Question About JsonSerializer.DeserializeAsyncEnumerable Behavior #56055

tpeczek · 2021-07-20T22:44:29Z

Hi,

I have a question around JsonSerializer.DeserializeAsyncEnumerable. I was experimenting with async streaming between ASP.NET Core and HttpClient in .NET 6. I have created two methods on the client side. One which outputs the raw data returned by the ASP.NET Core endpoint.

private static async Task NegotiateRawJsonStreamAsync()
{
	Console.WriteLine($"-- {nameof(NegotiateRawJsonStreamAsync)} --");
	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Receving weather forecasts . . .");

	using HttpClient httpClient = new();
	httpClient.DefaultRequestHeaders.Add("Accept", "application/json");

	using HttpResponseMessage response = await httpClient.GetAsync("https://localhost:5001/api/WeatherForecasts/negotiate-stream", HttpCompletionOption.ResponseHeadersRead).ConfigureAwait(false);

	response.EnsureSuccessStatusCode();
	using Stream responseStream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);

	while (true)
	{
		byte[] buffer = ArrayPool<byte>.Shared.Rent(128);
		int bytesRead = await responseStream.ReadAsync(buffer);

		Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] ({bytesRead}/{buffer.Length}) {Encoding.UTF8.GetString(buffer)}");

                ArrayPool<byte>.Shared.Return(buffer);

		if (bytesRead == 0)
		{
			break;
		}
	}

	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Weather forecasts has been received.");
	Console.WriteLine();
}

And one which uses JsonSerializer.DeserializeAsyncEnumerable to deserialize the stream.

private static async Task NegotiateJsonStreamAsync()
{
	Console.WriteLine($"-- {nameof(NegotiateJsonStreamAsync)} --");
	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Receving weather forecasts . . .");

	using HttpClient httpClient = new();
	httpClient.DefaultRequestHeaders.Add("Accept", "application/json");

	using HttpResponseMessage response = await httpClient.GetAsync("https://localhost:5001/api/WeatherForecasts/negotiate-stream", HttpCompletionOption.ResponseHeadersRead).ConfigureAwait(false);

	response.EnsureSuccessStatusCode();
	using Stream responseStream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);

	await foreach (WeatherForecast weatherForecast in JsonSerializer.DeserializeAsyncEnumerable<WeatherForecast>(responseStream, new JsonSerializerOptions { PropertyNameCaseInsensitive = true, DefaultBufferSize = 128 }))
	{
		Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] {weatherForecast.Summary}");
	}

	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Weather forecasts has been received.");
	Console.WriteLine();
}

The output from the first one is as follows.

-- NegotiateRawJsonStreamAsync --
[10:35:18.041] Receving weather forecasts . . .
[10:35:18.075] (1/128) [
[10:35:18.184] (89/128) {"dateFormatted":"22.07.2021","temperatureC":49,"temperatureF":120,"summary":"Scorching"}
[10:35:18.286] (89/128) ,{"dateFormatted":"23.07.2021","temperatureC":-20,"temperatureF":-3,"summary":"Freezing"}
[10:35:18.396] (91/128) ,{"dateFormatted":"24.07.2021","temperatureC":49,"temperatureF":120,"summary":"Sweltering"}
[10:35:18.504] (88/128) ,{"dateFormatted":"25.07.2021","temperatureC":-18,"temperatureF":0,"summary":"Freezing"}
[10:35:18.612] (84/128) ,{"dateFormatted":"26.07.2021","temperatureC":30,"temperatureF":85,"summary":"Cool"}
[10:35:18.719] (86/128) ,{"dateFormatted":"27.07.2021","temperatureC":5,"temperatureF":40,"summary":"Bracing"}
[10:35:18.830] (87/128) ,{"dateFormatted":"28.07.2021","temperatureC":-6,"temperatureF":22,"summary":"Bracing"}
[10:35:18.952] (84/128) ,{"dateFormatted":"29.07.2021","temperatureC":13,"temperatureF":55,"summary":"Warm"}
[10:35:19.075] (85/128) ,{"dateFormatted":"30.07.2021","temperatureC":34,"temperatureF":93,"summary":"Balmy"}
[10:35:19.185] (85/128) ,{"dateFormatted":"31.07.2021","temperatureC":36,"temperatureF":96,"summary":"Warm"}]
[10:35:19.204] (0/128)
[10:35:19.212] Weather forecasts has been received.

Which confirms that ASP.NET Core is flushing the results as they come.

The output from the second is as follows.

