vendor/github.com/NYTimes/gziphandler/LICENSE

+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      copyright license to reproduce, prepare Derivative Works of,
+      publicly display, publicly perform, sublicense, and distribute the
+      Work and such Derivative Works in Source or Object form.
+
+   3. Grant of Patent License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
+      where such license applies only to those patent claims licensable
+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
+      granted to You under this License for that Work shall terminate
+      as of the date such litigation is filed.
+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
+          that You distribute, all copyright, patent, trademark, and
+          attribution notices from the Source form of the Work,
+          excluding those notices that do not pertain to any part of
+          the Derivative Works; and
+
+      (d) If the Work includes a "NOTICE" text file as part of its
+          distribution, then any Derivative Works that You distribute must
+          include a readable copy of the attribution notices contained
+          within such NOTICE file, excluding those notices that do not
+          pertain to any part of the Derivative Works, in at least one
+          of the following places: within a NOTICE text file distributed
+          as part of the Derivative Works; within the Source form or
+          documentation, if provided along with the Derivative Works; or,
+          within a display generated by the Derivative Works, if and
+          wherever such third-party notices normally appear. The contents
+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright 2016-2017 The New York Times Company
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.

vendor/github.com/NYTimes/gziphandler/README.md

+Gzip Handler
+============
+
+This is a tiny Go package which wraps HTTP handlers to transparently gzip the
+response body, for clients which support it. Although it's usually simpler to
+leave that to a reverse proxy (like nginx or Varnish), this package is useful
+when that's undesirable.
+
+## Install
+```bash
+go get -u github.com/NYTimes/gziphandler
+```
+
+## Usage
+
+Call `GzipHandler` with any handler (an object which implements the
+`http.Handler` interface), and it'll return a new handler which gzips the
+response. For example:
+
+```go
+package main
+
+import (
+	"io"
+	"net/http"
+	"github.com/NYTimes/gziphandler"
+)
+
+func main() {
+	withoutGz := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/plain")
+		io.WriteString(w, "Hello, World")
+	})
+
+	withGz := gziphandler.GzipHandler(withoutGz)
+
+	http.Handle("/", withGz)
+	http.ListenAndServe("0.0.0.0:8000", nil)
+}
+```
+
+
+## Documentation
+
+The docs can be found at [godoc.org][docs], as usual.
+
+
+## License
+
+[Apache 2.0][license].
+
+
+
+
+[docs]:     https://godoc.org/github.com/NYTimes/gziphandler
+[license]:  https://github.com/NYTimes/gziphandler/blob/master/LICENSE

