[committed] Fix previously latent bug in reorg affecting cris port

[official-gcc.git] / libgo / go / net / http / request.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// HTTP Request reading and parsing.

package http

import (
        "bufio"
        "bytes"
        "context"
        "crypto/tls"
        "encoding/base64"
        "errors"
        "fmt"
        "io"
        "mime"
        "mime/multipart"
        "net"
        "net/http/httptrace"
        "net/http/internal/ascii"
        "net/textproto"
        "net/url"
        urlpkg "net/url"
        "strconv"
        "strings"
        "sync"

        "golang.org/x/net/idna"
)

const (
        defaultMaxMemory = 32 << 20 // 32 MB
)

// ErrMissingFile is returned by FormFile when the provided file field name
// is either not present in the request or not a file field.
var ErrMissingFile = errors.New("http: no such file")

// ProtocolError represents an HTTP protocol error.
//
// Deprecated: Not all errors in the http package related to protocol errors
// are of type ProtocolError.
type ProtocolError struct {
        ErrorString string
}

func (pe *ProtocolError) Error() string { return pe.ErrorString }

var (
        // ErrNotSupported is returned by the Push method of Pusher
        // implementations to indicate that HTTP/2 Push support is not
        // available.
        ErrNotSupported = &ProtocolError{"feature not supported"}

        // Deprecated: ErrUnexpectedTrailer is no longer returned by
        // anything in the net/http package. Callers should not
        // compare errors against this variable.
        ErrUnexpectedTrailer = &ProtocolError{"trailer header without chunked transfer encoding"}

        // ErrMissingBoundary is returned by Request.MultipartReader when the
        // request's Content-Type does not include a "boundary" parameter.
        ErrMissingBoundary = &ProtocolError{"no multipart boundary param in Content-Type"}

        // ErrNotMultipart is returned by Request.MultipartReader when the
        // request's Content-Type is not multipart/form-data.
        ErrNotMultipart = &ProtocolError{"request Content-Type isn't multipart/form-data"}

        // Deprecated: ErrHeaderTooLong is no longer returned by
        // anything in the net/http package. Callers should not
        // compare errors against this variable.
        ErrHeaderTooLong = &ProtocolError{"header too long"}

        // Deprecated: ErrShortBody is no longer returned by
        // anything in the net/http package. Callers should not
        // compare errors against this variable.
        ErrShortBody = &ProtocolError{"entity body too short"}

        // Deprecated: ErrMissingContentLength is no longer returned by
        // anything in the net/http package. Callers should not
        // compare errors against this variable.
        ErrMissingContentLength = &ProtocolError{"missing ContentLength in HEAD response"}
)

func badStringError(what, val string) error { return fmt.Errorf("%s %q", what, val) }

// Headers that Request.Write handles itself and should be skipped.
var reqWriteExcludeHeader = map[string]bool{
        "Host":              true, // not in Header map anyway
        "User-Agent":        true,
        "Content-Length":    true,
        "Transfer-Encoding": true,
        "Trailer":           true,
}

// A Request represents an HTTP request received by a server
// or to be sent by a client.
//
// The field semantics differ slightly between client and server
// usage. In addition to the notes on the fields below, see the
// documentation for Request.Write and RoundTripper.
type Request struct {
        // Method specifies the HTTP method (GET, POST, PUT, etc.).
        // For client requests, an empty string means GET.
        //
        // Go's HTTP client does not support sending a request with
        // the CONNECT method. See the documentation on Transport for
        // details.
        Method string

        // URL specifies either the URI being requested (for server
        // requests) or the URL to access (for client requests).
        //
        // For server requests, the URL is parsed from the URI
        // supplied on the Request-Line as stored in RequestURI.  For
        // most requests, fields other than Path and RawQuery will be
        // empty. (See RFC 7230, Section 5.3)
        //
        // For client requests, the URL's Host specifies the server to
        // connect to, while the Request's Host field optionally
        // specifies the Host header value to send in the HTTP
        // request.
        URL *url.URL

        // The protocol version for incoming server requests.
        //
        // For client requests, these fields are ignored. The HTTP
        // client code always uses either HTTP/1.1 or HTTP/2.
        // See the docs on Transport for details.
        Proto      string // "HTTP/1.0"
        ProtoMajor int    // 1
        ProtoMinor int    // 0

        // Header contains the request header fields either received
        // by the server or to be sent by the client.
        //
        // If a server received a request with header lines,
        //
        //      Host: example.com
        //      accept-encoding: gzip, deflate
        //      Accept-Language: en-us
        //      fOO: Bar
        //      foo: two
        //
        // then
        //
        //      Header = map[string][]string{
        //              "Accept-Encoding": {"gzip, deflate"},
        //              "Accept-Language": {"en-us"},
        //              "Foo": {"Bar", "two"},
        //      }
        //
        // For incoming requests, the Host header is promoted to the
        // Request.Host field and removed from the Header map.
        //
        // HTTP defines that header names are case-insensitive. The
        // request parser implements this by using CanonicalHeaderKey,
        // making the first character and any characters following a
        // hyphen uppercase and the rest lowercase.
        //
        // For client requests, certain headers such as Content-Length
        // and Connection are automatically written when needed and
        // values in Header may be ignored. See the documentation
        // for the Request.Write method.
        Header Header

        // Body is the request's body.
        //
        // For client requests, a nil body means the request has no
        // body, such as a GET request. The HTTP Client's Transport
        // is responsible for calling the Close method.
        //
        // For server requests, the Request Body is always non-nil
        // but will return EOF immediately when no body is present.
        // The Server will close the request body. The ServeHTTP
        // Handler does not need to.
        //
        // Body must allow Read to be called concurrently with Close.
        // In particular, calling Close should unblock a Read waiting
        // for input.
        Body io.ReadCloser

        // GetBody defines an optional func to return a new copy of
        // Body. It is used for client requests when a redirect requires
        // reading the body more than once. Use of GetBody still
        // requires setting Body.
        //
        // For server requests, it is unused.
        GetBody func() (io.ReadCloser, error)