-- NegotiateJsonStreamAsync --
[10:35:19.218] Receving weather forecasts . . .
[10:35:20.361] Bracing
[10:35:20.362] Mild
[10:35:20.363] Sweltering
[10:35:20.363] Balmy
[10:35:20.363] Bracing
[10:35:20.363] Bracing
[10:35:20.363] Sweltering
[10:35:20.364] Hot
[10:35:20.364] Balmy
[10:35:20.364] Sweltering
[10:35:20.364] Weather forecasts has been received.

This suggest that JsonSerializer.DeserializeAsyncEnumerable is waiting for the entire stream before it starts deserializing.

I haven't found this explained in documentation, so my question would be if this is expected behavior or am I doing something wrong?

The project where I'm plaining with this is available here.

The text was updated successfully, but these errors were encountered:

ghost · 2021-07-20T22:44:32Z

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

Issue Details

Hi,

I have a question around JsonSerializer.DeserializeAsyncEnumerable. I was experimenting with async streaming between ASP.NET Core and HttpClient in .NET 6. I have created two methods on the client side. One which outputs the raw data returned by the ASP.NET Core endpoint.

private static async Task NegotiateRawJsonStreamAsync()
{
	Console.WriteLine($"-- {nameof(NegotiateRawJsonStreamAsync)} --");
	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Receving weather forecasts . . .");

	using HttpClient httpClient = new();
	httpClient.DefaultRequestHeaders.Add("Accept", "application/json");

	using HttpResponseMessage response = await httpClient.GetAsync("https://localhost:5001/api/WeatherForecasts/negotiate-stream", HttpCompletionOption.ResponseHeadersRead).ConfigureAwait(false);

	response.EnsureSuccessStatusCode();

	using Stream contentStream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);
	while (true)
	{
		byte[] buffer = ArrayPool<byte>.Shared.Rent(16 * 1024); ;
		int bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length);

		Console.Out.Write($"[{DateTime.UtcNow:hh:mm:ss.fff}] ({bytesRead}/{buffer.Length}) ");
		Console.Out.Write(Encoding.UTF8.GetString(buffer));
		Console.Out.WriteLine();

		if (bytesRead == 0)
		{
			break;
		}
	}

	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Weather forecasts has been received.");
	Console.WriteLine();
}

And one which uses JsonSerializer.DeserializeAsyncEnumerable to deserialize the stream.

private static async Task NegotiateJsonStreamAsync()
{
	Console.WriteLine($"-- {nameof(NegotiateJsonStreamAsync)} --");
	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Receving weather forecasts . . .");

	using HttpClient httpClient = new();
	httpClient.DefaultRequestHeaders.Add("Accept", "application/json");

	using HttpResponseMessage response = await httpClient.GetAsync("https://localhost:5001/api/WeatherForecasts/negotiate-stream", HttpCompletionOption.ResponseHeadersRead).ConfigureAwait(false);

	response.EnsureSuccessStatusCode();

	using Stream responseStream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);
	await foreach (WeatherForecast weatherForecast in JsonSerializer.DeserializeAsyncEnumerable<WeatherForecast>(responseStream, new JsonSerializerOptions { PropertyNameCaseInsensitive = true, DefaultBufferSize = 128 }))
	{
		Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] {weatherForecast.Summary}");
	}

	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Weather forecasts has been received.");
	Console.WriteLine();
}

The output from the first one is as follows.

-- NegotiateRawJsonStreamAsync --
[10:35:18.041] Receving weather forecasts . . .
[10:35:18.075] (1/16384) [
[10:35:18.184] (89/16384) {"dateFormatted":"22.07.2021","temperatureC":49,"temperatureF":120,"summary":"Scorching"}
[10:35:18.286] (89/16384) ,{"dateFormatted":"23.07.2021","temperatureC":-20,"temperatureF":-3,"summary":"Freezing"}
[10:35:18.396] (91/16384) ,{"dateFormatted":"24.07.2021","temperatureC":49,"temperatureF":120,"summary":"Sweltering"}
[10:35:18.504] (88/16384) ,{"dateFormatted":"25.07.2021","temperatureC":-18,"temperatureF":0,"summary":"Freezing"}
[10:35:18.612] (84/16384) ,{"dateFormatted":"26.07.2021","temperatureC":30,"temperatureF":85,"summary":"Cool"}
[10:35:18.719] (86/16384) ,{"dateFormatted":"27.07.2021","temperatureC":5,"temperatureF":40,"summary":"Bracing"}
[10:35:18.830] (87/16384) ,{"dateFormatted":"28.07.2021","temperatureC":-6,"temperatureF":22,"summary":"Bracing"}
[10:35:18.952] (84/16384) ,{"dateFormatted":"29.07.2021","temperatureC":13,"temperatureF":55,"summary":"Warm"}
[10:35:19.075] (85/16384) ,{"dateFormatted":"30.07.2021","temperatureC":34,"temperatureF":93,"summary":"Balmy"}
[10:35:19.185] (85/16384) ,{"dateFormatted":"31.07.2021","temperatureC":36,"temperatureF":96,"summary":"Warm"}]
[10:35:19.204] (0/16384)
[10:35:19.212] Weather forecasts has been received.

