[master] d77da13b9 Move decision on fetch_chunksize to the storage engine

[Nils Goroll]

commit d77da13b9baf268196075bda0808d0d2e8721470
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Wed Feb 14 19:28:24 2024 +0100

    Move decision on fetch_chunksize to the storage engine
    
    For chunked encoding, we do not know how big the object is ultimately
    going to be, so VFP_GetStorage() called ObjGetSpace() with the
    fetch_chunksize parameter in this case.
    
    Yet which size is best might differ for different storage engines, and
    having the information that the caller does not know the final size
    might be relevant. Storage engines could guess that if a request came
    in for fetch_chunksize that this _might_ be the "chunked" case, but
    that heuristic would be wrong for Objects of just that size advertised
    via Content-Length.
    
    So this patch takes the guesswork out of the game by just passing the
    magic 0 value down to the storage engine to mean "give me some good
    chunk of bytes, I do not know how much I am going to need".

diff --git a/bin/varnishd/cache/cache_fetch_proc.c b/bin/varnishd/cache/cache_fetch_proc.c
index 150b473f9..704262b60 100644
--- a/bin/varnishd/cache/cache_fetch_proc.c
+++ b/bin/varnishd/cache/cache_fetch_proc.c
@@ -71,19 +71,15 @@ VFP_Error(struct vfp_ctx *vc, const char *fmt, ...)
 enum vfp_status
 VFP_GetStorage(struct vfp_ctx *vc, ssize_t *sz, uint8_t **ptr)
 {
-	ssize_t l;
 
 	CHECK_OBJ_NOTNULL(vc, VFP_CTX_MAGIC);
 	AN(sz);
 	assert(*sz >= 0);
 	AN(ptr);
 
-	l = fetchfrag;
-	if (l == 0)
-		l = *sz;
-	if (l == 0)
-		l = cache_param->fetch_chunksize;
-	*sz = l;
+	if (fetchfrag > 0)
+		*sz = fetchfrag;
+
 	if (!ObjGetSpace(vc->wrk, vc->oc, sz, ptr)) {
 		*sz = 0;
 		*ptr = NULL;
diff --git a/bin/varnishd/cache/cache_obj.c b/bin/varnishd/cache/cache_obj.c
index 2ff54cb8e..ec819bf8c 100644
--- a/bin/varnishd/cache/cache_obj.c
+++ b/bin/varnishd/cache/cache_obj.c
@@ -190,6 +190,7 @@ ObjIterate(struct worker *wrk, struct objcore *oc,
  * is no free space, some will be added first.
  *
  * The "sz" argument is an input hint of how much space is desired.
+ * 0 means "unknown", return some default size (maybe fetch_chunksize)
  */
 
 int
@@ -201,7 +202,7 @@ ObjGetSpace(struct worker *wrk, struct objcore *oc, ssize_t *sz, uint8_t **ptr)
 	CHECK_OBJ_NOTNULL(oc->boc, BOC_MAGIC);
 	AN(sz);
 	AN(ptr);
-	assert(*sz > 0);
+	assert(*sz >= 0);
 
 	AN(om->objgetspace);
 	return (om->objgetspace(wrk, oc, sz, ptr));
diff --git a/bin/varnishd/storage/storage_debug.c b/bin/varnishd/storage/storage_debug.c
index 290606ba6..f2500d8ed 100644
--- a/bin/varnishd/storage/storage_debug.c
+++ b/bin/varnishd/storage/storage_debug.c
@@ -57,7 +57,7 @@ smd_lsp_getspace(struct worker *wrk, struct objcore *oc, ssize_t *sz,
     uint8_t **ptr)
 {
 	AN(sz);
-	if (*sz > 1)
+	if (*sz > 2)
 		(*sz)--;
 	return (SML_methods.objgetspace(wrk, oc, sz, ptr));
 }
diff --git a/bin/varnishd/storage/storage_simple.c b/bin/varnishd/storage/storage_simple.c
index c34f6e394..c92304593 100644
--- a/bin/varnishd/storage/storage_simple.c
+++ b/bin/varnishd/storage/storage_simple.c
@@ -476,6 +476,8 @@ sml_getspace(struct worker *wrk, struct objcore *oc, ssize_t *sz,
 	CHECK_OBJ_NOTNULL(wrk, WORKER_MAGIC);
 	AN(sz);
 	AN(ptr);
+	if (*sz == 0)
+		*sz = cache_param->fetch_chunksize;
 	assert(*sz > 0);
 
 	o = sml_getobj(wrk, oc);