        // ContentLength records the length of the associated content.
        // The value -1 indicates that the length is unknown.
        // Values >= 0 indicate that the given number of bytes may
        // be read from Body.
        //
        // For client requests, a value of 0 with a non-nil Body is
        // also treated as unknown.
        ContentLength int64

        // TransferEncoding lists the transfer encodings from outermost to
        // innermost. An empty list denotes the "identity" encoding.
        // TransferEncoding can usually be ignored; chunked encoding is
        // automatically added and removed as necessary when sending and
        // receiving requests.
        TransferEncoding []string

        // Close indicates whether to close the connection after
        // replying to this request (for servers) or after sending this
        // request and reading its response (for clients).
        //
        // For server requests, the HTTP server handles this automatically
        // and this field is not needed by Handlers.
        //
        // For client requests, setting this field prevents re-use of
        // TCP connections between requests to the same hosts, as if
        // Transport.DisableKeepAlives were set.
        Close bool

        // For server requests, Host specifies the host on which the
        // URL is sought. For HTTP/1 (per RFC 7230, section 5.4), this
        // is either the value of the "Host" header or the host name
        // given in the URL itself. For HTTP/2, it is the value of the
        // ":authority" pseudo-header field.
        // It may be of the form "host:port". For international domain
        // names, Host may be in Punycode or Unicode form. Use
        // golang.org/x/net/idna to convert it to either format if
        // needed.
        // To prevent DNS rebinding attacks, server Handlers should
        // validate that the Host header has a value for which the
        // Handler considers itself authoritative. The included
        // ServeMux supports patterns registered to particular host
        // names and thus protects its registered Handlers.
        //
        // For client requests, Host optionally overrides the Host
        // header to send. If empty, the Request.Write method uses
        // the value of URL.Host. Host may contain an international
        // domain name.
        Host string

        // Form contains the parsed form data, including both the URL
        // field's query parameters and the PATCH, POST, or PUT form data.
        // This field is only available after ParseForm is called.
        // The HTTP client ignores Form and uses Body instead.
        Form url.Values

        // PostForm contains the parsed form data from PATCH, POST
        // or PUT body parameters.
        //
        // This field is only available after ParseForm is called.
        // The HTTP client ignores PostForm and uses Body instead.
        PostForm url.Values

        // MultipartForm is the parsed multipart form, including file uploads.
        // This field is only available after ParseMultipartForm is called.
        // The HTTP client ignores MultipartForm and uses Body instead.
        MultipartForm *multipart.Form

        // Trailer specifies additional headers that are sent after the request
        // body.
        //
        // For server requests, the Trailer map initially contains only the
        // trailer keys, with nil values. (The client declares which trailers it
        // will later send.)  While the handler is reading from Body, it must
        // not reference Trailer. After reading from Body returns EOF, Trailer
        // can be read again and will contain non-nil values, if they were sent
        // by the client.
        //
        // For client requests, Trailer must be initialized to a map containing
        // the trailer keys to later send. The values may be nil or their final
        // values. The ContentLength must be 0 or -1, to send a chunked request.
        // After the HTTP request is sent the map values can be updated while
        // the request body is read. Once the body returns EOF, the caller must
        // not mutate Trailer.
        //
        // Few HTTP clients, servers, or proxies support HTTP trailers.
        Trailer Header

        // RemoteAddr allows HTTP servers and other software to record
        // the network address that sent the request, usually for
        // logging. This field is not filled in by ReadRequest and
        // has no defined format. The HTTP server in this package
        // sets RemoteAddr to an "IP:port" address before invoking a
        // handler.
        // This field is ignored by the HTTP client.
        RemoteAddr string

        // RequestURI is the unmodified request-target of the
        // Request-Line (RFC 7230, Section 3.1.1) as sent by the client
        // to a server. Usually the URL field should be used instead.
        // It is an error to set this field in an HTTP client request.
        RequestURI string

        // TLS allows HTTP servers and other software to record
        // information about the TLS connection on which the request
        // was received. This field is not filled in by ReadRequest.
        // The HTTP server in this package sets the field for
        // TLS-enabled connections before invoking a handler;
        // otherwise it leaves the field nil.
        // This field is ignored by the HTTP client.
        TLS *tls.ConnectionState

        // Cancel is an optional channel whose closure indicates that the client
        // request should be regarded as canceled. Not all implementations of
        // RoundTripper may support Cancel.
        //
        // For server requests, this field is not applicable.
        //
        // Deprecated: Set the Request's context with NewRequestWithContext
        // instead. If a Request's Cancel field and context are both
        // set, it is undefined whether Cancel is respected.
        Cancel <-chan struct{}

        // Response is the redirect response which caused this request
        // to be created. This field is only populated during client
        // redirects.
        Response *Response

        // ctx is either the client or server context. It should only
        // be modified via copying the whole Request using WithContext.
        // It is unexported to prevent people from using Context wrong
        // and mutating the contexts held by callers of the same request.
        ctx context.Context
}

// Context returns the request's context. To change the context, use
// WithContext.
//
// The returned context is always non-nil; it defaults to the
// background context.
//
// For outgoing client requests, the context controls cancellation.
//
// For incoming server requests, the context is canceled when the
// client's connection closes, the request is canceled (with HTTP/2),
// or when the ServeHTTP method returns.
func (r *Request) Context() context.Context {
        if r.ctx != nil {
                return r.ctx
        }
        return context.Background()
}

// WithContext returns a shallow copy of r with its context changed
// to ctx. The provided ctx must be non-nil.
//
// For outgoing client request, the context controls the entire
// lifetime of a request and its response: obtaining a connection,
// sending the request, and reading the response headers and body.
//
// To create a new request with a context, use NewRequestWithContext.
// To change the context of a request, such as an incoming request you
// want to modify before sending back out, use Request.Clone. Between
// those two uses, it's rare to need WithContext.
func (r *Request) WithContext(ctx context.Context) *Request {
        if ctx == nil {
                panic("nil context")
        }
        r2 := new(Request)
        *r2 = *r
        r2.ctx = ctx
        r2.URL = cloneURL(r.URL) // legacy behavior; TODO: try to remove. Issue 23544
        return r2
}

