Fix flex checksum nil dereference issue (#2964)

* fix nil deref bug in checksum setter * add changelog * update changelog and code comment * update comment

Author: wty-Bryant

.changelog/2e03eae07dff4beb94963939b6549426.json

@@ -0,0 +1,8 @@
+{
+ "id": "2e03eae0-7dff-4beb-9496-3939b6549426",
+ "type": "bugfix",
+ "description": "Fix nil dereference panic for operations that require checksums, but do not have an input setting for which algorithm to use.",
+ "modules": [
+ "service/internal/checksum"
+ ]
+}

service/internal/checksum/middleware_setup_context.go

@@ -46,9 +46,12 @@ func (m *setupInputContext) HandleInitialize(
 ) (
 out middleware.InitializeOutput, metadata middleware.Metadata, err error,
 ) {
-if algorithm, ok := m.GetAlgorithm(in.Parameters); ok {
-ctx = internalcontext.SetChecksumInputAlgorithm(ctx, algorithm)
-return next.HandleInitialize(ctx, in)
+// nil check here is for operations that require checksum but do not have input algorithm setting
+if m.GetAlgorithm != nil {
+if algorithm, ok := m.GetAlgorithm(in.Parameters); ok {
+ctx = internalcontext.SetChecksumInputAlgorithm(ctx, algorithm)
+return next.HandleInitialize(ctx, in)
+}
 }
 
 if m.RequireChecksum || m.RequestChecksumCalculation == aws.RequestChecksumCalculationWhenSupported {