VCL-VARIABLES(7)

NAME
VCL-Variables - The complete album

DESCRIPTION

This is a list of all variables in the VCL language.

Variable names take the form scope.variable[.index], for instance:

req.url
beresp.http.date
client.ip

Which operations are possible on each variable is described below, often with the shorthand "backend" which covers the vcl_backend_* {} subroutines and "client" which covers the rest, except vcl_init {} and vcl_fini {}.

  local, server, remote and client

These variables describe the network connection between the client and varnishd.

Without PROXY protocol:

     client    server
     remote    local
       v          v
CLIENT ------------ VARNISHD

With PROXY protocol:

     client    server   remote     local
       v          v       v          v
CLIENT ------------ PROXY ------------ VARNISHD

client.identity Type: STRING

Readable from: client, backend

Writable from: client

Identification of the client, used to load balance in the client director. Defaults to client.ip

This variable can be overwritten with more precise information, for instance extracted from a Cookie: header.

client.ip Type: IP

Readable from: client, backend

The client's IP address, either the same as remote.ip or what the PROXY protocol told us.

server.hostname Type: STRING

Readable from: all

The host name of the server, as returned by the gethostname(3) system function.

server.identity Type: STRING

Readable from: all

The identity of the server, as set by the -i parameter.

If an -i parameter is not passed to varnishd, the return value from gethostname(3) system function will be used.

server.ip Type: IP

Readable from: client, backend

The IP address of the socket on which the client connection was received, either the same as server.ip or what the PROXY protocol told us.

remote.ip Type: IP

Readable from: client, backend

The IP address of the other end of the TCP connection. This can either be the clients IP, or the outgoing IP of a proxy server.

If the connection is a UNIX domain socket, the value will be 0.0.0.0:0

local.endpoint VCL >= 4.1 Type: STRING

Readable from: client, backend

The address of the '-a' socket the session was accepted on.

If the argument was -a foo=:81 this would be ":81"

local.ip Type: IP

Readable from: client, backend

The IP address (and port number) of the local end of the TCP connection, for instance 192.168.1.1:81

If the connection is a UNIX domain socket, the value will be 0.0.0.0:0

local.socket VCL >= 4.1 Type: STRING

Readable from: client, backend

The name of the '-a' socket the session was accepted on.

If the argument was -a foo=:81 this would be "foo".

Note that all '-a' gets a default name on the form a%d if no name is provided.

  req and req_top

These variables describe the present request, and when ESI:include requests are being processed, req_top points to the request received from the client.

req Type: HTTP

Readable from: client

The entire request HTTP data structure. Mostly useful for passing to VMODs.

req.backend_hint Type: BACKEND

Readable from: client

Writable from: client

Set bereq.backend to this if we attempt to fetch. When set to a director, reading this variable returns an actual backend if the director has resolved immediately, or the director otherwise. When used in string context, returns the name of the director or backend, respectively.

req.can_gzip Type: BOOL

Readable from: client

True if the client provided gzip or x-gzip in the Accept-Encoding header.

req.esi VCL <= 4.0 Type: BOOL

Readable from: client

Writable from: client

Set to false to disable ESI processing regardless of any value in beresp.do_esi. Defaults to true. This variable is replaced by resp.do_esi in VCL 4.1.

req.esi_level Type: INT

Readable from: client

A count of how many levels of ESI requests we're currently at.

req.grace Type: DURATION

Readable from: client

Writable from: client

Upper limit on the object grace.

During lookup the minimum of req.grace and the object's stored grace value will be used as the object's grace.

req.hash Type: BLOB

Readable from: vcl_hit, vcl_miss, vcl_pass, vcl_purge, vcl_deliver

The hash key of this request. Mostly useful for passing to VMODs, but can also be useful for debugging hit/miss status.

req.hash_always_miss Type: BOOL

Readable from: client

Writable from: client

Default: false.

Force a cache miss for this request, even if perfectly good matching objects are in the cache.

This is useful to force-update the cache without invalidating existing entries in case the fetch fails.

req.hash_ignore_busy Type: BOOL

Readable from: client

Writable from: client

Default: false.

