Now it returns the entire underlying buffer, still accompanied by the error <code>ErrBufferFull</code>. -</p> -</dd> -</dl> - -<dl id="bytes"><dt><a href="/pkg/bytes/">bytes</a></dt> - -<dd> -<p> -The new functions -<a href="/pkg/bytes/#ContainsAny"><code>ContainsAny</code></a> and -<a href="/pkg/bytes/#ContainsRune"><code>ContainsRune</code></a> -have been added for symmetry with -the <a href="/pkg/strings/"><code>strings</code></a> package. -</p> - -<p> -In previous releases of Go, if -<a href="/pkg/bytes/#Reader"><code>Reader</code></a>'s -<a href="/pkg/bytes/#Reader.Read"><code>Read</code></a> method -were asked for zero bytes with no data remaining, it would -return a count of 0 and no error. -Now it returns a count of 0 and the error -<a href="/pkg/io/#EOF"><code>io.EOF</code></a>. -</p> - -<p> -The -<a href="/pkg/bytes/#Reader"><code>Reader</code></a> type has a new method -<a href="/pkg/bytes/#Reader.Reset"><code>Reset</code></a> to allow reuse of a <code>Reader</code>. -</p> -</dd> -</dl> - -<dl id="compress_flate"><dt><a href="/pkg/compress/flate/">compress/flate</a></dt> - -<dd> -<p> -There are many performance optimizations throughout the package. -Decompression speed is improved by about 10%, -while compression for <code>DefaultCompression</code> is twice as fast. -</p> - -<p> -In addition to those general improvements, -the -<code>BestSpeed</code> -compressor has been replaced entirely and uses an -algorithm similar to <a href="https://github.com/google/snappy">Snappy</a>, -resulting in about a 2.5X speed increase, -although the output can be 5-10% larger than with the previous algorithm. -</p> - -<p> -There is also a new compression level -<code>HuffmanOnly</code> -that applies Huffman but not Lempel-Ziv encoding. -<a href="https://blog.klauspost.com/constant-time-gzipzip-compression/">Forgoing Lempel-Ziv encoding</a> means that -<code>HuffmanOnly</code> runs about 3X faster than the new <code>BestSpeed</code> -but at the cost of producing compressed outputs that are 20-40% larger than those -generated by the new <code>BestSpeed</code>. -</p> - -<p> -It is important to note that both -<code>BestSpeed</code> and <code>HuffmanOnly</code> produce a compressed output that is -<a href="https://tools.ietf.org/html/rfc1951">RFC 1951</a> compliant. -In other words, any valid DEFLATE decompressor will continue to be able to decompress these outputs. -</p> - -<p> -Lastly, there is a minor change to the decompressor's implementation of -<a href="/pkg/io/#Reader"><code>io.Reader</code></a>. In previous versions, -the decompressor deferred reporting -<a href="/pkg/io/#EOF"><code>io.EOF</code></a> until exactly no more bytes could be read. -Now, it reports -<a href="/pkg/io/#EOF"><code>io.EOF</code></a> more eagerly when reading the last set of bytes. -</p> -</dd> -</dl> - -<dl id="crypto_tls"><dt><a href="/pkg/crypto/tls/">crypto/tls</a></dt> - -<dd> -<p> -The TLS implementation sends the first few data packets on each connection -using small record sizes, gradually increasing to the TLS maximum record size. -This heuristic reduces the amount of data that must be received before -the first packet can be decrypted, improving communication latency over -low-bandwidth networks. -Setting -<a href="/pkg/crypto/tls/#Config"><code>Config</code></a>'s -<code>DynamicRecordSizingDisabled</code> field to true -forces the behavior of Go 1.6 and earlier, where packets are -as large as possible from the start of the connection. -</p> - -<p> -The TLS client now has optional, limited support for server-initiated renegotiation, -enabled by setting the -<a href="/pkg/crypto/tls/#Config"><code>Config</code></a>'s -<code>Renegotiation</code> field. -This is needed for