Couchbase Developer's Guide 2.0 - Chapter 8. Developing a Client Library

8.1.1. List Mechanisms
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8.1.1. List Mechanisms

We start the SASL authentication by asking the memcached server for the mechanisms it supports. This is achieved by sending the following packet:

Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 80 | 20 | 00 | 00 |
+---------------+---------------+---------------+---------------+
4| 00 | 00 | 00 | 00 |
+---------------+---------------+---------------+---------------+
8| 00 | 00 | 00 | 00 |
+---------------+---------------+---------------+---------------+
12| 00 | 00 | 00 | 00 |
+---------------+---------------+---------------+---------------+
16| 00 | 00 | 00 | 00 |
+---------------+---------------+---------------+---------------+
20| 00 | 00 | 00 | 00 |

Header breakdown
Field (offset) (value)
Magic (0): 0x80 (PROTOCOL_BINARY_REQ)
Opcode (1): 0x20 (sasl list mechs)
Key length (2-3): 0x0000 (0)
Extra length (4): 0x00
Data type (5): 0x00
vBucket (6-7): 0x0000 (0)
Total body (8-11): 0x00000000 (0)
Opaque (12-15): 0x00000000 (0)
CAS (16-23): 0x0000000000000000 (0)

If the server supports SASL authentication the following packet is returned:

Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 81 | 20 | 00 | 00 |
+---------------+---------------+---------------+---------------+
4| 00 | 00 | 00 | 00 |
+---------------+---------------+---------------+---------------+
8| 00 | 00 | 00 | 05 |
+---------------+---------------+---------------+---------------+
12| 00 | 00 | 00 | 00 |
+---------------+---------------+---------------+---------------+
16| 00 | 00 | 00 | 00 |
+---------------+---------------+---------------+---------------+
20| 00 | 00 | 00 | 00 |
+---------------+---------------+---------------+---------------+
24| 50 ('P') | 4c ('L') | 41 ('A') | 49 ('I') |
+---------------+---------------+---------------+---------------+

28| 4e ('N') |

Header breakdown
Field (offset) (value)
Magic (0): 0x81 (PROTOCOL_BINARY_RES)
Opcode (1): 0x20 (sasl list mechs)
Key length (2-3): 0x0000 (0)
Extra length (4): 0x00
Data type (5): 0x00
Status (6-7): 0x0000 (SUCCESS)
Total body (8-11): 0x00000005 (5)
Opaque (12-15): 0x00000000 (0)
CAS (16-23): 0x0000000000000000 (0)
Mechanisms (24-28): PLAIN

Please note that the server may support a different set of mechanisms. The list of mechanisms is a space-separated list of SASL mechanism names (e.g. "PLAIN CRAM-MD5 GSSAPI").