[JAVA] Codegen - swagger type=string format=byte not serialised correctly

[jritmeijer-muhimbi]

Description

I am currently creating frameworks for the various supported languages using Codegen. Generated clients for Python, PHP, Ruby and C# work as expected, as do other 3rd party systems that support Swagger files (e.g. Microsoft Flow). However, the JSON generated by the Codegen Java client is not correct, or at least not in line with the JSON generated by the other languages.

Related snippet from the Swagger file

        "source_file_content": {
          "description": "Content of the file to convert",
          "x-ms-summary": "Source file content",
          "type": "string",
          "format": "byte",
          "uniqueItems": false
        }

The Java code that is generated (snippets from the same model file):

  @SerializedName("source_file_content")
  private byte[] sourceFileContent = null;

  public ConvertData sourceFileContent(byte[] sourceFileContent) {
    this.sourceFileContent = sourceFileContent;
    return this;
  }

  @ApiModelProperty(example = "null", required = true, value = "Content of the file to convert")
  public byte[] getSourceFileContent() {
    return sourceFileContent;
  }

  public void setSourceFileContent(byte[] sourceFileContent) {
    this.sourceFileContent = sourceFileContent;
  }

When I make the REST call this is serialised to the following JSON

    {
        "use_async_pattern":false,
        "source_file_name":"test.txt",
        "source_file_content":[83,71,86,108,98,71,56,61],
        "output_format":"PDF",
        "copy_metadata":false,
        "fail_on_error":true
    }

As you can see the byte array is serialised as the individual bytes in the array,

However, the JSON generated by the clients for the other languages serialise to a string, which is what we need. (Please ignore that the string is base64 encoded, that is not done by the client framework, but rather by the application that calls the framework)

    {
         "use_async_pattern":false,
         "source_file_name":"test.txt",
         "source_file_content":" UEsDBBQAB[string truncated for brevity]==",
         "output_format":"PDF",
         "copy_metadata":false,
         "fail_on_error":true
    }

When I change the byte[] types in the generated model to String then all works well.

  @SerializedName("source_file_content")
  private String sourceFileContent = null;

  public ConvertData sourceFileContent(String sourceFileContent) {
    this.sourceFileContent = sourceFileContent;
    return this;
  }

  @ApiModelProperty(example = "null", required = true, value = "Content of the file to convert")
  public String getSourceFileContent() {
    return sourceFileContent;
  }

  public void setSourceFileContent(String sourceFileContent) {
    this.sourceFileContent = sourceFileContent;
  }

Swagger-codegen version

I have tried both the current stable (2.2.1) as well as the Master. Both exhibit the same behaviour.

Swagger declaration file content or url

The Swagger file can be found at https://api.muhimbi.com/api-docs/v1/swagger.json

Command line used for generation

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate \
   -i https://api.muhimbi.com/api-docs/v1/swagger.json \
   -l java \
   -o java-client-new

Steps to reproduce

1. Generate client framework as per the above command.
2. Open the model/ConvertData.java file and inspect the sourceFileContent related properties.

Related issues

Issue #669 (Support binary data in body). It appears that this may actually be the cause of this bug, though not 100% sure.

Suggest a Fix

I am afraid that my knowledge of Java is limited, so I am in no position to fix this myself. However, based on the behaviour described above, as well as the way other codegen clients behave, when type=string and format=byte the data type of the generated Java property should be String, not byte[].

When I manually make this change in the generated model, the correct JSON is generated and our API works well when used from Java. There is no need to change the serialisation logic, just the data types.

Interestingly, looking at the C# code generated by Codegen, that also uses the byte[] type for these properties. As that client generates the correct JSON, the serialiser must behave differently.

If this issue results in a change I am able (and happy) to test it.

[wing328]

@jritmeijer-muhimbi thanks for reporting the issue. I think it has to do with the serializer in the Java API client.

We'll mark this as "Need community contribution"

For the time being, please use string as a workaround.

[RoeeShlomo]

In my case, I tracked down the issue to the generated ApiClient#parameterToString.
The generated code converts byte[] to String with String.valueOf. If I change it to one of the String constructors that accepts byte[] then it works as expected.

If there are no other side effects to this change then the fix would be a simple change in ApiClient.mustache.

[wing328]

@RoeeShlomo can you please file a PR with the suggested fix?

[benrobot]

Here's the work around I am using until this issue can be resolved:

Create Gson type adapter for the Byte Array:

public class ByteArrayAdapter implements JsonSerializer<byte[]>, JsonDeserializer<byte[]> {
    @Override
    public JsonElement serialize(byte[] src, Type typeOfSrc, JsonSerializationContext context) {
        if (src == null) {
            return JsonNull.INSTANCE;
        } else {
        	String base64 = Base64.getEncoder().encodeToString(src); // JDK 8 specific, if on older JDK use a library
            return new JsonPrimitive(base64);
        }
    }

    @Override
    public byte[] deserialize(JsonElement json, Type byteArray, JsonDeserializationContext context) throws JsonParseException {
        String str = json.getAsJsonPrimitive().getAsString();
        try {
        	return Base64.getDecoder().decode(str); // JDK 8 specific, if on older JDK use a library
        } catch (RuntimeException e) {
            throw new JsonParseException(e);
        }
    }
}

Register the new type adapter:

ApiClient client = new ApiClient();
JSON swaggersJson = new JSON(client);
Gson gson = swaggersJson.getGson();
GsonBuilder gsonBuilder = new GsonBuilder();

//Re-register whatever types already registered by the JSON() constructor (inspect it to verify)
gsonBuilder.registerTypeAdapter(Date.class, gson.getAdapter(Date.class));
gsonBuilder.registerTypeAdapter(OffsetDateTime.class, gson.getAdapter(OffsetDateTime.class));
gsonBuilder.registerTypeAdapter(LocalDate.class, gson.getAdapter(LocalDate.class));

// Register our new ByterArray type adapter
gsonBuilder.registerTypeAdapter(byte[].class, new ByteArrayAdapter(client));

swaggersJson.setGson(gsonBuilder.create());
client.setJSON(swaggersJson);

[wing328]

@benrobot thanks for sharing the workaround.

[cbornet]

@benrobot this is more the fix than a workaround. Would you do a PR ?