Ignore any busy object during cache lookup.

You only want to do this when you have two server looking up content sideways from each other to avoid deadlocks.

req.hash_ignore_vary Type: BOOL

Readable from: client

Writable from: client

Default: false.

Ignore objects vary headers during cache lookup.

This returns the very first match regardless of the object compatibility with the client request. This is useful when variants are irrelevant to certain clients, and differences in the way the resouce is presented don't change how the client will interpret it.

Use with caution.

req.http.* Type: HEADER

Readable from: client

Writable from: client

Unsetable from: client

The headers of request, things like req.http.date.

The RFCs allow multiple headers with the same name, and both set and unset will remove all headers with the name given.

The header name * is a VCL symbol and as such cannot, for example, start with a numeral. To work with valid header that can't be represented as VCL symbols it is possible to quote the name, like req.http."grammatically.valid". None of the HTTP headers present in IANA registries need to be quoted, so the quoted syntax is discouraged but available for interoperability.

Some headers that cannot be tampered with for proper HTTP fetch or delivery are read-only.

req.http.content-length Type: HEADER

Readable from: client

The content-length header field is protected, see protected_headers.

req.http.transfer-encoding Type: HEADER

Readable from: client

The transfer-encoding header field is protected, see protected_headers.

req.is_hitmiss Type: BOOL

Readable from: client

If this request resulted in a hitmiss

req.is_hitpass Type: BOOL

Readable from: client

If this request resulted in a hitpass

req.method Type: STRING

Readable from: client

Writable from: client

The request method (e.g. "GET", "HEAD", ...)

req.proto VCL <= 4.0 Type: STRING

Readable from: client

Writable from: client

The HTTP protocol version used by the client, usually "HTTP/1.1" or "HTTP/2.0".

req.proto VCL >= 4.1 Type: STRING

Readable from: client

The HTTP protocol version used by the client, usually "HTTP/1.1" or "HTTP/2.0".

req.restarts Type: INT

Readable from: client

A count of how many times this request has been restarted.

req.storage Type: STEVEDORE

Readable from: client

Writable from: client

The storage backend to use to save this request body.

req.time Type: TIME

Readable from: client

The time when the request was fully received, remains constant across restarts.

req.trace Type: BOOL

Readable from: client

Writable from: client

Controls if VCL_trace VSL records are emitted for the current request, see vsl(7).

Defaults to the setting of the feature trace parameter, see varnishd(1). Does not get reset by a rollback.

req.transport Type: STRING

Readable from: client

The transport protocol which brought this request.

req.ttl Type: DURATION

Readable from: client

Writable from: client

Upper limit on the object age for cache lookups to return hit.

req.url Type: STRING

Readable from: client

Writable from: client

The requested URL, for instance "/robots.txt".

req.xid Type: INT

Readable from: client

Unique ID of this request.

req_top.http.* Type: HEADER

Readable from: client

HTTP headers of the top-level request in a tree of ESI requests. Identical to req.http. in non-ESI requests.

See req.http for general notes.

req_top.method Type: STRING

Readable from: client

The request method of the top-level request in a tree of ESI requests. (e.g. "GET", "HEAD"). Identical to req.method in non-ESI requests.

req_top.proto Type: STRING

Readable from: client

HTTP protocol version of the top-level request in a tree of ESI requests. Identical to req.proto in non-ESI requests.

req_top.time Type: TIME

Readable from: client

The time when the top-level request was fully received, remains constant across restarts.

req_top.url Type: STRING

Readable from: client

The requested URL of the top-level request in a tree of ESI requests. Identical to req.url in non-ESI requests.

  bereq

This is the request we send to the backend, it is built from the clients req.* fields by filtering out "per-hop" fields which should not be passed along (Connection:, Range: and similar).

