Refactor logging in more Go idiomatic style (#6816)

This refactor brings a change which allows
targets to be added in a cleaner way and also
audit is now moved out.

This PR also simplifies logger dependency for auditing

cmd/logger/message/audit/entry.go

@@ -0,0 +1,90 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package audit
+
+import (
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/gorilla/mux"
+	"github.com/minio/minio/pkg/handlers"
+)
+
+// Version - represents the current version of audit log structure.
+const Version = "1"
+
+// Entry - audit entry logs.
+type Entry struct {
+	Version      string `json:"version"`
+	DeploymentID string `json:"deploymentid,omitempty"`
+	Time         string `json:"time"`
+	API          struct {
+		Name       string `json:"name,omitempty"`
+		Bucket     string `json:"bucket,omitempty"`
+		Object     string `json:"object,omitempty"`
+		Status     string `json:"status,omitempty"`
+		StatusCode int    `json:"statusCode,omitempty"`
+	} `json:"api"`
+	RemoteHost string            `json:"remotehost,omitempty"`
+	RequestID  string            `json:"requestID,omitempty"`
+	UserAgent  string            `json:"userAgent,omitempty"`
+	ReqQuery   map[string]string `json:"requestQuery,omitempty"`
+	ReqHeader  map[string]string `json:"requestHeader,omitempty"`
+	RespHeader map[string]string `json:"responseHeader,omitempty"`
+}
+
+// ToEntry - constructs an audit entry object.
+func ToEntry(w http.ResponseWriter, r *http.Request, api string, statusCode int) Entry {
+	vars := mux.Vars(r)
+	bucket := vars["bucket"]
+	object := vars["object"]
+
+	reqQuery := make(map[string]string)
+	for k, v := range r.URL.Query() {
+		reqQuery[k] = strings.Join(v, ",")
+	}
+	reqHeader := make(map[string]string)
+	for k, v := range r.Header {
+		reqHeader[k] = strings.Join(v, ",")
+	}
+	respHeader := make(map[string]string)
+	for k, v := range w.Header() {
+		respHeader[k] = strings.Join(v, ",")
+	}
+	respHeader["Etag"] = strings.Trim(respHeader["Etag"], `"`)
+
+	entry := Entry{
+		Version:      Version,
+		DeploymentID: w.Header().Get("x-minio-deployment-id"),
+		RemoteHost:   handlers.GetSourceIP(r),
+		RequestID:    w.Header().Get("x-amz-request-id"),
+		UserAgent:    r.UserAgent(),
+		Time:         time.Now().UTC().Format(time.RFC3339Nano),
+		ReqQuery:     reqQuery,
+		ReqHeader:    reqHeader,
+		RespHeader:   respHeader,
+	}
+
+	entry.API.Name = api
+	entry.API.Bucket = bucket
+	entry.API.Object = object
+	entry.API.Status = http.StatusText(statusCode)
+	entry.API.StatusCode = statusCode
+
+	return entry
+}

cmd/logger/message/log/entry.go

@@ -0,0 +1,50 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package log
+
+// Args - defines the arguments for the API.
+type Args struct {
+	Bucket   string            `json:"bucket,omitempty"`
+	Object   string            `json:"object,omitempty"`
+	Metadata map[string]string `json:"metadata,omitempty"`
+}
+
+// Trace - defines the trace.
+type Trace struct {
+	Message   string            `json:"message,omitempty"`
+	Source    []string          `json:"source,omitempty"`
+	Variables map[string]string `json:"variables,omitempty"`
+}
+
+// API - defines the api type and its args.
+type API struct {
+	Name string `json:"name,omitempty"`
+	Args *Args  `json:"args,omitempty"`
+}
+
+// Entry - defines fields and values of each log entry.
+type Entry struct {
+	DeploymentID string `json:"deploymentid,omitempty"`
+	Level        string `json:"level"`
+	Time         string `json:"time"`
+	API          *API   `json:"api,omitempty"`
+	RemoteHost   string `json:"remotehost,omitempty"`
+	RequestID    string `json:"requestID,omitempty"`
+	UserAgent    string `json:"userAgent,omitempty"`
+	Message      string `json:"message,omitempty"`
+	Trace        *Trace `json:"error,omitempty"`
+}