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package provider
import (
"bytes"
"context"
"encoding/json"
"errors"
"fmt"
"io"
"net"
"net/http"
"strings"
"time"
"aigw/internal/config"
"aigw/internal/domain"
"aigw/internal/providerhealth"
"aigw/internal/telemetry"
)
type Result struct {
Response *http.Response
Route domain.Route
Attempts int
AttemptStartedAt time.Time
}
type Forwarder struct {
client *http.Client
metrics *telemetry.Metrics
health *providerhealth.Tracker
}
func New(cfg config.UpstreamHTTPConfig, metrics *telemetry.Metrics, trackers ...*providerhealth.Tracker) *Forwarder {
transport := &http.Transport{
Proxy: http.ProxyFromEnvironment,
DialContext: (&net.Dialer{Timeout: 5 * time.Second, KeepAlive: 30 * time.Second}).DialContext,
ForceAttemptHTTP2: true,
MaxIdleConns: cfg.MaxIdleConnections,
MaxIdleConnsPerHost: cfg.MaxIdleConnectionsPerHost,
IdleConnTimeout: time.Duration(cfg.IdleConnectionTimeoutSecs) * time.Second,
TLSHandshakeTimeout: 10 * time.Second,
ResponseHeaderTimeout: time.Duration(cfg.ResponseHeaderTimeoutSecs) * time.Second,
ExpectContinueTimeout: time.Second,
}
forwarder := &Forwarder{client: &http.Client{Transport: transport}, metrics: metrics}
if len(trackers) > 0 {
forwarder.health = trackers[0]
}
return forwarder
}
func (f *Forwarder) Forward(ctx context.Context, protocol domain.Protocol, requestID, modelID string, originalBody []byte, sourceHeaders http.Header, routes []domain.Route) (Result, error) {
var lastErr error
for i, route := range routes {
if err := ctx.Err(); err != nil {
return Result{Attempts: i}, err
}
body, err := rewriteRequestWithWireAPI(originalBody, route.UpstreamModel, protocol, route.Provider.EffectiveWireAPI())
if err != nil {
return Result{Attempts: i}, err
}
request, err := http.NewRequestWithContext(ctx, http.MethodPost, endpointURL(route.Provider, protocol), bytes.NewReader(body))
if err != nil {
return Result{Attempts: i}, fmt.Errorf("build upstream request: %w", err)
}
setHeaders(request.Header, sourceHeaders, route.Provider, protocol, requestID)
f.metrics.UpstreamAttempt()
attemptStarted := time.Now()
response, err := f.client.Do(request)
if err != nil {
if ctx.Err() != nil {
return Result{Attempts: i + 1}, ctx.Err()
}
f.observe(modelID, route, 0, time.Since(attemptStarted), true)
lastErr = err
continue
}
attempts := i + 1
f.observe(modelID, route, response.StatusCode, time.Since(attemptStarted), retryableStatus(response.StatusCode))
if retryableStatus(response.StatusCode) && attempts < len(routes) {
_, _ = io.CopyN(io.Discard, response.Body, 8<<10)
_ = response.Body.Close()
lastErr = fmt.Errorf("upstream %s returned %d", route.Provider.ID, response.StatusCode)
continue
}
return Result{Response: response, Route: route, Attempts: attempts, AttemptStartedAt: attemptStarted}, nil
}
if lastErr == nil {
lastErr = errors.New("all upstream routes failed")
}
return Result{Attempts: len(routes)}, lastErr
}
func (f *Forwarder) observe(modelID string, route domain.Route, statusCode int, latency time.Duration, failed bool) {
if f.health == nil {
return
}
f.health.Observe(providerhealth.RouteKey{ModelID: modelID, ProviderID: route.Provider.ID, WireAPI: route.Provider.EffectiveWireAPI()},
providerhealth.Observation{StatusCode: statusCode, Latency: latency, Failed: failed})
}
// ObserveTTFT feeds the first user-visible output latency into adaptive route
// selection. It is deliberately separate from the header/circuit observation
// because streaming TTFT is only known after response forwarding begins.
func (f *Forwarder) ObserveTTFT(modelID string, route domain.Route, latency time.Duration) {
if f.health == nil || latency <= 0 {
return
}
f.health.ObserveTTFT(providerhealth.RouteKey{ModelID: modelID, ProviderID: route.Provider.ID, WireAPI: route.Provider.EffectiveWireAPI()}, latency)
if f.metrics != nil {
f.metrics.UpstreamTTFT(latency)
}
}
func rewriteModel(body []byte, upstreamModel string) ([]byte, error) {
return rewriteRequest(body, upstreamModel, domain.ProtocolOpenAI)
}
func rewriteRequest(body []byte, upstreamModel string, protocol domain.Protocol) ([]byte, error) {
wireAPI := "chat_completions"
if protocol == domain.ProtocolAnthropic {
wireAPI = "messages"
}
return rewriteRequestWithWireAPI(body, upstreamModel, protocol, wireAPI)
}
func rewriteRequestWithWireAPI(body []byte, upstreamModel string, protocol domain.Protocol, wireAPI string) ([]byte, error) {
var object map[string]json.RawMessage
if err := json.Unmarshal(body, &object); err != nil {
return nil, fmt.Errorf("decode request body: %w", err)
}
encoded, _ := json.Marshal(upstreamModel)
object["model"] = encoded
if protocol == domain.ProtocolOpenAI && wireAPI == "chat_completions" {
var stream bool
_ = json.Unmarshal(object["stream"], &stream)
if stream {
var options map[string]json.RawMessage
_ = json.Unmarshal(object["stream_options"], &options)
if options == nil {
options = map[string]json.RawMessage{}
}
options["include_usage"] = json.RawMessage("true")
object["stream_options"], _ = json.Marshal(options)
}
}
result, err := json.Marshal(object)
if err != nil {
return nil, fmt.Errorf("encode upstream request: %w", err)
}
return result, nil
}
func endpointURL(provider domain.Provider, _ domain.Protocol) string {
baseURL := strings.TrimRight(provider.BaseURL, "/")
switch provider.EffectiveWireAPI() {
case "embeddings":
return baseURL + "/embeddings"
case "responses":
return baseURL + "/responses"
case "messages":
return baseURL + "/messages"
case "chat_completions":
fallthrough
default:
return baseURL + "/chat/completions"
}
}
func setHeaders(target, source http.Header, provider domain.Provider, protocol domain.Protocol, requestID string) {
target.Set("Content-Type", "application/json")
target.Set("Accept", source.Get("Accept"))
if target.Get("Accept") == "" {
target.Set("Accept", "application/json")
}
target.Set("User-Agent", "aigw/0.1")
target.Set("X-Request-ID", requestID)
if protocol == domain.ProtocolAnthropic {
target.Set("x-api-key", provider.APIKey)
version := source.Get("anthropic-version")
if version == "" {
version = "2023-06-01"
}
target.Set("anthropic-version", version)
if beta := source.Get("anthropic-beta"); beta != "" {
target.Set("anthropic-beta", beta)
}
return
}
target.Set("Authorization", "Bearer "+provider.APIKey)
}
func retryableStatus(status int) bool {
switch status {
case http.StatusTooManyRequests, http.StatusBadGateway, http.StatusServiceUnavailable, http.StatusGatewayTimeout:
return true
default:
return false
}
}
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