POUNDCTL.TMPL(5)

NAME
poundctl.tmpl - templates for poundctl.

DESCRIPTION
The syntax of poundctl templates is modelled after and mostly conforming to the specifications of the golang template module (https://pkg.go.dev/text/template).

Templates are executed by applying them to a JSON object. Annotations in a template refer to attributes of the object to control execution and derive values to be displayed. Execution of the template walks the structure and sets the cursor, represented by a period (called dot), to the value at the current location in the object as execution proceeds.

The input text for a template is as ASCII text is arbitrary format. Actions -- data evaluations or control structures -- are delimited by {{ and }}; all text outside actions is copied to the output verbatim.

To aid in formatting template source code, if {{ is followed immediately by a minus sign and white space, all trailing white space is trimmed from the immediately preceding text. Similarly, if }} is preceded by white space and a minus sign, all leading white space is trimmed from the immediately following text. Notice that the presence of the whitespace in these trim markers is mandatory: "{{- 3}}" trims the immediately preceding text and outputs "3", while "{{-3}}" parses as an action containing the number -3.

  Actions
Here is the list of actions. Arguments and pipelines are evaluations of data, defined in detail in the corresponding sections that follow.

{{ }}
    Empty action is discarded. It may be useful to trim the preceding or following whitespace, as in {{- -}} .

{{/* a comment */}}
    Comments are discarded. They may span multiple lines of text. Comments do not nest and must start immediately after the opening delimiter (with optional dash and whitespace in between). A comment may be followed by any action described below.

    Comments may be used to control trailing and leading whitespace as well:

        {{- a comment trimming the surrounding whitespace -}}

{{pipeline}}
    Pipeline is evaluated, and the default textual representation of its value is copied to the output.

{{if pipeline}} T1 {{end}}
    If the value of the pipeline is empty, no output is generated; otherwise, T1 is executed. The empty values are null, false, numeric 0, null, empty string (""),
    array ([]), or object ({}).     Dot is unaffected.

{{if pipeline}} T1 {{else}} T0 {{end}}
    If the value of the pipeline is empty, T0 is executed; otherwise, T1 is executed. Dot is unaffected.

{{if pipeline}} T1 {{else if pipeline}} T2 {{else}} T0 {{end}}
    A shortcut to simplify writing the if-else chains. Equivalent to (newlines added for readability):

        {{if pipeline }}
          T1
        {{else -}}
         {{if pipeline }}
           T2
         {{else}}
           T0
         {{end}}
        {{end}}

{{range pipeline}} T1 {{end}}
    The value of pipeline must be an object or array. If it is of length zero, nothing is output. Otherwise, dot is set to the successive elements of the array or object and T1
    is executed.  For objects, the elements will be    visited in sorted key
    order.

{{range pipeline}} T1 {{else}} T0 {{end}}
    Same as above, except that if the value of the pipeline is of length zero, T0 is executed with dot unaffected.

    Within the {{range}} action, the following two keywords may appear:

{{break}}
    The innermost {{range pipeline}} loop is ended early, stopping the current iteration and bypassing all remaining iterations.

{{continue}}
    The current iteration of the innermost {{range pipeline}} loop is stopped, and the loop starts the next iteration.

{{define "name"}} text {{end}}
    The text is collected and stored for the further use as template with the given name. It can be invoked using the {{template}} action (see below).

{{template "name"}}
    The template with the specified name (see the {{define}} above) is executed with dot set to null.

{{template "name" value}}
    The template with the specified name (see the {{define}} above) is executed with dot set to value.

{{block "name" pipeline}} T1 {{end}}
    A block is shorthand for defining a template

        {{define "name"}} T1 {{end}}

    and then executing it in place

        {{template "name" pipeline}}

{{with pipeline}} T1 {{end}}
    If the value of the pipeline is empty, no output is generated; otherwise, dot is set to the value of the pipeline and T1 is executed.

{{with pipeline}} T1 {{else}} T0 {{end}}
    Same as above, but if the value of the pipeline is empty, T0 is executed with dot unchanged.

