HTTP: Implement persistent connections (keep-alive)

Both at API and at CLI level (for the CMP app only, so far)
there is a new parameter/option: keep_alive.
* 0 means HTTP connections are not kept open after
receiving a response, which is the default behavior for HTTP 1.0.
* 1 means that persistent connections are requested.
* 2 means that persistent connections are required, i.e.,
in case the server does not grant them an error occurs.

For the CMP app the default value is 1, which means preferring to keep
the connection open. For all other internal uses of the HTTP client
(fetching an OCSP response, a cert, or a CRL) it does not matter
because these operations just take one round trip.

If the client application requested or required a persistent connection
and this was granted by the server, it can keep the OSSL_HTTP_REQ_CTX *
as long as it wants to send further requests and OSSL_HTTP_is_alive()
returns nonzero,
else it should call OSSL_HTTP_REQ_CTX_free() or OSSL_HTTP_close().
In case the client application keeps the OSSL_HTTP_REQ_CTX *
but the connection then dies for any reason at the server side, it will
notice this obtaining an I/O error when trying to send the next request.

This requires extending the HTTP header parsing and
rearranging the high-level HTTP client API. In particular:
* Split the monolithic OSSL_HTTP_transfer() into OSSL_HTTP_open(),
  OSSL_HTTP_set_request(), a lean OSSL_HTTP_transfer(), and OSSL_HTTP_close().
* Split the timeout functionality accordingly and improve default behavior.
* Extract part of OSSL_HTTP_REQ_CTX_new() to OSSL_HTTP_REQ_CTX_set_expected().
* Extend struct ossl_http_req_ctx_st accordingly.

Use the new feature for the CMP client, which requires extending
related transaction management of CMP client and test server.

Update the documentation and extend the tests accordingly.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15053)

1 files changed, 10 insertions, 5 deletions

diff --git a/apps/include/http_server.h b/apps/include/http_server.h
index 9520eb4dac..ed3f597fbd 100644
--- a/apps/include/http_server.h
+++ b/apps/include/http_server.h
@@ -67,10 +67,12 @@ BIO *http_server_init_bio(const char *prog, const char *port);
  * Accept an ASN.1-formatted HTTP request
  * it: the expected request ASN.1 type
  * preq: pointer to variable where to place the parsed request
- * pcbio: pointer to variable where to place the BIO for sending the response to
  * ppath: pointer to variable where to place the request path, or NULL
+ * pcbio: pointer to variable where to place the BIO for sending the response to
  * acbio: the listening bio (typically as returned by http_server_init_bio())
- * prog: the name of the current app
+ * found_keep_alive: for returning flag if client requests persistent connection
+ * prog: the name of the current app, for diagnostics only
+ * port: the local port listening to, for diagnostics only
  * accept_get: whether to accept GET requests (in addition to POST requests)
  * timeout: connection timeout (in seconds), or 0 for none/infinite
  * returns 0 in case caller should retry, then *preq == *ppath == *pcbio == NULL
@@ -83,19 +85,22 @@ BIO *http_server_init_bio(const char *prog, const char *port);
  */
 int http_server_get_asn1_req(const ASN1_ITEM *it, ASN1_VALUE **preq,
                              char **ppath, BIO **pcbio, BIO *acbio,
-                             const char *prog, int accept_get, int timeout);
+                             int *found_keep_alive,
+                             const char *prog, const char *port,
+                             int accept_get, int timeout);
 
 /*-
  * Send an ASN.1-formatted HTTP response
  * cbio: destination BIO (typically as returned by http_server_get_asn1_req())
  *       note: cbio should not do an encoding that changes the output length
+ * keep_alive: grant persistent connnection
  * content_type: string identifying the type of the response
  * it: the response ASN.1 type
- * valit: the response ASN.1 type
  * resp: the response to send
  * returns 1 on success, 0 on failure
  */
-int http_server_send_asn1_resp(BIO *cbio, const char *content_type,
+int http_server_send_asn1_resp(BIO *cbio, int keep_alive,
+                               const char *content_type,
                                const ASN1_ITEM *it, const ASN1_VALUE *resp);
 
 /*-