connecting to many Microsoft Azure servers. -</p> - -<p> -The errors returned by the package now consistently begin with a -<code>tls:</code> prefix. -In past releases, some errors used a <code>crypto/tls:</code> prefix, -some used a <code>tls:</code> prefix, and some had no prefix at all. -</p> - -<p> -When generating self-signed certificates, the package no longer sets the -“Authority Key Identifier” field by default. -</p> -</dd> -</dl> - -<dl id="crypto_x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt> - -<dd> -<p> -The new function -<a href="/pkg/crypto/x509/#SystemCertPool"><code>SystemCertPool</code></a> -provides access to the entire system certificate pool if available. -There is also a new associated error type -<a href="/pkg/crypto/x509/#SystemRootsError"><code>SystemRootsError</code></a>. -</p> -</dd> -</dl> - -<dl id="debug_dwarf"><dt><a href="/pkg/debug/dwarf/">debug/dwarf</a></dt> - -<dd> -<p> -The -<a href="/pkg/debug/dwarf/#Reader"><code>Reader</code></a> type's new -<a href="/pkg/debug/dwarf/#Reader.SeekPC"><code>SeekPC</code></a> method and the -<a href="/pkg/debug/dwarf/#Data"><code>Data</code></a> type's new -<a href="/pkg/debug/dwarf/#Ranges"><code>Ranges</code></a> method -help to find the compilation unit to pass to a -<a href="/pkg/debug/dwarf/#LineReader"><code>LineReader</code></a> -and to identify the specific function for a given program counter. -</p> -</dd> -</dl> - -<dl id="debug_elf"><dt><a href="/pkg/debug/elf/">debug/elf</a></dt> - -<dd> -<p> -The new -<a href="/pkg/debug/elf/#R_390"><code>R_390</code></a> relocation type -and its many predefined constants -support the S390 port. -</p> -</dd> -</dl> - -<dl id="encoding_asn1"><dt><a href="/pkg/encoding/asn1/">encoding/asn1</a></dt> - -<dd> -<p> -The ASN.1 decoder now rejects non-minimal integer encodings. -This may cause the package to reject some invalid but formerly accepted ASN.1 data. -</p> -</dd> -</dl> - -<dl id="encoding_json"><dt><a href="/pkg/encoding/json/">encoding/json</a></dt> - -<dd> -<p> -The -<a href="/pkg/encoding/json/#Encoder"><code>Encoder</code></a>'s new -<a href="/pkg/encoding/json/#Encoder.SetIndent"><code>SetIndent</code></a> method -sets the indentation parameters for JSON encoding, -like in the top-level -<a href="/pkg/encoding/json/#Indent"><code>Indent</code></a> function. -</p> - -<p> -The -<a href="/pkg/encoding/json/#Encoder"><code>Encoder</code></a>'s new -<a href="/pkg/encoding/json/#Encoder.SetEscapeHTML"><code>SetEscapeHTML</code></a> method -controls whether the -<code>&</code>, <code><</code>, and <code>></code> -characters in quoted strings should be escaped as -<code>\u0026</code>, <code>\u003c</code>, and <code>\u003e</code>, -respectively. -As in previous releases, the encoder defaults to applying this escaping, -to avoid certain problems that can arise when embedding JSON in HTML. -</p> - -<p> -In earlier versions of Go, this package only supported encoding and decoding -maps using keys with string types. -Go 1.7 adds support for maps using keys with integer types: -the encoding uses a quoted decimal representation as the JSON key. -Go 1.7 also adds support for encoding maps using non-string keys that implement -the <code>MarshalText</code> -(see -<a href="/pkg/encoding/#TextMarshaler"><code>encoding.TextMarshaler</code></a>) -method, -as well as support for decoding maps using non-string keys that implement -the <code>UnmarshalText</code> -(see -<a href="/pkg/encoding/#TextUnmarshaler"><code>encoding.TextUnmarshaler</code></a>) -method. -These methods are ignored for keys with string types in order to preserve -the encoding and decoding used in earlier versions of Go. -</p> - -<p> -When encoding a slice of typed bytes, -<a