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linkTitle: HTTP request and connection spans
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# Semantic Conventions for network spans emitted by .NET

**Status**: [Mixed][DocumentStatus]

This article defines semantic conventions for HTTP client, DNS and TLS spans emitted by .NET.

<!-- toc -->

- [HTTP client request](#http-client-request)
- [HTTP client request: wait for connection](#http-client-request-wait-for-connection)
- [HTTP connection setup](#http-connection-setup)
- [DNS lookup](#dns-lookup)
- [Socket connect](#socket-connect)
- [TLS handshake](#tls-handshake)
- [Examples](#examples)
  - [HTTP request was performed on a connection that was immediately available](#http-request-was-performed-on-a-connection-that-was-immediately-available)
  - [HTTP request has to wait for connection setup](#http-request-has-to-wait-for-connection-setup)
  - [HTTP request has to wait for connection setup and other requests on that connection to complete](#http-request-has-to-wait-for-connection-setup-and-other-requests-on-that-connection-to-complete)
  - [HTTP request fails because connection cannot be established](#http-request-fails-because-connection-cannot-be-established)

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.NET `HttpClient` reports HTTP client request spans according to [HTTP Semantic Conventions](/docs/http/http-spans.md#http-client-span).

In addition to stable HTTP client request spans, HTTP client handlers reports experimental
spans describing HTTP connection establishment and its stages.

The connection lifetime is usually measured in minutes, so when application is under the load but connection pool is not
overloaded, the rate of connection-related spans is expected to be much lower than the rate of
HTTP client request spans.

Applications are encouraged to enable *HTTP client request* spans by default in production environments.

Connection-level spans are experimental - their semantics may be changed in the future in a breaking manner.
Using connection-level instrumentation in production environments should be done after appropriate validation.

The connection-related spans are reported only by [HttpClientHandler](https://learn.microsoft.com/dotnet/api/system.net.http.httpclienthandler)
and [SocketsHttpHandler](https://learn.microsoft.com/dotnet/api/system.net.http.socketshttphandler) which may not be supported
on certain platforms or may not be used by a particular application.

## HTTP client request

**Status**: [Stable][DocumentStatus]

.NET `HttpClient` reports client request spans according to [HTTP Client Semantic Conventions](/docs/http/http-spans.md#http-client-span) with the following
specific details:

- `network.protocol.name`, `network.peer.port`, and `http.request.resend_count` attributes are not reported
- `url.full` is redacted by default - query parameter values are replaced with `*`. Redaction can be disabled by setting `AppContext` switch `System.Net.Http.DisableQueryRedaction` to `true`.
- When the `error.type` attribute is reported, it contains one of [HTTP Request errors](https://learn.microsoft.com/dotnet/api/system.net.http.httprequesterror) in snake_case, a full exception type name, or a string representation of received status code.
- All attributes are reported after `Activity` is started, none are provided at creation time.
- In case redirects occur, each redirected request is reported as a separate span.
- `SocketsHttpHandler` may retry requests on connection failure. Such retries are not reported as separate spans.

Corresponding `Activity.OperationName` is `System.Net.Http.HttpRequestOut`, `ActivitySource` name - `System.Net.Http`.
Span with HTTP semantics was added in .NET 9.

## HTTP client request: wait for connection

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**Status:** ![Development](https://img.shields.io/badge/-development-blue)

The span describes the time it takes for the HTTP request to obtain a connection from the connection pool.

The span is reported only if there was no connection readily available when request has started.
It's reported as a child of *HTTP client request* span.

The span ends when the connection is obtained - it could happen when an existing connection becomes available or once
a new connection is established, so the duration of *Wait For Connection* span is different from duration of the
[*HTTP connection setup*](/docs/dotnet/dotnet-network-traces.md#http-connection-setup) span.

The time it takes to get a connection from the pool is also reported by the
[`http.client.request.time_in_queue` metric](/docs/dotnet/dotnet-http-metrics.md#metric-httpclientrequesttime_in_queue).

