Add structured logging and OpenMetrics endpoint

[yulmwu]

• Add structured logging
• Removed Discord/Slack webhook sender
• (WIP) Add OpenMetrics endpoint

Refs: #9

[codecov]

Codecov Report

❌ Patch coverage is 78.57143% with 54 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/logging/logging.go	74.19%	27 Missing and 5 partials ⚠️
internal/http/middleware/recovery_logger.go	0.00%	16 Missing ⚠️
internal/http/handlers/errors.go	88.23%	1 Missing and 1 partial ⚠️
internal/http/middleware/request_logger.go	90.47%	2 Missing ⚠️
internal/http/router.go	0.00%	2 Missing ⚠️

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[Copilot]

Pull request overview

This PR modernizes the logging infrastructure by migrating from a custom file-based logging system with webhook support to Go's standard log/slog package for structured JSON logging. The webhook functionality for Discord and Slack has been removed as indicated in the related issue #9.

Changes:

• Replaced custom logging implementation with Go's log/slog structured logging library
• Removed Discord/Slack webhook integration and all related configuration
• Updated all logging call sites to use structured logging with JSON output and proper attribute typing

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/logging/logging.go	Complete rewrite to use slog with custom handlers for level-based routing (stdout/stderr/file), removed webhook sender implementation
internal/logging/logging_test.go	Removed webhook-related tests, updated test logger initialization to include Options parameter
internal/http/middleware/request_logger.go	Converted from string-formatted logs to structured logging with slog.Group for HTTP attributes
internal/http/middleware/recovery_logger.go	New middleware for panic recovery using structured logging (replaces gin.Recovery)
internal/http/middleware/request_logger_test.go	Updated tests to parse JSON logs and extract structured fields instead of string matching
internal/http/router.go	Updated middleware setup to use new RecoveryLogger and removed gin default writers
internal/config/config.go	Removed webhook-related configuration fields (DiscordWebhookURL, SlackWebhookURL, etc.) and updated FormatForLog to return structured map instead of string
internal/config/config_test.go	Updated tests to remove webhook configuration validation and adapt to new FormatForLog signature
cmd/server/main.go	Converted all log statements to structured logging with slog, added Options parameter to logger initialization
internal/http/integration/testenv_test.go	Updated logger initialization with Options parameter
README.md	Added JSON schema documentation for log format, removed webhook-related environment variables
.env.example	Removed webhook-related environment variable examples

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[yulmwu]

We will now apply the same changes to the container-provisioner as well.

[yulmwu]

A critical issue where most 5xx errors were not being logged has been fixed. This issue does not affect the container-provisioner.

[yulmwu]

The JSON schema for structured logging is as follows. It may differ slightly from the actual implementation; please use analysis tools such as Ajv or AWS Glue Crawler if necessary.

{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "title": "SMCTF Log Event",
    "type": "object",
    "additionalProperties": true,
    "required": ["ts", "level", "msg", "app"],
    "properties": {
        "ts": {
            "type": "string",
            "format": "date-time",
            "description": "RFC3339 timestamp with timezone"
        },
        "level": {
            "type": "string",
            "enum": ["debug", "info", "warn", "error"]
        },
        "msg": { "type": "string" },
        "app": { "type": "string" },
        "legacy": { "type": "boolean" },
        "error": {},
        "stack": { "type": "string" },
        "http": {
            "type": "object",
            "additionalProperties": true,
            "properties": {
                "method": { "type": "string" },
                "path": { "type": "string" },
                "status": { "type": "integer" },
                "latency": { "type": "string" },
                "ip": { "type": "string" },
                "query": { "type": "string" },
                "user_agent": { "type": "string" },
                "content_type": { "type": "string" },
                "content_length": { "type": "integer" },
                "user_id": { "type": "integer" },
                "body": { "type": "string" }
            }
        }
    }
}