Slightly more fields are allowed through for pass` fetches than for `miss` fetches, for instance ``Range.

bereq Type: HTTP

Readable from: backend

The entire backend request HTTP data structure. Mostly useful as argument to VMODs.

bereq.backend Type: BACKEND

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

This is the backend or director we attempt to fetch from. When set to a director, reading this variable returns an actual backend if the director has resolved immediately, or the director otherwise. When used in string context, returns the name of the director or backend, respectively.

bereq.between_bytes_timeout Type: DURATION

Readable from: backend

Writable from: backend

Default: .between_bytes_timeout attribute from the backend_definition, which defaults to the between_bytes_timeout parameter, see varnishd(1).

The time in seconds to wait between each received byte from the backend. Not available in pipe mode.

bereq.body Type: BODY

Unsetable from: vcl_backend_fetch

The request body.

Unset will also remove bereq.http.content-length.

bereq.connect_timeout Type: DURATION

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

Default: .connect_timeout attribute from the backend_definition, which defaults to the connect_timeout parameter, see varnishd(1).

The time in seconds to wait for a backend connection to be established.

bereq.first_byte_timeout Type: DURATION

Readable from: backend

Writable from: backend

Default: .first_byte_timeout attribute from the backend_definition, which defaults to the first_byte_timeout parameter, see varnishd(1).

The time in seconds to wait getting the first byte back from the backend. Not available in pipe mode.

bereq.hash Type: BLOB

Readable from: vcl_pipe, backend

The hash key of this request, a copy of req.hash.

bereq.http.* Type: HEADER

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

Unsetable from: vcl_pipe, backend

The headers to be sent to the backend.

See req.http for general notes.

bereq.http.content-length Type: HEADER

Readable from: client

The content-length header field is protected, see protected_headers.

bereq.http.transfer-encoding Type: HEADER

Readable from: client

The transfer-encoding header field is protected, see protected_headers.

bereq.is_bgfetch Type: BOOL

Readable from: backend

True for fetches where the client got a hit on an object in grace, and this fetch was kicked of in the background to get a fresh copy.

bereq.is_hitmiss Type: BOOL

Readable from: backend

If this backend request was caused by a hitmiss.

bereq.is_hitpass Type: BOOL

Readable from: backend

If this backend request was caused by a hitpass.

bereq.method Type: STRING

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

The request type (e.g. "GET", "HEAD").

Regular (non-pipe, non-pass) fetches are always "GET"

bereq.proto VCL <= 4.0 Type: STRING

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

The HTTP protocol version, "HTTP/1.1" unless a pass or pipe request has "HTTP/1.0" in req.proto

bereq.proto VCL >= 4.1 Type: STRING

Readable from: vcl_pipe, backend

The HTTP protocol version, "HTTP/1.1" unless a pass or pipe request has "HTTP/1.0" in req.proto

bereq.retries Type: INT

Readable from: backend

A count of how many times this request has been retried.

bereq.time Type: TIME

Readable from: vcl_pipe, backend

The time when we started preparing the first backend request, remains constant across retries.

bereq.trace Type: BOOL

Readable from: backend

Writable from: backend

Controls if VCL_trace VSL records are emitted for the current request, see vsl(7).

Inherits the value of req.trace when the backend request is created. Does not get reset by a rollback.

bereq.uncacheable Type: BOOL

Readable from: backend

Indicates whether this request is uncacheable due to a pass in the client side or a hit on an hit-for-pass object.

bereq.url Type: STRING

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

The requested URL, copied from req.url

bereq.xid Type: INT

Readable from: vcl_pipe, backend

Unique ID of this request.

  beresp

The response received from the backend, one cache misses, the store object is built from beresp.

beresp Type: HTTP

Readable from: vcl_backend_response, vcl_backend_error

The entire backend response HTTP data structure, useful as argument to VMOD functions.

beresp.age Type: DURATION

Readable from: vcl_backend_response, vcl_backend_error

Default: Age header, or zero.

The age of the object.

beresp.backend Type: BACKEND

Readable from: vcl_backend_response, vcl_backend_error

This is the backend we fetched from. If bereq.backend was set to a director, this will be the backend selected by the director. When used in string context, returns its name.

beresp.backend.ip VCL <= 4.0 Type: IP

Readable from: vcl_backend_response

IP of the backend this response was fetched from.

beresp.backend.name Type: STRING

Readable from: vcl_backend_response, vcl_backend_error

Name of the backend this response was fetched from. Same as beresp.backend.

beresp.body Type: BODY

Writable from: vcl_backend_error

For producing a synthetic body.

beresp.do_esi Type: BOOL

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

Default: false.