Corresponding `Activity.OperationName` is `Experimental.System.Net.Http.Connections.WaitForConnection`, `ActivitySource` name - `Experimental.System.Net.Http`.
Added in .NET 9.

**Span name** SHOULD be `HTTP wait_for_connection {server.address}:{server.port}`.

**Span kind** SHOULD be `INTERNAL`.

**Span status** SHOULD follow the [Recording Errors](/docs/general/recording-errors.md) document.

| Attribute  | Type | Description  | Examples  | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability |
|---|---|---|---|---|---|
| [`error.type`](/docs/registry/attributes/error.md) | string | One of the [HTTP Request errors](https://learn.microsoft.com/dotnet/api/system.net.http.httprequesterror) in snake_case, or a full exception type. | `version_negotiation_error`; `System.OperationCanceledException` | `Conditionally Required` if and only if an error has occurred. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

---

`error.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value  | Description | Stability |
|---|---|---|
| `_OTHER` | A fallback error value to be used when the instrumentation doesn't define a custom value. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

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## HTTP connection setup

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**Status:** ![Development](https://img.shields.io/badge/-development-blue)

The span describes the establishment of the HTTP connection. It includes the time it takes to resolve the DNS, establish the socket connection, and perform the TLS handshake.

There is no parent-child relationship between the [*HTTP client request*](/docs/dotnet/dotnet-network-traces.md#http-client-request) and the
[*HTTP connection setup*]/docs/dotnet/dotnet-network-traces.md(/docs/dotnet/dotnet-network-traces.md#http-connection-setup) spans;
the latter will always be a root span, defining a separate trace.

However, if the connection attempt represented by the [*HTTP connection setup*](/docs/dotnet/dotnet-network-traces.md#http-connection-setup) span results in a
successful HTTP connection, and that connection is picked up by a request to serve it, the instrumentation adds a link
to the [*HTTP client request*](/docs/dotnet/dotnet-network-traces.md#http-client-request) span pointing to the *HTTP connection setup* span.
I.e., each request is linked to the connection that served this request.

Corresponding `Activity.OperationName` is `Experimental.System.Net.Http.Connections.ConnectionSetup`, `ActivitySource` name - `Experimental.System.Net.Http.Connections`.
Added in .NET 9.

**Span name** SHOULD be `HTTP connection_setup {server.address}:{server.port}`.

**Span kind** SHOULD be `INTERNAL`.

**Span status** SHOULD follow the [Recording Errors](/docs/general/recording-errors.md) document.

| Attribute  | Type | Description  | Examples  | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability |
|---|---|---|---|---|---|
| [`error.type`](/docs/registry/attributes/error.md) | string | One of the [HTTP Request errors](https://learn.microsoft.com/dotnet/api/system.net.http.httprequesterror) in snake_case, or a full exception type. | `name_resolution_error`; `System.OperationCanceledException` | `Conditionally Required` if and only if an error has occurred. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`network.peer.address`](/docs/registry/attributes/network.md) | string | Peer IP address of the socket connection. [1] | `10.1.2.80`; `/tmp/my.sock` | `Recommended` | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`server.address`](/docs/registry/attributes/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [2] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`server.port`](/docs/registry/attributes/server.md) | int | Server port number. [3] | `80`; `8080`; `443` | `Recommended` | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`url.scheme`](/docs/registry/attributes/url.md) | string | The [URI scheme](https://www.rfc-editor.org/rfc/rfc3986#section-3.1) component identifying the used protocol. | `https`; `ftp`; `telnet` | `Recommended` | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

**[1] `network.peer.address`:** The `network.peer.address` attribute is available only if the connection was successfully established and only for IP sockets.

**[2] `server.address`:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available.

**[3] `server.port`:** When observed from the client side, and when communicating through an intermediary, `server.port` SHOULD represent the server port behind any intermediaries, for example proxies, if it's available.

---

`error.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value  | Description | Stability |
|---|---|---|
| `_OTHER` | A fallback error value to be used when the instrumentation doesn't define a custom value. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

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## DNS lookup

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**Status:** ![Development](https://img.shields.io/badge/-development-blue)

The span describes DNS lookup or reverse lookup performed with one of the methods on [System.Net.Dns](https://learn.microsoft.com/dotnet/api/system.net.dns) class.

