filetransport.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package http
     6  
     7  import (
     8  	"fmt"
     9  	"io"
    10  )
    11  
    12  // fileTransport implements RoundTripper for the 'file' protocol.
    13  type fileTransport struct {
    14  	fh fileHandler
    15  }
    16  
    17  // NewFileTransport returns a new RoundTripper, serving the provided
    18  // FileSystem. The returned RoundTripper ignores the URL host in its
    19  // incoming requests, as well as most other properties of the
    20  // request.
    21  //
    22  // The typical use case for NewFileTransport is to register the "file"
    23  // protocol with a Transport, as in:
    24  //
    25  //   t := &http.Transport{}
    26  //   t.RegisterProtocol("file", http.NewFileTransport(http.Dir("/")))
    27  //   c := &http.Client{Transport: t}
    28  //   res, err := c.Get("file:///etc/passwd")
    29  //   ...
    30  func NewFileTransport(fs FileSystem) RoundTripper {
    31  	return fileTransport{fileHandler{fs}}
    32  }
    33  
    34  func (t fileTransport) RoundTrip(req *Request) (resp *Response, err error) {
    35  	// We start ServeHTTP in a goroutine, which may take a long
    36  	// time if the file is large. The newPopulateResponseWriter
    37  	// call returns a channel which either ServeHTTP or finish()
    38  	// sends our *Response on, once the *Response itself has been
    39  	// populated (even if the body itself is still being
    40  	// written to the res.Body, a pipe)
    41  	rw, resc := newPopulateResponseWriter()
    42  	go func() {
    43  		t.fh.ServeHTTP(rw, req)
    44  		rw.finish()
    45  	}()
    46  	return <-resc, nil
    47  }
    48  
    49  func newPopulateResponseWriter() (*populateResponse, <-chan *Response) {
    50  	pr, pw := io.Pipe()
    51  	rw := &populateResponse{
    52  		ch: make(chan *Response),
    53  		pw: pw,
    54  		res: &Response{
    55  			Proto:      "HTTP/1.0",
    56  			ProtoMajor: 1,
    57  			Header:     make(Header),
    58  			Close:      true,
    59  			Body:       pr,
    60  		},
    61  	}
    62  	return rw, rw.ch
    63  }
    64  
    65  // populateResponse is a ResponseWriter that populates the *Response
    66  // in res, and writes its body to a pipe connected to the response
    67  // body. Once writes begin or finish() is called, the response is sent
    68  // on ch.
    69  type populateResponse struct {
    70  	res          *Response
    71  	ch           chan *Response
    72  	wroteHeader  bool
    73  	hasContent   bool
    74  	sentResponse bool
    75  	pw           *io.PipeWriter
    76  }
    77  
    78  func (pr *populateResponse) finish() {
    79  	if !pr.wroteHeader {
    80  		pr.WriteHeader(500)
    81  	}
    82  	if !pr.sentResponse {
    83  		pr.sendResponse()
    84  	}
    85  	pr.pw.Close()
    86  }
    87  
    88  func (pr *populateResponse) sendResponse() {
    89  	if pr.sentResponse {
    90  		return
    91  	}
    92  	pr.sentResponse = true
    93  
    94  	if pr.hasContent {
    95  		pr.res.ContentLength = -1
    96  	}
    97  	pr.ch <- pr.res
    98  }
    99  
   100  func (pr *populateResponse) Header() Header {
   101  	return pr.res.Header
   102  }
   103  
   104  func (pr *populateResponse) WriteHeader(code int) {
   105  	if pr.wroteHeader {
   106  		return
   107  	}
   108  	pr.wroteHeader = true
   109  
   110  	pr.res.StatusCode = code
   111  	pr.res.Status = fmt.Sprintf("%d %s", code, StatusText(code))
   112  }
   113  
   114  func (pr *populateResponse) Write(p []byte) (n int, err error) {
   115  	if !pr.wroteHeader {
   116  		pr.WriteHeader(StatusOK)
   117  	}
   118  	pr.hasContent = true
   119  	if !pr.sentResponse {
   120  		pr.sendResponse()
   121  	}
   122  	return pr.pw.Write(p)
   123  }
   124
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