vendor/github.com/NYTimes/gziphandler/gzip.go

+package gziphandler // import "github.com/NYTimes/gziphandler"
+
+import (
+	"bufio"
+	"compress/gzip"
+	"fmt"
+	"io"
+	"mime"
+	"net"
+	"net/http"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+const (
+	vary            = "Vary"
+	acceptEncoding  = "Accept-Encoding"
+	contentEncoding = "Content-Encoding"
+	contentType     = "Content-Type"
+	contentLength   = "Content-Length"
+)
+
+type codings map[string]float64
+
+const (
+	// DefaultQValue is the default qvalue to assign to an encoding if no explicit qvalue is set.
+	// This is actually kind of ambiguous in RFC 2616, so hopefully it's correct.
+	// The examples seem to indicate that it is.
+	DefaultQValue = 1.0
+
+	// DefaultMinSize is the default minimum size until we enable gzip compression.
+	// 1500 bytes is the MTU size for the internet since that is the largest size allowed at the network layer.
+	// If you take a file that is 1300 bytes and compress it to 800 bytes, it’s still transmitted in that same 1500 byte packet regardless, so you’ve gained nothing.
+	// That being the case, you should restrict the gzip compression to files with a size greater than a single packet, 1400 bytes (1.4KB) is a safe value.
+	DefaultMinSize = 1400
+)
+
+// gzipWriterPools stores a sync.Pool for each compression level for reuse of
+// gzip.Writers. Use poolIndex to covert a compression level to an index into
+// gzipWriterPools.
+var gzipWriterPools [gzip.BestCompression - gzip.BestSpeed + 2]*sync.Pool
+
+func init() {
+	for i := gzip.BestSpeed; i <= gzip.BestCompression; i++ {
+		addLevelPool(i)
+	}
+	addLevelPool(gzip.DefaultCompression)
+}
+
+// poolIndex maps a compression level to its index into gzipWriterPools. It
+// assumes that level is a valid gzip compression level.
+func poolIndex(level int) int {
+	// gzip.DefaultCompression == -1, so we need to treat it special.
+	if level == gzip.DefaultCompression {
+		return gzip.BestCompression - gzip.BestSpeed + 1
+	}
+	return level - gzip.BestSpeed
+}
+
+func addLevelPool(level int) {
+	gzipWriterPools[poolIndex(level)] = &sync.Pool{
+		New: func() interface{} {
+			// NewWriterLevel only returns error on a bad level, we are guaranteeing
+			// that this will be a valid level so it is okay to ignore the returned
+			// error.
+			w, _ := gzip.NewWriterLevel(nil, level)
+			return w
+		},
+	}
+}
+
+// GzipResponseWriter provides an http.ResponseWriter interface, which gzips
+// bytes before writing them to the underlying response. This doesn't close the
+// writers, so don't forget to do that.
+// It can be configured to skip response smaller than minSize.
+type GzipResponseWriter struct {
+	http.ResponseWriter
+	index int // Index for gzipWriterPools.
+	gw    *gzip.Writer
+
+	code int // Saves the WriteHeader value.
+
+	minSize int    // Specifed the minimum response size to gzip. If the response length is bigger than this value, it is compressed.
+	buf     []byte // Holds the first part of the write before reaching the minSize or the end of the write.
+	ignore  bool   // If true, then we immediately passthru writes to the underlying ResponseWriter.
+
+	contentTypes []parsedContentType // Only compress if the response is one of these content-types. All are accepted if empty.
+}
+
+type GzipResponseWriterWithCloseNotify struct {
+	*GzipResponseWriter
+}
+
+func (w GzipResponseWriterWithCloseNotify) CloseNotify() <-chan bool {
+	return w.ResponseWriter.(http.CloseNotifier).CloseNotify()
+}
+
+// Write appends data to the gzip writer.
+func (w *GzipResponseWriter) Write(b []byte) (int, error) {
+	// GZIP responseWriter is initialized. Use the GZIP responseWriter.
+	if w.gw != nil {
+		return w.gw.Write(b)
+	}
+
+	// If we have already decided not to use GZIP, immediately passthrough.
+	if w.ignore {
+		return w.ResponseWriter.Write(b)
+	}
+
+	// Save the write into a buffer for later use in GZIP responseWriter (if content is long enough) or at close with regular responseWriter.
+	// On the first write, w.buf changes from nil to a valid slice
+	w.buf = append(w.buf, b...)
+
+	var (
+		cl, _ = strconv.Atoi(w.Header().Get(contentLength))
+		ct    = w.Header().Get(contentType)
+		ce    = w.Header().Get(contentEncoding)
+	)
+	// Only continue if they didn't already choose an encoding or a known unhandled content length or type.
+	if ce == "" && (cl == 0 || cl >= w.minSize) && (ct == "" || handleContentType(w.contentTypes, ct)) {
+		// If the current buffer is less than minSize and a Content-Length isn't set, then wait until we have more data.
+		if len(w.buf) < w.minSize && cl == 0 {
+			return len(b), nil
+		}
+		// If the Content-Length is larger than minSize or the current buffer is larger than minSize, then continue.
+		if cl >= w.minSize || len(w.buf) >= w.minSize {
+			// If a Content-Type wasn't specified, infer it from the current buffer.
+			if ct == "" {
+				ct = http.DetectContentType(w.buf)
+				w.Header().Set(contentType, ct)
+			}
+			// If the Content-Type is acceptable to GZIP, initialize the GZIP writer.
+			if handleContentType(w.contentTypes, ct) {
+				if err := w.startGzip(); err != nil {
+					return 0, err
+				}
+				return len(b), nil
+			}
+		}
+	}
+	// If we got here, we should not GZIP this response.
+	if err := w.startPlain(); err != nil {
+		return 0, err
+	}
+	return len(b), nil
+}
+
+// startGzip initializes a GZIP writer and writes the buffer.
+func (w *GzipResponseWriter) startGzip() error {
+	// Set the GZIP header.
+	w.Header().Set(contentEncoding, "gzip")
+
+	// if the Content-Length is already set, then calls to Write on gzip
