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httpcall.go
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httpcall.go
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// Package httpcall takes boilerplate out of typical non-streaming HTTP API calls.
package httpcall
import (
"bytes"
"context"
"encoding/json"
"errors"
"io"
"maps"
"net/http"
"net/url"
"strings"
"time"
)
var (
DefaultMaxResponseLength int64 = 100 * 1024 * 1024 // 100 MB seems like a fine safety limit
DefaultRetryDelay time.Duration = 500 * time.Millisecond
)
var (
ErrResponseTooLong = errors.New("response too long")
)
type (
Request struct {
Context context.Context
CallID string
Method string
BaseURL string
Path string
PathParams map[string]string
QueryParams url.Values
FullURLOverride string // for APIs using REST-style links, completely overrides BaseURL, Path and QueryParams
Input any
RawRequestBody []byte
RequestBodyContentType string
Headers http.Header
BasicAuth BasicAuth
HTTPRequest *http.Request
OutputPtr any
MaxResponseLength int64
HTTPClient *http.Client
MaxAttempts int
RetryDelay time.Duration
LastRetryDelay time.Duration
ShouldStart func(r *Request) error
Started func(r *Request)
ValidateOutput func() error
ParseResponse func(r *Request) error
ParseErrorResponse func(r *Request)
Failed func(r *Request)
Finished func(r *Request)
UserObject any
UserData map[string]any
Attempts int
HTTPResponse *http.Response
RawResponseBody []byte
Error *Error
Duration time.Duration
initDone bool
}
BasicAuth struct {
Username string
Password string
}
)
func (r *Request) Clone() *Request {
result := new(Request)
*result = *r
if result.QueryParams != nil {
result.QueryParams = maps.Clone(result.QueryParams)
}
if result.Headers != nil {
result.Headers = maps.Clone(result.Headers)
}
return result
}
func (r *Request) IsIdempotent() bool {
r.Init()
return r.HTTPRequest.Method == http.MethodGet || r.HTTPRequest.Method == http.MethodHead
}
func (r *Request) StatusCode() int {
if r.HTTPResponse == nil {
return 0
}
return r.HTTPResponse.StatusCode
}
func (r *Request) SetHeader(key, value string) {
if r.Headers == nil {
r.Headers = make(http.Header)
}
r.Headers.Set(key, value)
}
func (r *Request) OnShouldStart(f func(r *Request) error) {
if f == nil {
return
}
if prev := r.ShouldStart; prev != nil {
r.ShouldStart = func(r *Request) error {
if err := prev(r); err != nil {
return err
}
return f(r)
}
} else {
r.ShouldStart = f
}
}
func (r *Request) OnStarted(f func(r *Request)) {
if f == nil {
return
}
if prev := r.Started; prev != nil {
r.Started = func(r *Request) {
prev(r)
f(r)
}
} else {
r.Started = f
}
}
func (r *Request) OnFailed(f func(r *Request)) {
if f == nil {
return
}
if prev := r.Failed; prev != nil {
r.Failed = func(r *Request) {
f(r)
prev(r)
}
} else {
r.Failed = f
}
}
func (r *Request) OnFinished(f func(r *Request)) {
if f == nil {
return
}
if prev := r.Finished; prev != nil {
r.Finished = func(r *Request) {
f(r)
prev(r)
}
} else {
r.Finished = f
}
}
func (r *Request) OnValidate(f func() error) {
if f == nil {
return
}
if prev := r.ValidateOutput; prev != nil {
r.ValidateOutput = func() error {
if err := prev(); err != nil {
return err
}
return f()
}
} else {
r.ValidateOutput = f
}
}
func (r *Request) Init() {
if r.initDone {
return
}
r.initDone = true
if r.Context == nil {
r.Context = context.Background()
}
if r.HTTPRequest == nil {
for k, v := range r.PathParams {
r.Path = strings.ReplaceAll(r.Path, k, url.PathEscape(v))
}
var urlStr string
if r.FullURLOverride != "" {
urlStr = r.FullURLOverride
} else {
if r.BaseURL == "" && r.Path == "" {
panic("BaseURL and/or Path must be specified (or HTTPRequest)")
}
urlStr = buildURL(r.BaseURL, r.Path, r.QueryParams).String()
}
if r.Method == "" {
panic("Method must be specified (or HTTPRequest)")
}
if r.Input != nil || r.RawRequestBody != nil {
if r.Method == http.MethodGet || r.Method == http.MethodHead {
panic("GET incompatible with body (Input / RawRequestBody)")
}
if r.RawRequestBody == nil {
if v, ok := r.Input.(url.Values); ok {
r.RawRequestBody = []byte(v.Encode())
if r.RequestBodyContentType == "" {
r.RequestBodyContentType = "application/x-www-form-urlencoded; charset=utf-8"
}
} else {
r.RawRequestBody = must(json.Marshal(r.Input))
if r.RequestBodyContentType == "" {
r.RequestBodyContentType = "application/json"
}
}
}
r.HTTPRequest = must(http.NewRequestWithContext(r.Context, r.Method, urlStr, bytes.NewReader(r.RawRequestBody)))
if r.RequestBodyContentType != "" {
r.HTTPRequest.Header.Set("Content-Type", r.RequestBodyContentType)
}
} else {
r.HTTPRequest = must(http.NewRequestWithContext(r.Context, r.Method, urlStr, nil))
// We allow setting hr.RequestBodyContentType even when it's not necessary,
// so that it's easy to provide a default value without checking the method.