DNS spans track logical operations rather than physical DNS calls and the actual behavior depends on the
resolver implementation which could be changed in the future versions of .NET.
.NET 9 uses OS DNS resolver which may do zero or more physical lookups for one API call.

When the *DNS lookup* span is reported along with *HTTP connection setup* and *socket connect* span,
the *DNS lookup* span span becomes a child of *HTTP connection setup* and a sibling of *socket connect*.

DNS lookup duration is also reported by [`dns.lookup.duration` metric](/docs/dotnet/dotnet-dns-metrics.md#metric-dnslookupduration).

Corresponding `Activity.OperationName` is `Experimental.System.Net.NameResolution.DnsLookup`, `ActivitySource` name - `Experimental.System.Net.NameResolution`.
Added in .NET 9.

**Span name** SHOULD be `DNS lookup {dns.question.name}` for DNS lookup (IP addresses from host name)
and `DNS reverse lookup {dns.question.name}` for reverse lookup (host names from IP address).

**Span kind** SHOULD be `INTERNAL`.

**Span status** SHOULD follow the [Recording Errors](/docs/general/recording-errors.md) document.

| Attribute  | Type | Description  | Examples  | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability |
|---|---|---|---|---|---|
| [`error.type`](/docs/registry/attributes/error.md) | string | The error code or exception name returned by [System.Net.Dns](https://learn.microsoft.com/dotnet/api/system.net.dns). [1] | `host_not_found`; `try_again` | `Conditionally Required` if and only if an error has occurred. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`dns.answers`](/docs/registry/attributes/dns.md) | string[] | List of resolved IP addresses (for DNS lookup) or a single element containing domain name (for reverse lookup). | `["10.0.0.1", "2001:0db8:85a3:0000:0000:8a2e:0370:7334"]` | `Recommended` if DNS lookup was successful. | ![Development](https://img.shields.io/badge/-development-blue) |
| [`dns.question.name`](/docs/registry/attributes/dns.md) | string | The domain name or an IP address being queried. | `www.example.com`; `opentelemetry.io` | `Recommended` | ![Development](https://img.shields.io/badge/-development-blue) |

**[1] `error.type`:** The following errors are reported:

- `host_not_found`
- `try_again`
- `no_recovery`
- `address_family_not_supported`
- the full exception type name

See [SocketError](https://learn.microsoft.com/dotnet/api/system.net.sockets.socketerror) for more details.

---

`error.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value  | Description | Stability |
|---|---|---|
| `_OTHER` | A fallback error value to be used when the instrumentation doesn't define a custom value. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

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## Socket connect

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**Status:** ![Development](https://img.shields.io/badge/-development-blue)

The span describes the establishment of the socket connection.

It's different from [*HTTP connection setup*](/docs/dotnet/dotnet-network-traces.md#http-connection-setup) span, which also covers the DNS lookup and TLS handshake.

When *socket connect* span is reported along with *HTTP connection setup* span, the socket span becomes a child of HTTP connection setup.

Corresponding `Activity.OperationName` is `Experimental.System.Net.Sockets.Connect`, `ActivitySource` name - `Experimental.System.Net.Sockets`.
Added in .NET 9.

**Span name** SHOULD be `socket connect {network.peer.address}:{network.peer.port}` when socket address family has a
notion of port and `socket connect {network.peer.address}`
otherwise.

