nat: 1:1 policy NAT

A NAT sub-plugin doing statically configured match/rewrite on IP4 input or output.
It's stateless (no connection tracking).
Currently it supports rewriting of SA, DA and TCP/UDP ports.
It should be simple to add new rewrites if required.

API:
pnat_binding_add, pnat_binding_del, pnat_bindings_get, pnat_interfaces_get

CLI:
set pnat translation interface <name> match <5-tuple> rewrite <5-tuple> {in|out} [del]
show pnat translations
show pnat interfaces

Trying a new C based unit testing scheme. Where the graph node is tested
in isolation. See pnat/pnat_test.c.
Also added new cmake targets to generate coverage directly.
E.g.:
make test_pnat-ccov-report

File '/vpp/sdnat/src/plugins/nat/pnat/pnat.c':
Name                               Regions    Miss   Cover     Lines    Miss   Cover
------------------------------------------------------------------------------------
pnat_interface_by_sw_if_index           39       8  79.49%        13       0 100.00%
pnat_instructions_from_mask              9       0 100.00%        13       0 100.00%
pnat_binding_add                        64       8  87.50%        31       2  93.55%
pnat_flow_lookup                         4       4   0.00%        10      10   0.00%
pnat_binding_attach                    104      75  27.88%        33       6  81.82%
pnat_binding_detach                     30       5  83.33%        23       2  91.30%
pnat_binding_del                        97      33  65.98%        17       3  82.35%
pnat.c:pnat_calc_key_from_5tuple         9       1  88.89%        14       1  92.86%
pnat.c:pnat_interface_check_mask        10       2  80.00%        11       2  81.82%
pnat.c:pnat_enable                       5       0 100.00%        11       0 100.00%
pnat.c:pnat_enable_interface           107      26  75.70%        60      15  75.00%
pnat.c:pnat_disable_interface           91      30  67.03%        32       7  78.12%
pnat.c:pnat_disable                      7       2  71.43%        13       7  46.15%
------------------------------------------------------------------------------------
TOTAL                                  576     194  66.32%       281      55  80.43%

File '/vpp/sdnat/src/plugins/nat/pnat/pnat_node.h':
Name                               Regions    Miss   Cover     Lines    Miss   Cover
------------------------------------------------------------------------------------
pnat_test.c:pnat_node_inline            67      11  83.58%       115       1  99.13%
pnat_test.c:pnat_calc_key                9       2  77.78%        14       2  85.71%
pnat_test.c:pnat_rewrite_ip4            55      11  80.00%        60      12  80.00%
pnat_test.c:format_pnat_trace            1       1   0.00%        12      12   0.00%
pnat_node.c:pnat_node_inline            63      63   0.00%       115     115   0.00%
pnat_node.c:pnat_calc_key                9       9   0.00%        14      14   0.00%
pnat_node.c:pnat_rewrite_ip4            55      55   0.00%        60      60   0.00%
pnat_node.c:format_pnat_trace            5       5   0.00%        12      12   0.00%
------------------------------------------------------------------------------------
TOTAL                                  264     157  40.53%       402     228  43.28%

Type: feature
Change-Id: I9c897f833603054a8303e7369ebff6512517c9e0
Signed-off-by: Ole Troan <ot@cisco.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/src/plugins/nat/pnat/pnat.md b/src/plugins/nat/pnat/pnat.md
new file mode 100644
index 00000000000..a7c33766b90
--- /dev/null
+++ b/src/plugins/nat/pnat/pnat.md
@@ -0,0 +1,37 @@
+# PNAT: 1:1 match and rewrite programmable NAT
+
+PNAT is a stateless statically configured, match and rewrite plugin.
+It uses a set of match and rewrite rules that are applied on the IP
+input and output feature paths. A PNAT rule is unidirectional.
+
+The match is done using up to a 6-tuple; IP source and destination address,
+IP protocol, transport layer source and destination ports, and FIB table / interface index.
+
+While multiple match/rewrite rules can be applied to an interface (per direction), the match
+pattern must be the same across all rules on that interface/direction.
+
+If required in the future, matching could be done using the general classifier, allowing matching
+on any protocol field, as well having an ordered set of match patterns.
+
+If the packet does not match, it will by default be passed to the next graph node in the feature chain.
+If desired a different miss behaviour could be implemented, e.g. similarly to dynamic NAT, the packet punted to a slow path.
+
+## Rewrite instructions
+
+``` c
+typedef enum {
+  PNAT_INSTR_NONE                   = 1 << 0,
+  PNAT_INSTR_SOURCE_ADDRESS         = 1 << 1,
+  PNAT_INSTR_SOURCE_PORT            = 1 << 2,
+  PNAT_INSTR_DESTINATION_ADDRESS    = 1 << 3,
+  PNAT_INSTR_DESTINATION_PORT       = 1 << 4,
+} pnat_instructions_t;
+```
+
+These are the supported rewrite instructions.
+The IP checksum and the TCP/UDP checksum are incrementally updated as required.
+
+There are only a few "sanity checks" on the rewrites. For example, the rewrite in the outbound direction
+is applied on the ip-output feature chain. If one were to rewrite the IP destination address, the routing
+decision and determination of the next-hop has already been done, and the packet would still be forwarded
+to the original next-hop.