feat: ✨ allow some environment variables to be logged as attributes

Author: jbleduigou

README.md

@@ -72,6 +72,28 @@ This will produce the following log statement in CloudWatch Logs:
 }
 ```
 
+### Adding environment variables as attributes to the log handler
+
+You might want to add some environment variables as attributes to the log handler.
+Typically you would want to add some environment variables that will help you identify the specific deployment of your lambda function.
+You can achieve this by passing the environment variable names as arguments to the `NewAWSLambdaHandler` function.
+
+```golang
+slog.SetDefault(slog.New(slogawslambda.NewAWSLambdaHandler(ctx, nil, "ENVIRONMENT", "REGION")))
+```
+
+This will produce the following log statement in CloudWatch Logs:
+```json
+{
+    "time": "2024-06-18T21:36:21.128059573Z",
+    "level": "INFO",
+    "msg": "Successfully downloaded configuration file from S3",
+    "environment": "production",
+    "region": "eu-west-1",
+    "function_arn": "arn:aws:lambda:eu-west-1:01234567890:function:myawesomefunction-chN9TDColFt1",
+    "request_id": "bdb96c48-c3bc-462d-abbd-6b56e6cb3050"
+}
+```
 
 ### Changing the key for request ID or function ARN
 

go.mod

@@ -3,7 +3,7 @@ module github.com/jbleduigou/slog-aws-lambda
 go 1.21
 
 require (
-	github.com/aws/aws-lambda-go v1.46.0
+	github.com/aws/aws-lambda-go v1.47.0
 	github.com/stretchr/testify v1.9.0
 )
 

go.sum

@@ -1,5 +1,5 @@
-github.com/aws/aws-lambda-go v1.46.0 h1:UWVnvh2h2gecOlFhHQfIPQcD8pL/f7pVCutmFl+oXU8=
-github.com/aws/aws-lambda-go v1.46.0/go.mod h1:dpMpZgvWx5vuQJfBt0zqBha60q7Dd7RfgJv23DymV8A=
+github.com/aws/aws-lambda-go v1.47.0 h1:0H8s0vumYx/YKs4sE7YM0ktwL2eWse+kfopsRI1sXVI=
+github.com/aws/aws-lambda-go v1.47.0/go.mod h1:dpMpZgvWx5vuQJfBt0zqBha60q7Dd7RfgJv23DymV8A=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=

handler.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"log/slog"
 	"os"
+	"strings"
 
 	"github.com/aws/aws-lambda-go/lambdacontext"
 )
@@ -12,7 +13,11 @@ type LambdaHandler struct {
 	slog.JSONHandler
 }
 
-func NewAWSLambdaHandler(ctx context.Context, opts *slog.HandlerOptions) slog.Handler {
+// NewAWSLambdaHandler creates a new AWS Lambda handler
+// ctx is the context of the lambda function
+// opts are the options for the handler
+// envVars is an optional list of environment variables to add to the handler
+func NewAWSLambdaHandler(ctx context.Context, opts *slog.HandlerOptions, envVars ...string) slog.Handler {
 	if opts == nil {
 		opts = &slog.HandlerOptions{}
 	}
@@ -33,9 +38,23 @@ func NewAWSLambdaHandler(ctx context.Context, opts *slog.HandlerOptions) slog.Ha
 	arn := lc.InvokedFunctionArn
 
 	// Create the Handler using the attributes from lambda context
-	return slog.NewJSONHandler(os.Stdout, opts).
+	h := slog.NewJSONHandler(os.Stdout, opts).
 		WithAttrs([]slog.Attr{slog.String("function_arn", arn)}).
 		WithAttrs([]slog.Attr{slog.String("request_id", requestID)})
+
+	if len(envVars) == 0 {
+		return h
+	}
+
+	// Add the environment variables to the handler as attributes
+	for _, name := range envVars {
+		val, found := os.LookupEnv(name)
+		if found && len(name) > 0 {
+			h = h.WithAttrs([]slog.Attr{slog.String(strings.ToLower(name), val)})
+		}
+	}
+
+	return h
 }
 
 func getLogLevel() slog.Leveler {