+	// will fail to set the Content-Length header since its already set
+	// See: https://github.com/golang/go/issues/14975.
+	w.Header().Del(contentLength)
+
+	// Write the header to gzip response.
+	if w.code != 0 {
+		w.ResponseWriter.WriteHeader(w.code)
+		// Ensure that no other WriteHeader's happen
+		w.code = 0
+	}
+
+	// Initialize and flush the buffer into the gzip response if there are any bytes.
+	// If there aren't any, we shouldn't initialize it yet because on Close it will
+	// write the gzip header even if nothing was ever written.
+	if len(w.buf) > 0 {
+		// Initialize the GZIP response.
+		w.init()
+		n, err := w.gw.Write(w.buf)
+
+		// This should never happen (per io.Writer docs), but if the write didn't
+		// accept the entire buffer but returned no specific error, we have no clue
+		// what's going on, so abort just to be safe.
+		if err == nil && n < len(w.buf) {
+			err = io.ErrShortWrite
+		}
+		return err
+	}
+	return nil
+}
+
+// startPlain writes to sent bytes and buffer the underlying ResponseWriter without gzip.
+func (w *GzipResponseWriter) startPlain() error {
+	if w.code != 0 {
+		w.ResponseWriter.WriteHeader(w.code)
+		// Ensure that no other WriteHeader's happen
+		w.code = 0
+	}
+	w.ignore = true
+	// If Write was never called then don't call Write on the underlying ResponseWriter.
+	if w.buf == nil {
+		return nil
+	}
+	n, err := w.ResponseWriter.Write(w.buf)
+	w.buf = nil
+	// This should never happen (per io.Writer docs), but if the write didn't
+	// accept the entire buffer but returned no specific error, we have no clue
+	// what's going on, so abort just to be safe.
+	if err == nil && n < len(w.buf) {
+		err = io.ErrShortWrite
+	}
+	return err
+}
+
+// WriteHeader just saves the response code until close or GZIP effective writes.
+func (w *GzipResponseWriter) WriteHeader(code int) {
+	if w.code == 0 {
+		w.code = code
+	}
+}
+
+// init graps a new gzip writer from the gzipWriterPool and writes the correct
+// content encoding header.
+func (w *GzipResponseWriter) init() {
+	// Bytes written during ServeHTTP are redirected to this gzip writer
+	// before being written to the underlying response.
+	gzw := gzipWriterPools[w.index].Get().(*gzip.Writer)
+	gzw.Reset(w.ResponseWriter)
+	w.gw = gzw
+}
+
+// Close will close the gzip.Writer and will put it back in the gzipWriterPool.
+func (w *GzipResponseWriter) Close() error {
+	if w.ignore {
+		return nil
+	}
+
+	if w.gw == nil {
+		// GZIP not triggered yet, write out regular response.
+		err := w.startPlain()
+		// Returns the error if any at write.
+		if err != nil {
+			err = fmt.Errorf("gziphandler: write to regular responseWriter at close gets error: %q", err.Error())
+		}
+		return err
+	}
+
+	err := w.gw.Close()
+	gzipWriterPools[w.index].Put(w.gw)
+	w.gw = nil
+	return err
+}
+
+// Flush flushes the underlying *gzip.Writer and then the underlying
+// http.ResponseWriter if it is an http.Flusher. This makes GzipResponseWriter
+// an http.Flusher.
+func (w *GzipResponseWriter) Flush() {
+	if w.gw == nil && !w.ignore {
+		// Only flush once startGzip or startPlain has been called.
+		//
+		// Flush is thus a no-op until we're certain whether a plain
+		// or gzipped response will be served.
+		return
+	}
+
+	if w.gw != nil {
+		w.gw.Flush()
+	}
+
+	if fw, ok := w.ResponseWriter.(http.Flusher); ok {
+		fw.Flush()
+	}
+}
+
+// Hijack implements http.Hijacker. If the underlying ResponseWriter is a
+// Hijacker, its Hijack method is returned. Otherwise an error is returned.
+func (w *GzipResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	if hj, ok := w.ResponseWriter.(http.Hijacker); ok {
+		return hj.Hijack()
+	}
+	return nil, nil, fmt.Errorf("http.Hijacker interface is not supported")
+}
+
+// verify Hijacker interface implementation
+var _ http.Hijacker = &GzipResponseWriter{}
+
+// MustNewGzipLevelHandler behaves just like NewGzipLevelHandler except that in
+// an error case it panics rather than returning an error.
+func MustNewGzipLevelHandler(level int) func(http.Handler) http.Handler {
+	wrap, err := NewGzipLevelHandler(level)
+	if err != nil {
+		panic(err)
+	}
+	return wrap
+}
+
+// NewGzipLevelHandler returns a wrapper function (often known as middleware)
+// which can be used to wrap an HTTP handler to transparently gzip the response
+// body if the client supports it (via the Accept-Encoding header). Responses will
+// be encoded at the given gzip compression level. An error will be returned only
+// if an invalid gzip compression level is given, so if one can ensure the level
+// is valid, the returned error can be safely ignored.
+func NewGzipLevelHandler(level int) (func(http.Handler) http.Handler, error) {
+	return NewGzipLevelAndMinSize(level, DefaultMinSize)
+}
+
+// NewGzipLevelAndMinSize behave as NewGzipLevelHandler except it let the caller
+// specify the minimum size before compression.
+func NewGzipLevelAndMinSize(level, minSize int) (func(http.Handler) http.Handler, error) {
+	return GzipHandlerWithOpts(CompressionLevel(level), MinSize(minSize))
+}
+
+func GzipHandlerWithOpts(opts ...option) (func(http.Handler) http.Handler, error) {
+	c := &config{
+		level:   gzip.DefaultCompression,
+		minSize: DefaultMinSize,
+	}
+
+	for _, o := range opts {
+		o(c)
+	}
+
+	if err := c.validate(); err != nil {
+		return nil, err
+	}
+
+	return func(h http.Handler) http.Handler {
+		index := poolIndex(c.level)
+
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Add(vary, acceptEncoding)
+			if acceptsGzip(r) {
+				gw := &GzipResponseWriter{
+					ResponseWriter: w,
+					index:          index,
+					minSize:        c.minSize,
