Squashed commit of the following:

commit d214ad5c92073cb754c70ab73e6cf229cba01c72
Author: Marius <maerious@gmail.com>
Date:   Tue Feb 28 20:38:47 2017 +0100

    Minor code and comment cleanups

commit 2826227404296d98a2d83519efaa754cc07a47b1
Merge: db47c89 1a58d6e
Author: Marius <maerious@gmail.com>
Date:   Tue Feb 28 20:13:15 2017 +0100

    Merge branch 'metrics_race_condition' of https://github.com/oliverpool/tusd into oliverpool-metrics_race_condition

commit 1a58d6e084
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Tue Feb 28 19:14:21 2017 +0100

    prometheus metrics typo

commit db47c8976489917a8afc53878335ab66d73fe60d
Merge: 168942b 12054be
Author: Marius <maerious@gmail.com>
Date:   Tue Feb 28 17:36:47 2017 +0100

    Merge branch 'metrics_race_condition' of https://github.com/oliverpool/tusd into oliverpool-metrics_race_condition

commit 12054be4e7
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Tue Feb 28 12:07:43 2017 +0100

    add go vet on travis

commit 16e95d2d91
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Tue Feb 28 11:58:58 2017 +0100

    add one go vet on appveyor

commit 13bc64517b
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Tue Feb 28 11:57:56 2017 +0100

    use even less pointers

commit db7130f18a
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Mon Feb 27 22:12:45 2017 +0100

    use pointer only when needed

commit 647f7390c6
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Thu Feb 23 16:29:01 2017 +0100

    Prevent lock malfunction

    literal copies lock value from metrics

commit 1ce196ed35
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Wed Feb 22 12:22:19 2017 +0100

    handle read timeout simplification in metrics

commit 338017c9f4
Merge: c378bc9 45a9278
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Wed Feb 22 12:21:42 2017 +0100

    Merge branch 'master' into metrics_race_condition

commit c378bc9798
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Wed Feb 22 11:51:56 2017 +0100

    consistent naming

commit e2b0050b8d
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Wed Feb 22 11:44:05 2017 +0100

    Use a simplfied error structure for error counting

commit 3da4095c08
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Mon Feb 20 16:38:27 2017 +0100

    split ptr retrieval and incrementation

commit ebd6873cbb
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Sun Feb 5 22:01:34 2017 +0100

    Useless initialization

commit 691224cdbf
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Thu Feb 2 08:25:55 2017 +0100

    increment the pointer

commit 3d9395e1df
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Thu Feb 2 08:25:42 2017 +0100

    Simplify lock logic

commit d7a4619080
Author: oliverpool <oliverpool@hotmail.fr>
Date:   Wed Feb 1 08:37:46 2017 +0100

    Prevent race condition on errorstotal increment

    The HTTPError interface is used to have detailed metrics (by code as
    well)

.scripts/test_all.sh

@@ -26,3 +26,5 @@ go get -u github.com/prometheus/client_golang/prometheus
 
 # Test all packages which are allowed on all Go versions
 go test $packages
+
+go vet $packages

appveyor.yml

@@ -23,3 +23,5 @@ test_script:
   - go test ./memorylocker
   - go test ./consullocker
   - go test ./s3store
+
+  - go vet ./prometheuscollector

metrics.go

@@ -1,6 +1,9 @@
 package tusd
 
 import (
+	"errors"
+	"net"
+	"sync"
 	"sync/atomic"
 )
 
@@ -13,7 +16,7 @@ type Metrics struct {
 	// RequestTotal counts the number of incoming requests per method
 	RequestsTotal map[string]*uint64
 	// ErrorsTotal counts the number of returned errors by their message
-	ErrorsTotal       map[string]*uint64
+	ErrorsTotal       *ErrorsTotalMap
 	BytesReceived     *uint64
 	UploadsFinished   *uint64
 	UploadsCreated    *uint64
@@ -29,16 +32,9 @@ func (m Metrics) incRequestsTotal(method string) {
 }
 
 // incErrorsTotal increases the counter for this error atomically by one.
-func (m Metrics) incErrorsTotal(err error) {
+func (m Metrics) incErrorsTotal(err HTTPError) {
-	msg := err.Error()
+	ptr := m.ErrorsTotal.retrievePointerFor(err)
-
+	atomic.AddUint64(ptr, 1)
-	if addr, ok := m.ErrorsTotal[msg]; ok {
-		atomic.AddUint64(addr, 1)
-	} else {
-		addr := new(uint64)
-		*addr = 1
-		m.ErrorsTotal[msg] = addr
-	}
 }
 
 // incBytesReceived increases the number of received bytes atomically be the
@@ -80,7 +76,73 @@ func newMetrics() Metrics {
 	}
 }
 