// Clone returns a deep copy of r with its context changed to ctx.
// The provided ctx must be non-nil.
//
// For an outgoing client request, the context controls the entire
// lifetime of a request and its response: obtaining a connection,
// sending the request, and reading the response headers and body.
func (r *Request) Clone(ctx context.Context) *Request {
        if ctx == nil {
                panic("nil context")
        }
        r2 := new(Request)
        *r2 = *r
        r2.ctx = ctx
        r2.URL = cloneURL(r.URL)
        if r.Header != nil {
                r2.Header = r.Header.Clone()
        }
        if r.Trailer != nil {
                r2.Trailer = r.Trailer.Clone()
        }
        if s := r.TransferEncoding; s != nil {
                s2 := make([]string, len(s))
                copy(s2, s)
                r2.TransferEncoding = s2
        }
        r2.Form = cloneURLValues(r.Form)
        r2.PostForm = cloneURLValues(r.PostForm)
        r2.MultipartForm = cloneMultipartForm(r.MultipartForm)
        return r2
}

// ProtoAtLeast reports whether the HTTP protocol used
// in the request is at least major.minor.
func (r *Request) ProtoAtLeast(major, minor int) bool {
        return r.ProtoMajor > major ||
                r.ProtoMajor == major && r.ProtoMinor >= minor
}

// UserAgent returns the client's User-Agent, if sent in the request.
func (r *Request) UserAgent() string {
        return r.Header.Get("User-Agent")
}

// Cookies parses and returns the HTTP cookies sent with the request.
func (r *Request) Cookies() []*Cookie {
        return readCookies(r.Header, "")
}

// ErrNoCookie is returned by Request's Cookie method when a cookie is not found.
var ErrNoCookie = errors.New("http: named cookie not present")

// Cookie returns the named cookie provided in the request or
// ErrNoCookie if not found.
// If multiple cookies match the given name, only one cookie will
// be returned.
func (r *Request) Cookie(name string) (*Cookie, error) {
        for _, c := range readCookies(r.Header, name) {
                return c, nil
        }
        return nil, ErrNoCookie
}

// AddCookie adds a cookie to the request. Per RFC 6265 section 5.4,
// AddCookie does not attach more than one Cookie header field. That
// means all cookies, if any, are written into the same line,
// separated by semicolon.
// AddCookie only sanitizes c's name and value, and does not sanitize
// a Cookie header already present in the request.
func (r *Request) AddCookie(c *Cookie) {
        s := fmt.Sprintf("%s=%s", sanitizeCookieName(c.Name), sanitizeCookieValue(c.Value))
        if c := r.Header.Get("Cookie"); c != "" {
                r.Header.Set("Cookie", c+"; "+s)
        } else {
                r.Header.Set("Cookie", s)
        }
}

// Referer returns the referring URL, if sent in the request.
//
// Referer is misspelled as in the request itself, a mistake from the
// earliest days of HTTP.  This value can also be fetched from the
// Header map as Header["Referer"]; the benefit of making it available
// as a method is that the compiler can diagnose programs that use the
// alternate (correct English) spelling req.Referrer() but cannot
// diagnose programs that use Header["Referrer"].
func (r *Request) Referer() string {
        return r.Header.Get("Referer")
}

// multipartByReader is a sentinel value.
// Its presence in Request.MultipartForm indicates that parsing of the request
// body has been handed off to a MultipartReader instead of ParseMultipartForm.
var multipartByReader = &multipart.Form{
        Value: make(map[string][]string),
        File:  make(map[string][]*multipart.FileHeader),
}

// MultipartReader returns a MIME multipart reader if this is a
// multipart/form-data or a multipart/mixed POST request, else returns nil and an error.
// Use this function instead of ParseMultipartForm to
// process the request body as a stream.
func (r *Request) MultipartReader() (*multipart.Reader, error) {
        if r.MultipartForm == multipartByReader {
                return nil, errors.New("http: MultipartReader called twice")
        }
        if r.MultipartForm != nil {
                return nil, errors.New("http: multipart handled by ParseMultipartForm")
        }
        r.MultipartForm = multipartByReader
        return r.multipartReader(true)
}

func (r *Request) multipartReader(allowMixed bool) (*multipart.Reader, error) {
        v := r.Header.Get("Content-Type")
        if v == "" {
                return nil, ErrNotMultipart
        }
        d, params, err := mime.ParseMediaType(v)
        if err != nil || !(d == "multipart/form-data" || allowMixed && d == "multipart/mixed") {
                return nil, ErrNotMultipart
        }
        boundary, ok := params["boundary"]
        if !ok {
                return nil, ErrMissingBoundary
        }
        return multipart.NewReader(r.Body, boundary), nil
}

// isH2Upgrade reports whether r represents the http2 "client preface"
// magic string.
func (r *Request) isH2Upgrade() bool {
        return r.Method == "PRI" && len(r.Header) == 0 && r.URL.Path == "*" && r.Proto == "HTTP/2.0"
}

// Return value if nonempty, def otherwise.
func valueOrDefault(value, def string) string {
        if value != "" {
                return value
        }
        return def
}

// NOTE: This is not intended to reflect the actual Go version being used.
// It was changed at the time of Go 1.1 release because the former User-Agent
// had ended up blocked by some intrusion detection systems.
// See https://codereview.appspot.com/7532043.
const defaultUserAgent = "Go-http-client/1.1"

// Write writes an HTTP/1.1 request, which is the header and body, in wire format.
// This method consults the following fields of the request:
//      Host
//      URL
//      Method (defaults to "GET")
//      Header
//      ContentLength
//      TransferEncoding
//      Body
//
// If Body is present, Content-Length is <= 0 and TransferEncoding
// hasn't been set to "identity", Write adds "Transfer-Encoding:
// chunked" to the header. Body is closed after it is sent.
func (r *Request) Write(w io.Writer) error {
        return r.write(w, false, nil, nil)
}

