slog-context

slog-context

Use golang structured logging (slog) with context. Add and retrieve logger to and from context. Add attributes to context. Automatically read any custom context values, such as OpenTelemetry TraceID.

This library supports two different workflows for using slog and context. These workflows can be used individually or together at the same time.

Attributes Extracted from Context Workflow:

Using the Handler lets us Prepend and Append attributes to log lines, even when a logger is not passed into a function or in code we don't control. This is done without storing the logger in the context; instead the attributes are stored in the context and the Handler picks them up later whenever a new log line is written.

In that same workflow, the HandlerOptions and AttrExtractor types let us extract any custom values from a context and have them automatically be prepended or appended to all log lines using that context. By default, there are extractors for anything added via Prepend and Append, but this repository contains some optional Extractors that can be added:

• slogotel.ExtractTraceSpanID extractor will automatically extract the OTEL (OpenTelemetry) TraceID and SpanID, and add them to the log record, while also annotating the Span with an error code if the log is at error level.
• sloghttp.ExtractAttrCollection extractor will automatically add to the log record any attributes added by sloghttp.With after the sloghttp.AttrCollection http middleware. This allows other middlewares to log with attributes that would normally be out of scope, because they were added by a later middleware or the final http handler in the chain.

Logger in Context Workflow:

Using NewCtx and FromCtx lets us store the logger itself within a context, and get it back out again. Wrapper methods With/WithGroup/Debug/Info/ Warn/Error/Log/LogAttrs let us work directly with a logger residing with the context (or the default logger if no logger is stored in the context).

Compatibility with both Slog and Logr

slog-context is compatible with both standard library slog and with logr, which is an alternative logging api/interface/frontend.

If only slog is used, only *slog.Logger's will be stored in the context. If both slog and logr are used, *slog.Logger will be automatically converted to a logr.Logger as needed, and vice versa. This allows full interoperability down the stack and with any libraries that use either slog-context or logr.

Other Great SLOG Utilities

• slogctx: Add attributes to context and have them automatically added to all log lines. Work with a logger stored in context.
• slogotel: Automatically extract and add OpenTelemetry TraceID's to all log lines.
• sloggrpc: Instrument GRPC with automatic logging of all requests and responses.
• slogdedup: Middleware that deduplicates and sorts attributes. Particularly useful for JSON logging. Format logs for aggregators (Graylog, GCP/Stackdriver, etc).
• slogbugsnag: Middleware that pipes Errors to Bugsnag.
• slogjson: Formatter that uses the JSON v2 library, with optional single-line pretty-printing.

Install

go get github.com/veqryn/slog-context

import (
	slogctx "github.com/veqryn/slog-context"
)

Usage

Examples in repo

Logger in Context Workflow

…

Attributes Extracted from Context Workflow

Append and Prepend

…

Custom Context Value Extractor

…

OpenTelemetry TraceID SpanID Extractor

In order to avoid making all users of this repo require all the OTEL libraries, the OTEL extractor is in a separate module in this repo:

go get github.com/veqryn/slog-context/otel

…

Slog Attribute Collection HTTP Middleware and Extractor

…

gRPC Logging Interceptors/Middlewares

Server Interceptors

…

go import "github.com/veqryn/slog-context" var h = slogcontext.NewHandler(slog.NewJSONHandler(os.Stdout, nil), nil)

To this:
```go
import "github.com/veqryn/slog-context"
var h = slogctx.NewHandler(slog.NewJSONHandler(os.Stdout, nil), nil)

Named imports are unaffected.