+					contentTypes:   c.contentTypes,
+				}
+				defer gw.Close()
+
+				if _, ok := w.(http.CloseNotifier); ok {
+					gwcn := GzipResponseWriterWithCloseNotify{gw}
+					h.ServeHTTP(gwcn, r)
+				} else {
+					h.ServeHTTP(gw, r)
+				}
+
+			} else {
+				h.ServeHTTP(w, r)
+			}
+		})
+	}, nil
+}
+
+// Parsed representation of one of the inputs to ContentTypes.
+// See https://golang.org/pkg/mime/#ParseMediaType
+type parsedContentType struct {
+	mediaType string
+	params    map[string]string
+}
+
+// equals returns whether this content type matches another content type.
+func (pct parsedContentType) equals(mediaType string, params map[string]string) bool {
+	if pct.mediaType != mediaType {
+		return false
+	}
+	// if pct has no params, don't care about other's params
+	if len(pct.params) == 0 {
+		return true
+	}
+
+	// if pct has any params, they must be identical to other's.
+	if len(pct.params) != len(params) {
+		return false
+	}
+	for k, v := range pct.params {
+		if w, ok := params[k]; !ok || v != w {
+			return false
+		}
+	}
+	return true
+}
+
+// Used for functional configuration.
+type config struct {
+	minSize      int
+	level        int
+	contentTypes []parsedContentType
+}
+
+func (c *config) validate() error {
+	if c.level != gzip.DefaultCompression && (c.level < gzip.BestSpeed || c.level > gzip.BestCompression) {
+		return fmt.Errorf("invalid compression level requested: %d", c.level)
+	}
+
+	if c.minSize < 0 {
+		return fmt.Errorf("minimum size must be more than zero")
+	}
+
+	return nil
+}
+
+type option func(c *config)
+
+func MinSize(size int) option {
+	return func(c *config) {
+		c.minSize = size
+	}
+}
+
+func CompressionLevel(level int) option {
+	return func(c *config) {
+		c.level = level
+	}
+}
+
+// ContentTypes specifies a list of content types to compare
+// the Content-Type header to before compressing. If none
+// match, the response will be returned as-is.
+//
+// Content types are compared in a case-insensitive, whitespace-ignored
+// manner.
+//
+// A MIME type without any other directive will match a content type
+// that has the same MIME type, regardless of that content type's other
+// directives. I.e., "text/html" will match both "text/html" and
+// "text/html; charset=utf-8".
+//
+// A MIME type with any other directive will only match a content type
+// that has the same MIME type and other directives. I.e.,
+// "text/html; charset=utf-8" will only match "text/html; charset=utf-8".
+//
+// By default, responses are gzipped regardless of
+// Content-Type.
+func ContentTypes(types []string) option {
+	return func(c *config) {
+		c.contentTypes = []parsedContentType{}
+		for _, v := range types {
+			mediaType, params, err := mime.ParseMediaType(v)
+			if err == nil {
+				c.contentTypes = append(c.contentTypes, parsedContentType{mediaType, params})
+			}
+		}
+	}
+}
+
+// GzipHandler wraps an HTTP handler, to transparently gzip the response body if
+// the client supports it (via the Accept-Encoding header). This will compress at
+// the default compression level.
+func GzipHandler(h http.Handler) http.Handler {
+	wrapper, _ := NewGzipLevelHandler(gzip.DefaultCompression)
+	return wrapper(h)
+}
+
+// acceptsGzip returns true if the given HTTP request indicates that it will
+// accept a gzipped response.
+func acceptsGzip(r *http.Request) bool {
+	acceptedEncodings, _ := parseEncodings(r.Header.Get(acceptEncoding))
+	return acceptedEncodings["gzip"] > 0.0
+}
+
+// returns true if we've been configured to compress the specific content type.
+func handleContentType(contentTypes []parsedContentType, ct string) bool {
+	// If contentTypes is empty we handle all content types.
+	if len(contentTypes) == 0 {
+		return true
+	}
+
+	mediaType, params, err := mime.ParseMediaType(ct)
+	if err != nil {
+		return false
+	}
+
+	for _, c := range contentTypes {
+		if c.equals(mediaType, params) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// parseEncodings attempts to parse a list of codings, per RFC 2616, as might
+// appear in an Accept-Encoding header. It returns a map of content-codings to
+// quality values, and an error containing the errors encountered. It's probably
+// safe to ignore those, because silently ignoring errors is how the internet
+// works.
+//
+// See: http://tools.ietf.org/html/rfc2616#section-14.3.
+func parseEncodings(s string) (codings, error) {
+	c := make(codings)
+	var e []string
+
+	for _, ss := range strings.Split(s, ",") {
+		coding, qvalue, err := parseCoding(ss)
+
+		if err != nil {
+			e = append(e, err.Error())
+		} else {
+			c[coding] = qvalue
+		}
+	}
+
+	// TODO (adammck): Use a proper multi-error struct, so the individual errors
+	//                 can be extracted if anyone cares.
+	if len(e) > 0 {
+		return c, fmt.Errorf("errors while parsing encodings: %s", strings.Join(e, ", "))
+	}
+
+	return c, nil
+}
+
+// parseCoding parses a single conding (content-coding with an optional qvalue),
+// as might appear in an Accept-Encoding header. It attempts to forgive minor
+// formatting errors.
+func parseCoding(s string) (coding string, qvalue float64, err error) {
+	for n, part := range strings.Split(s, ";") {
+		part = strings.TrimSpace(part)
+		qvalue = DefaultQValue
+
+		if n == 0 {
+			coding = strings.ToLower(part)
+		} else if strings.HasPrefix(part, "q=") {
+			qvalue, err = strconv.ParseFloat(strings.TrimPrefix(part, "q="), 64)
+
+			if qvalue < 0.0 {
+				qvalue = 0.0
+			} else if qvalue > 1.0 {
+				qvalue = 1.0
+			}
+		}
+	}
+
+	if coding == "" {
+		err = fmt.Errorf("empty content-coding")
+	}
+
+	return
+}