// WriteProxy is like Write but writes the request in the form
// expected by an HTTP proxy. In particular, WriteProxy writes the
// initial Request-URI line of the request with an absolute URI, per
// section 5.3 of RFC 7230, including the scheme and host.
// In either case, WriteProxy also writes a Host header, using
// either r.Host or r.URL.Host.
func (r *Request) WriteProxy(w io.Writer) error {
        return r.write(w, true, nil, nil)
}

// errMissingHost is returned by Write when there is no Host or URL present in
// the Request.
var errMissingHost = errors.New("http: Request.Write on Request with no Host or URL set")

// extraHeaders may be nil
// waitForContinue may be nil
// always closes body
func (r *Request) write(w io.Writer, usingProxy bool, extraHeaders Header, waitForContinue func() bool) (err error) {
        trace := httptrace.ContextClientTrace(r.Context())
        if trace != nil && trace.WroteRequest != nil {
                defer func() {
                        trace.WroteRequest(httptrace.WroteRequestInfo{
                                Err: err,
                        })
                }()
        }
        closed := false
        defer func() {
                if closed {
                        return
                }
                if closeErr := r.closeBody(); closeErr != nil && err == nil {
                        err = closeErr
                }
        }()

        // Find the target host. Prefer the Host: header, but if that
        // is not given, use the host from the request URL.
        //
        // Clean the host, in case it arrives with unexpected stuff in it.
        host := cleanHost(r.Host)
        if host == "" {
                if r.URL == nil {
                        return errMissingHost
                }
                host = cleanHost(r.URL.Host)
        }

        // According to RFC 6874, an HTTP client, proxy, or other
        // intermediary must remove any IPv6 zone identifier attached
        // to an outgoing URI.
        host = removeZone(host)

        ruri := r.URL.RequestURI()
        if usingProxy && r.URL.Scheme != "" && r.URL.Opaque == "" {
                ruri = r.URL.Scheme + "://" + host + ruri
        } else if r.Method == "CONNECT" && r.URL.Path == "" {
                // CONNECT requests normally give just the host and port, not a full URL.
                ruri = host
                if r.URL.Opaque != "" {
                        ruri = r.URL.Opaque
                }
        }
        if stringContainsCTLByte(ruri) {
                return errors.New("net/http: can't write control character in Request.URL")
        }
        // TODO: validate r.Method too? At least it's less likely to
        // come from an attacker (more likely to be a constant in
        // code).

        // Wrap the writer in a bufio Writer if it's not already buffered.
        // Don't always call NewWriter, as that forces a bytes.Buffer
        // and other small bufio Writers to have a minimum 4k buffer
        // size.
        var bw *bufio.Writer
        if _, ok := w.(io.ByteWriter); !ok {
                bw = bufio.NewWriter(w)
                w = bw
        }

        _, err = fmt.Fprintf(w, "%s %s HTTP/1.1\r\n", valueOrDefault(r.Method, "GET"), ruri)
        if err != nil {
                return err
        }

        // Header lines
        _, err = fmt.Fprintf(w, "Host: %s\r\n", host)
        if err != nil {
                return err
        }
        if trace != nil && trace.WroteHeaderField != nil {
                trace.WroteHeaderField("Host", []string{host})
        }

        // Use the defaultUserAgent unless the Header contains one, which
        // may be blank to not send the header.
        userAgent := defaultUserAgent
        if r.Header.has("User-Agent") {
                userAgent = r.Header.Get("User-Agent")
        }
        if userAgent != "" {
                _, err = fmt.Fprintf(w, "User-Agent: %s\r\n", userAgent)
                if err != nil {
                        return err
                }
                if trace != nil && trace.WroteHeaderField != nil {
                        trace.WroteHeaderField("User-Agent", []string{userAgent})
                }
        }

        // Process Body,ContentLength,Close,Trailer
        tw, err := newTransferWriter(r)
        if err != nil {
                return err
        }
        err = tw.writeHeader(w, trace)
        if err != nil {
                return err
        }

        err = r.Header.writeSubset(w, reqWriteExcludeHeader, trace)
        if err != nil {
                return err
        }

        if extraHeaders != nil {
                err = extraHeaders.write(w, trace)
                if err != nil {
                        return err
                }
        }

        _, err = io.WriteString(w, "\r\n")
        if err != nil {
                return err
        }

        if trace != nil && trace.WroteHeaders != nil {
                trace.WroteHeaders()
        }

        // Flush and wait for 100-continue if expected.
        if waitForContinue != nil {
                if bw, ok := w.(*bufio.Writer); ok {
                        err = bw.Flush()
                        if err != nil {
                                return err
                        }
                }
                if trace != nil && trace.Wait100Continue != nil {
                        trace.Wait100Continue()
                }
                if !waitForContinue() {
                        closed = true
                        r.closeBody()
                        return nil
                }
        }

        if bw, ok := w.(*bufio.Writer); ok && tw.FlushHeaders {
                if err := bw.Flush(); err != nil {
                        return err
                }
        }

        // Write body and trailer
        closed = true
        err = tw.writeBody(w)
        if err != nil {
                if tw.bodyReadError == err {
                        err = requestBodyReadError{err}
                }
                return err
        }

        if bw != nil {
                return bw.Flush()
        }
        return nil
}

// requestBodyReadError wraps an error from (*Request).write to indicate
// that the error came from a Read call on the Request.Body.
// This error type should not escape the net/http package to users.
type requestBodyReadError struct{ error }

func idnaASCII(v string) (string, error) {
        // TODO: Consider removing this check after verifying performance is okay.
        // Right now punycode verification, length checks, context checks, and the
        // permissible character tests are all omitted. It also prevents the ToASCII
        // call from salvaging an invalid IDN, when possible. As a result it may be
        // possible to have two IDNs that appear identical to the user where the
        // ASCII-only version causes an error downstream whereas the non-ASCII
        // version does not.
        // Note that for correct ASCII IDNs ToASCII will only do considerably more
        // work, but it will not cause an allocation.
        if ascii.Is(v) {
                return v, nil
        }
        return idna.Lookup.ToASCII(v)
}

