api: add new stream message convention

Instead of having to wrap dump/detail calls in control ping, send details messages in between a normal
reply / request pair. As expressed in the below service statement.

Example:

service {
  rpc map_domains_gets returns map_domains_get_reply
    stream map_domain_details;
};

define map_domains_get
{
  u32 client_index;
  u32 context;
  u32 cursor;
};

define map_domains_get_reply
{
  u32 context;
  i32 retval;
  u32 cursor;
};

To avoid blocking the main thread for too long, the replies are now sent in client message queue size
chunks. The reply message returns VNET_API_ERROR_EAGAIN when there is more to read.
The API handler must also include a "cursor" that is used to the next call to the get function.

API handler example:
  REPLY_AND_DETAILS_MACRO (VL_API_MAP_DOMAINS_GET_REPLY, mm->domains,
  ({
    send_domain_details (cursor, rp, mp->context);
  }));

The macro starts from cursor and iterates through the pool
until vl_api_process_may_suspend() returns true or the iteration
reaches the end of the list.

Client Example:

cursor = 0
d = []
while True:
    rv, details = map_domains_get(cursor=cursor)
    d += details
    if rv.retval == 0 or rv.retval != -165:
        break
    cursor = rv.cursor

or the convenience iterator:
for x in vpp.details_iter(vpp.api.map_domains_get):
  pass

or

list(details_iter(map_domains_get))

Change-Id: Iad9f6b41b0ef886adb584c97708dd91cf552749e
Type: feature
Signed-off-by: Ole Troan <ot@cisco.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/vnet/api_errno.h b/src/vnet/api_errno.h
index 15b17a86d5d..dd206ce6e88 100644
--- a/src/vnet/api_errno.h
+++ b/src/vnet/api_errno.h
@@ -156,6 +156,7 @@ _(MISSING_CERT_KEY, -161, "Missing certifcate or key")                  \
 _(LIMIT_EXCEEDED, -162, "limit exceeded")                               \
 _(IKE_NO_PORT, -163, "port not managed by IKE")                         \
 _(UDP_PORT_TAKEN, -164, "UDP port already taken")                       \
+_(EAGAIN, -165, "Retry stream call with cursor")                        \
 
 typedef enum
 {