Handle multi-value query parameters appropriately

We use APIGateway multi-value query parameters which will always use an array
value for query parameters, even if they're specified only once, and even if
that single specification does not have a value. This changes our logic to
not reject an array with a single value when parsing the value for a
scalar-bound query parameter, which fixes our handling of query parameters.

Author: adamthom-amzn

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/integration/HttpBindingProtocolGenerator.java

@@ -1829,13 +1829,22 @@ private void readDirectQueryBindings(GenerationContext context, List<HttpBinding
                     writer.addImport("SerializationException",
                             "__SerializationException",
                             "@aws-smithy/server-common");
-                    writer.openBlock("if (Array.isArray(query[$1S])) {", "}",
+                    writer.write("let queryValue: string;");
+                    writer.openBlock("if (Array.isArray(query[$S])) {", "}",
                             binding.getLocationName(),
                             () -> {
-                                writer.write("throw new __SerializationException();");
+                                writer.openBlock("if (query[$S].length === 1) {", "}",
+                                    binding.getLocationName(),
+                                    () -> {
+                                        writer.write("queryValue = query[$S][0];", binding.getLocationName());
+                                    });
+                                writer.openBlock("else {", "}", () -> {
+                                    writer.write("throw new __SerializationException();");
+                                });
                             });
-                    writer.write("const queryValue = query[$1S] as string;",
-                            binding.getLocationName());
+                    writer.openBlock("else {", "}", () -> {
+                        writer.write("queryValue = query[$S] as string;", binding.getLocationName());
+                    });
                 }
                 String queryValue = getOutputValue(context, binding.getLocation(), "queryValue",
                         binding.getMember(), target);
@@ -1855,6 +1864,7 @@ private void readMappedQueryBindings(GenerationContext context, HttpBinding mapp
         }
         writer.write("let parsedQuery: { [key: string]: $L } = {}", valueType);
         writer.openBlock("for (const [key, value] of Object.entries(query)) {", "}", () -> {
+            writer.write("let queryValue: string;");
             final String parsedValue;
             if (valueShape instanceof CollectionShape) {
                 writer.write("const valueArray = Array.isArray(value) ? (value as string[]) : [value as string];");
@@ -1866,10 +1876,19 @@ private void readMappedQueryBindings(GenerationContext context, HttpBinding mapp
                         "@aws-smithy/server-common");
                 writer.openBlock("if (Array.isArray(value)) {", "}",
                         () -> {
-                            writer.write("throw new __SerializationException();");
+                            writer.openBlock("if (value.length === 1) {", "}",
+                                    () -> {
+                                        writer.write("queryValue = value[0];");
+                                    });
+                            writer.openBlock("else {", "}", () -> {
+                                writer.write("throw new __SerializationException();");
+                            });
                         });
+                writer.openBlock("else {", "}", () -> {
+                    writer.write("queryValue = value as string;");
+                });
                 parsedValue = getOutputValue(context, mappedBinding.getLocation(),
-                                "value as string", target.getValue(), valueShape);
+                                "queryValue", target.getValue(), valueShape);
             }
             writer.write("parsedQuery[key] = $L;", parsedValue);
         });