// cleanHost cleans up the host sent in request's Host header.
//
// It both strips anything after '/' or ' ', and puts the value
// into Punycode form, if necessary.
//
// Ideally we'd clean the Host header according to the spec:
//   https://tools.ietf.org/html/rfc7230#section-5.4 (Host = uri-host [ ":" port ]")
//   https://tools.ietf.org/html/rfc7230#section-2.7 (uri-host -> rfc3986's host)
//   https://tools.ietf.org/html/rfc3986#section-3.2.2 (definition of host)
// But practically, what we are trying to avoid is the situation in
// issue 11206, where a malformed Host header used in the proxy context
// would create a bad request. So it is enough to just truncate at the
// first offending character.
func cleanHost(in string) string {
        if i := strings.IndexAny(in, " /"); i != -1 {
                in = in[:i]
        }
        host, port, err := net.SplitHostPort(in)
        if err != nil { // input was just a host
                a, err := idnaASCII(in)
                if err != nil {
                        return in // garbage in, garbage out
                }
                return a
        }
        a, err := idnaASCII(host)
        if err != nil {
                return in // garbage in, garbage out
        }
        return net.JoinHostPort(a, port)
}

// removeZone removes IPv6 zone identifier from host.
// E.g., "[fe80::1%en0]:8080" to "[fe80::1]:8080"
func removeZone(host string) string {
        if !strings.HasPrefix(host, "[") {
                return host
        }
        i := strings.LastIndex(host, "]")
        if i < 0 {
                return host
        }
        j := strings.LastIndex(host[:i], "%")
        if j < 0 {
                return host
        }
        return host[:j] + host[i:]
}

// ParseHTTPVersion parses an HTTP version string according to RFC 7230, section 2.6.
// "HTTP/1.0" returns (1, 0, true). Note that strings without
// a minor version, such as "HTTP/2", are not valid.
func ParseHTTPVersion(vers string) (major, minor int, ok bool) {
        switch vers {
        case "HTTP/1.1":
                return 1, 1, true
        case "HTTP/1.0":
                return 1, 0, true
        }
        if !strings.HasPrefix(vers, "HTTP/") {
                return 0, 0, false
        }
        if len(vers) != len("HTTP/X.Y") {
                return 0, 0, false
        }
        if vers[6] != '.' {
                return 0, 0, false
        }
        maj, err := strconv.ParseUint(vers[5:6], 10, 0)
        if err != nil {
                return 0, 0, false
        }
        min, err := strconv.ParseUint(vers[7:8], 10, 0)
        if err != nil {
                return 0, 0, false
        }
        return int(maj), int(min), true
}

func validMethod(method string) bool {
        /*
             Method         = "OPTIONS"                ; Section 9.2
                            | "GET"                    ; Section 9.3
                            | "HEAD"                   ; Section 9.4
                            | "POST"                   ; Section 9.5
                            | "PUT"                    ; Section 9.6
                            | "DELETE"                 ; Section 9.7
                            | "TRACE"                  ; Section 9.8
                            | "CONNECT"                ; Section 9.9
                            | extension-method
           extension-method = token
             token          = 1*<any CHAR except CTLs or separators>
        */
        return len(method) > 0 && strings.IndexFunc(method, isNotToken) == -1
}

// NewRequest wraps NewRequestWithContext using context.Background.
func NewRequest(method, url string, body io.Reader) (*Request, error) {
        return NewRequestWithContext(context.Background(), method, url, body)
}

// NewRequestWithContext returns a new Request given a method, URL, and
// optional body.
//
// If the provided body is also an io.Closer, the returned
// Request.Body is set to body and will be closed by the Client
// methods Do, Post, and PostForm, and Transport.RoundTrip.
//
// NewRequestWithContext returns a Request suitable for use with
// Client.Do or Transport.RoundTrip. To create a request for use with
// testing a Server Handler, either use the NewRequest function in the
// net/http/httptest package, use ReadRequest, or manually update the
// Request fields. For an outgoing client request, the context
// controls the entire lifetime of a request and its response:
// obtaining a connection, sending the request, and reading the
// response headers and body. See the Request type's documentation for
// the difference between inbound and outbound request fields.
//
// If body is of type *bytes.Buffer, *bytes.Reader, or
// *strings.Reader, the returned request's ContentLength is set to its
// exact value (instead of -1), GetBody is populated (so 307 and 308
// redirects can replay the body), and Body is set to NoBody if the
// ContentLength is 0.
func NewRequestWithContext(ctx context.Context, method, url string, body io.Reader) (*Request, error) {
        if method == "" {
                // We document that "" means "GET" for Request.Method, and people have
                // relied on that from NewRequest, so keep that working.
                // We still enforce validMethod for non-empty methods.
                method = "GET"
        }
        if !validMethod(method) {
                return nil, fmt.Errorf("net/http: invalid method %q", method)
        }
        if ctx == nil {
                return nil, errors.New("net/http: nil Context")
        }
        u, err := urlpkg.Parse(url)
        if err != nil {
                return nil, err
        }
        rc, ok := body.(io.ReadCloser)
        if !ok && body != nil {
                rc = io.NopCloser(body)
        }
        // The host's colon:port should be normalized. See Issue 14836.
        u.Host = removeEmptyPort(u.Host)
        req := &Request{
                ctx:        ctx,
                Method:     method,
                URL:        u,
                Proto:      "HTTP/1.1",
                ProtoMajor: 1,
                ProtoMinor: 1,
                Header:     make(Header),
                Body:       rc,
                Host:       u.Host,
        }
        if body != nil {
                switch v := body.(type) {
                case *bytes.Buffer:
                        req.ContentLength = int64(v.Len())
                        buf := v.Bytes()
                        req.GetBody = func() (io.ReadCloser, error) {
                                r := bytes.NewReader(buf)
                                return io.NopCloser(r), nil
                        }
                case *bytes.Reader:
                        req.ContentLength = int64(v.Len())
                        snapshot := *v
                        req.GetBody = func() (io.ReadCloser, error) {
                                r := snapshot
                                return io.NopCloser(&r), nil
                        }
                case *strings.Reader:
                        req.ContentLength = int64(v.Len())
                        snapshot := *v
                        req.GetBody = func() (io.ReadCloser, error) {
                                r := snapshot
                                return io.NopCloser(&r), nil
                        }
                default:
                        // This is where we'd set it to -1 (at least
                        // if body != NoBody) to mean unknown, but
                        // that broke people during the Go 1.8 testing
                        // period. People depend on it being 0 I
                        // guess. Maybe retry later. See Issue 18117.
                }
                // For client requests, Request.ContentLength of 0
                // means either actually 0, or unknown. The only way
                // to explicitly say that the ContentLength is zero is
                // to set the Body to nil. But turns out too much code
                // depends on NewRequest returning a non-nil Body,
                // so we use a well-known ReadCloser variable instead
                // and have the http package also treat that sentinel
                // variable to mean explicitly zero.
                if req.GetBody != nil && req.ContentLength == 0 {
                        req.Body = NoBody
                        req.GetBody = func() (io.ReadCloser, error) { return NoBody, nil }
                }
        }