}
} else {
if r.Method == "" {
r.Method = r.HTTPRequest.Method
}
if r.Path == "" {
r.Path = r.HTTPRequest.URL.Path
}
}
if r.BasicAuth != (BasicAuth{}) {
r.HTTPRequest.SetBasicAuth(r.BasicAuth.Username, r.BasicAuth.Password)
}
for k, vv := range r.Headers {
r.HTTPRequest.Header[k] = vv
}
r.Headers = r.HTTPRequest.Header
}
func (r *Request) Do() error {
r.Init()
r.Attempts = 0 // reset in case we're doing same request twice
for {
r.Attempts++
if r.ShouldStart != nil {
if err := r.ShouldStart(r); err != nil {
return &Error{
CallID: r.CallID,
Cause: err,
}
}
}
if r.Started != nil {
r.Started(r)
}
start := time.Now()
r.Error = r.doOnce()
r.Duration = time.Since(start)
if r.Error != nil && r.Failed != nil {
r.Failed(r)
}
if r.Error == nil || !r.Error.IsRetriable || r.Attempts >= r.MaxAttempts {
break
}
delay := r.Error.RetryDelay
if delay == 0 {
delay = r.RetryDelay
}
if delay == 0 {
delay = DefaultRetryDelay
}
r.LastRetryDelay = delay
sleep(r.Context, delay)
}
if r.Finished != nil {
r.Finished(r)
}
if r.Error == nil {
return nil // avoid returning non-nil error interface with nil *Error inside
}
return r.Error
}
func (r *Request) doOnce() *Error {
client := r.HTTPClient
if client == nil {
client = http.DefaultClient
}
maxLen := r.MaxResponseLength
if maxLen == 0 {
maxLen = DefaultMaxResponseLength
}
resp, err := client.Do(r.HTTPRequest)
if err != nil {
return &Error{
CallID: r.CallID,
IsNetwork: true,
IsRetriable: true,
Cause: err,
}
}
defer resp.Body.Close()
r.HTTPResponse = resp
if maxLen > 0 {
r.RawResponseBody, err = io.ReadAll(&limitedReader{resp.Body, maxLen})
} else {
r.RawResponseBody, err = io.ReadAll(resp.Body)
}
if err != nil {
isNetwork := !errors.Is(err, ErrResponseTooLong)
return &Error{
CallID: r.CallID,
IsNetwork: isNetwork,
IsRetriable: isNetwork,
Cause: err,
}
}
if resp.StatusCode >= 200 && resp.StatusCode <= 299 {
var err error
var isNetwork bool
if r.ParseResponse != nil {
err = r.ParseResponse(r)
} else if r.OutputPtr == nil {
// ignore body
} else if bytePtr, ok := r.OutputPtr.(*[]byte); ok {
*bytePtr = r.RawResponseBody
} else {
err := json.Unmarshal(r.RawResponseBody, r.OutputPtr)
if err != nil {
isNetwork = (len(r.RawResponseBody) == 0 || (r.RawResponseBody[0] != '{' && r.RawResponseBody[0] != '['))
}
}
if err != nil {
return &Error{
CallID: r.CallID,
IsNetwork: isNetwork,
IsRetriable: isNetwork,
StatusCode: resp.StatusCode,
Message: "error parsing response",
RawResponseBody: r.RawResponseBody,
PrintResponseBody: true,
Cause: err,
}
}
if r.ValidateOutput != nil {
err := r.ValidateOutput()
if err != nil {
return &Error{
CallID: r.CallID,
IsNetwork: false,
IsRetriable: false,
StatusCode: resp.StatusCode,
RawResponseBody: r.RawResponseBody,
PrintResponseBody: true,
Cause: err,
}
}
}
return nil
} else {
r.Error = &Error{
CallID: r.CallID,
StatusCode: resp.StatusCode,
IsRetriable: (resp.StatusCode >= 500 && resp.StatusCode <= 599),
RawResponseBody: r.RawResponseBody,
PrintResponseBody: true,
}
if r.ParseErrorResponse != nil {
r.ParseErrorResponse(r)
if r.Error == nil {
return nil // avoid returning non-nil error interface with nil *Error inside
}
}
return r.Error
}
}
func buildURL(baseURL, path string, queryParams url.Values) *url.URL {
if baseURL == "" {
baseURL, path = path, ""
}
u := must(url.Parse(baseURL))
u.Path = joinURLPath(u.Path, path)
if len(queryParams) > 0 {
u.RawQuery = queryParams.Encode()
}
return u
}
func must[T any](v T, err error) T {
if err != nil {
panic(err)
}
return v
}
func joinURLPath(base, url string) string {
if base == "" {
return url
}
if url == "" {
return base
}
return strings.TrimSuffix(base, "/") + "/" + strings.TrimPrefix(url, "/")
}
func sleep(ctx context.Context, dur time.Duration) {
ctxDone := ctx.Done()
if ctxDone == nil {
time.Sleep(dur)
} else {
timer := time.NewTimer(dur)
select {
case <-timer.C:
break
case <-ctx.Done():
timer.Stop()
}
}
}
// Like io.LimitedReader, but returns ErrResponseTooLong instead of EOF.
type limitedReader struct {
R io.Reader // underlying reader
N int64 // max bytes remaining
}
func (l *limitedReader) Read(p []byte) (n int, err error) {
if l.N <= 0 {
return 0, ErrResponseTooLong
}
if int64(len(p)) > l.N {
p = p[0:l.N]
}
n, err = l.R.Read(p)
l.N -= int64(n)
return
}