private: Adds support for httpChecksumRequired trait (aws#3272)

aws/types.go

@@ -239,3 +239,26 @@ func (es errors) Error() string {
 
 	return strings.Join(parts, "\n")
 }
+
+// CopySeekableBody copies the seekable body to an io.Writer
+func CopySeekableBody(dst io.Writer, src io.ReadSeeker) (int64, error) {
+	curPos, err := src.Seek(0, sdkio.SeekCurrent)
+	if err != nil {
+		return 0, err
+	}
+
+	// copy errors may be assumed to be from the body.
+	n, err := io.Copy(dst, src)
+	if err != nil {
+		return n, err
+	}
+
+	// seek back to the first position after reading to reset
+	// the body for transmission.
+	_, err = src.Seek(curPos, sdkio.SeekStart)
+	if err != nil {
+		return n, err
+	}
+
+	return n, nil
+}

private/checksum/content_md5.go

@@ -0,0 +1,53 @@
+package checksum
+
+import (
+	"crypto/md5"
+	"encoding/base64"
+	"fmt"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/awserr"
+	"github.com/aws/aws-sdk-go/aws/request"
+)
+
+const contentMD5Header = "Content-Md5"
+
+// AddBodyContentMD5Handler computes and sets the HTTP Content-MD5 header for requests that
+// require it.
+func AddBodyContentMD5Handler(r *request.Request) {
+	// if Content-MD5 header is already present, return
+	if v := r.HTTPRequest.Header.Get(contentMD5Header); len(v) != 0 {
+		return
+	}
+
+	// if S3DisableContentMD5Validation flag is set, return
+	if aws.BoolValue(r.Config.S3DisableContentMD5Validation) {
+		return
+	}
+
+	// if request is presigned, return
+	if r.IsPresigned() {
+		return
+	}
+
+	// if body is not seekable, return
+	if !aws.IsReaderSeekable(r.Body) {
+		if r.Config.Logger != nil {
+			r.Config.Logger.Log(fmt.Sprintf(
+				"Unable to compute Content-MD5 for unseekable body, S3.%s",
+				r.Operation.Name))
+		}
+		return
+	}
+
+	h := md5.New()
+
+	if _, err := aws.CopySeekableBody(h, r.Body); err != nil {
+		r.Error = awserr.New("ContentMD5", "failed to compute body MD5", err)
+		return
+	}
+
+	// encode the md5 checksum in base64 and set the request header.
+	v := base64.StdEncoding.EncodeToString(h.Sum(nil))
+	r.HTTPRequest.Header.Set(contentMD5Header, v)
+}

private/model/api/operation.go

@@ -31,9 +31,10 @@ type Operation struct {
 
 	EventStreamAPI *EventStreamAPI
 
-	IsEndpointDiscoveryOp bool               `json:"endpointoperation"`
-	EndpointDiscovery     *EndpointDiscovery `json:"endpointdiscovery"`
-	Endpoint              *EndpointTrait     `json:"endpoint"`
+	IsEndpointDiscoveryOp  bool               `json:"endpointoperation"`
+	EndpointDiscovery      *EndpointDiscovery `json:"endpointdiscovery"`
+	Endpoint               *EndpointTrait     `json:"endpoint"`
+	IsHttpChecksumRequired bool               `json:"httpChecksumRequired"`
 }
 
 // EndpointTrait provides the structure of the modeled endpoint trait, and its
@@ -310,6 +311,14 @@ func (c *{{ .API.StructName }}) {{ .ExportedName }}Request(` +
 	{{- range $_, $handler := $.CustomBuildHandlers }}
 		req.Handlers.Build.PushBackNamed({{ $handler }})
 	{{- end }}
+
+	{{- if .IsHttpChecksumRequired }}
+		{{- $_ := .API.AddSDKImport "private/checksum" }}
+		req.Handlers.Build.PushBackNamed(request.NamedHandler{
+			Name: "contentMd5Handler",
+			Fn: checksum.AddBodyContentMD5Handler,
+		})
+	{{- end }}
 	return
 }