Which confirms that ASP.NET Core is flushing the results as they come.

The output from the second is as follows.

-- NegotiateJsonStreamAsync --
[10:35:19.218] Receving weather forecasts . . .
[10:35:20.361] Bracing
[10:35:20.362] Mild
[10:35:20.363] Sweltering
[10:35:20.363] Balmy
[10:35:20.363] Bracing
[10:35:20.363] Bracing
[10:35:20.363] Sweltering
[10:35:20.364] Hot
[10:35:20.364] Balmy
[10:35:20.364] Sweltering
[10:35:20.364] Weather forecasts has been received.

This suggest that JsonSerializer.DeserializeAsyncEnumerable is waiting for the entire stream before it starts deserializing.

I haven't found this explained in documentation, so my question would be if this is expected behavior or am I doing something wrong?

The project where I'm plaining with this is available here.

Author:	tpeczek
Assignees:	-
Labels:	`area-System.Net.Http`, `untriaged`
Milestone:	-

ghost · 2021-07-21T08:26:56Z

Tagging subscribers to this area: @eiriktsarpalis, @layomia
See info in area-owners.md if you want to be subscribed.

Issue Details

Hi,

I have a question around JsonSerializer.DeserializeAsyncEnumerable. I was experimenting with async streaming between ASP.NET Core and HttpClient in .NET 6. I have created two methods on the client side. One which outputs the raw data returned by the ASP.NET Core endpoint.

private static async Task NegotiateRawJsonStreamAsync()
{
	Console.WriteLine($"-- {nameof(NegotiateRawJsonStreamAsync)} --");
	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Receving weather forecasts . . .");

	using HttpClient httpClient = new();
	httpClient.DefaultRequestHeaders.Add("Accept", "application/json");

	using HttpResponseMessage response = await httpClient.GetAsync("https://localhost:5001/api/WeatherForecasts/negotiate-stream", HttpCompletionOption.ResponseHeadersRead).ConfigureAwait(false);

	response.EnsureSuccessStatusCode();
	using Stream responseStream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);

	while (true)
	{
		byte[] buffer = ArrayPool<byte>.Shared.Rent(128);
		int bytesRead = await responseStream.ReadAsync(buffer);

		Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] ({bytesRead}/{buffer.Length}) {Encoding.UTF8.GetString(buffer)}");

                ArrayPool<byte>.Shared.Return(buffer);

		if (bytesRead == 0)
		{
			break;
		}
	}

	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Weather forecasts has been received.");
	Console.WriteLine();
}

And one which uses JsonSerializer.DeserializeAsyncEnumerable to deserialize the stream.

private static async Task NegotiateJsonStreamAsync()
{
	Console.WriteLine($"-- {nameof(NegotiateJsonStreamAsync)} --");
	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Receving weather forecasts . . .");

	using HttpClient httpClient = new();
	httpClient.DefaultRequestHeaders.Add("Accept", "application/json");

	using HttpResponseMessage response = await httpClient.GetAsync("https://localhost:5001/api/WeatherForecasts/negotiate-stream", HttpCompletionOption.ResponseHeadersRead).ConfigureAwait(false);

	response.EnsureSuccessStatusCode();
	using Stream responseStream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);

	await foreach (WeatherForecast weatherForecast in JsonSerializer.DeserializeAsyncEnumerable<WeatherForecast>(responseStream, new JsonSerializerOptions { PropertyNameCaseInsensitive = true, DefaultBufferSize = 128 }))
	{
		Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] {weatherForecast.Summary}");
	}

	Console.WriteLine($"[{DateTime.UtcNow:hh:mm:ss.fff}] Weather forecasts has been received.");
	Console.WriteLine();
}

The output from the first one is as follows.