href="/pkg/encoding/json/#Marshal"><code>Marshal</code></a> -now generates an array of elements encoded using -that byte type's -<code>MarshalJSON</code> -or -<code>MarshalText</code> -method if present, -only falling back to the default base64-encoded string data if neither method is available. -Earlier versions of Go accept both the original base64-encoded string encoding -and the array encoding (assuming the byte type also implements -<code>UnmarshalJSON</code> -or -<code>UnmarshalText</code> -as appropriate), -so this change should be semantically backwards compatible with earlier versions of Go, -even though it does change the chosen encoding. -</p> -</dd> -</dl> - -<dl id="go_build"><dt><a href="/pkg/go/build/">go/build</a></dt> - -<dd> -<p> -To implement the go command's new support for binary-only packages -and for Fortran code in cgo-based packages, -the -<a href="/pkg/go/build/#Package"><code>Package</code></a> type -adds new fields <code>BinaryOnly</code>, <code>CgoFFLAGS</code>, and <code>FFiles</code>. -</p> -</dd> -</dl> - -<dl id="go_doc"><dt><a href="/pkg/go/doc/">go/doc</a></dt> - -<dd> -<p> -To support the corresponding change in <code>go</code> <code>test</code> described above, -<a href="/pkg/go/doc/#Example"><code>Example</code></a> struct adds a Unordered field -indicating whether the example may generate its output lines in any order. -</p> -</dd> -</dl> - -<dl id="io"><dt><a href="/pkg/io/">io</a></dt> - -<dd> -<p> -The package adds new constants -<code>SeekStart</code>, <code>SeekCurrent</code>, and <code>SeekEnd</code>, -for use with -<a href="/pkg/io/#Seeker"><code>Seeker</code></a> -implementations. -These constants are preferred over <code>os.SEEK_SET</code>, <code>os.SEEK_CUR</code>, and <code>os.SEEK_END</code>, -but the latter will be preserved for compatibility. -</p> -</dd> -</dl> - -<dl id="math_big"><dt><a href="/pkg/math/big/">math/big</a></dt> - -<dd> -<p> -The -<a href="/pkg/math/big/#Float"><code>Float</code></a> type adds -<a href="/pkg/math/big/#Float.GobEncode"><code>GobEncode</code></a> and -<a href="/pkg/math/big/#Float.GobDecode"><code>GobDecode</code></a> methods, -so that values of type <code>Float</code> can now be encoded and decoded using the -<a href="/pkg/encoding/gob/"><code>encoding/gob</code></a> -package. -</p> -</dd> -</dl> - -<dl id="math_rand"><dt><a href="/pkg/math/rand/">math/rand</a></dt> - -<dd> -<p> -The -<a href="/pkg/math/rand/#Read"><code>Read</code></a> function and -<a href="/pkg/math/rand/#Rand"><code>Rand</code></a>'s -<a href="/pkg/math/rand/#Rand.Read"><code>Read</code></a> method -now produce a pseudo-random stream of bytes that is consistent and not -dependent on the size of the input buffer. -</p> - -<p> -The documentation clarifies that -Rand's <a href="/pkg/math/rand/#Rand.Seed"><code>Seed</code></a> -and <a href="/pkg/math/rand/#Rand.Read"><code>Read</code></a> methods -are not safe to call concurrently, though the global -functions <a href="/pkg/math/rand/#Seed"><code>Seed</code></a> -and <a href="/pkg/math/rand/#Read"><code>Read</code></a> are (and have -always been) safe. -</p> -</dd> -</dl> - -<dl id="mime_multipart"><dt><a href="/pkg/mime/multipart/">mime/multipart</a></dt> - -<dd> -<p> -The -<a href="/pkg/mime/multipart/#Writer"><code>Writer</code></a> -implementation now emits each multipart section's header sorted by key. -Previously, iteration over a map caused the section header to use a -non-deterministic order. -</p> -</dd> -</dl> - -<dl id="net"><dt><a href="/pkg/net/">net</a></dt> - -<dd> -<p> -As part of the introduction of <a href="#context">context</a>, the -<a href="/pkg/net/#Dialer"><code>Dialer</code></a> type has a new method -<a