Set it to true to parse the object for ESI directives. This is necessary for later ESI processing on the client side. If beresp.do_esi is false when an object enters the cache, client side ESI processing will not be possible (obj.can_esi will be false).

It is a VCL error to use beresp.do_esi after setting beresp.filters.

beresp.do_gunzip Type: BOOL

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

Default: false.

Set to true to gunzip the object while storing it in the cache.

If http_gzip_support is disabled, setting this variable has no effect.

It is a VCL error to use beresp.do_gunzip after setting beresp.filters.

beresp.do_gzip Type: BOOL

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

Default: false.

Set to true to gzip the object while storing it.

If http_gzip_support is disabled, setting this variable has no effect.

It is a VCL error to use beresp.do_gzip after setting beresp.filters.

beresp.do_stream Type: BOOL

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

Default: true.

Deliver the object to the client while fetching the whole object into varnish.

For uncacheable objects, storage for parts of the body which have been sent to the client may get freed early, depending on the storage engine used.

This variable has no effect if beresp.do_esi is true or when the response body is empty.

beresp.filters Type: STRING

Readable from: vcl_backend_response

Writable from: vcl_backend_response

List of Varnish Fetch Processor (VFP) filters the beresp.body will be pulled through. The order left to right signifies processing from backend to cache, iow the leftmost filter is run first on the body as received from the backend after decoding of any transfer encodings.

VFP Filters change the body before going into the cache and/or being handed to the client side, where it may get processed again by resp.filters.

The following VFP filters exist in varnish-cache:

•   gzip: compress a body using gzip

•   testgunzip: Test if a body is valid gzip and refuse it otherwise

•   gunzip: Uncompress gzip content

•   esi: ESI-process plain text content

•   esi_gzip: Save gzipped snippets for efficient ESI-processing

    This filter enables stitching together ESI from individually gzipped fragments, saving processing power for re-compression on the client side at the expense of some compression efficiency.

    Additional VFP filters are available from VMODs.

    By default, beresp.filters is constructed as follows:

•   gunzip gets added for gzipped content if beresp.do_gunzip or beresp.do_esi are true.

•   esi_gzip gets added if beresp.do_esi is true together with beresp.do_gzip or content is already compressed.

•   esi gets added if beresp.do_esi is true

•   gzip gets added for uncompressed content if beresp.do_gzip is true

•   testgunzip gets added for compressed content if beresp.do_gunzip is false.

    After beresp.filters is set, using any of the beforementioned beresp.do_* switches is a VCL error.

    beresp.grace Type: DURATION

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    Default: Cache-Control stale-while-revalidate directive, or default_grace parameter.

    Set to a period to enable grace.

    beresp.http.* Type: HEADER

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    Unsetable from: vcl_backend_response, vcl_backend_error

    The HTTP headers returned from the server.

    See req.http for general notes.

    beresp.http.content-length Type: HEADER

    Readable from: client

    The content-length header field is protected, see protected_headers.

    beresp.http.transfer-encoding Type: HEADER

    Readable from: client

    The transfer-encoding header field is protected, see protected_headers.

    beresp.keep Type: DURATION

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    Default: default_keep parameter.

    Set to a period to enable conditional backend requests.

    The keep time is cache lifetime in addition to the ttl.

    Objects with ttl expired but with keep time left may be used to issue conditional (If-Modified-Since / If-None-Match) requests to the backend to refresh them.

    beresp.proto VCL <= 4.0 Type: STRING

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    The HTTP protocol version the backend replied with.

    beresp.proto VCL >= 4.1 Type: STRING

    Readable from: vcl_backend_response, vcl_backend_error

    The HTTP protocol version the backend replied with.

    beresp.reason Type: STRING

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    The HTTP status message returned by the server.

    beresp.status Type: INT

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    The HTTP status code returned by the server.