        return req, nil
}

// BasicAuth returns the username and password provided in the request's
// Authorization header, if the request uses HTTP Basic Authentication.
// See RFC 2617, Section 2.
func (r *Request) BasicAuth() (username, password string, ok bool) {
        auth := r.Header.Get("Authorization")
        if auth == "" {
                return "", "", false
        }
        return parseBasicAuth(auth)
}

// parseBasicAuth parses an HTTP Basic Authentication string.
// "Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==" returns ("Aladdin", "open sesame", true).
func parseBasicAuth(auth string) (username, password string, ok bool) {
        const prefix = "Basic "
        // Case insensitive prefix match. See Issue 22736.
        if len(auth) < len(prefix) || !ascii.EqualFold(auth[:len(prefix)], prefix) {
                return "", "", false
        }
        c, err := base64.StdEncoding.DecodeString(auth[len(prefix):])
        if err != nil {
                return "", "", false
        }
        cs := string(c)
        username, password, ok = strings.Cut(cs, ":")
        if !ok {
                return "", "", false
        }
        return username, password, true
}

// SetBasicAuth sets the request's Authorization header to use HTTP
// Basic Authentication with the provided username and password.
//
// With HTTP Basic Authentication the provided username and password
// are not encrypted.
//
// Some protocols may impose additional requirements on pre-escaping the
// username and password. For instance, when used with OAuth2, both arguments
// must be URL encoded first with url.QueryEscape.
func (r *Request) SetBasicAuth(username, password string) {
        r.Header.Set("Authorization", "Basic "+basicAuth(username, password))
}

// parseRequestLine parses "GET /foo HTTP/1.1" into its three parts.
func parseRequestLine(line string) (method, requestURI, proto string, ok bool) {
        method, rest, ok1 := strings.Cut(line, " ")
        requestURI, proto, ok2 := strings.Cut(rest, " ")
        if !ok1 || !ok2 {
                return "", "", "", false
        }
        return method, requestURI, proto, true
}

var textprotoReaderPool sync.Pool

func newTextprotoReader(br *bufio.Reader) *textproto.Reader {
        if v := textprotoReaderPool.Get(); v != nil {
                tr := v.(*textproto.Reader)
                tr.R = br
                return tr
        }
        return textproto.NewReader(br)
}

func putTextprotoReader(r *textproto.Reader) {
        r.R = nil
        textprotoReaderPool.Put(r)
}

// ReadRequest reads and parses an incoming request from b.
//
// ReadRequest is a low-level function and should only be used for
// specialized applications; most code should use the Server to read
// requests and handle them via the Handler interface. ReadRequest
// only supports HTTP/1.x requests. For HTTP/2, use golang.org/x/net/http2.
func ReadRequest(b *bufio.Reader) (*Request, error) {
        req, err := readRequest(b)
        if err != nil {
                return nil, err
        }

        delete(req.Header, "Host")
        return req, err
}

func readRequest(b *bufio.Reader) (req *Request, err error) {
        tp := newTextprotoReader(b)
        req = new(Request)

        // First line: GET /index.html HTTP/1.0
        var s string
        if s, err = tp.ReadLine(); err != nil {
                return nil, err
        }
        defer func() {
                putTextprotoReader(tp)
                if err == io.EOF {
                        err = io.ErrUnexpectedEOF
                }
        }()

        var ok bool
        req.Method, req.RequestURI, req.Proto, ok = parseRequestLine(s)
        if !ok {
                return nil, badStringError("malformed HTTP request", s)
        }
        if !validMethod(req.Method) {
                return nil, badStringError("invalid method", req.Method)
        }
        rawurl := req.RequestURI
        if req.ProtoMajor, req.ProtoMinor, ok = ParseHTTPVersion(req.Proto); !ok {
                return nil, badStringError("malformed HTTP version", req.Proto)
        }

        // CONNECT requests are used two different ways, and neither uses a full URL:
        // The standard use is to tunnel HTTPS through an HTTP proxy.
        // It looks like "CONNECT www.google.com:443 HTTP/1.1", and the parameter is
        // just the authority section of a URL. This information should go in req.URL.Host.
        //
        // The net/rpc package also uses CONNECT, but there the parameter is a path
        // that starts with a slash. It can be parsed with the regular URL parser,
        // and the path will end up in req.URL.Path, where it needs to be in order for
        // RPC to work.
        justAuthority := req.Method == "CONNECT" && !strings.HasPrefix(rawurl, "/")
        if justAuthority {
                rawurl = "http://" + rawurl
        }

        if req.URL, err = url.ParseRequestURI(rawurl); err != nil {
                return nil, err
        }

        if justAuthority {
                // Strip the bogus "http://" back off.
                req.URL.Scheme = ""
        }