vendor/github.com/NYTimes/gziphandler/gzip_go18.go

+// +build go1.8
+
+package gziphandler
+
+import "net/http"
+
+// Push initiates an HTTP/2 server push.
+// Push returns ErrNotSupported if the client has disabled push or if push
+// is not supported on the underlying connection.
+func (w *GzipResponseWriter) Push(target string, opts *http.PushOptions) error {
+	pusher, ok := w.ResponseWriter.(http.Pusher)
+	if ok && pusher != nil {
+		return pusher.Push(target, setAcceptEncodingForPushOptions(opts))
+	}
+	return http.ErrNotSupported
+}
+
+// setAcceptEncodingForPushOptions sets "Accept-Encoding" : "gzip" for PushOptions without overriding existing headers.
+func setAcceptEncodingForPushOptions(opts *http.PushOptions) *http.PushOptions {
+
+	if opts == nil {
+		opts = &http.PushOptions{
+			Header: http.Header{
+				acceptEncoding: []string{"gzip"},
+			},
+		}
+		return opts
+	}
+
+	if opts.Header == nil {
+		opts.Header = http.Header{
+			acceptEncoding: []string{"gzip"},
+		}
+		return opts
+	}
+
+	if encoding := opts.Header.Get(acceptEncoding); encoding == "" {
+		opts.Header.Add(acceptEncoding, "gzip")
+		return opts
+	}
+
+	return opts
+}

vendor/github.com/cenkalti/backoff/v4/.gitignore

+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+
+# IDEs
+.idea/

vendor/github.com/cenkalti/backoff/v4/.travis.yml

+language: go
+go:
+  - 1.13
+  - 1.x
+  - tip
+before_install:
+  - go get github.com/mattn/goveralls
+  - go get golang.org/x/tools/cmd/cover
+script:
+  - $HOME/gopath/bin/goveralls -service=travis-ci

vendor/github.com/cenkalti/backoff/README.md → vendor/github.com/cenkalti/backoff/v4/README.md

@@ -9,7 +9,9 @@ The retries exponentially increase and stop increasing when a certain threshold
 
 ## Usage
 
-See https://godoc.org/github.com/cenkalti/backoff#pkg-examples
+Import path is `github.com/cenkalti/backoff/v4`. Please note the version part at the end.
+
+Use https://pkg.go.dev/github.com/cenkalti/backoff/v4 to view the documentation.
 
 ## Contributing
 
@@ -17,7 +19,7 @@ See https://godoc.org/github.com/cenkalti/backoff#pkg-examples
 * Please don't send a PR without opening an issue and discussing it first.
 * If proposed change is not a common use case, I will probably not accept it.
 
-[godoc]: https://godoc.org/github.com/cenkalti/backoff
+[godoc]: https://pkg.go.dev/github.com/cenkalti/backoff/v4
 [godoc image]: https://godoc.org/github.com/cenkalti/backoff?status.png
 [travis]: https://travis-ci.org/cenkalti/backoff
 [travis image]: https://travis-ci.org/cenkalti/backoff.png?branch=master
@@ -27,4 +29,4 @@ See https://godoc.org/github.com/cenkalti/backoff#pkg-examples
 [google-http-java-client]: https://github.com/google/google-http-java-client/blob/da1aa993e90285ec18579f1553339b00e19b3ab5/google-http-client/src/main/java/com/google/api/client/util/ExponentialBackOff.java
 [exponential backoff wiki]: http://en.wikipedia.org/wiki/Exponential_backoff
 