    More information in the HTTP response status section.

    beresp.storage Type: STEVEDORE

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    The storage backend to use to save this object.

    beresp.storage_hint VCL <= 4.0 Type: STRING

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    Deprecated since varnish 5.1 and discontinued since VCL 4.1 (varnish 6.0). Use beresp.storage instead.

    Hint to Varnish that you want to save this object to a particular storage backend.

    beresp.time Type: TIME

    Readable from: vcl_backend_response, vcl_backend_error

    When the backend headers were fully received just before vcl_backend_response {} was entered, or when vcl_backend_error {} was entered.

    beresp.transit_buffer Type: BYTES

    Readable from: vcl_backend_response

    Writable from: vcl_backend_response

    Default: transit_buffer parameter, see varnishd(1).

    The maximum number of bytes the client can be ahead of the backend during a streaming pass if beresp is uncacheable. See also transit_buffer parameter documentation in varnishd(1).

    beresp.ttl Type: DURATION

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    Default: Cache-Control s-maxage or max-age directives, or a value computed from the Expires header's deadline, or the default_ttl parameter.

    The object's remaining time to live, in seconds.

    beresp.uncacheable Type: BOOL

    Readable from: vcl_backend_response, vcl_backend_error

    Writable from: vcl_backend_response, vcl_backend_error

    Inherited from bereq.uncacheable, see there.

    Setting this variable makes the object uncacheable.

    This may may produce a hit-for-miss object in the cache.

    Clearing the variable has no effect and will log the warning "Ignoring attempt to reset beresp.uncacheable".

    beresp.was_304 Type: BOOL

    Readable from: vcl_backend_response, vcl_backend_error

    When true this indicates that we got a 304 response to our conditional fetch from the backend and turned that into beresp.status = 200

  obj

This is the object we found in cache. It cannot be modified.

obj.age Type: DURATION

Readable from: vcl_hit, vcl_deliver

The age of the object.

obj.can_esi Type: BOOL

Readable from: vcl_hit, vcl_deliver

If the object can be ESI processed, that is if setting resp.do_esi or adding esi to resp.filters in vcl_deliver {} would cause the response body to be ESI processed.

obj.grace Type: DURATION

Readable from: vcl_hit, vcl_deliver

The object's grace period in seconds.

obj.hits Type: INT

Readable from: vcl_hit, vcl_deliver

The count of cache-hits on this object.

In vcl_deliver a value of 0 indicates a cache miss.

obj.http.* Type: HEADER

Readable from: vcl_hit

The HTTP headers stored in the object.

See req.http for general notes.

obj.keep Type: DURATION

Readable from: vcl_hit, vcl_deliver

The object's keep period in seconds.

obj.proto Type: STRING

Readable from: vcl_hit

The HTTP protocol version stored in the object.

obj.reason Type: STRING

Readable from: vcl_hit

The HTTP reason phrase stored in the object.

obj.status Type: INT

Readable from: vcl_hit

The HTTP status code stored in the object.

More information in the HTTP response status section.

obj.storage Type: STEVEDORE

Readable from: vcl_hit, vcl_deliver

The storage backend where this object is stored.

obj.time Type: TIME

Readable from: vcl_hit, vcl_deliver

The time the object was created from the perspective of the server which generated it. This will roughly be equivalent to now - obj.age.

obj.ttl Type: DURATION

Readable from: vcl_hit, vcl_deliver

The object's remaining time to live, in seconds.

obj.uncacheable Type: BOOL

Readable from: vcl_deliver

Whether the object is uncacheable (pass, hit-for-pass or hit-for-miss).

  resp

This is the response we send to the client, it is built from either beresp (pass/miss), obj (hits) or created from whole cloth (synth).

With the exception of resp.body all resp.* variables available in both vcl_deliver{} and vcl_synth{} as a matter of symmetry.

resp Type: HTTP

Readable from: vcl_deliver, vcl_synth

The entire response HTTP data structure, useful as argument to VMODs.

resp.body Type: BODY

Writable from: vcl_synth

To produce a synthetic response body, for instance for errors.

resp.do_esi VCL >= 4.1 Type: BOOL

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

Default: obj.can_esi

This can be used to selectively disable ESI processing, even though ESI parsing happened during fetch (see beresp.do_esi). This is useful when Varnish caches peer with each other.

