Support get http header and x-ratelimit-* headers (#507)

* feat: add headers to http response

* feat: support rate limit headers

* fix: go lint

* fix: test coverage

* refactor streamReader

* refactor streamReader

* refactor: NewRateLimitHeaders to newRateLimitHeaders

* refactor: RateLimitHeaders Resets filed

* refactor: move RateLimitHeaders struct

ratelimit.go

@@ -0,0 +1,43 @@
+package openai
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+)
+
+// RateLimitHeaders struct represents Openai rate limits headers.
+type RateLimitHeaders struct {
+	LimitRequests     int       `json:"x-ratelimit-limit-requests"`
+	LimitTokens       int       `json:"x-ratelimit-limit-tokens"`
+	RemainingRequests int       `json:"x-ratelimit-remaining-requests"`
+	RemainingTokens   int       `json:"x-ratelimit-remaining-tokens"`
+	ResetRequests     ResetTime `json:"x-ratelimit-reset-requests"`
+	ResetTokens       ResetTime `json:"x-ratelimit-reset-tokens"`
+}
+
+type ResetTime string
+
+func (r ResetTime) String() string {
+	return string(r)
+}
+
+func (r ResetTime) Time() time.Time {
+	d, _ := time.ParseDuration(string(r))
+	return time.Now().Add(d)
+}
+
+func newRateLimitHeaders(h http.Header) RateLimitHeaders {
+	limitReq, _ := strconv.Atoi(h.Get("x-ratelimit-limit-requests"))
+	limitTokens, _ := strconv.Atoi(h.Get("x-ratelimit-limit-tokens"))
+	remainingReq, _ := strconv.Atoi(h.Get("x-ratelimit-remaining-requests"))
+	remainingTokens, _ := strconv.Atoi(h.Get("x-ratelimit-remaining-tokens"))
+	return RateLimitHeaders{
+		LimitRequests:     limitReq,
+		LimitTokens:       limitTokens,
+		RemainingRequests: remainingReq,
+		RemainingTokens:   remainingTokens,
+		ResetRequests:     ResetTime(h.Get("x-ratelimit-reset-requests")),
+		ResetTokens:       ResetTime(h.Get("x-ratelimit-reset-tokens")),
+	}
+}