-[advanced example]: https://godoc.org/github.com/cenkalti/backoff#example_
+[advanced example]: https://pkg.go.dev/github.com/cenkalti/backoff/v4?tab=doc#pkg-examples

vendor/github.com/cenkalti/backoff/context.go → vendor/github.com/cenkalti/backoff/v4/context.go

@@ -7,7 +7,7 @@ import (
 
 // BackOffContext is a backoff policy that stops retrying after the context
 // is canceled.
-type BackOffContext interface {
+type BackOffContext interface { // nolint: golint
 	BackOff
 	Context() context.Context
 }
@@ -20,7 +20,7 @@ type backOffContext struct {
 // WithContext returns a BackOffContext with context ctx
 //
 // ctx must not be nil
-func WithContext(b BackOff, ctx context.Context) BackOffContext {
+func WithContext(b BackOff, ctx context.Context) BackOffContext { // nolint: golint
 	if ctx == nil {
 		panic("nil context")
 	}
@@ -38,11 +38,14 @@ func WithContext(b BackOff, ctx context.Context) BackOffContext {
 	}
 }
 
-func ensureContext(b BackOff) BackOffContext {
+func getContext(b BackOff) context.Context {
 	if cb, ok := b.(BackOffContext); ok {
-		return cb
+		return cb.Context()
 	}
-	return WithContext(b, context.Background())
+	if tb, ok := b.(*backOffTries); ok {
+		return getContext(tb.delegate)
+	}
+	return context.Background()
 }
 
 func (b *backOffContext) Context() context.Context {
@@ -54,10 +57,6 @@ func (b *backOffContext) NextBackOff() time.Duration {
 	case <-b.ctx.Done():
 		return Stop
 	default:
+		return b.BackOff.NextBackOff()
 	}
-	next := b.BackOff.NextBackOff()
-	if deadline, ok := b.ctx.Deadline(); ok && deadline.Sub(time.Now()) < next {
-		return Stop
-	}
-	return next
 }

vendor/github.com/cenkalti/backoff/exponential.go → vendor/github.com/cenkalti/backoff/v4/exponential.go

@@ -56,9 +56,10 @@ type ExponentialBackOff struct {
 	RandomizationFactor float64
 	Multiplier          float64
 	MaxInterval         time.Duration
-	// After MaxElapsedTime the ExponentialBackOff stops.
+	// After MaxElapsedTime the ExponentialBackOff returns Stop.
 	// It never stops if MaxElapsedTime == 0.
 	MaxElapsedTime time.Duration
+	Stop           time.Duration
 	Clock          Clock
 
 	currentInterval time.Duration
@@ -87,6 +88,7 @@ func NewExponentialBackOff() *ExponentialBackOff {
 		Multiplier:          DefaultMultiplier,
 		MaxInterval:         DefaultMaxInterval,
 		MaxElapsedTime:      DefaultMaxElapsedTime,
+		Stop:                Stop,
 		Clock:               SystemClock,
 	}
 	b.Reset()
@@ -103,20 +105,23 @@ func (t systemClock) Now() time.Time {
 var SystemClock = systemClock{}
 
 // Reset the interval back to the initial retry interval and restarts the timer.
+// Reset must be called before using b.
 func (b *ExponentialBackOff) Reset() {
 	b.currentInterval = b.InitialInterval
 	b.startTime = b.Clock.Now()
 }
 
 // NextBackOff calculates the next backoff interval using the formula:
-// 	Randomized interval = RetryInterval +/- (RandomizationFactor * RetryInterval)
+// 	Randomized interval = RetryInterval * (1 ± RandomizationFactor)
 func (b *ExponentialBackOff) NextBackOff() time.Duration {
 	// Make sure we have not gone over the maximum elapsed time.
-	if b.MaxElapsedTime != 0 && b.GetElapsedTime() > b.MaxElapsedTime {
-		return Stop
+	elapsed := b.GetElapsedTime()
+	next := getRandomValueFromInterval(b.RandomizationFactor, rand.Float64(), b.currentInterval)
+	b.incrementCurrentInterval()
+	if b.MaxElapsedTime != 0 && elapsed+next > b.MaxElapsedTime {
+		return b.Stop
 	}
-	defer b.incrementCurrentInterval()
-	return getRandomValueFromInterval(b.RandomizationFactor, rand.Float64(), b.currentInterval)
+	return next
 }
 
 // GetElapsedTime returns the elapsed time since an ExponentialBackOff instance
@@ -140,8 +145,11 @@ func (b *ExponentialBackOff) incrementCurrentInterval() {
 }
 
 // Returns a random value from the following interval:
-// 	[randomizationFactor * currentInterval, randomizationFactor * currentInterval].
+// 	[currentInterval - randomizationFactor * currentInterval, currentInterval + randomizationFactor * currentInterval].
 func getRandomValueFromInterval(randomizationFactor, random float64, currentInterval time.Duration) time.Duration {
+	if randomizationFactor == 0 {
+		return currentInterval // make sure no randomness is used when randomizationFactor is 0.
+	}
 	var delta = randomizationFactor * float64(currentInterval)
 	var minInterval = float64(currentInterval) - delta
 	var maxInterval = float64(currentInterval) + delta

vendor/github.com/cenkalti/backoff/retry.go → vendor/github.com/cenkalti/backoff/v4/retry.go

 package backoff
 
-import "time"
+import (
+	"errors"
+	"time"
+)
 
