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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.

package httputil

import (
        "bufio"
        "bytes"
        "fmt"
        "io"
        "io/ioutil"
        "net"
        "net/http"
        "strings"
        "time"
)

// One of the copies, say from b to r2, could be avoided by using a more
// elaborate trick where the other copy is made during Request/Response.Write.
// This would complicate things too much, given that these functions are for
// debugging only.
func drainBody(b io.ReadCloser) (r1, r2 io.ReadCloser, err error) {
        var buf bytes.Buffer
        if _, err = buf.ReadFrom(b); err != nil {
                return nil, nil, err
        }
        if err = b.Close(); err != nil {
                return nil, nil, err
        }
        return ioutil.NopCloser(&buf), ioutil.NopCloser(bytes.NewBuffer(buf.Bytes())), nil
}

// dumpConn is a net.Conn which writes to Writer and reads from Reader
type dumpConn struct {
        io.Writer
        io.Reader
}

func (c *dumpConn) Close() error                       { return nil }
func (c *dumpConn) LocalAddr() net.Addr                { return nil }
func (c *dumpConn) RemoteAddr() net.Addr               { return nil }
func (c *dumpConn) SetDeadline(t time.Time) error      { return nil }
func (c *dumpConn) SetReadDeadline(t time.Time) error  { return nil }
func (c *dumpConn) SetWriteDeadline(t time.Time) error { return nil }

// DumpRequestOut is like DumpRequest but includes
// headers that the standard http.Transport adds,
// such as User-Agent.
func DumpRequestOut(req *http.Request, body bool) ([]byte, error) {
        save := req.Body
        if !body || req.Body == nil {
                req.Body = nil
        } else {
                var err error
                save, req.Body, err = drainBody(req.Body)
                if err != nil {
                        return nil, err
                }
        }

        // Use the actual Transport code to record what we would send
        // on the wire, but not using TCP.  Use a Transport with a
        // customer dialer that returns a fake net.Conn that waits
        // for the full input (and recording it), and then responds
        // with a dummy response.
        var buf bytes.Buffer // records the output
        pr, pw := io.Pipe()
        dr := &delegateReader{c: make(chan io.Reader)}
        // Wait for the request before replying with a dummy response:
        go func() {
                http.ReadRequest(bufio.NewReader(pr))
                dr.c <- strings.NewReader("HTTP/1.1 204 No Content\r\n\r\n")
        }()

        t := &http.Transport{
                Dial: func(net, addr string) (net.Conn, error) {
                        return &dumpConn{io.MultiWriter(pw, &buf), dr}, nil
                },
        }

        _, err := t.RoundTrip(req)

        req.Body = save
        if err != nil {
                return nil, err
        }
        return buf.Bytes(), nil
}

// delegateReader is a reader that delegates to another reader,
// once it arrives on a channel.
type delegateReader struct {
        c chan io.Reader
        r io.Reader // nil until received from c
}

func (r *delegateReader) Read(p []byte) (int, error) {
        if r.r == nil {
                r.r = <-r.c
        }
        return r.r.Read(p)
}

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

var reqWriteExcludeHeaderDump = map[string]bool{
        "Host":              true, // not in Header map anyway
        "Content-Length":    true,
        "Transfer-Encoding": true,
        "Trailer":           true,
}

// dumpAsReceived writes req to w in the form as it was received, or
// at least as accurately as possible from the information retained in
// the request.
func dumpAsReceived(req *http.Request, w io.Writer) error {
        return nil
}

// DumpRequest returns the as-received wire representation of req,
// optionally including the request body, for debugging.
// DumpRequest is semantically a no-op, but in order to
// dump the body, it reads the body data into memory and
// changes req.Body to refer to the in-memory copy.
// The documentation for http.Request.Write details which fields
// of req are used.
func DumpRequest(req *http.Request, body bool) (dump []byte, err error) {
        save := req.Body
        if !body || req.Body == nil {
                req.Body = nil
        } else {
                save, req.Body, err = drainBody(req.Body)
                if err != nil {
                        return
                }
        }

        var b bytes.Buffer

        fmt.Fprintf(&b, "%s %s HTTP/%d.%d\r\n", valueOrDefault(req.Method, "GET"),
                req.URL.RequestURI(), req.ProtoMajor, req.ProtoMinor)

        host := req.Host
        if host == "" && req.URL != nil {
                host = req.URL.Host
        }
        if host != "" {
                fmt.Fprintf(&b, "Host: %s\r\n", host)
        }

        chunked := len(req.TransferEncoding) > 0 && req.TransferEncoding[0] == "chunked"
        if len(req.TransferEncoding) > 0 {
                fmt.Fprintf(&b, "Transfer-Encoding: %s\r\n", strings.Join(req.TransferEncoding, ","))
        }
        if req.Close {
                fmt.Fprintf(&b, "Connection: close\r\n")
        }

        err = req.Header.WriteSubset(&b, reqWriteExcludeHeaderDump)
        if err != nil {
                return
        }

        io.WriteString(&b, "\r\n")

        if req.Body != nil {
                var dest io.Writer = &b
                if chunked {
                        dest = NewChunkedWriter(dest)
                }
                _, err = io.Copy(dest, req.Body)
                if chunked {
                        dest.(io.Closer).Close()
                        io.WriteString(&b, "\r\n")
                }
        }

        req.Body = save
        if err != nil {
                return
        }
        dump = b.Bytes()
        return
}

// DumpResponse is like DumpRequest but dumps a response.
func DumpResponse(resp *http.Response, body bool) (dump []byte, err error) {
        var b bytes.Buffer
        save := resp.Body
        savecl := resp.ContentLength
        if !body || resp.Body == nil {
                resp.Body = nil
                resp.ContentLength = 0
        } else {
                save, resp.Body, err = drainBody(resp.Body)
                if err != nil {
                        return
                }
        }
        err = resp.Write(&b)
        resp.Body = save
        resp.ContentLength = savecl
        if err != nil {
                return
        }
        dump = b.Bytes()
        return
}