Add transfer-encoding to watchdog env-vars if present

The Content-Type header must be ignored when the Transfer
Encoding is set to "chunked" because the length is unknown

Go sets this to -1 and we pass that onto the user:
https://golang.org/src/net/http/transfer.go



The value of Content_Length is currently set to -1 in this
scenario, however it caused some confusion for at least one
user in issue: #1422.

The Http_Transfer_Encoding value was tested by running the
watchdog on Linux with "env" as the fprocess and an extra
header to "curl"

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

watchdog/README.md

@@ -38,9 +38,9 @@ Here's how to package your function if you don't want to use the CLI or have exi
 Example Dockerfile for an `echo` function:
 
 ```
-FROM alpine:3.8
+FROM alpine:3.11
 
-ADD https://github.com/openfaas/faas/releases/download/0.9.14/fwatchdog /usr/bin
+ADD https://github.com/openfaas/faas/releases/download/0.18.10/fwatchdog /usr/bin
 RUN chmod +x /usr/bin/fwatchdog
 
 # Define your binary here
@@ -134,9 +134,10 @@ The `X-Forwarded-By` header becomes available as `Http_X_Forwarded_By`
 
 * `Http_Method` - GET/POST etc
 * `Http_Query` - QueryString value
-* `Http_ContentLength` - gives the total content-length of the incoming HTTP request received by the watchdog.
+* `Http_ContentLength` and `Http_Content_Length` - gives the total content-length of the incoming HTTP request received by the watchdog, see note below
+* `Http_Transfer_Encoding` - only set when provided, if set to `chunked` the Content-Length will be `-1` to show that it does not apply
 
-> This behaviour is enabled by the `cgi_headers` environmental variable which is enabled by default.
+> This behaviour is enabled by the `cgi_headers` environmental variable which is enabled (`true`) by default.
 
 Here's an example of a POST request with an additional header and a query-string.
 

watchdog/handler.go

@@ -237,6 +237,10 @@ func getAdditionalEnvs(config *WatchdogConfig, r *http.Request, method string) [
 		envs = append(envs, fmt.Sprintf("Http_ContentLength=%d", r.ContentLength))
 		envs = append(envs, fmt.Sprintf("Http_Content_Length=%d", r.ContentLength))
 
+		if len(r.TransferEncoding) > 0 {
+			envs = append(envs, fmt.Sprintf("Http_Transfer_Encoding=%s", r.TransferEncoding[0]))
+		}
+
 		if config.writeDebug {
 			log.Println("Query ", r.URL.RawQuery)
 		}