-- NegotiateRawJsonStreamAsync --
[10:35:18.041] Receving weather forecasts . . .
[10:35:18.075] (1/128) [
[10:35:18.184] (89/128) {"dateFormatted":"22.07.2021","temperatureC":49,"temperatureF":120,"summary":"Scorching"}
[10:35:18.286] (89/128) ,{"dateFormatted":"23.07.2021","temperatureC":-20,"temperatureF":-3,"summary":"Freezing"}
[10:35:18.396] (91/128) ,{"dateFormatted":"24.07.2021","temperatureC":49,"temperatureF":120,"summary":"Sweltering"}
[10:35:18.504] (88/128) ,{"dateFormatted":"25.07.2021","temperatureC":-18,"temperatureF":0,"summary":"Freezing"}
[10:35:18.612] (84/128) ,{"dateFormatted":"26.07.2021","temperatureC":30,"temperatureF":85,"summary":"Cool"}
[10:35:18.719] (86/128) ,{"dateFormatted":"27.07.2021","temperatureC":5,"temperatureF":40,"summary":"Bracing"}
[10:35:18.830] (87/128) ,{"dateFormatted":"28.07.2021","temperatureC":-6,"temperatureF":22,"summary":"Bracing"}
[10:35:18.952] (84/128) ,{"dateFormatted":"29.07.2021","temperatureC":13,"temperatureF":55,"summary":"Warm"}
[10:35:19.075] (85/128) ,{"dateFormatted":"30.07.2021","temperatureC":34,"temperatureF":93,"summary":"Balmy"}
[10:35:19.185] (85/128) ,{"dateFormatted":"31.07.2021","temperatureC":36,"temperatureF":96,"summary":"Warm"}]
[10:35:19.204] (0/128)
[10:35:19.212] Weather forecasts has been received.

Which confirms that ASP.NET Core is flushing the results as they come.

The output from the second is as follows.

-- NegotiateJsonStreamAsync --
[10:35:19.218] Receving weather forecasts . . .
[10:35:20.361] Bracing
[10:35:20.362] Mild
[10:35:20.363] Sweltering
[10:35:20.363] Balmy
[10:35:20.363] Bracing
[10:35:20.363] Bracing
[10:35:20.363] Sweltering
[10:35:20.364] Hot
[10:35:20.364] Balmy
[10:35:20.364] Sweltering
[10:35:20.364] Weather forecasts has been received.

This suggest that JsonSerializer.DeserializeAsyncEnumerable is waiting for the entire stream before it starts deserializing.

I haven't found this explained in documentation, so my question would be if this is expected behavior or am I doing something wrong?

The project where I'm plaining with this is available here.

Author:	tpeczek
Assignees:	-
Labels:	`area-System.Text.Json`, `untriaged`
Milestone:	-

eiriktsarpalis · 2021-07-21T10:58:10Z

Hi @tpeczek, thanks for reporting this issue. It's a regression introduced by #51702. I have submitted #56080 that should fix the bug.

tpeczek · 2021-07-21T11:36:38Z

Hi @eiriktsarpalis , thank you for taking a look at this. My only two questions would be if there is a chance that fix is going to make it into Preview 7, and are there past previews which have the correct behavior?

eiriktsarpalis · 2021-07-21T11:43:51Z

Once merged the fix would be committed to the RC1 branch and not Preview 7. I believe preview4 might not incorporate the regression although that release is no longer supported.

tpeczek · 2021-07-21T11:49:47Z

Thank you!

dotnet-issue-labeler bot added area-System.Net.Http untriaged New issue has not been triaged by the area owner labels Jul 20, 2021

ManickaP added area-System.Text.Json and removed area-System.Net.Http labels Jul 21, 2021

eiriktsarpalis mentioned this issue Jul 21, 2021

Fix DeserializeAsyncEnumerable streaming behavior #56080

Merged

ghost added the in-pr There is an active PR which will close this issue when it is merged label Jul 21, 2021

eiriktsarpalis added bug and removed untriaged New issue has not been triaged by the area owner labels Jul 21, 2021

eiriktsarpalis added this to the 6.0.0 milestone Jul 21, 2021

eiriktsarpalis self-assigned this Jul 21, 2021

eiriktsarpalis closed this as completed in #56080 Jul 22, 2021

ghost removed the in-pr There is an active PR which will close this issue when it is merged label Jul 22, 2021

ghost locked as resolved and limited conversation to collaborators Aug 21, 2021

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Question About JsonSerializer.DeserializeAsyncEnumerable Behavior #56055

Question About JsonSerializer.DeserializeAsyncEnumerable Behavior #56055

tpeczek commented Jul 20, 2021 •

edited

Loading

ghost commented Jul 20, 2021

ghost commented Jul 21, 2021

eiriktsarpalis commented Jul 21, 2021

tpeczek commented Jul 21, 2021

eiriktsarpalis commented Jul 21, 2021

tpeczek commented Jul 21, 2021

Question About JsonSerializer.DeserializeAsyncEnumerable Behavior #56055

Question About JsonSerializer.DeserializeAsyncEnumerable Behavior #56055

Comments

tpeczek commented Jul 20, 2021 • edited Loading

ghost commented Jul 20, 2021

ghost commented Jul 21, 2021

eiriktsarpalis commented Jul 21, 2021

tpeczek commented Jul 21, 2021

eiriktsarpalis commented Jul 21, 2021

tpeczek commented Jul 21, 2021

tpeczek commented Jul 20, 2021 •

edited

Loading