  Arguments
An argument is a simple value, i.e. any of the following:

Numeric value (integer or floating point)

Boolean value: true or false.

Quoted string.

A dot (.)
    This represents the cursor value.

Attribute: .Attr
    This is the value of the attribute Attr in the current value (dot).

    Attribute references can be nested, as in .Attr.Xattr.Yattr.

A variable reference: $var.
    Here, var is the name of the variable defined in the range action. See the subsection Variables, below.

Function call in parentheses, for grouping.

  Pipelines
A pipeline is a series of one or more commands delimited by pipe sign (|). Each command is either an argument or a function call, in form:

    func arg1 arg2...

where func is the name of one of the built-in functions discussed below.

Pipelines are executed from left to right, with the result of the previous command implicitly added to the list of argument of each subsequent command. For example, the pipeline

    .attr | eq $x

is equivalent to

    eq $x .attr

i.e. it calls the built-in function eq with two arguments: the value of the variable x and attribute attr of the cursor value.

The following built-in functions are defined:

and A1 A2
    Evaluates to true if pipelines A1 and A2 both evaluate to true. Notice, that there is no boolean shortcut evaluation: both pipelines are evaluated prior to calling and.

or A1 A2
    Evaluates to true if at least one of the pipelines A1 and A2 evaluates to true. Notice, that there is no boolean shortcut evaluation: both pipelines are evaluated prior to calling and.

index A1 A2...
    Returns the result of indexing its first argument by the following arguments. Thus, if . is an array, then:

        index . 5

    evaluates to its fifth element (.[5]).

len A1
    Returns the integer length of its argument.

not A1
    Returns true if its argument evaluates to false.

eq A1 A2
    Returns true if both its arguments are equal. This applies only if both A1 and A2 are numeric or if they both are strings.

ne A1 A2
    Returns true if its arguments (both must be numeric or strings) are not strings.

lt A1 A2
    Returns true if A1 is numerically less than A2.

le A1 A2
    Returns true if A1 is numerically less than or equal to A2.

gt A1 A2
    Returns true if A1 is numerically greater than A2.

ge A1 A2
    Returns true if A1 is numerically greater than or equal to A2.

even A1
    Returns true if A1, which must evaluate to an integer value, is divisible by 2.

printf FMT A1...
    Implements the printf(3) function. FMT must evaluate to a string. Rest of arguments is interpreted according to the conversion specifications in FMT. The result is a formatted string.

    In addition to the standard conversion specifications described in printf(3), the "%v" specifier is implemented: it formats its argument in the best way, depending on its actual type.

typeof A1
    Evaluates to the type of its argument, one of: null, bool, number, integer, string, array, object.

exists A1 A2
    A1 must evaluate to an object and A2 to string. The function evaluates to true if the attribute A2 is present in A1.

add A1 A2...
    Returns the sum of its arguments.

sub A1 A2
    Returns the difference A1 - A2.

mul A1 A2
    Multiplies A1 by A2.

div A1 A2
    Divides A1 by A2.

  Variables
Variables (referred to as $name) can be defined in range and with actions. For range, the syntax is:

    {{range $index, $element = pipeline}} T1 {{end}}

where index and element are arbitrary variable names. When executing this action, during each iteration $index and $element are set to the index (attribute name) and value of each successive element. Dot remains unaffected.

For with, the syntax is:

    {{with $var = pipeline}} T1 {{end}}

Pipeline is evaluated, its result is assigned to $var and the T1 block is executed with dot unchanged.

A variable's scope extends to the end action of the control structure (with or range) in which it is declared. This includes any nested statements that may appear in between.

INPUT OBJECT
Depending on the request issued by poundctl, the invoked template can receive as its argument (dot) an object of the following types: full listing, listener, service, or backend.

