refactor(agent): extract agent pool and HTTP utilities to dedicated package

Moved non-agent-specific logic from agent/pkg/agent/ to internal/agentpool/:
- pool.go: Agent pool management (Get, Add, Remove, List, Iter, etc.)
- http_requests.go: HTTP utilities (health checks, forwarding, websockets, reverse proxy)
- agent.go: Agent struct with HTTP client management

This separates general-purpose pool management from agent-specific configuration,
improving code organization and making the agent package focused on agent config only.

internal/agentpool/http_requests.go

@@ -0,0 +1,96 @@
+package agentpool
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+
+	"github.com/bytedance/sonic"
+	"github.com/gorilla/websocket"
+	"github.com/valyala/fasthttp"
+	"github.com/yusing/godoxy/agent/pkg/agent"
+	"github.com/yusing/goutils/http/reverseproxy"
+)
+
+func (cfg *Agent) Do(ctx context.Context, method, endpoint string, body io.Reader) (*http.Response, error) {
+	req, err := http.NewRequestWithContext(ctx, method, agent.APIBaseURL+endpoint, body)
+	if err != nil {
+		return nil, err
+	}
+	return cfg.httpClient.Do(req)
+}
+
+func (cfg *Agent) Forward(req *http.Request, endpoint string) (*http.Response, error) {
+	req.URL.Host = agent.AgentHost
+	req.URL.Scheme = "https"
+	req.URL.Path = agent.APIEndpointBase + endpoint
+	req.RequestURI = ""
+	resp, err := cfg.httpClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	return resp, nil
+}
+
+type HealthCheckResponse struct {
+	Healthy bool          `json:"healthy"`
+	Detail  string        `json:"detail"`
+	Latency time.Duration `json:"latency"`
+}
+
+func (cfg *Agent) DoHealthCheck(timeout time.Duration, query string) (ret HealthCheckResponse, err error) {
+	req := fasthttp.AcquireRequest()
+	defer fasthttp.ReleaseRequest(req)
+
+	resp := fasthttp.AcquireResponse()
+	defer fasthttp.ReleaseResponse(resp)
+
+	req.SetRequestURI(agent.APIBaseURL + agent.EndpointHealth + "?" + query)
+	req.Header.SetMethod(fasthttp.MethodGet)
+	req.Header.Set("Accept-Encoding", "identity")
+	req.SetConnectionClose()
+
+	start := time.Now()
+	err = cfg.fasthttpHcClient.DoTimeout(req, resp, timeout)
+	ret.Latency = time.Since(start)
+	if err != nil {
+		return ret, err
+	}
+
+	if status := resp.StatusCode(); status != http.StatusOK {
+		ret.Detail = fmt.Sprintf("HTTP %d %s", status, resp.Body())
+		return ret, nil
+	} else {
+		err = sonic.Unmarshal(resp.Body(), &ret)
+		if err != nil {
+			return ret, err
+		}
+	}
+	return ret, nil
+}
+
+func (cfg *Agent) Websocket(ctx context.Context, endpoint string) (*websocket.Conn, *http.Response, error) {
+	transport := cfg.Transport()
+	dialer := websocket.Dialer{
+		NetDialContext:    transport.DialContext,
+		NetDialTLSContext: transport.DialTLSContext,
+	}
+	return dialer.DialContext(ctx, agent.APIBaseURL+endpoint, http.Header{
+		"Host": {agent.AgentHost},
+	})
+}
+
+// ReverseProxy reverse proxies the request to the agent
+//
+// It will create a new request with the same context, method, and body, but with the agent host and scheme, and the endpoint
+// If the request has a query, it will be added to the proxy request's URL
+func (cfg *Agent) ReverseProxy(w http.ResponseWriter, req *http.Request, endpoint string) {
+	rp := reverseproxy.NewReverseProxy("agent", agent.AgentURL, cfg.Transport())
+	req.URL.Host = agent.AgentHost
+	req.URL.Scheme = "https"
+	req.URL.Path = endpoint
+	req.RequestURI = ""
+	rp.ServeHTTP(w, req)
+}