-func newErrorsTotalMap() map[string]*uint64 {
+// ErrorsTotalMap stores the counters for the different HTTP errors.
-	m := make(map[string]*uint64, 20)
+type ErrorsTotalMap struct {
+	lock    sync.RWMutex
+	counter map[simpleHTTPError]*uint64
+}
+
+type simpleHTTPError struct {
+	Message    string
+	StatusCode int
+}
+
+func simplifyHTTPError(err HTTPError) simpleHTTPError {
+	var msg string
+	// Errors for read timeouts contain too much information which is not
+	// necessary for us and makes grouping for the metrics harder. The error
+	// message looks like: read tcp 127.0.0.1:1080->127.0.0.1:53673: i/o timeout
+	// Therefore, we use a common error message for all of them.
+	if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
+		msg = "read tcp: i/o timeout"
+	} else {
+		msg = err.Error()
+	}
+	return simpleHTTPError{
+		Message:    msg,
+		StatusCode: err.StatusCode(),
+	}
+}
+
+func newErrorsTotalMap() *ErrorsTotalMap {
+	m := make(map[simpleHTTPError]*uint64, 20)
+	return &ErrorsTotalMap{
+		counter: m,
+	}
+}
+
+// retrievePointerFor returns (after creating it if necessary) the pointer to
+// the counter for the error.
+func (e *ErrorsTotalMap) retrievePointerFor(err HTTPError) *uint64 {
+	serr := simplifyHTTPError(err)
+	e.lock.RLock()
+	ptr, ok := e.counter[serr]
+	e.lock.RUnlock()
+	if ok {
+		return ptr
+	}
+
+	// For pointer creation, a write-lock is required
+	e.lock.Lock()
+	// We ensure that the pointer wasn't created in the meantime
+	if ptr, ok = e.counter[serr]; !ok {
+		ptr = new(uint64)
+		e.counter[serr] = ptr
+	}
+	e.lock.Unlock()
+
+	return ptr
+}
+
+// Load retrieves the map of the counter pointers atomically
+func (e *ErrorsTotalMap) Load() map[HTTPError]*uint64 {
+	m := make(map[HTTPError]*uint64, len(e.counter))
+	e.lock.RLock()
+	for err, ptr := range e.counter {
+		httpErr := NewHTTPError(errors.New(err.Message), err.StatusCode)
+		m[httpErr] = ptr
+	}
+	e.lock.RUnlock()
+
 	return m
 }

prometheuscollector/prometheuscollector.go

@@ -9,6 +9,7 @@
 package prometheuscollector
 
 import (
+	"strconv"
 	"sync/atomic"
 
 	"github.com/tus/tusd"
@@ -23,8 +24,8 @@ var (
 		[]string{"method"}, nil)
 	errorsTotalDesc = prometheus.NewDesc(
 		"tusd_errors_total",
-		"Total number of erorrs per cause.",
+		"Total number of errors per status.",
-		[]string{"cause"}, nil)
+		[]string{"status", "message"}, nil)
 	bytesReceivedDesc = prometheus.NewDesc(
 		"tusd_bytes_received",
 		"Number of bytes received for uploads.",
@@ -39,7 +40,7 @@ var (
 		nil, nil)
 	uploadsTerminatedDesc = prometheus.NewDesc(
 		"tusd_uploads_terminated",
-		"Number of terminted uploads.",
+		"Number of terminated uploads.",
 		nil, nil)
 )
 
@@ -73,12 +74,13 @@ func (c Collector) Collect(metrics chan<- prometheus.Metric) {
 		)
 	}
 
-	for error, valuePtr := range c.metrics.ErrorsTotal {
+	for httpError, valuePtr := range c.metrics.ErrorsTotal.Load() {
 		metrics <- prometheus.MustNewConstMetric(
 			errorsTotalDesc,
 			prometheus.GaugeValue,
 			float64(atomic.LoadUint64(valuePtr)),
-			error,
+			strconv.Itoa(httpError.StatusCode()),
+			httpError.Error(),
 		)
 	}
 

unrouted_handler.go

@@ -5,7 +5,6 @@ import (
 	"errors"
 	"io"
 	"log"
-	"net"
 	"net/http"
 	"os"
 	"regexp"
@@ -612,17 +611,9 @@ func (handler *UnroutedHandler) sendError(w http.ResponseWriter, r *http.Request
 		err = ErrNotFound
 	}
 
-	// Errors for read timeouts contain too much information which is not
+	statusErr, ok := err.(HTTPError)
-	// necessary for us and makes grouping for the metrics harder. The error
+	if !ok {
-	// message looks like: read tcp 127.0.0.1:1080->127.0.0.1:53673: i/o timeout
+		statusErr = NewHTTPError(err, http.StatusInternalServerError)
-	// Therefore, we use a common error message for all of them.
-	if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
-		err = errors.New("read tcp: i/o timeout")
-	}
-
-	status := 500
-	if statusErr, ok := err.(HTTPError); ok {
-		status = statusErr.StatusCode()
 	}
 
 	reason := err.Error() + "\n"
@@ -632,12 +623,12 @@ func (handler *UnroutedHandler) sendError(w http.ResponseWriter, r *http.Request
 
 	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 	w.Header().Set("Content-Length", strconv.Itoa(len(reason)))
-	w.WriteHeader(status)
+	w.WriteHeader(statusErr.StatusCode())
 	w.Write([]byte(reason))
 
-	handler.log("ResponseOutgoing", "status", strconv.Itoa(status), "method", r.Method, "path", r.URL.Path, "error", err.Error())
+	handler.log("ResponseOutgoing", "status", strconv.Itoa(statusErr.StatusCode()), "method", r.Method, "path", r.URL.Path, "error", err.Error())
 
-	go handler.Metrics.incErrorsTotal(err)
+	go handler.Metrics.incErrorsTotal(statusErr)
 }
 
 // sendResp writes the header to w with the specified status code.