Since there is no explicit indication of the object type being passed, templates normally use heuristics based on the presence or absence of certain attribute to deduce the object type in question. The recommended approach is described in the following pseudo-code fragment:

    {{if exists . "listeners" }}
      {{/* This is a full listing, as requested by poundctl list. */}}
      ...
    {{else if exists . "services"}}
      {{/* Single listener, as requested by poundctl list /L.
           Notice that this attribute is present in the full listing as
           well, so presence of "listeners" should be checked first. */}}
      ...
    {{else if exists . "backends"}}
      {{/* Single service, as requested by poundctl list /L/S. */}}
      ...
    {{else}}
      {{/* Backend listing (poundctl list /L/S/B) */}}
      ...
    {{end}}

Structures of each object are discussed in subsections that follow.

  Full listing
A full listing contains the following attributes:

listeners
    An array of listener objects. See below for a description.

services
    An array of services objects, representing services defined in the global scope of the pound configuration file.

pid PID of the running pound daemon.

version
    Pound version number (string).

workers
    Workers statistics. This is a JSON object with the following attributes:

    active
        Number of active threads.

    count
        Number of threads currently running.

    max Maximum number of threads.

    min Minimum number of threads.

    timeout
        Thread idle timeout.

queue_len
    Number of incoming HTTP requests in the queue (integer).

timestamp
    Current time on the server, formatted as ISO 8601 date-time with microsecond precision, e.g.: "2023-01-05T22:43:18.071559".

  Listener
A listener object represents a single HTTP or HTTPS listener in pound configuration. It has the following attributes:

address
    String. Address of this listener. A string formatted as "IP:PORT" for IPv4 and IPv6 addresses or containing socket file name, for UNIX sockets.

protocol
    String. Protocol used: either http or https.

services
    Array of service objects representing services defined in this listener. See below for a definition of service object.

enabled
    Boolean. Whether this listener is enabled or not.

nohttps11
    Integer. Value of the NoHTTPS11 configuration statement for this listener. One of: 0, 1, 2.

  Service
A service object describes a single service.

name
    String. Symbolic name of this service.

enabled
    Boolean. Whether this service is enabled or not.

tot_pri
    Integer. Sum of priority values of active backends in this service.

abs_pri
    Integer. Sum of priority values of all defined backends in this service.

session_type
    String. Name of the session handling algorithm for this service. One of: IP, BASIC, URL, PARM, COOKIE, HEADER.

sessions
    List of active sessions in this service. Each session is represented as object with the following attributes:

    key String. Session key.

    backend
        Integer. Number of the backend assigned to handle requests with this session.

    expire
        Timestamp. Expiration time of this session, with microsecond precision.

backends
    List of backends defined for this service.

emergency
    Emergency backend object, or null if no such backend is defined.

  Backend
The following attributes are always present in each backend object:

alive
    Boolean. Whether or not this backend is alive.

conn_to
    Integer. Connection timeout for this backend (seconds).

enabled
    Boolean. Whether or not this backend is enabled.

io_to
    Integer. I/O timeout for this backend (seconds).

priority
    Integer in range 0-9. Priority value assigned to this backend.

protocol
    String. Protocol used by this backend: either http or https.

type
    String. Backend type. One of: acme, backend, control, redirect.

ws_to
    Integer Websocket timeout (seconds).

Depending on the backend type, the following attributes may be present:

acme

    path
        String. Directory where ACME challenges are stored.

backend

    address
        String. Backend address.

redirect

    url String. URL to redirect to.

    code
        Integer. HTTP code for redirection responses. One of: 301, 302, 307.

    redir_req
        Boolean. Whether to append the original request path to the resulting location.

If backend statistics is enabled (see BackendStats in pound(8)), the stats object will be present, with the following attributes:

request_count
    Total number of requests processed by this backend.

request_time_avg
    Average time per request, in nanoseconds.

request_time_stddev
    Standard deviation of the above.

SEE ALSO
pound(8), poundctl(8).

REPORTING BUGS
Report bugs to <gray@gnu.org>. You may also use github issue tracker at https://github.com/graygnuorg/pound/issues.

COPYRIGHT
Copyright © 2023 Sergey Poznyakoff

License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.