 // An Operation is executing by Retry() or RetryNotify().
 // The operation will be retried using a backoff policy if it returns an error.
@@ -21,15 +24,31 @@ type Notify func(error, time.Duration)
 //
 // Retry sleeps the goroutine for the duration returned by BackOff after a
 // failed operation returns.
-func Retry(o Operation, b BackOff) error { return RetryNotify(o, b, nil) }
+func Retry(o Operation, b BackOff) error {
+	return RetryNotify(o, b, nil)
+}
 
 // RetryNotify calls notify function with the error and wait duration
 // for each failed attempt before sleep.
 func RetryNotify(operation Operation, b BackOff, notify Notify) error {
+	return RetryNotifyWithTimer(operation, b, notify, nil)
+}
+
+// RetryNotifyWithTimer calls notify function with the error and wait duration using the given Timer
+// for each failed attempt before sleep.
+// A default timer that uses system timer is used when nil is passed.
+func RetryNotifyWithTimer(operation Operation, b BackOff, notify Notify, t Timer) error {
 	var err error
 	var next time.Duration
+	if t == nil {
+		t = &defaultTimer{}
+	}
+
+	defer func() {
+		t.Stop()
+	}()
 
-	cb := ensureContext(b)
+	ctx := getContext(b)
 
 	b.Reset()
 	for {
@@ -37,11 +56,16 @@ func RetryNotify(operation Operation, b BackOff, notify Notify) error {
 			return nil
 		}
 
-		if permanent, ok := err.(*PermanentError); ok {
+		var permanent *PermanentError
+		if errors.As(err, &permanent) {
 			return permanent.Err
 		}
 
-		if next = cb.NextBackOff(); next == Stop {
+		if next = b.NextBackOff(); next == Stop {
+			if cerr := ctx.Err(); cerr != nil {
+				return cerr
+			}
+
 			return err
 		}
 
@@ -49,13 +73,12 @@ func RetryNotify(operation Operation, b BackOff, notify Notify) error {
 			notify(err, next)
 		}
 
-		t := time.NewTimer(next)
+		t.Start(next)
 
 		select {
-		case <-cb.Context().Done():
-			t.Stop()
-			return err
-		case <-t.C:
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-t.C():
 		}
 	}
 }
@@ -69,8 +92,20 @@ func (e *PermanentError) Error() string {
 	return e.Err.Error()
 }
 
+func (e *PermanentError) Unwrap() error {
+	return e.Err
+}
+
+func (e *PermanentError) Is(target error) bool {
+	_, ok := target.(*PermanentError)
+	return ok
+}
+
 // Permanent wraps the given err in a *PermanentError.
-func Permanent(err error) *PermanentError {
+func Permanent(err error) error {
+	if err == nil {
+		return nil
+	}
 	return &PermanentError{
 		Err: err,
 	}

vendor/github.com/cenkalti/backoff/ticker.go → vendor/github.com/cenkalti/backoff/v4/ticker.go

 package backoff
 
 import (
+	"context"
 	"sync"
 	"time"
 )
@@ -12,7 +13,9 @@ import (
 type Ticker struct {
 	C        <-chan time.Time
 	c        chan time.Time
-	b        BackOffContext
+	b        BackOff
+	ctx      context.Context
+	timer    Timer
 	stop     chan struct{}
 	stopOnce sync.Once
 }
@@ -24,12 +27,23 @@ type Ticker struct {
 // provided backoff policy (notably calling NextBackOff or Reset)
 // while the ticker is running.
 func NewTicker(b BackOff) *Ticker {
+	return NewTickerWithTimer(b, &defaultTimer{})
+}
+
+// NewTickerWithTimer returns a new Ticker with a custom timer.
+// A default timer that uses system timer is used when nil is passed.
+func NewTickerWithTimer(b BackOff, timer Timer) *Ticker {
+	if timer == nil {
+		timer = &defaultTimer{}
+	}
 	c := make(chan time.Time)
 	t := &Ticker{
-		C:    c,
-		c:    c,
-		b:    ensureContext(b),
-		stop: make(chan struct{}),
+		C:     c,
+		c:     c,
+		b:     b,
+		ctx:   getContext(b),
+		timer: timer,
+		stop:  make(chan struct{}),
 	}
 	t.b.Reset()
 	go t.run()
@@ -59,7 +73,7 @@ func (t *Ticker) run() {
 		case <-t.stop:
 			t.c = nil // Prevent future ticks from being sent to the channel.
 			return
-		case <-t.b.Context().Done():
+		case <-t.ctx.Done():
 			return
 		}
 	}
@@ -78,5 +92,6 @@ func (t *Ticker) send(tick time.Time) <-chan time.Time {
 		return nil
 	}
 
