fix response payload and incorrectly parsing error response

[AllanZhengYP]

reopen #63

Two fixes:

1. Currently when response body is a payload member, the SDK either
   keeps reponse intact if it has a streaming trait, or parse the body
   to JS object.
   
   Actually when response payload is not streaming, it is
   NOT always parsable(not a valid JSON or XML string). Specificly,
   when payload is String, we shouldn't
   parse it with XML or JSON parser; We should also treat Blob shape
   differently as we should encode the binaries into string; Only when
   shape is Union or Structure can we assume payload is parsable
   by JSON or XML parser.

2. For some protocols, error type flag exists in error response body,
   then we need to collect response stream to JS object and parse the
   error type; For other protocols, error type flag doesn't exist in
   error response body, then we don't need to collect the response
   stream in error dispatcher. Instead, we can treat the error like
   normal response. So that error shape supports the same traits as
   normal responses like streaming, payload etc.
   
   This is done by adding a new class member in Protocol generator--
   isErrorCodeInBody. When it is true, it means error type flag
   exists in error response body, then body is parsed in errors
   dispatcher, and each error deser only need to deal with parsed
   response body in JS object format;

Example:

//Exception dispatcher
async function exceptionDispatcher(
  output: __HttpResponse,
  context: __SerdeContext,
): Promise<CommandOutput> {
    const parsedOutput: any = { // parse output in dispatcher
    ...output,
    body: await parseBody(output.body, context),
  };
  let response: __SmithyException & __MetadataBearer;
  let errorCode: String;
  const errorTypeParts: String = parsedOutput.body["__type"].split('#');
  errorCode = (errorTypeParts[1] === undefined) ? errorTypeParts[0] : errorTypeParts[1];
  switch (errorCode) {
     case "com.amazon.aws.sdk.foo#FooException":
        response = await deserializeFooExceptionResponse(parsedOutput, context);
        break;
  //other cases
  }
}

const deserializeFooExceptionResponse = async (
  output: any,
  context: __SerdeContext
): Promise<FooException> => {
  //Don't parse response again in error deser
  const deserialized: any = deserializeFooException(output.body, context);
  const contents: FooException = {
    __type: "FooException",
    $fault: "client",
    $metadata: deserializeMetadata(output),
    ...deserialized,
  };
  return contents;
};

When it is false, it means
error type can be inferred without touching response body, then
error deser can access the error response intact.

async function exceptionDispatcher (
  output: __HttpResponse,
  context: __SerdeContext,
): Promise<CommandOutput> {
  const errorOutput: any = { // No need to parse response here
    ...output,
    body: output.body,
  };
  let response: __SmithyException & __MetadataBearer;
  let errorCode: String;
  errorCode = output.headers["x-amzn-errortype"].split(':')[0];
  switch (errorCode) {
     case "FooException":
      response = await deserializeFooExceptionResponse(errorOutput, context);
      break;
    //other cases
  }
}

const deserializeFooExceptionResponse = async (
  output: any,
  context: __SerdeContext
): Promise<FooException> => {
  const contents: FooException = {
    __type: "FooException",
    $fault: "client",
    $metadata: deserializeMetadata(output),
    Code: undefined,
    Message: undefined,
  };
  const data: any = await parseBody(output.body, context); //parse response here.
  //parse the error members
  return contents;
};

/cc @kstich

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[kstich]

References to this.isErrorCodeInBody don't need this. if there's not another variable named that in scope. That should be all cases except the constructor.

[kstich]

References to this.isErrorCodeInBody don't need this. if there's not another variable named that in scope. That should be all cases except the constructor.

[kstich]

This will short circuit deserializing any modeled content in the document of an error response. There is no call to deserializeOutputDocument and any shapes that may need to be deserialized won't be added to the deserializingDocumentShapes set here.

[kstich]

Nit: This doesn't need to fall to a new line.

[kstich]

A boolean that indicates if the error code for the implementing protocol is located in the error response body, meaning this generator will parse the body before attempting to load an error code.

[kstich]

This object name toggle is used in multiple places, can this logic exist once and be stored?

[kstich]

See updated text in other file.

[kstich]

This will contain all response bindings for the error shape, use Location.DOCUMENT to refine this.

[AllanZhengYP]

Will update this.