**Span kind** SHOULD be `INTERNAL`.

**Span status** SHOULD follow the [Recording Errors](/docs/general/recording-errors.md) document.

| Attribute  | Type | Description  | Examples  | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability |
|---|---|---|---|---|---|
| [`error.type`](/docs/registry/attributes/error.md) | string | Socket error code. [1] | `connection_refused`; `address_not_available` | `Conditionally Required` if and only if an error has occurred. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`network.peer.address`](/docs/registry/attributes/network.md) | string | Peer address of the network connection - IP address or Unix domain socket name. | `10.1.2.80`; `/tmp/my.sock` | `Recommended` | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`network.peer.port`](/docs/registry/attributes/network.md) | int | Peer port number of the network connection. | `65123` | `Recommended` [2] | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`network.transport`](/docs/registry/attributes/network.md) | string | [OSI transport layer](https://wikipedia.org/wiki/Transport_layer) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [3] | `tcp`; `udp`; `unix` | `Recommended` [4] | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`network.type`](/docs/registry/attributes/network.md) | string | [OSI network layer](https://wikipedia.org/wiki/Network_layer) or non-OSI equivalent. [5] | `ipv4`; `ipv6` | `Recommended` if `network.peer.address` is an IP address. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

**[1] `error.type`:** The following errors codes are reported:

- `network_down`
- `address_already_in_use`
- `interrupted`
- `in_progress`
- `already_in_progress`
- `address_not_available`
- `address_family_not_supported`
- `connection_refused`
- `fault`
- `invalid_argument`
- `is_connected`
- `network_unreachable`
- `host_unreachable`
- `no_buffer_space_available`
- `timed_out`
- `access_denied`
- `protocol_type`

See socket errors on [Windows](https://learn.microsoft.com/windows/win32/api/winsock2/nf-winsock2-connect#return-value) and
[Linux](https://man7.org/linux/man-pages/man2/connect.2.html) for more details.

**[2] `network.peer.port`:** If port is supported for the socket address family.

**[3] `network.transport`:** The value SHOULD be normalized to lowercase.

Consider always setting the transport when setting a port number, since
a port number is ambiguous without knowing the transport. For example
different processes could be listening on TCP port 12345 and UDP port 12345.

**[4] `network.transport`:** If value is not `tcp`. When missing, the value is assumed to be `tcp`.

**[5] `network.type`:** The value SHOULD be normalized to lowercase.

---

`error.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value  | Description | Stability |
|---|---|---|
| `_OTHER` | A fallback error value to be used when the instrumentation doesn't define a custom value. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

---

`network.transport` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value  | Description | Stability |
|---|---|---|
| `pipe` | Named or anonymous pipe. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| `quic` | QUIC | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| `tcp` | TCP | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| `udp` | UDP | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| `unix` | Unix domain socket | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

---

`network.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value  | Description | Stability |
|---|---|---|
| `ipv4` | IPv4 | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| `ipv6` | IPv6 | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

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## TLS handshake

Span name SHOULD be `TLS client handshake {server.address}` when authenticating on the client side and `TLS server handshake` when authenticating the server.
Span kind SHOULD be `INTERNAL` in both cases.

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**Status:** ![Development](https://img.shields.io/badge/-development-blue)

The span describes TLS client or server handshake performed with [System.Net.Security.SslStream](https://learn.microsoft.com/dotnet/api/system.net.security.sslstream).

When *TLS* span is reported for client-side authentication along with *HTTP connection setup* and *socket connect* span, the *TLS* span becomes a child of *HTTP connection setup*.

Corresponding `Activity.OperationName` is `Experimental.System.Net.Security.TlsHandshake`, `ActivitySource` name - `Experimental.System.Net.Security`.
Added in .NET 9.

**Span name** SHOULD be `TLS client handshake {server.address}` when authenticating on the client
side and `TLS server handshake` when authenticating the server.

