Implement async HTTP responses

Sometimes, library users cannot return a HTTP response as soon as the
request is received, or the operations that are required to generate it
can take a long time.

In order to solve this, libweb adds a new member to struct
http_response, namely step, which must be assigned to a function
whenever a HTTP response should be generated in a non-blocking manner.
Leaving the function pointer as null will fall back to the default
behaviour.

1 files changed, 19 insertions, 0 deletions

diff --git a/doc/man7/libweb_http.7 b/doc/man7/libweb_http.7
index f11c1ef..c3bec8b 100644
--- a/doc/man7/libweb_http.7
+++ b/doc/man7/libweb_http.7
@@ -562,6 +562,7 @@ struct http_response
     unsigned long long \fIn\fP;
     size_t \fIn_headers\fP;
     void (*\fIfree\fP)(void *);
+    int (*\fIstep\fP)(const struct http_payload *, struct http_response *, void *);
 };
 .EE
 .in
@@ -669,6 +670,24 @@ is a valid pointer. Otherwise,
 .I free
 must be a null pointer.
 
+.I step
+allows implementations to generate a response in a non-blocking manner.
+When a response is not immediately available when a payload is received,
+.I step
+must be assigned to a function that can generate it later.
+.I libweb
+shall then call this function immediately later,
+without blocking other clients.
+Assigning
+.I step
+to a null pointer falls back to the default behaviour
+i.e., a response is returned immediately.
+Note that a non-null
+.I step
+shall always take priority, thus ignoring any other information inside the
+.I "struct http_response"
+instance.
+
 .SS Transport Layer Security (TLS)
 By design,
 .I libweb