        // Subsequent lines: Key: value.
        mimeHeader, err := tp.ReadMIMEHeader()
        if err != nil {
                return nil, err
        }
        req.Header = Header(mimeHeader)
        if len(req.Header["Host"]) > 1 {
                return nil, fmt.Errorf("too many Host headers")
        }

        // RFC 7230, section 5.3: Must treat
        //      GET /index.html HTTP/1.1
        //      Host: www.google.com
        // and
        //      GET http://www.google.com/index.html HTTP/1.1
        //      Host: doesntmatter
        // the same. In the second case, any Host line is ignored.
        req.Host = req.URL.Host
        if req.Host == "" {
                req.Host = req.Header.get("Host")
        }

        fixPragmaCacheControl(req.Header)

        req.Close = shouldClose(req.ProtoMajor, req.ProtoMinor, req.Header, false)

        err = readTransfer(req, b)
        if err != nil {
                return nil, err
        }

        if req.isH2Upgrade() {
                // Because it's neither chunked, nor declared:
                req.ContentLength = -1

                // We want to give handlers a chance to hijack the
                // connection, but we need to prevent the Server from
                // dealing with the connection further if it's not
                // hijacked. Set Close to ensure that:
                req.Close = true
        }
        return req, nil
}

// MaxBytesReader is similar to io.LimitReader but is intended for
// limiting the size of incoming request bodies. In contrast to
// io.LimitReader, MaxBytesReader's result is a ReadCloser, returns a
// non-EOF error for a Read beyond the limit, and closes the
// underlying reader when its Close method is called.
//
// MaxBytesReader prevents clients from accidentally or maliciously
// sending a large request and wasting server resources.
func MaxBytesReader(w ResponseWriter, r io.ReadCloser, n int64) io.ReadCloser {
        if n < 0 { // Treat negative limits as equivalent to 0.
                n = 0
        }
        return &maxBytesReader{w: w, r: r, n: n}
}

type maxBytesReader struct {
        w   ResponseWriter
        r   io.ReadCloser // underlying reader
        n   int64         // max bytes remaining
        err error         // sticky error
}

func (l *maxBytesReader) Read(p []byte) (n int, err error) {
        if l.err != nil {
                return 0, l.err
        }
        if len(p) == 0 {
                return 0, nil
        }
        // If they asked for a 32KB byte read but only 5 bytes are
        // remaining, no need to read 32KB. 6 bytes will answer the
        // question of the whether we hit the limit or go past it.
        if int64(len(p)) > l.n+1 {
                p = p[:l.n+1]
        }
        n, err = l.r.Read(p)

        if int64(n) <= l.n {
                l.n -= int64(n)
                l.err = err
                return n, err
        }

        n = int(l.n)
        l.n = 0

        // The server code and client code both use
        // maxBytesReader. This "requestTooLarge" check is
        // only used by the server code. To prevent binaries
        // which only using the HTTP Client code (such as
        // cmd/go) from also linking in the HTTP server, don't
        // use a static type assertion to the server
        // "*response" type. Check this interface instead:
        type requestTooLarger interface {
                requestTooLarge()
        }
        if res, ok := l.w.(requestTooLarger); ok {
                res.requestTooLarge()
        }
        l.err = errors.New("http: request body too large")
        return n, l.err
}

func (l *maxBytesReader) Close() error {
        return l.r.Close()
}

func copyValues(dst, src url.Values) {
        for k, vs := range src {
                dst[k] = append(dst[k], vs...)
        }
}

func parsePostForm(r *Request) (vs url.Values, err error) {
        if r.Body == nil {
                err = errors.New("missing form body")
                return
        }
        ct := r.Header.Get("Content-Type")
        // RFC 7231, section 3.1.1.5 - empty type
        //   MAY be treated as application/octet-stream
        if ct == "" {
                ct = "application/octet-stream"
        }
        ct, _, err = mime.ParseMediaType(ct)
        switch {
        case ct == "application/x-www-form-urlencoded":
                var reader io.Reader = r.Body
                maxFormSize := int64(1<<63 - 1)
                if _, ok := r.Body.(*maxBytesReader); !ok {
                        maxFormSize = int64(10 << 20) // 10 MB is a lot of text.
                        reader = io.LimitReader(r.Body, maxFormSize+1)
                }
                b, e := io.ReadAll(reader)
                if e != nil {
                        if err == nil {
                                err = e
                        }
                        break
                }
                if int64(len(b)) > maxFormSize {
                        err = errors.New("http: POST too large")
                        return
                }
                vs, e = url.ParseQuery(string(b))
                if err == nil {
                        err = e
                }
        case ct == "multipart/form-data":
                // handled by ParseMultipartForm (which is calling us, or should be)
                // TODO(bradfitz): there are too many possible
                // orders to call too many functions here.
                // Clean this up and write more tests.
                // request_test.go contains the start of this,
                // in TestParseMultipartFormOrder and others.
        }
        return
}

// ParseForm populates r.Form and r.PostForm.
//
// For all requests, ParseForm parses the raw query from the URL and updates
// r.Form.
//
// For POST, PUT, and PATCH requests, it also reads the request body, parses it
// as a form and puts the results into both r.PostForm and r.Form. Request body
// parameters take precedence over URL query string values in r.Form.
//
// If the request Body's size has not already been limited by MaxBytesReader,
// the size is capped at 10MB.
//
// For other HTTP methods, or when the Content-Type is not
// application/x-www-form-urlencoded, the request Body is not read, and
// r.PostForm is initialized to a non-nil, empty value.
//
// ParseMultipartForm calls ParseForm automatically.
// ParseForm is idempotent.
func (r *Request) ParseForm() error {
        var err error
        if r.PostForm == nil {
                if r.Method == "POST" || r.Method == "PUT" || r.Method == "PATCH" {
                        r.PostForm, err = parsePostForm(r)
                }
                if r.PostForm == nil {
                        r.PostForm = make(url.Values)
                }
        }
        if r.Form == nil {
                if len(r.PostForm) > 0 {
                        r.Form = make(url.Values)
                        copyValues(r.Form, r.PostForm)
                }
                var newValues url.Values
                if r.URL != nil {
                        var e error
                        newValues, e = url.ParseQuery(r.URL.RawQuery)
                        if err == nil {
                                err = e
                        }
                }
                if newValues == nil {
                        newValues = make(url.Values)
                }
                if r.Form == nil {
                        r.Form = newValues
                } else {
                        copyValues(r.Form, newValues)
                }
        }
        return err
}

