Logger support in otelhttp

[seanpburke]

Problem Statement

The otelhttp middleware is an ideal place to log HTTP transactions, because important data are available, such as:

• HTTP status code
• Elapsed Time
• Bytes read and written

Now that the minimal Go version is 1.21, in which the package log/slog is part of the standard library,
a standard API is available to generate structured log records.

OpenTelemetry loggers can be used with the log/slog API via go.opentelemetry.io/contrib/bridges/otelslog.

Proposed Solution

The middleware can optionally be configured with a *slog.Logger:

    mware := otelhttp.NewMiddleware(operation, otelhttp.WithLogger(logger))

If a Logger has been configured, a log record will be emitted with the same attributes as the Span:

{
  "time": "2024-04-05T15:42:16.926178547-07:00",
  "level": "INFO",
  "msg": "operation",
  "http.method": "GET",
  "http.scheme": "http",
  "net.host.name": "tonio.attlocal.net",
  "net.host.port": 8080,
  "net.protocol.name": "http",
  "net.protocol.version": "1.1",
  "http.status_code": 200, 
  "http.wrote_bytes": 3954,
  "http.server.duration": 4.426442,
}

Alternatives

Middlewares already exist to generate access logs from HTTP servers based onnet/http and similar routers,
such as https://pkg.go.dev/github.com/gorilla/handlers?utm_source=godoc#LoggingHandler . The drawbacks are that:

• It is wasteful to have more than one httpsnoop in your middleware stack (and perhaps dangerous?)
• The middlewares i have found cannot be configured with a slog.Logger.

Prior Art

N/A

Additional Context

N/A

[MrAlias]

Please open an issue with the OTel semantic conventions: https://github.com/open-telemetry/semantic-conventions

We do not plan to add logging to the canonical library without a standardization across OpenTelemetry.