Support ${headers.NAME} syntax to forward upstream API headers to toolsets #1725
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,135 @@ | ||
| // Package upstream provides utilities for propagating HTTP headers | ||
| // from incoming API requests to outbound toolset HTTP calls. | ||
| package upstream | ||
|
|
||
| import ( | ||
| "context" | ||
| "fmt" | ||
| "net/http" | ||
| "regexp" | ||
| "strings" | ||
|
|
||
| "github.com/dop251/goja" | ||
| ) | ||
|
|
||
| type contextKey struct{} | ||
|
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| // WithHeaders returns a new context carrying the given HTTP headers. | ||
| func WithHeaders(ctx context.Context, h http.Header) context.Context { | ||
| return context.WithValue(ctx, contextKey{}, h) | ||
| } | ||
|
|
||
| // HeadersFromContext retrieves upstream HTTP headers from the context. | ||
| // Returns nil if no headers are present. | ||
| func HeadersFromContext(ctx context.Context) http.Header { | ||
| h, _ := ctx.Value(contextKey{}).(http.Header) | ||
| return h | ||
| } | ||
|
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| // Handler wraps an http.Handler to store the incoming HTTP request | ||
| // headers in the request context for downstream toolset forwarding. | ||
| func Handler(next http.Handler) http.Handler { | ||
| return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { | ||
| ctx := WithHeaders(r.Context(), r.Header.Clone()) | ||
| next.ServeHTTP(w, r.WithContext(ctx)) | ||
| }) | ||
| } | ||
|
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| // NewHeaderTransport wraps an http.RoundTripper to set custom headers on | ||
| // every outbound request. Header values may contain ${headers.NAME} | ||
| // placeholders that are resolved at request time from upstream headers | ||
| // stored in the request context. | ||
| func NewHeaderTransport(base http.RoundTripper, headers map[string]string) http.RoundTripper { | ||
| return &headerTransport{base: base, headers: headers} | ||
| } | ||
|
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| type headerTransport struct { | ||
| base http.RoundTripper | ||
| headers map[string]string | ||
| } | ||
|
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| func (t *headerTransport) RoundTrip(req *http.Request) (*http.Response, error) { | ||
| req = req.Clone(req.Context()) | ||
| for key, value := range ResolveHeaders(req.Context(), t.headers) { | ||
| req.Header.Set(key, value) | ||
| } | ||
| return t.base.RoundTrip(req) | ||
| } | ||
|
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| // ResolveHeaders resolves ${headers.NAME} placeholders in header values | ||
| // using upstream headers from the context. Header names in the placeholder | ||
| // are case-insensitive, matching HTTP header convention. | ||
| // | ||
| // For example, given the config header: | ||
| // | ||
| // Authorization: ${headers.Authorization} | ||
| // | ||
| // and an upstream request with "Authorization: Bearer token", the resolved | ||
| // value will be "Bearer token". | ||
| func ResolveHeaders(ctx context.Context, headers map[string]string) map[string]string { | ||
| if len(headers) == 0 { | ||
| return headers | ||
| } | ||
|
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| upstream := HeadersFromContext(ctx) | ||
| if upstream == nil { | ||
| return headers | ||
| } | ||
|
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| vm := goja.New() | ||
| _ = vm.Set("headers", vm.NewDynamicObject(headerAccessor(func(name string) goja.Value { | ||
| return vm.ToValue(upstream.Get(name)) | ||
| }))) | ||
|
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| resolved := make(map[string]string, len(headers)) | ||
| for k, v := range headers { | ||
| resolved[k] = expandTemplate(vm, v) | ||
| } | ||
| return resolved | ||
| } | ||
|
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| // headerAccessor implements [goja.DynamicObject] for case-insensitive | ||
| // HTTP header lookups. | ||
| type headerAccessor func(string) goja.Value | ||
|
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| func (h headerAccessor) Get(k string) goja.Value { return h(k) } | ||
| func (headerAccessor) Set(string, goja.Value) bool { return false } | ||
| func (headerAccessor) Has(string) bool { return true } | ||
| func (headerAccessor) Delete(string) bool { return false } | ||
| func (headerAccessor) Keys() []string { return nil } | ||
|
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| // headerPlaceholderRe matches ${headers.NAME} and captures the header | ||
| // name so we can rewrite it to bracket notation for the JS runtime. | ||
| var headerPlaceholderRe = regexp.MustCompile(`\$\{\s*headers\.([^}]+)\}`) | ||
|
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| // expandTemplate evaluates a string as a JavaScript template literal, | ||
| // resolving any ${...} expressions via the goja runtime. | ||
| // Before evaluation it rewrites ${headers.NAME} to ${headers["NAME"]} | ||
| // so that header names containing hyphens (e.g. X-Request-Id) are | ||
| // accessed correctly. | ||
| func expandTemplate(vm *goja.Runtime, text string) string { | ||
| if !strings.Contains(text, "${") { | ||
| return text | ||
| } | ||
|
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| // Rewrite dotted header access to bracket notation so names with | ||
| // hyphens work: ${headers.X-Req-Id} → ${headers["X-Req-Id"]} | ||
| text = headerPlaceholderRe.ReplaceAllStringFunc(text, func(m string) string { | ||
| parts := headerPlaceholderRe.FindStringSubmatch(m) | ||
| name := strings.TrimSpace(parts[1]) | ||
| return `${headers["` + name + `"]}` | ||
| }) | ||
|
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| escaped := strings.ReplaceAll(text, "\\", "\\\\") | ||
| escaped = strings.ReplaceAll(escaped, "`", "\\`") | ||
| script := "`" + escaped + "`" | ||
|
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| v, err := vm.RunString(script) | ||
| if err != nil { | ||
| return text | ||
| } | ||
| if v == nil || v.Export() == nil { | ||
| return "" | ||
| } | ||
| return fmt.Sprintf("%v", v.Export()) | ||
| } |
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Context may not contain upstream headers for placeholder resolution
The
setHeadersfunction is called to resolve${headers.NAME}placeholders fromreq.Context(). However, the context comes from thectxparameter passed tocallTool. If this tool is invoked outside the normal HTTP handler middleware chain (or if theupstream.Handlermiddleware wasn't applied), the context won't contain upstream headers and placeholders won't resolve.Current flow:
upstream.Handlermiddleware → stores headers in contextcallTool(ctx, ...)setHeaderstries to resolve placeholders fromctxThe implementation assumes the
ctxparameter contains upstream headers, but this isn't validated or guaranteed.Evidence: The test cases in
api_test.goall uset.Context()(a plain testing context with no upstream headers) and don't test placeholder resolution.Suggestion: Either:
upstream.Handler