Async hot hdr fix (#604)

* fn: for async hot requests ensure/fix content-length/type

* fn: added tests for FromModel for content type/length

* fn: restrict the content-length fix to async in FromModel()

api/agent/call.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strconv"
 	"strings"
 	"time"
 
@@ -205,11 +206,31 @@ func FromModel(mCall *models.Call) CallOpt {
 	return func(a *agent, c *call) error {
 		c.Call = mCall
 
-		// NOTE this adds content length based on payload length
 		req, err := http.NewRequest(c.Method, c.URL, strings.NewReader(c.Payload))
 		if err != nil {
 			return err
 		}
+
+		// HACK: only applies to async below, for async we need to restore
+		// content-length and content-type of the original request, which are
+		// derived from Payload and original content-type which now is in
+		// Fn_header_content_type
+		if c.Type == models.TypeAsync {
+			// Hoist original request content type into async request
+			if req.Header.Get("Content-Type") == "" {
+				content_type, ok := c.EnvVars["Fn_header_content_type"]
+				if ok {
+					req.Header.Set("Content-Type", content_type)
+				}
+			}
+
+			// Ensure content-length in async requests for protocol/http DumpRequestTo()
+			if req.ContentLength == -1 || req.Header.Get("Content-Length") == "" {
+				req.ContentLength = int64(len(c.Payload))
+				req.Header.Set("Content-Length", strconv.FormatInt(int64(len(c.Payload)), 10))
+			}
+		}
+
 		for k, v := range c.EnvVars {
 			// TODO if we don't store env as []string headers are messed up
 			req.Header.Set(k, v)