-	return time.After(next)
+	t.timer.Start(next)
+	return t.timer.C()
 }

vendor/github.com/cenkalti/backoff/v4/timer.go

+package backoff
+
+import "time"
+
+type Timer interface {
+	Start(duration time.Duration)
+	Stop()
+	C() <-chan time.Time
+}
+
+// defaultTimer implements Timer interface using time.Timer
+type defaultTimer struct {
+	timer *time.Timer
+}
+
+// C returns the timers channel which receives the current time when the timer fires.
+func (t *defaultTimer) C() <-chan time.Time {
+	return t.timer.C
+}
+
+// Start starts the timer to fire after the given duration
+func (t *defaultTimer) Start(duration time.Duration) {
+	if t.timer == nil {
+		t.timer = time.NewTimer(duration)
+	} else {
+		t.timer.Reset(duration)
+	}
+}
+
+// Stop is called when the timer is not used anymore and resources may be freed.
+func (t *defaultTimer) Stop() {
+	if t.timer != nil {
+		t.timer.Stop()
+	}
+}

vendor/github.com/cenkalti/backoff/tries.go → vendor/github.com/cenkalti/backoff/v4/tries.go

@@ -20,6 +20,9 @@ type backOffTries struct {
 }
 
 func (b *backOffTries) NextBackOff() time.Duration {
+	if b.maxTries == 0 {
+		return Stop
+	}
 	if b.maxTries > 0 {
 		if b.maxTries <= b.numTries {
 			return Stop

vendor/github.com/cespare/xxhash/v2/LICENSE.txt

+Copyright (c) 2016 Caleb Spare
+
+MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/github.com/cespare/xxhash/v2/README.md

+# xxhash
+
+[![Go Reference](https://pkg.go.dev/badge/github.com/cespare/xxhash/v2.svg)](https://pkg.go.dev/github.com/cespare/xxhash/v2)
+[![Test](https://github.com/cespare/xxhash/actions/workflows/test.yml/badge.svg)](https://github.com/cespare/xxhash/actions/workflows/test.yml)
+
+xxhash is a Go implementation of the 64-bit
+[xxHash](http://cyan4973.github.io/xxHash/) algorithm, XXH64. This is a
+high-quality hashing algorithm that is much faster than anything in the Go
+standard library.
+
+This package provides a straightforward API:
+
+```
+func Sum64(b []byte) uint64
+func Sum64String(s string) uint64
+type Digest struct{ ... }
+    func New() *Digest
+```
+
+The `Digest` type implements hash.Hash64. Its key methods are:
+
+```
+func (*Digest) Write([]byte) (int, error)
+func (*Digest) WriteString(string) (int, error)
+func (*Digest) Sum64() uint64
+```
+
+This implementation provides a fast pure-Go implementation and an even faster
+assembly implementation for amd64.
+
+## Compatibility
+
+This package is in a module and the latest code is in version 2 of the module.
+You need a version of Go with at least "minimal module compatibility" to use
+github.com/cespare/xxhash/v2:
+
+* 1.9.7+ for Go 1.9
+* 1.10.3+ for Go 1.10
+* Go 1.11 or later
+
+I recommend using the latest release of Go.
+
+## Benchmarks
+
+Here are some quick benchmarks comparing the pure-Go and assembly
+implementations of Sum64.
+
+| input size | purego | asm |
+| --- | --- | --- |
+| 5 B   |  979.66 MB/s |  1291.17 MB/s  |
+| 100 B | 7475.26 MB/s | 7973.40 MB/s  |
+| 4 KB  | 17573.46 MB/s | 17602.65 MB/s |
+| 10 MB | 17131.46 MB/s | 17142.16 MB/s |
+
+These numbers were generated on Ubuntu 18.04 with an Intel i7-8700K CPU using
+the following commands under Go 1.11.2:
+
+```
+$ go test -tags purego -benchtime 10s -bench '/xxhash,direct,bytes'
+$ go test -benchtime 10s -bench '/xxhash,direct,bytes'
+```
+
+## Projects using this package
+
+- [InfluxDB](https://github.com/influxdata/influxdb)
+- [Prometheus](https://github.com/prometheus/prometheus)
+- [VictoriaMetrics](https://github.com/VictoriaMetrics/VictoriaMetrics)
+- [FreeCache](https://github.com/coocood/freecache)
+- [FastCache](https://github.com/VictoriaMetrics/fastcache)

vendor/github.com/cespare/xxhash/v2/xxhash_amd64.go

+// +build !appengine
+// +build gc
+// +build !purego
+
+package xxhash
+
+// Sum64 computes the 64-bit xxHash digest of b.
+//
+//go:noescape
+func Sum64(b []byte) uint64
+
+//go:noescape
+func writeBlocks(d *Digest, b []byte) int