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// 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 Response reading and parsing.

package http

import (
        "bufio"
        "errors"
        "io"
        "net/textproto"
        "net/url"
        "strconv"
        "strings"
)

var respExcludeHeader = map[string]bool{
        "Content-Length":    true,
        "Transfer-Encoding": true,
        "Trailer":           true,
}

// Response represents the response from an HTTP request.
//
type Response struct {
        Status     string // e.g. "200 OK"
        StatusCode int    // e.g. 200
        Proto      string // e.g. "HTTP/1.0"
        ProtoMajor int    // e.g. 1
        ProtoMinor int    // e.g. 0

        // Header maps header keys to values.  If the response had multiple
        // headers with the same key, they will be concatenated, with comma
        // delimiters.  (Section 4.2 of RFC 2616 requires that multiple headers
        // be semantically equivalent to a comma-delimited sequence.) Values
        // duplicated by other fields in this struct (e.g., ContentLength) are
        // omitted from Header.
        //
        // Keys in the map are canonicalized (see CanonicalHeaderKey).
        Header Header

        // Body represents the response body.
        //
        // The http Client and Transport guarantee that Body is always
        // non-nil, even on responses without a body or responses with
        // a zero-lengthed body.
        Body io.ReadCloser

        // ContentLength records the length of the associated content.  The
        // value -1 indicates that the length is unknown.  Unless RequestMethod
        // is "HEAD", values >= 0 indicate that the given number of bytes may
        // be read from Body.
        ContentLength int64

        // Contains transfer encodings from outer-most to inner-most. Value is
        // nil, means that "identity" encoding is used.
        TransferEncoding []string

        // Close records whether the header directed that the connection be
        // closed after reading Body.  The value is advice for clients: neither
        // ReadResponse nor Response.Write ever closes a connection.
        Close bool

        // Trailer maps trailer keys to values, in the same
        // format as the header.
        Trailer Header

        // The Request that was sent to obtain this Response.
        // Request's Body is nil (having already been consumed).
        // This is only populated for Client requests.
        Request *Request
}

// Cookies parses and returns the cookies set in the Set-Cookie headers.
func (r *Response) Cookies() []*Cookie {
        return readSetCookies(r.Header)
}

var ErrNoLocation = errors.New("http: no Location header in response")

// Location returns the URL of the response's "Location" header,
// if present.  Relative redirects are resolved relative to
// the Response's Request.  ErrNoLocation is returned if no
// Location header is present.
func (r *Response) Location() (*url.URL, error) {
        lv := r.Header.Get("Location")
        if lv == "" {
                return nil, ErrNoLocation
        }
        if r.Request != nil && r.Request.URL != nil {
                return r.Request.URL.Parse(lv)
        }
        return url.Parse(lv)
}

// ReadResponse reads and returns an HTTP response from r.  The
// req parameter specifies the Request that corresponds to
// this Response.  Clients must call resp.Body.Close when finished
// reading resp.Body.  After that call, clients can inspect
// resp.Trailer to find key/value pairs included in the response
// trailer.
func ReadResponse(r *bufio.Reader, req *Request) (resp *Response, err error) {

        tp := textproto.NewReader(r)
        resp = new(Response)

        resp.Request = req
        resp.Request.Method = strings.ToUpper(resp.Request.Method)

        // Parse the first line of the response.
        line, err := tp.ReadLine()
        if err != nil {
                if err == io.EOF {
                        err = io.ErrUnexpectedEOF
                }
                return nil, err
        }
        f := strings.SplitN(line, " ", 3)
        if len(f) < 2 {
                return nil, &badStringError{"malformed HTTP response", line}
        }
        reasonPhrase := ""
        if len(f) > 2 {
                reasonPhrase = f[2]
        }
        resp.Status = f[1] + " " + reasonPhrase
        resp.StatusCode, err = strconv.Atoi(f[1])
        if err != nil {
                return nil, &badStringError{"malformed HTTP status code", f[1]}
        }

        resp.Proto = f[0]
        var ok bool
        if resp.ProtoMajor, resp.ProtoMinor, ok = ParseHTTPVersion(resp.Proto); !ok {
                return nil, &badStringError{"malformed HTTP version", resp.Proto}
        }

        // Parse the response headers.
        mimeHeader, err := tp.ReadMIMEHeader()
        if err != nil {
                return nil, err
        }
        resp.Header = Header(mimeHeader)

        fixPragmaCacheControl(resp.Header)

        err = readTransfer(resp, r)
        if err != nil {
                return nil, err
        }

        return resp, nil
}

// RFC2616: Should treat
//      Pragma: no-cache
// like
//      Cache-Control: no-cache
func fixPragmaCacheControl(header Header) {
        if hp, ok := header["Pragma"]; ok && len(hp) > 0 && hp[0] == "no-cache" {
                if _, presentcc := header["Cache-Control"]; !presentcc {
                        header["Cache-Control"] = []string{"no-cache"}
                }
        }
}

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

// Writes the response (header, body and trailer) in wire format. This method
// consults the following fields of the response:
//
//  StatusCode
//  ProtoMajor
//  ProtoMinor
//  RequestMethod
//  TransferEncoding
//  Trailer
//  Body
//  ContentLength
//  Header, values for non-canonical keys will have unpredictable behavior
//
func (r *Response) Write(w io.Writer) error {

        // RequestMethod should be upper-case
        if r.Request != nil {
                r.Request.Method = strings.ToUpper(r.Request.Method)
        }

        // Status line
        text := r.Status
        if text == "" {
                var ok bool
                text, ok = statusText[r.StatusCode]
                if !ok {
                        text = "status code " + strconv.Itoa(r.StatusCode)
                }
        }
        io.WriteString(w, "HTTP/"+strconv.Itoa(r.ProtoMajor)+".")
        io.WriteString(w, strconv.Itoa(r.ProtoMinor)+" ")
        io.WriteString(w, strconv.Itoa(r.StatusCode)+" "+text+"\r\n")

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

        // Rest of header
        err = r.Header.WriteSubset(w, respExcludeHeader)
        if err != nil {
                return err
        }

        // End-of-header
        io.WriteString(w, "\r\n")

        // Write body and trailer
        err = tw.WriteBody(w)
        if err != nil {
                return err
        }

        // Success
        return nil
}