// ParseMultipartForm parses a request body as multipart/form-data.
// The whole request body is parsed and up to a total of maxMemory bytes of
// its file parts are stored in memory, with the remainder stored on
// disk in temporary files.
// ParseMultipartForm calls ParseForm if necessary.
// If ParseForm returns an error, ParseMultipartForm returns it but also
// continues parsing the request body.
// After one call to ParseMultipartForm, subsequent calls have no effect.
func (r *Request) ParseMultipartForm(maxMemory int64) error {
        if r.MultipartForm == multipartByReader {
                return errors.New("http: multipart handled by MultipartReader")
        }
        var parseFormErr error
        if r.Form == nil {
                // Let errors in ParseForm fall through, and just
                // return it at the end.
                parseFormErr = r.ParseForm()
        }
        if r.MultipartForm != nil {
                return nil
        }

        mr, err := r.multipartReader(false)
        if err != nil {
                return err
        }

        f, err := mr.ReadForm(maxMemory)
        if err != nil {
                return err
        }

        if r.PostForm == nil {
                r.PostForm = make(url.Values)
        }
        for k, v := range f.Value {
                r.Form[k] = append(r.Form[k], v...)
                // r.PostForm should also be populated. See Issue 9305.
                r.PostForm[k] = append(r.PostForm[k], v...)
        }

        r.MultipartForm = f

        return parseFormErr
}

// FormValue returns the first value for the named component of the query.
// POST and PUT body parameters take precedence over URL query string values.
// FormValue calls ParseMultipartForm and ParseForm if necessary and ignores
// any errors returned by these functions.
// If key is not present, FormValue returns the empty string.
// To access multiple values of the same key, call ParseForm and
// then inspect Request.Form directly.
func (r *Request) FormValue(key string) string {
        if r.Form == nil {
                r.ParseMultipartForm(defaultMaxMemory)
        }
        if vs := r.Form[key]; len(vs) > 0 {
                return vs[0]
        }
        return ""
}

// PostFormValue returns the first value for the named component of the POST,
// PATCH, or PUT request body. URL query parameters are ignored.
// PostFormValue calls ParseMultipartForm and ParseForm if necessary and ignores
// any errors returned by these functions.
// If key is not present, PostFormValue returns the empty string.
func (r *Request) PostFormValue(key string) string {
        if r.PostForm == nil {
                r.ParseMultipartForm(defaultMaxMemory)
        }
        if vs := r.PostForm[key]; len(vs) > 0 {
                return vs[0]
        }
        return ""
}

// FormFile returns the first file for the provided form key.
// FormFile calls ParseMultipartForm and ParseForm if necessary.
func (r *Request) FormFile(key string) (multipart.File, *multipart.FileHeader, error) {
        if r.MultipartForm == multipartByReader {
                return nil, nil, errors.New("http: multipart handled by MultipartReader")
        }
        if r.MultipartForm == nil {
                err := r.ParseMultipartForm(defaultMaxMemory)
                if err != nil {
                        return nil, nil, err
                }
        }
        if r.MultipartForm != nil && r.MultipartForm.File != nil {
                if fhs := r.MultipartForm.File[key]; len(fhs) > 0 {
                        f, err := fhs[0].Open()
                        return f, fhs[0], err
                }
        }
        return nil, nil, ErrMissingFile
}

func (r *Request) expectsContinue() bool {
        return hasToken(r.Header.get("Expect"), "100-continue")
}

func (r *Request) wantsHttp10KeepAlive() bool {
        if r.ProtoMajor != 1 || r.ProtoMinor != 0 {
                return false
        }
        return hasToken(r.Header.get("Connection"), "keep-alive")
}

func (r *Request) wantsClose() bool {
        if r.Close {
                return true
        }
        return hasToken(r.Header.get("Connection"), "close")
}

func (r *Request) closeBody() error {
        if r.Body == nil {
                return nil
        }
        return r.Body.Close()
}

func (r *Request) isReplayable() bool {
        if r.Body == nil || r.Body == NoBody || r.GetBody != nil {
                switch valueOrDefault(r.Method, "GET") {
                case "GET", "HEAD", "OPTIONS", "TRACE":
                        return true
                }
                // The Idempotency-Key, while non-standard, is widely used to
                // mean a POST or other request is idempotent. See
                // https://golang.org/issue/19943#issuecomment-421092421
                if r.Header.has("Idempotency-Key") || r.Header.has("X-Idempotency-Key") {
                        return true
                }
        }
        return false
}

// outgoingLength reports the Content-Length of this outgoing (Client) request.
// It maps 0 into -1 (unknown) when the Body is non-nil.
func (r *Request) outgoingLength() int64 {
        if r.Body == nil || r.Body == NoBody {
                return 0
        }
        if r.ContentLength != 0 {
                return r.ContentLength
        }
        return -1
}

// requestMethodUsuallyLacksBody reports whether the given request
// method is one that typically does not involve a request body.
// This is used by the Transport (via
// transferWriter.shouldSendChunkedRequestBody) to determine whether
// we try to test-read a byte from a non-nil Request.Body when
// Request.outgoingLength() returns -1. See the comments in
// shouldSendChunkedRequestBody.
func requestMethodUsuallyLacksBody(method string) bool {
        switch method {
        case "GET", "HEAD", "DELETE", "OPTIONS", "PROPFIND", "SEARCH":
                return true
        }
        return false
}

// requiresHTTP1 reports whether this request requires being sent on
// an HTTP/1 connection.
func (r *Request) requiresHTTP1() bool {
        return hasToken(r.Header.Get("Connection"), "upgrade") &&
                ascii.EqualFold(r.Header.Get("Upgrade"), "websocket")
}