httplog - httplog.go

     1  // Package httplog is used to create wrappers around http.Handler's to gather
     2  // information about a request and its response.
     3  package httplog // import "vimagination.zapto.org/httplog"
     4  
     5  import (
     6  	"errors"
     7  	"io"
     8  	"net/http"
     9  	"sync"
    10  	"text/template"
    11  	"time"
    12  
    13  	"vimagination.zapto.org/httpwrap"
    14  )
    15  
    16  // DefaultFormat is a simple template to output log data in something reminiscent
    17  // on the Apache default format.
    18  const DefaultFormat = "{{.RemoteAddr}} - {{.URL.User.Username}} - [{{.StartTime.Format \"02/01/2006:15:04:05 +0700\"}}] \"{{.Method}} {{.URL.RequestURI}} {{.Proto}}\" {{.Status}} {{.RequestLength}} {{.StartTime.Sub .EndTime}}"
    19  
    20  // Details is a collection of data about the request and response.
    21  type Details struct {
    22  	*http.Request
    23  	Status, ResponseLength int
    24  	StartTime, EndTime     time.Time
    25  }
    26  
    27  type wrapRW struct {
    28  	http.ResponseWriter
    29  	status, contentLength *int
    30  }
    31  
    32  func (w *wrapRW) WriteHeader(n int) {
    33  	*w.status = n
    34  
    35  	w.ResponseWriter.WriteHeader(n)
    36  }
    37  
    38  type logMux struct {
    39  	http.Handler
    40  	Logger
    41  }
    42  
    43  // Logger allows clients to specify how collected data is handled.
    44  type Logger interface {
    45  	Log(d Details)
    46  }
    47  
    48  // Wrap wraps an existing http.Handler and collects data about the request
    49  // and response and passes it to a logger.
    50  func Wrap(m http.Handler, l Logger) http.Handler {
    51  	if m == nil {
    52  		m = http.DefaultServeMux
    53  	}
    54  
    55  	return &logMux{Handler: m, Logger: l}
    56  }
    57  
    58  var responsePool = sync.Pool{
    59  	New: func() interface{} {
    60  		return new(wrapRW)
    61  	},
    62  }
    63  
    64  // ServeHTTP satisfies the http.Handler interface.
    65  func (l *logMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    66  	d := Details{
    67  		Request: r,
    68  		Status:  200,
    69  	}
    70  
    71  	rw := responsePool.Get().(*wrapRW)
    72  
    73  	*rw = wrapRW{
    74  		w,
    75  		&d.Status,
    76  		&d.ResponseLength,
    77  	}
    78  	d.StartTime = time.Now()
    79  
    80  	l.Handler.ServeHTTP(
    81  		httpwrap.Wrap(w, httpwrap.OverrideWriter(rw), httpwrap.OverrideHeaderWriter(rw)),
    82  		r,
    83  	)
    84  
    85  	d.EndTime = time.Now()
    86  	*rw = wrapRW{}
    87  
    88  	responsePool.Put(rw)
    89  
    90  	go l.Logger.Log(d)
    91  }
    92  
    93  // WriteLogger is a Logger which formats log data to a given template and
    94  // writes it to a given io.Writer.
    95  type WriteLogger struct {
    96  	mu       sync.Mutex
    97  	w        io.Writer
    98  	template *template.Template
    99  }
   100  
   101  // NewWriteLogger uses the given format as a template to write log data to the
   102  // given io.Writer.
   103  func NewWriteLogger(w io.Writer, format string) (Logger, error) {
   104  	if format == "" {
   105  		return nil, errors.New("invalid format")
   106  	}
   107  
   108  	if format[len(format)-1] != '\n' {
   109  		format += "\n"
   110  	}
   111  
   112  	t, err := template.New("").Parse(format)
   113  	if err != nil {
   114  		return nil, err
   115  	}
   116  
   117  	return &WriteLogger{
   118  		w:        w,
   119  		template: t,
   120  	}, nil
   121  }
   122  
   123  // Log satisfies the Logger interface.
   124  func (w *WriteLogger) Log(d Details) {
   125  	w.mu.Lock()
   126  	w.template.Execute(w.w, d)
   127  	w.mu.Unlock()
   128  }
   129