GraphQL.Attachments

Provides access to a HTTP stream (via JavaScript on a web page) in GraphQL Mutations or Queries. Attachments are transferred via a multipart form.

See Milestones for release notes.

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NuGet package

https://nuget.org/packages/GraphQL.Attachments/

PM> Install-Package GraphQL.Attachments

Usage in Graphs

Incoming and Outgoing attachments can be accessed via the ResolveFieldContext:

Field<ResultGraph>("withAttachment")
    .Argument<NonNullGraphType<StringGraphType>>("argument")
    .Resolve(context =>
    {
        var incomingAttachments = context.IncomingAttachments();
        var outgoingAttachments = context.OutgoingAttachments();

        foreach (var incoming in incomingAttachments.Values)
        {
            // For sample purpose echo the incoming request
            // stream to the outgoing response stream
            var memoryStream = new MemoryStream();
            incoming.CopyTo(memoryStream);
            memoryStream.Position = 0;
            outgoingAttachments.AddStream(incoming.Name, memoryStream);
        }

        return new Result
        {
            Argument = context.GetArgument<string>("argument"),
        };
    });

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Server-side Middleware

RequestReader instead of binding

When using Attachments the incoming request also requires the incoming form data to be parse. To facilitate this RequestReader is used.:

public async Task InvokeAsync(HttpContext context, RequestDelegate next)
{
    var cancel = context.RequestAborted;
    var response = context.Response;
    var request = context.Request;
    var isGet = HttpMethods.IsGet(request.Method);
    var isPost = HttpMethods.IsPost(request.Method);

    if (isGet)
    {
        var (query, inputs, operation) = readerWriter.ReadGet(request);
        await Execute(response, query, operation, null, inputs, cancel);
        return;
    }

    if (isPost)
    {
        var (query, inputs, attachments, operation) = await readerWriter.ReadPost(request, cancel);
        await Execute(response, query, operation, attachments, inputs, cancel);
        return;
    }

    response.Headers.Allow = "GET, POST";
    response.StatusCode = (int) HttpStatusCode.BadRequest;
}

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Query Execution

To expose the attachments to the queries, the attachment context needs to be added to the IDocumentExecuter. This is done using AttachmentsExtensions.ExecuteWithAttachments:

var result = await executer.ExecuteWithAttachments(options, attachments);

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Result Writing

As with RequestReader for the incoming data, the outgoing data needs to be written with any resulting attachments. To facilitate this ResponseWriter is used.

await readerWriter.WriteResult(response, result, cancel);

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Client - JavaScript

The JavaScript that submits the query does so through by building up a FormData object and POSTing that via the Fetch API.

Helper method for builgin post settings

function BuildPostSettings() {
    var data = new FormData();
    var files = document.getElementById("files").files;
    for (var i = 0; i < files.length; i++) {
        data.append('files[]', files[i], files[i].name);
    }
    data.append(
        "query",
        'mutation{ withAttachment (argument: "argumentValue"){argument}}'
    );

    return {
        method: 'POST',
        body: data
    };
}

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Post mutation and download result

function PostMutationAndDownloadFile() {

    var postSettings = BuildPostSettings();
    return fetch('graphql', postSettings)
        .then(function (data) {
            return data.formData().then(x => {
                var resultContent = '';
                x.forEach(e => {
                    // This is the attachments
                    if (e.name) {
                        var a = document.createElement('a');
                        var blob = new Blob([e]);
                        a.href = window.URL.createObjectURL(blob);
                        a.download = e.name;
                        a.click();
                    }
                    else {
                        resultContent += JSON.stringify(e);
                    }
                });
                result.innerHTML = resultContent;
            });
        });
}

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Post mutation and display text result

function PostMutationWithTextResult() {
    var postSettings = BuildPostSettings();
    return fetch('graphql', postSettings)
        .then(function (data) {
            return data.text().then(x => {
                result.innerHTML = x;
            });
        });
}

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Client - .NET

Creating and posting a multipart form can be done using a combination of MultipartFormDataContent and HttpClient.PostAsync. To simplify this action the ClientQueryExecutor class can be used:

namespace GraphQL.Attachments;

public class QueryExecutor
{
    HttpClient client;
    string uri;

    public QueryExecutor(HttpClient client, string uri = "graphql")
    {
        Guard.AgainstNullWhiteSpace(uri);

        this.client = client;
        this.uri = uri;
    }

    public Task<QueryResult> ExecutePost(string query, Cancel cancel = default)
    {
        Guard.AgainstNullWhiteSpace(query);
        return ExecutePost(new PostRequest(query), cancel);
    }

    public async Task<QueryResult> ExecutePost(PostRequest request, Cancel cancel = default)
    {
        using var content = new MultipartFormDataContent();
        content.AddQueryAndVariables(request.Query, request.Variables, request.OperationName);

        if (request.Action != null)
        {
            var postContext = new PostContext(content);
            request.Action?.Invoke(postContext);
            postContext.HeadersAction?.Invoke(content.Headers);
        }

        var response = await client.PostAsync(uri, content, cancel);
        var result = await response.ProcessResponse(cancel);
        return new(result.Stream, result.Attachments, response.Content.Headers, response.Headers, response.StatusCode);
    }

    public Task<QueryResult> ExecuteGet(string query, Cancel cancel = default)
    {
        Guard.AgainstNullWhiteSpace(query);
        return ExecuteGet(new GetRequest(query), cancel);
    }

    public async Task<QueryResult> ExecuteGet(GetRequest request, Cancel cancel = default)
    {
        var compressed = Compress.Query(request.Query);
        var variablesString = RequestAppender.ToJson(request.Variables);
        var getUri = UriBuilder.GetUri(uri, variablesString, compressed, request.OperationName);

        using var getRequest = new HttpRequestMessage(HttpMethod.Get, getUri);
        request.HeadersAction?.Invoke(getRequest.Headers);
        var response = await client.SendAsync(getRequest, cancel);
        return await response.ProcessResponse(cancel);
    }
}

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This can be useful when performing Integration testing in ASP.NET Core.

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memory designed by H Alberto Gongora from The Noun Project