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DOC: config: clarify the legacy cookie and header captures

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As reported in issue #2195, cookie captures and header captures are no
longer the recommended way to proceed. Let's mention that this is the
legacy way and provide a few pointers to the recommended functions and
actions to use the modern methods.
This commit is contained in:
Willy Tarreau 2025-05-26 08:56:33 +02:00
parent da8d6d1b2c
commit 38456f63a3
1 changed files with 28 additions and 5 deletions
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doc/configuration.txt
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@ -28041,18 +28041,41 @@ wrong cookie to a client, leading to session crossing.
# capture the first cookie whose name is exactly "vgnvisitor"
capture cookie vgnvisitor= len 32
It is possible to perform more advanced captures using "http-request" and
"http-response" rules to assign cookies to variables of scope "txn". The cookie
values may then be extracted from the request or response using the "req.cook"
and "res.cook" sample fetch functions (see section 7.3.6) and assigned to a
variable using the "set-var" or "set-var-fmt" actions (see section 4.3). A
custom log-format will then permit to present these variables where desired
(see section 8.2.6).
8.8. Capturing HTTP headers
---------------------------
8.8. Capturing HTTP headers (legacy)
------------------------------------
Header captures are useful to track unique request identifiers set by an upper
proxy, virtual host names, user-agents, POST content-length, referrers, etc. In
the response, one can search for information about the response length, how the
server asked the cache to behave, or an object location during a redirection.
Header captures are performed using the "capture request header" and "capture
response header" statements in the frontend. Please consult their definition in
section 4.2 for more details.
There are two ways to perform header captures. The modern one involves setting
variables from the headers to be captured, or from composite samples returned
by "req.hdr_names", "req.hdrs", "res.hdr_names", "res.hdrs" (see section 7.3.6)
for all possibilities. These can be assigned to variables of scope "txn" using
the "set-var" and "set-var-fmt" actions from the "http-request" and
"http-response" rulesets (see section 4.3), which can then be referenced from
custom log formats (see section 8.2.6). This is the recommended way to capture
HTTP headers.
There is also the legacy method which predates the http-request rules and
variables, which does not involve adjusting the log format, and which has also
long been used both for logging and as an artificial way to convey request
information all along the HTTP transaction, using the older "capture" rulesets.
This is what is described in this section.
Legacy header captures are performed using the "capture request header" and
"capture response header" statements in the frontend. Please consult their
definition in section 4.2 for more details.
It is possible to include both request headers and response headers at the same
time. Non-existent headers are logged as empty strings, and if one header