Fix design issues with async responses, add async example

struct http_response did not provide users any void * that could be used
to maintain a state between calls to an asynchronous HTTP response.
On the other hand, the user pointer could not be used for this purpose,
since it is shared among all HTTP clients for a given struct handler
instance.

Moreover, the length callback was still not supporting this feature,
which in fact might be required by some users. Implementing this was
particularly challenging, as this broke the current assumption that
all bytes on a call to http_read were being processed.

Now, since a client request can only be partially processed because of
the length callback, http_read must take this into account so that the
remaining bytes are still available for future calls, before reading
again from the file descriptor.

1 files changed, 9 insertions, 1 deletions

diff --git a/include/libweb/http.h b/include/libweb/http.h
index f18b5c4..87edf8a 100644
--- a/include/libweb/http.h
+++ b/include/libweb/http.h
@@ -109,7 +109,15 @@ struct http_response
     unsigned long long n;
     size_t n_headers;
     void (*free)(void *);
-    int (*step)(const struct http_payload *, struct http_response *, void *);
+    void *step_args;
+
+    union http_step
+    {
+        int (*length)(unsigned long long len, const struct http_cookie *c,
+            struct http_response *r, void *user, void *step_args);
+        int (*payload)(const struct http_payload *p, struct http_response *r,
+            void *user, void *step_args);
+    } step;
 };
 
 struct http_cfg