**Span kind** SHOULD be `INTERNAL` in both cases.

**Span status** SHOULD follow the [Recording Errors](/docs/general/recording-errors.md) document.

| Attribute  | Type | Description  | Examples  | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability |
|---|---|---|---|---|---|
| [`error.type`](/docs/registry/attributes/error.md) | string | Describes a class of error the operation ended with. | `System.Net.Security.Authentication.AuthenticationException`; `System.OperationCanceledException` | `Conditionally Required` if and only if an error has occurred. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`server.address`](/docs/registry/attributes/server.md) | string | The [server name indication (SNI)](https://en.wikipedia.org/wiki/Server_Name_Indication) used in the 'Client Hello' message during TLS handshake. [1] | `opentelemetry.io`; `example.com` | `Recommended` when authenticating the client. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |
| [`tls.protocol.name`](/docs/registry/attributes/tls.md) | string | Normalized lowercase protocol name parsed from original string of the negotiated [SSL/TLS protocol version](https://docs.openssl.org/1.1.1/man3/SSL_get_version/#return-values) | `ssl`; `tls` | `Recommended` when available | ![Development](https://img.shields.io/badge/-development-blue) |
| [`tls.protocol.version`](/docs/registry/attributes/tls.md) | string | Numeric part of the version parsed from the original string of the negotiated [SSL/TLS protocol version](https://docs.openssl.org/1.1.1/man3/SSL_get_version/#return-values) | `1.2`; `3` | `Recommended` when available | ![Development](https://img.shields.io/badge/-development-blue) |

**[1] `server.address`:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available.

---

`error.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value  | Description | Stability |
|---|---|---|
| `_OTHER` | A fallback error value to be used when the instrumentation doesn't define a custom value. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) |

---

`tls.protocol.name` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

| Value  | Description | Stability |
|---|---|---|
| `ssl` | ssl | ![Development](https://img.shields.io/badge/-development-blue) |
| `tls` | tls | ![Development](https://img.shields.io/badge/-development-blue) |

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## Examples

### HTTP request was performed on a connection that was immediately available

If connection is immediately available for the request, `HttpClient` creates one span for HTTP request
and links it to the *HTTP connection_setup* span associated with this connection.

The *HTTP connection_setup* span has already ended at this point.

```
<- HTTP connection_setup - (trace=t1, span=s1) ->
<--- DNS --->
             <--- socket connect --->
                                     <--- TLS -->
                                                  <--- GET / (INTERNAL, trace=t2, span=s2, link_to=t1,s1) --->
```

### HTTP request has to wait for connection setup

If connection was not immediately available for the request, HTTP client and handlers create HTTP request and
*Wait for connection* spans. In this example, a new connection was created and the request was executed on it immediately
after the connection was created. Instrumentation added a link to *HTTP connection_setup* span on the HTTP request `GET` span.

```
<--------- HTTP connection_setup (trace=t1, span=s1) -------->
<--- DNS --->
             <--------- socket connect -------->
                                                <--- TLS --->


<----------------------- GET / (trace=t2, span=s2, link_to=t1,s1) -------------------------------->
<--------- HTTP wait_for_connection (trace=t2, span=s3) ------>
```

### HTTP request has to wait for connection setup and other requests on that connection to complete

If connection was not immediately available for the request, HTTP client and handlers create HTTP request and
*Wait for connection* spans. In this example, request was performed on an existing connection,
but this connection served other requests in the queue before it became available for this request.

```
<- HTTP connection_setup - (t1,s1) ->
                                        <--------------------- GET / (trace=t2, span=s2) ----------------------------------------->
                                        <---- HTTP wait_for_connection (trace=t2, span=s2, link_to=t1,s1) ---->
```

The *HTTP connection_setup* span has started before this request, the corresponding connection
was serving other requests until it became available to the GET request above.

The long *Wait for connection* span here is indicating that there is a queue of requests
and a high demand for connections in the pool.

### HTTP request fails because connection cannot be established

If HTTP request fails before connection is established:

- all attempts to establish connections are recorded as *HTTP connection_setup* spans
- HTTP request `GET` span is recorded with the corresponding error type along with *Wait for connection* span.
- HTTP request `GET` span is **not** linked to any of the *HTTP connection_setup* spans since these connections were never associated with corresponding request.

```
<- HTTP connection_setup - (trace=t1, span=s1) - ERROR ->
<------------------- DNS - timeout ---------------->

<---------- GET / (trace=t2, span=s2) - ERROR ---------->
<- HTTP wait_for_connection (trace=t2, span=s3) - ERROR ->
```

[DocumentStatus]: https://opentelemetry.io/docs/specs/otel/document-status