href="/pkg/net/#Dialer.DialContext"><code>DialContext</code></a>, like -<a href="/pkg/net/#Dialer.Dial"><code>Dial</code></a> but adding the -<a href="/pkg/context/#Context"><code>context.Context</code></a> -for the dial operation. -The context is intended to obsolete the <code>Dialer</code>'s -<code>Cancel</code> and <code>Deadline</code> fields, -but the implementation continues to respect them, -for backwards compatibility. -</p> - -<p> -The -<a href="/pkg/net/#IP"><code>IP</code></a> type's -<a href="/pkg/net/#IP.String"><code>String</code></a> method has changed its result for invalid <code>IP</code> addresses. -In past releases, if an <code>IP</code> byte slice had length other than 0, 4, or 16, <code>String</code> -returned <code>"?"</code>. -Go 1.7 adds the hexadecimal encoding of the bytes, as in <code>"?12ab"</code>. -</p> - -<p> -The pure Go <a href="/pkg/net/#hdr-Name_Resolution">name resolution</a> -implementation now respects <code>nsswitch.conf</code>'s -stated preference for the priority of DNS lookups compared to -local file (that is, <code>/etc/hosts</code>) lookups. -</p> -</dd> -</dl> - -<dl id="net_http"><dt><a href="/pkg/net/http/">net/http</a></dt> - -<dd> -<p> -<a href="/pkg/net/http/#ResponseWriter"><code>ResponseWriter</code></a>'s -documentation now makes clear that beginning to write the response -may prevent future reads on the request body. -For maximal compatibility, implementations are encouraged to -read the request body completely before writing any part of the response. -</p> - -<p> -As part of the introduction of <a href="#context">context</a>, the -<a href="/pkg/net/http/#Request"><code>Request</code></a> has a new methods -<a href="/pkg/net/http/#Request.Context"><code>Context</code></a>, to retrieve the associated context, and -<a href="/pkg/net/http/#Request.WithContext"><code>WithContext</code></a>, to construct a copy of <code>Request</code> -with a modified context. -</p> - -<p> -In the -<a href="/pkg/net/http/#Server"><code>Server</code></a> implementation, -<a href="/pkg/net/http/#Server.Serve"><code>Serve</code></a> records in the request context -both the underlying <code>*Server</code> using the key <code>ServerContextKey</code> -and the local address on which the request was received (a -<a href="/pkg/net/#Addr"><code>Addr</code></a>) using the key <code>LocalAddrContextKey</code>. -For example, the address on which a request received is -<code>req.Context().Value(http.LocalAddrContextKey).(net.Addr)</code>. -</p> - -<p> -The server's <a href="/pkg/net/http/#Server.Serve"><code>Serve</code></a> method -now only enables HTTP/2 support if the <code>Server.TLSConfig</code> field is <code>nil</code> -or includes <code>"h2"</code> in its <code>TLSConfig.NextProtos</code>. -</p> - -<p> -The server implementation now -pads response codes less than 100 to three digits -as required by the protocol, -so that <code>w.WriteHeader(5)</code> uses the HTTP response -status <code>005</code>, not just <code>5</code>. -</p> - -<p> -The server implementation now correctly sends only one "Transfer-Encoding" header when "chunked" -is set explicitly, following <a href="https://tools.ietf.org/html/rfc7230#section-3.3.1">RFC 7230</a>. -</p> - -<p> -The server implementation is now stricter about rejecting requests with invalid HTTP versions. -Invalid requests claiming to be HTTP/0.x are now rejected (HTTP/0.9 was never fully supported), -and plaintext HTTP/2 requests other than the "PRI * HTTP/2.0" upgrade request are now rejected as well. -The server continues to handle encrypted HTTP/2 requests. -</p> - -<p> -In the server, a 200 status code is sent back by the timeout handler on an empty -response body, instead of sending back 0 as the status