Handle checksum for unseekable 0-length s3 request body (#3086)

* Handle checksum for unseekable body with 0 content length

Author: Madrigal

.changelog/0e919f9c00d14acd87fcf6c0f1de614f.json

@@ -0,0 +1,8 @@
+{
+ "id": "0e919f9c-00d1-4acd-87fc-f6c0f1de614f",
+ "type": "bugfix",
+ "description": "Handle checksum for unseekable body with 0 content length",
+ "modules": [
+ "service/internal/checksum"
+ ]
+}

service/internal/checksum/middleware_compute_input_checksum.go

@@ -179,7 +179,7 @@ func (m *ComputeInputPayloadChecksum) HandleFinalize(
 
 // Only seekable streams are supported for non-trailing checksums, because
 // the stream needs to be rewound before the handler can continue.
-if stream != nil && !req.IsStreamSeekable() {
+if stream != nil && !req.IsStreamSeekable() && streamLength != 0 {
 return out, metadata, computeInputHeaderChecksumError{
 Msg: "unseekable stream is not supported without TLS and trailing checksum",
 }
@@ -194,11 +194,13 @@ func (m *ComputeInputPayloadChecksum) HandleFinalize(
 Err: err,
 }
 }
-
-if err := req.RewindStream(); err != nil {
-return out, metadata, computeInputHeaderChecksumError{
-Msg: "failed to rewind stream",
-Err: err,
+// only attempt rewind if the stream length has been determined and is non-zero
+if streamLength > 0 {
+if err := req.RewindStream(); err != nil {
+return out, metadata, computeInputHeaderChecksumError{
+Msg: "failed to rewind stream",
+Err: err,
+}
 }
 }
 
@@ -414,7 +416,7 @@ func computeStreamChecksum(algorithm Algorithm, stream io.Reader, computePayload
 }
 
 func getRequestStreamLength(req *smithyhttp.Request) (int64, error) {
-if v := req.ContentLength; v > 0 {
+if v := req.ContentLength; v >= 0 {
 return v, nil
 }
 

service/internal/checksum/middleware_compute_input_checksum_test.go

@@ -4,6 +4,7 @@
 package checksum
 
 import (
+"bufio"
 "bytes"
 "context"
 "fmt"
@@ -239,16 +240,16 @@ func TestComputeInputPayloadChecksum(t *testing.T) {
 r := smithyhttp.NewStackRequest().(*smithyhttp.Request)
 r.URL, _ = url.Parse("https://example.aws")
 r.ContentLength = 0
-r = requestMust(r.SetStream(&bytes.Buffer{}))
+r = requestMust(r.SetStream(bufio.NewReader(bytes.NewBuffer([]byte{}))))
 return r
 }(),
 },
 expectHeader: http.Header{
 "X-Amz-Checksum-Crc32": []string{"AAAAAA=="},
 },
 expectContentLength: 0,
-expectPayload: nil,
-expectPayloadHash: "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+expectPayload: []byte{},
+// payload hash is set via a different middleware, so not checking it here
 expectChecksumMetadata: map[string]string{
 "CRC32": "AAAAAA==",
 },