It is a VCL error to use resp.do_esi after setting resp.filters.

resp.filters Type: STRING

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

List of VDP filters the resp.body will be pushed through.

Before resp.filters is set, the value read will be the default filter list as determined by varnish based on resp.do_esi and request headers.

After resp.filters is set, changing any of the conditions which otherwise determine the filter selection will have no effiect. Using resp.do_esi is an error once resp.filters is set.

resp.http.* Type: HEADER

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

Unsetable from: vcl_deliver, vcl_synth

The HTTP headers that will be returned.

See req.http for general notes.

resp.http.content-length Type: HEADER

Readable from: client

The content-length header field is protected, see protected_headers.

resp.http.transfer-encoding Type: HEADER

Readable from: client

The transfer-encoding header field is protected, see protected_headers.

resp.is_streaming Type: BOOL

Readable from: vcl_deliver, vcl_synth

Returns true when the response will be streamed while being fetched from the backend.

resp.proto VCL <= 4.0 Type: STRING

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

The HTTP protocol version to use for the response.

resp.proto VCL >= 4.1 Type: STRING

Readable from: vcl_deliver, vcl_synth

The HTTP protocol version to use for the response.

resp.reason Type: STRING

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

The HTTP status message that will be returned.

resp.status Type: INT

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

The HTTP status code that will be returned.

More information in the HTTP response status section.

resp.status 200 will get changed into 304 by core code after a return(deliver) from vcl_deliver for conditional requests to cached content if validation succeeds.

For the validation, first req.http.If-None-Match is compared against resp.http.Etag. If they compare equal according to the rules for weak validation (see RFC7232), a 304 is sent.

Secondly, req.http.If-Modified-Since is compared against resp.http.Last-Modified or, if it is unset or weak, against the point in time when the object was last modified based on the Date and Age headers received with the backend response which created the object. If the object has not been modified based on that comparison, a 304 is sent.

resp.time Type: TIME

Readable from: vcl_deliver, vcl_synth

The time when we started preparing the response, just before entering vcl_synth {} or vcl_deliver {}.

  Special variables

now Type: TIME

Readable from: all

The current time, in seconds since the UNIX epoch.

When converted to STRING in expressions it returns a formatted timestamp like Tue, 20 Feb 2018 09:30:31 GMT

now remains stable for the duration of any built-in VCL subroutine to make time-based calculations predictable and avoid edge cases.

In other words, even if considerable amounts of time are spent in VCL, now will always represent the point in time when the respective built-in VCL subroutine was entered. now is thus not suitable for any kind of time measurements. See std.timestamp(), std.now() and std.timed_call() in vmod_std(3).

  sess

A session corresponds to the "conversation" that Varnish has with a single client connection, over which one or more request/response transactions may take place. It may comprise the traffic over an HTTP/1 keep-alive connection, or the multiplexed traffic over an HTTP/2 connection.

sess.idle_send_timeout Type: DURATION

Readable from: client

Writable from: client

Send timeout for individual pieces of data on client connections, defaults to the idle_send_timeout parameter, see varnishd(1)

sess.send_timeout Type: DURATION

Readable from: client

Writable from: client

Total timeout for ordinary HTTP1 responses, defaults to the send_timeout parameter, see varnishd(1)

sess.timeout_idle Type: DURATION

Readable from: client

Writable from: client

Idle timeout for this session, defaults to the timeout_idle parameter, see varnishd(1)

sess.timeout_linger Type: DURATION

Readable from: client

Writable from: client

Linger timeout for this session, defaults to the timeout_linger parameter, see varnishd(1)

sess.xid VCL >= 4.1 Type: INT

Readable from: client, backend

Unique ID of this session.

  storage

storage.<name>.free_space Type: BYTES

Readable from: client, backend

Free space available in the named stevedore. Only available for the malloc stevedore.

storage.<name>.happy Type: BOOL

Readable from: client, backend

Health status for the named stevedore. Not available in any of the current stevedores.

storage.<name>.used_space Type: BYTES

Readable from: client, backend

Used space in the named stevedore. Only available for the malloc stevedore.

