vmod_std: New partial arg for std.cache_req_body()

This parameter defaults to false to avoid breaking existing code.

bin/varnishtest/tests/s00013.vtc

@@ -0,0 +1,50 @@
+varnishtest "partial std.cache_req_body()"
+
+barrier b1 sock 2
+
+server s1 {
+	close
+
+	accept
+	rxreq
+	expect req.bodylen == 150
+	txresp
+} -start
+
+varnish v1 -cliok "param.set debug +syncvsl,+flush_head,+slow_bereq"
+varnish v1 -vcl+backend {
+	import std;
+	import vtc;
+
+	sub vcl_recv {
+		std.cache_req_body(100b, partial=true);
+	}
+
+	sub vcl_backend_fetch {
+		if (bereq.retries == 1) {
+			vtc.barrier_sync("${b1_sock}");
+		}
+	}
+
+	sub vcl_backend_error {
+		return (retry);
+	}
+} -start
+
+logexpect l1 -v v1 -i FetchError -g raw {
+	expect 0 1002 FetchError "Failed to send a partial req.body"
+	expect 0 1002 FetchError "backend write error"
+} -start
+
+client c1 {
+	txreq -method POST -nolen -hdr "transfer-encoding: chunked"
+	chunkedlen 100
+	barrier b1 sync
+	chunkedlen 50
+	chunkedlen 0
+	rxresp
+	expect resp.status == 200
+} -run
+
+logexpect l1 -wait
+server s1 -wait

vmod/vmod_std.c

@@ -239,11 +239,11 @@ vmod_timestamp(VRT_CTX, VCL_STRING label)
 }
 
 VCL_BOOL v_matchproto_(td_std_cache_req_body)
-vmod_cache_req_body(VRT_CTX, VCL_BYTES size)
+vmod_cache_req_body(VRT_CTX, VCL_BYTES size, VCL_BOOL partial)
 {
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
 	size = vmax_t(VCL_BYTES, size, 0);
-	if (VRT_CacheReqBody(ctx, (size_t)size, 0) < 0)
+	if (VRT_CacheReqBody(ctx, (size_t)size, partial) < 0)
 		return (0);
 	return (1);
 }

vmod/vmod_std.vcc

@@ -505,14 +505,18 @@ Example::
 	set req.http.My-Env = std.getenv("MY_ENV");
 
 
-$Function BOOL cache_req_body(BYTES size)
+$Function BOOL cache_req_body(BYTES size, BOOL partial = 0)
 
 Caches the request body if it is smaller than *size*.  Returns
 ``true`` if the body was cached, ``false`` otherwise.
 
 Normally the request body can only be sent once. Caching it enables
 retrying backend requests with a request body, as usually the case
-with ``POST`` and ``PUT``.
+with ``POST`` and ``PUT``. When the ``partial`` argument is ``true``,
+the request body may be larger than ``size`` and only up to ``size``
+bytes may be cached. This also enables retrying backend requests with
+a request body, unless request body bytes were consumed beyond the
+partial cached payload.
 
 Example::