code. -</p> - -<p> -In the client, the -<a href="/pkg/net/http/#Transport"><code>Transport</code></a> implementation passes the request context -to any dial operation connecting to the remote server. -If a custom dialer is needed, the new <code>Transport</code> field -<code>DialContext</code> is preferred over the existing <code>Dial</code> field, -to allow the transport to supply a context. -</p> - -<p> -The -<a href="/pkg/net/http/#Transport"><code>Transport</code></a> also adds fields -<code>IdleConnTimeout</code>, -<code>MaxIdleConns</code>, -and -<code>MaxResponseHeaderBytes</code> -to help control client resources consumed -by idle or chatty servers. -</p> - -<p> -A -<a href="/pkg/net/http/#Client"><code>Client</code></a>'s configured <code>CheckRedirect</code> function can now -return <code>ErrUseLastResponse</code> to indicate that the -most recent redirect response should be returned as the -result of the HTTP request. -That response is now available to the <code>CheckRedirect</code> function -as <code>req.Response</code>. -</p> - -<p> -Since Go 1, the default behavior of the HTTP client is -to request server-side compression -using the <code>Accept-Encoding</code> request header -and then to decompress the response body transparently, -and this behavior is adjustable using the -<a href="/pkg/net/http/#Transport"><code>Transport</code></a>'s <code>DisableCompression</code> field. -In Go 1.7, to aid the implementation of HTTP proxies, the -<a href="/pkg/net/http/#Response"><code>Response</code></a>'s new -<code>Uncompressed</code> field reports whether -this transparent decompression took place. -</p> - -<p> -<a href="/pkg/net/http/#DetectContentType"><code>DetectContentType</code></a> -adds support for a few new audio and video content types. -</p> -</dd> -</dl> - -<dl id="net_http_cgi"><dt><a href="/pkg/net/http/cgi/">net/http/cgi</a></dt> - -<dd> -<p> -The -<a href="/pkg/net/http/cgi/#Handler"><code>Handler</code></a> -adds a new field -<code>Stderr</code> -that allows redirection of the child process's -standard error away from the host process's -standard error. -</p> -</dd> -</dl> - -<dl id="net_http_httptest"><dt><a href="/pkg/net/http/httptest/">net/http/httptest</a></dt> - -<dd> -<p> -The new function -<a href="/pkg/net/http/httptest/#NewRequest"><code>NewRequest</code></a> -prepares a new -<a href="/pkg/net/http/#Request"><code>http.Request</code></a> -suitable for passing to an -<a href="/pkg/net/http/#Handler"><code>http.Handler</code></a> during a test. -</p> - -<p> -The -<a href="/pkg/net/http/httptest/#ResponseRecorder"><code>ResponseRecorder</code></a>'s new -<a href="/pkg/net/http/httptest/#ResponseRecorder.Result"><code>Result</code></a> method -returns the recorded -<a href="/pkg/net/http/#Response"><code>http.Response</code></a>. -Tests that need to check the response's headers or trailers -should call <code>Result</code> and inspect the response fields -instead of accessing -<code>ResponseRecorder</code>'s <code>HeaderMap</code> directly. -</p> -</dd> -</dl> - -<dl id="net_http_httputil"><dt><a href="/pkg/net/http/httputil/">net/http/httputil</a></dt> - -<dd> -<p> -The -<a href="/pkg/net/http/httputil/#ReverseProxy"><code>ReverseProxy</code></a> implementation now responds with “502 Bad Gateway” -when it cannot reach a back end; in earlier releases it responded with “500 Internal Server Error.” -</p> - -<p> -Both -<a href="/pkg/net/http/httputil/#ClientConn"><code>ClientConn</code></a> and -<a href="/pkg/net/http/httputil/#ServerConn"><code>ServerConn</code></a> have been documented as deprecated. -They are low-level, old, and unused by Go's current HTTP stack -and will no longer be updated. -Programs should use -<a