  Protected header fields

The content-length and transfer-encoding headers are read-only. They must be preserved to ensure HTTP/1 framing remains consistent and maintain a proper request and response synchronization with both clients and backends.

VMODs can still update these headers, when there is a reason to change the framing, such as a transformation of a request or response body.

  HTTP response status

A HTTP status code has 3 digits XYZ where X must be between 1 and 5 included. Since it is not uncommon to see HTTP clients or servers relying on non-standard or even invalid status codes, Varnish can work with any status between 100 and 999.

Within VCL code it is even possible to use status codes in the form VWXYZ as long as the overall value is lower than 65536, but only the XYZ part will be sent to the client, by which time the X must also have become non-zero.

The VWXYZ form of status codes can be communicate extra information in resp.status and beresp.status to return(synth(...)) and return(error(...)), to indicate which synthetic content to produce:

sub vcl_recv {
    if ([...]) {
        return synth(12404);
    }
}
sub vcl_synth {
    if (resp.status == 12404) {
        [...]       // this specific 404
    } else if (resp.status % 1000 == 404) {
        [...]       // all other 404's
    }
}

The obj.status variable will inherit the VWXYZ form, but in a ban expression only the XYZ part will be available. The VWXYZ form is strictly limited to VCL execution.

Assigning an HTTP standardized code to resp.status or beresp.status will also set resp.reason or beresp.reason to the corresponding status message.

  304 handling

For a 304 response, Varnish core code amends beresp before calling vcl_backend_response:

•   If the gzip status changed, Content-Encoding is unset and any Etag is weakened

•   Any headers not present in the 304 response are copied from the existing cache object. Content-Length is copied if present in the existing cache object and discarded otherwise.

•   The status gets set to 200.

    beresp.was_304 marks that this conditional response processing has happened.

    Note: Backend conditional requests are independent of client conditional requests, so clients may receive 304 responses no matter if a backend request was conditional.

  beresp.ttl / beresp.grace / beresp.keep

Before calling vcl_backend_response, core code sets beresp.ttl based on the response status and the response headers Age, Cache-Control or Expires and Date as follows:

•   If present and valid, the value of the Age header is effectively deduced from all ttl calculations.

•   For status codes 200, 203, 204, 300, 301, 304, 404, 410 and 414:

•   If Cache-Control contains an s-maxage or max-age field (in that order of preference), the ttl is set to the respective non-negative value or 0 if negative.

•   Otherwise, if no Expires header exists, the default ttl is used.

•   Otherwise, if Expires contains a time stamp before Date, the ttl is set to 0.

•   Otherwise, if no Date header is present or the Date header timestamp differs from the local clock by no more than the clock_skew parameter, the ttl is set to

•   0 if Expires denotes a past timestamp or

•   the difference between the local clock and the Expires header otherwise.

•   Otherwise, the ttl is set to the difference between Expires and Date

•   For status codes 302 and 307, the calculation is identical except that the default ttl is not used and -1 is returned if neither Cache-Control nor Expires exists.

•   For all other status codes, ttl -1 is returned.

    beresp.grace defaults to the default_grace parameter.

    For a non-negative ttl, if Cache-Control contains a stale-while-revalidate field value, beresp.grace is set to that value if non-negative or 0 otherwise.

    beresp.keep defaults to the default_keep parameter.

SEE ALSO

•   varnishd(1)

•   vcl(7)

HISTORY

VCL was developed by Poul-Henning Kamp in cooperation with Verdens Gang AS, Redpill Linpro and Varnish Software. This manual page is written by Per Buer, Poul-Henning Kamp, Martin Blix Grydeland, Kristian Lyngstøl, Lasse Karstensen and others.

COPYRIGHT

This document is licensed under the same license as Varnish itself. See LICENSE for details.

•   Copyright (c) 2006 Verdens Gang AS

•   Copyright (c) 2006-2021 Varnish Software AS