[apmazure] add blob storage (#1105)

* add azure blob storage instrumentation

docs/instrumenting.asciidoc

@@ -30,6 +30,7 @@ that framework's API. The request context can be used for reporting <<custom-ins
 * <<builtin-modules-apmelasticsearch>>
 * <<builtin-modules-apmmongo>>
 * <<builtin-modules-apmawssdkgo>>
+* <<builtin-modules-apmazure>>
 
 [[builtin-modules-apmhttp]]
 ==== module/apmhttp
@@ -904,3 +905,39 @@ func (s *server) handleRequest(w http.ResponseWriter, req *http.Request) {
   ...
 }
 ----
+
+[[builtin-modules-apmazure]]
+==== module/apmazure
+Package apmazure provides a means of instrumenting the
+https://github.com/Azure/azure-pipeline-go[Azure Pipeline Go] pipeline object,
+so that Azure requests are reported as spans within the current transaction.
+
+To create spans for Azure requests, you should create a new pipeline using the
+relevant service's `NewPipeline` function, like `azblob.NewPipeline`, then wrap
+the `pipeline.Pipeline` with `apmazure.WrapPipeline`. The returned `Pipeline`
+can be used as normal.
+
+The following services are supported:
+
+- Blob Storage
+
+
+[source,go]
+----
+import (
+  "github.com/Azure/azure-storage-blob-go/azblob"
+
+  "go.elastic.co/apm/module/apmazure"
+)
+
+func main() {
+  p := azblob.NewPipeline(azblob.NewAnonymousCredential(), po)
+  p = apmazure.WrapPipeline(p)
+  u, err := url.Parse("https://my-account.blob.core.windows.net")
+  serviceURL := azblob.NewServiceURL(*u, p)
+  containerURL := serviceURL.NewContainerURL("mycontainer")
+  blobURL := containerURL.NewBlobURL("readme.txt")
+  // Use the blobURL to interact with Blob Storage
+  ...
+}
+----

docs/supported-tech.asciidoc

@@ -308,6 +308,14 @@ https://github.com/aws/aws-sdk-go[AWS SDK Go].
 See <<builtin-modules-apmawssdkgo, module/apmawssdkgo>> for more information
 about AWS SDK Go instrumentation.
 
+[float]
+==== Azure Storage
+We provide instrumentation for Azure Storage. This is usable with
+github.com/Azure/azure-storage-blob-go/azblob[Azure Blob Storage].
+
+See <<builtin-modules-apmazure, module/apmazure>> for more information
+about Azure SDK Go instrumentation.
+
 [float]
 [[supported-tech-messaging-systems]]
 === Messaging Systems

module/apmazure/blob.go

@@ -0,0 +1,180 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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.
+
+//go:build go1.14
+// +build go1.14
+
+package apmazure // import "go.elastic.co/apm/module/apmazure"
+
+import (
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"github.com/Azure/azure-pipeline-go/pipeline"
+)
+
+type blobRPC struct {
+	accountName  string
+	resourceName string
+	req          pipeline.Request
+}
+
+func (b *blobRPC) name() string {
+	return fmt.Sprintf("AzureBlob %s %s", b.operation(), b.resourceName)
+}
+
+func (b *blobRPC) _type() string {
+	return "storage"
+}
+
+func (b *blobRPC) subtype() string {
+	return "azureblob"
+}
+
+func (b *blobRPC) storageAccountName() string {
+	return b.accountName
+}
+
+func (b *blobRPC) resource() string {
+	return b.resourceName
+}
+
+func (b *blobRPC) operation() string {
+	if b.req.Method == http.MethodDelete {
+		return "Delete"
+	}
+	q := b.req.URL.Query()
+	switch b.req.Method {
+	// From net/http documentation:
+	// For client requests, an empty string means GET.
+	case http.MethodGet, "":
+		return getOperation(q)
+	case http.MethodPost:
+		return postOperation(q)
+	case http.MethodHead:
+		return headOperation(q)
+	case http.MethodPut:
+		return putOperation(q, b.req.Header)
+	default:
+		return b.req.Method
+	}
+}
+
+func getOperation(v url.Values) string {
+	restype := v.Get("restype")
+	comp := v.Get("comp")
+	if (restype == "" && comp == "") || comp == "blocklist" {
+		return "Download"
+	}
+	if restype == "container" && comp == "" {
+		return "GetProperties"
+	}
+
+	switch comp {
+	case "metadata":
+		return "GetMetadata"
+	case "acl":
+		return "GetAcl"
+	case "list":
+		if restype == "container" {
+			return "ListBlobs"
+		}
+		return "ListContainers"
+	case "tags":
+		if v.Get("where") != "" {
+			return "FindTags"
+		}
+		return "GetTags"
+	default:
+		return "unknown operation"
+	}
+}
+
+func postOperation(v url.Values) string {
+	comp := v.Get("comp")
+	switch comp {
+	case "batch":
+		return "Batch"
+	case "query":
+		return "Query"
+	case "userdelegationkey":
+		return "GetUserDelegationKey"
+	default:
+		return "unknown operation"
+	}
+
+}
+func headOperation(v url.Values) string {
+	restype := v.Get("restype")
+	comp := v.Get("comp")
+	if restype == "" && comp == "" {
+		return "GetProperties"
+	}
+	if restype != "container" {
+		return "unknown operation"
+	}
+	switch comp {
+	case "metadata":
+		return "GetMetadata"
+	case "acl":
+		return "GetAcl"
+	default:
+		return "unknown operation"
+	}
+}
+func putOperation(v url.Values, h http.Header) string {
+	// header.Get canonicalizes the key, ie. x-ms-copy-source->X-Ms-Copy-Source.
+	// The headers used are all lowercase, so we access the map directly.
+	_, copySource := h["x-ms-copy-source"]
+	_, blobType := h["x-ms-blob-type"]
+	_, pageWrite := h["x-ms-page-write"]
+	restype := v.Get("restype")
+	comp := v.Get("comp")
+	if restype == "container" && comp == "acl" {
+		return "SetAcl"
+	}
+
+	if comp == "" && !(copySource || blobType || pageWrite) {
+		return "Create"
+	}
+	if copySource {
+		return "Copy"
+	}
+	if blobType {
+		return "Upload"
+	}
+	if comp == "page" && pageWrite {
+		return "Clear"
+	}
+
+	switch comp {
+	case "block", "blocklist", "page", "appendblock":
+		return "Upload"
+	case "copy":
+		return "Abort"
+	case "metadata":
+		return "SetMetadata"
+	case "lease", "snapshot", "undelete", "seal", "rename":
+		return strings.Title(comp)
+	case "properties", "tags", "tier", "expiry":
+		return "Set" + strings.Title(comp)
+	default:
+		return "unknown operation"
+	}
+}