href="/pkg/net/http/#Client"><code>http.Client</code></a>, -<a href="/pkg/net/http/#Transport"><code>http.Transport</code></a>, -and -<a href="/pkg/net/http/#Server"><code>http.Server</code></a> -instead. -</p> -</dd> -</dl> - -<dl id="net_http_pprof"><dt><a href="/pkg/net/http/pprof/">net/http/pprof</a></dt> - -<dd> -<p> -The runtime trace HTTP handler, installed to handle the path <code>/debug/pprof/trace</code>, -now accepts a fractional number in its <code>seconds</code> query parameter, -allowing collection of traces for intervals smaller than one second. -This is especially useful on busy servers. -</p> -</dd> -</dl> - -<dl><dt><a href="/pkg/net/mail/">net/mail</a></dt> - -<dd> -<p> -The address parser now allows unescaped UTF-8 text in addresses -following <a href="https://tools.ietf.org/html/rfc6532">RFC 6532</a>, -but it does not apply any normalization to the result. -For compatibility with older mail parsers, -the address encoder, namely -<a href="/pkg/net/mail/#Address"><code>Address</code></a>'s -<a href="/pkg/net/mail/#Address.String"><code>String</code></a> method, -continues to escape all UTF-8 text following <a href="https://tools.ietf.org/html/rfc5322">RFC 5322</a>. -</p> - -<p> -The <a href="/pkg/net/mail/#ParseAddress"><code>ParseAddress</code></a> -function and -the <a href="/pkg/net/mail/#AddressParser.Parse"><code>AddressParser.Parse</code></a> -method are stricter. -They used to ignore any characters following an e-mail address, but -will now return an error for anything other than whitespace. -</p> -</dd> -</dl> - -<dl id="net_url"><dt><a href="/pkg/net/url/">net/url</a></dt> - -<dd> -<p> -The -<a href="/pkg/net/url/#URL"><code>URL</code></a>'s -new <code>ForceQuery</code> field -records whether the URL must have a query string, -in order to distinguish URLs without query strings (like <code>/search</code>) -from URLs with empty query strings (like <code>/search?</code>). -</p> -</dd> -</dl> - -<dl id="os"><dt><a href="/pkg/os/">os</a></dt> - -<dd> -<p> -<a href="/pkg/os/#IsExist"><code>IsExist</code></a> now returns true for <code>syscall.ENOTEMPTY</code>, -on systems where that error exists. -</p> - -<p> -On Windows, -<a href="/pkg/os/#Remove"><code>Remove</code></a> now removes read-only files when possible, -making the implementation behave as on -non-Windows systems. -</p> -</dd> -</dl> - -<dl id="os_exec"><dt><a href="/pkg/os/exec/">os/exec</a></dt> - -<dd> -<p> -As part of the introduction of <a href="#context">context</a>, -the new constructor -<a href="/pkg/os/exec/#CommandContext"><code>CommandContext</code></a> -is like -<a href="/pkg/os/exec/#Command"><code>Command</code></a> but includes a context that can be used to cancel the command execution. -</p> -</dd> -</dl> - -<dl id="os_user"><dt><a href="/pkg/os/user/">os/user</a></dt> - -<dd> -<p> -The -<a href="/pkg/os/user/#Current"><code>Current</code></a> -function is now implemented even when cgo is not available. -</p> - -<p> -The new -<a href="/pkg/os/user/#Group"><code>Group</code></a> type, -along with the lookup functions -<a href="/pkg/os/user/#LookupGroup"><code>LookupGroup</code></a> and -<a href="/pkg/os/user/#LookupGroupId"><code>LookupGroupId</code></a> -and the new field <code>GroupIds</code> in the <code>User</code> struct, -provides access to system-specific user group information. -</p> -</dd> -</dl> - -<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt> - -<dd> -<p> -Although -<a href="/pkg/reflect/#Value"><code>Value</code></a>'s -<a href="/pkg/reflect/#Value.Field"><code>Field</code></a> method has always been documented to panic -if the given field number <code>i</code> is out of range, it has instead -silently returned a zero -<a