chore: initial commit of Go API gateway

Baseline for the Kong replacement on api.riotpiao.com. Brings the working
tree under version control for the first time: gateway source, the task
board that drives the agent runs, test fixtures, and K8s manifests.

Anchor the gateway ignore rule to the repo root. Unanchored, "gateway"
also matched the cmd/gateway/ source directory, so the program entrypoint
was excluded from every commit.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

internal/config/loader.go

@@ -0,0 +1,176 @@
+package config
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"time"
+
+	"gopkg.in/yaml.v3"
+)
+
+// rawConfig represents the structure of the YAML configuration file.
+type rawConfig struct {
+	Routes []rawRoute `yaml:"routes"`
+	Models []rawModel `yaml:"models"`
+}
+
+// rawRoute represents a single route in the YAML configuration.
+type rawRoute struct {
+	Name     string      `yaml:"name"`
+	Upstream rawUpstream `yaml:"upstream"`
+}
+
+// rawModel represents a single model entry in the YAML configuration.
+type rawModel struct {
+	Name    string `yaml:"name"`
+	Address string `yaml:"address"`
+	Path    string `yaml:"path"`
+}
+
+// rawUpstream represents upstream configuration in YAML.
+type rawUpstream struct {
+	Address        string `yaml:"address"`
+	PathRewrite    string `yaml:"pathRewrite"`
+	ConnectTimeout string `yaml:"connectTimeout"`
+	ReadTimeout    string `yaml:"readTimeout"`
+	WriteTimeout   string `yaml:"writeTimeout"`
+	MaxBodySize    int64  `yaml:"maxBodySize"`
+	AuthRequired   *bool  `yaml:"authRequired"`
+}
+
+// LoadRoutesAndModelsFromFile loads both route and model configuration from a YAML file.
+func LoadRoutesAndModelsFromFile(path string) (map[string]*Route, map[string]*ModelUpstream, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to read config file %q: %w", path, err)
+	}
+
+	var raw rawConfig
+	if err := yaml.Unmarshal(data, &raw); err != nil {
+		return nil, nil, fmt.Errorf("failed to parse config file %q: %w", path, err)
+	}
+
+	// Load routes
+	routes := make(map[string]*Route)
+	for _, rawRoute := range raw.Routes {
+		if rawRoute.Name == "" {
+			return nil, nil, fmt.Errorf("route has empty name")
+		}
+
+		if _, exists := routes[rawRoute.Name]; exists {
+			return nil, nil, fmt.Errorf("duplicate route: \"%s\"", rawRoute.Name)
+		}
+
+		upstream, err := parseUpstream(rawRoute.Name, rawRoute.Upstream)
+		if err != nil {
+			return nil, nil, err
+		}
+
+		routes[rawRoute.Name] = &Route{
+			Name:     rawRoute.Name,
+			Upstream: upstream,
+		}
+	}
+
+	// Load models
+	models := make(map[string]*ModelUpstream)
+	for _, rawModel := range raw.Models {
+		// Validate model name is not empty
+		if rawModel.Name == "" {
+			return nil, nil, fmt.Errorf("model has empty name")
+		}
+
+		// Check for duplicate model names
+		if _, exists := models[rawModel.Name]; exists {
+			return nil, nil, fmt.Errorf("duplicate model: \"%s\"", rawModel.Name)
+		}
+
+		// Validate address is not empty
+		if rawModel.Address == "" {
+			return nil, nil, fmt.Errorf("model \"%s\": field 'address' is required", rawModel.Name)
+		}
+
+		// Validate address format (host:port)
+		if _, _, err := net.SplitHostPort(rawModel.Address); err != nil {
+			return nil, nil, fmt.Errorf("model \"%s\": invalid address \"%s\": %w", rawModel.Name, rawModel.Address, err)
+		}
+
+		models[rawModel.Name] = &ModelUpstream{
+			Name:    rawModel.Name,
+			Address: rawModel.Address,
+			Path:    rawModel.Path,
+		}
+	}
+
+	return routes, models, nil
+}
+
+// LoadRoutesFromFile loads route configuration from a YAML file.
+// It validates that all required fields are present and have valid values.
+// Returns an error if the configuration is invalid.
+// Deprecated: Use LoadRoutesAndModelsFromFile instead.
+func LoadRoutesFromFile(path string) (map[string]*Route, error) {
+	routes, _, err := LoadRoutesAndModelsFromFile(path)
+	return routes, err
+}
+
+// parseUpstream validates and parses upstream configuration from raw YAML.
+func parseUpstream(routeName string, raw rawUpstream) (Upstream, error) {
+	// Validate address is not empty
+	if raw.Address == "" {
+		return Upstream{}, fmt.Errorf("route \"%s\": field 'address' is required", routeName)
+	}
+
+	// Validate address format (host:port)
+	if _, _, err := net.SplitHostPort(raw.Address); err != nil {
+		return Upstream{}, fmt.Errorf("route \"%s\": invalid address \"%s\": %w", routeName, raw.Address, err)
+	}
+
+	// Validate connectTimeout
+	if raw.ConnectTimeout == "" {
+		return Upstream{}, fmt.Errorf("route \"%s\": field 'connectTimeout' is required", routeName)
+	}
+	connectTimeout, err := time.ParseDuration(raw.ConnectTimeout)
+	if err != nil {
+		return Upstream{}, fmt.Errorf("route \"%s\": invalid connectTimeout \"%s\": %w", routeName, raw.ConnectTimeout, err)
+	}
+
+	// Validate readTimeout
+	if raw.ReadTimeout == "" {
+		return Upstream{}, fmt.Errorf("route \"%s\": field 'readTimeout' is required", routeName)
+	}
+	readTimeout, err := time.ParseDuration(raw.ReadTimeout)
+	if err != nil {
+		return Upstream{}, fmt.Errorf("route \"%s\": invalid readTimeout \"%s\": %w", routeName, raw.ReadTimeout, err)
+	}
+
+	// Validate writeTimeout
+	if raw.WriteTimeout == "" {
+		return Upstream{}, fmt.Errorf("route \"%s\": field 'writeTimeout' is required", routeName)
+	}
+	writeTimeout, err := time.ParseDuration(raw.WriteTimeout)
+	if err != nil {
+		return Upstream{}, fmt.Errorf("route \"%s\": invalid writeTimeout \"%s\": %w", routeName, raw.WriteTimeout, err)
+	}
+
+	// Validate maxBodySize is not zero (it must be explicitly set)
+	if raw.MaxBodySize == 0 {
+		return Upstream{}, fmt.Errorf("route \"%s\": field 'maxBodySize' is required and must be > 0", routeName)
+	}
+
+	// Validate authRequired is not missing
+	if raw.AuthRequired == nil {
+		return Upstream{}, fmt.Errorf("route \"%s\": field 'authRequired' is required", routeName)
+	}
+
+	return Upstream{
+		Address:        raw.Address,
+		PathRewrite:    raw.PathRewrite,
+		ConnectTimeout: connectTimeout,
+		ReadTimeout:    readTimeout,
+		WriteTimeout:   writeTimeout,
+		MaxBodySize:    raw.MaxBodySize,
+		AuthRequired:   *raw.AuthRequired,
+	}, nil
+}