href="/pkg/reflect/#Value"><code>Value</code></a>. -Go 1.7 changes the method to behave as documented. -</p> - -<p> -The new -<a href="/pkg/reflect/#StructOf"><code>StructOf</code></a> -function constructs a struct type at run time. -It completes the set of type constructors, joining -<a href="/pkg/reflect/#ArrayOf"><code>ArrayOf</code></a>, -<a href="/pkg/reflect/#ChanOf"><code>ChanOf</code></a>, -<a href="/pkg/reflect/#FuncOf"><code>FuncOf</code></a>, -<a href="/pkg/reflect/#MapOf"><code>MapOf</code></a>, -<a href="/pkg/reflect/#PtrTo"><code>PtrTo</code></a>, -and -<a href="/pkg/reflect/#SliceOf"><code>SliceOf</code></a>. -</p> - -<p> -<a href="/pkg/reflect/#StructTag"><code>StructTag</code></a>'s -new method -<a href="/pkg/reflect/#StructTag.Lookup"><code>Lookup</code></a> -is like -<a href="/pkg/reflect/#StructTag.Get"><code>Get</code></a> -but distinguishes the tag not containing the given key -from the tag associating an empty string with the given key. -</p> - -<p> -The -<a href="/pkg/reflect/#Type.Method"><code>Method</code></a> and -<a href="/pkg/reflect/#Type.NumMethod"><code>NumMethod</code></a> -methods of -<a href="/pkg/reflect/#Type"><code>Type</code></a> and -<a href="/pkg/reflect/#Value"><code>Value</code></a> -no longer return or count unexported methods. -</p> -</dd> -</dl> - -<dl id="strings"><dt><a href="/pkg/strings/">strings</a></dt> - -<dd> -<p> -In previous releases of Go, if -<a href="/pkg/strings/#Reader"><code>Reader</code></a>'s -<a href="/pkg/strings/#Reader.Read"><code>Read</code></a> method -were asked for zero bytes with no data remaining, it would -return a count of 0 and no error. -Now it returns a count of 0 and the error -<a href="/pkg/io/#EOF"><code>io.EOF</code></a>. -</p> - -<p> -The -<a href="/pkg/strings/#Reader"><code>Reader</code></a> type has a new method -<a href="/pkg/strings/#Reader.Reset"><code>Reset</code></a> to allow reuse of a <code>Reader</code>. -</p> -</dd> -</dl> - -<dl id="time"><dt><a href="/pkg/time/">time</a></dt> - -<dd> -<p> -<a href="/pkg/time/#Duration"><code>Duration</code></a>'s -time.Duration.String method now reports the zero duration as <code>"0s"</code>, not <code>"0"</code>. -<a href="/pkg/time/#ParseDuration"><code>ParseDuration</code></a> continues to accept both forms. -</p> - -<p> -The method call <code>time.Local.String()</code> now returns <code>"Local"</code> on all systems; -in earlier releases, it returned an empty string on Windows. -</p> - -<p> -The time zone database in -<code>$GOROOT/lib/time</code> has been updated -to IANA release 2016d. -This fallback database is only used when the system time zone database -cannot be found, for example on Windows. -The Windows time zone abbreviation list has also been updated. -</p> -</dd> -</dl> - -<dl id="syscall"><dt><a href="/pkg/syscall/">syscall</a></dt> - -<dd> -<p> -On Linux, the -<a href="/pkg/syscall/#SysProcAttr"><code>SysProcAttr</code></a> struct -(as used in -<a href="/pkg/os/exec/#Cmd"><code>os/exec.Cmd</code></a>'s <code>SysProcAttr</code> field) -has a new <code>Unshareflags</code> field. -If the field is nonzero, the child process created by -<a href="/pkg/syscall/#ForkExec"><code>ForkExec</code></a> -(as used in <code>exec.Cmd</code>'s <code>Run</code> method) -will call the -<a href="http://man7.org/linux/man-pages/man2/unshare.2.html"><i>unshare</i>(2)</a> -system call before executing the new program. -</p> -</dd> -</dl> - - -<dl id="unicode"><dt><a href="/pkg/unicode/">unicode</a></dt> - -<dd> -<p> -The <a href="/pkg/unicode/"><code>unicode</code></a> package and associated -support throughout the system has been upgraded from version 8.0 to -<a href="http://www.unicode.org/versions/Unicode9.0.0/">Unicode 9.0</a>. -</p> -</dd> -</dl> |