Edgestash

Description

Edgestash is a realtime templating engine built inside of Varnish Enterprise. Edgestash allows for JSON data to be composed into a response using Mustache syntax, E.g.: {{variable}}. Each response can be assigned its own JSON object for truly dynamic responses. JSON can either be fetched from a backend or generated via VCL and any number of JSONs can be assigned to a template.

An Edgestash template is fetched and compiled into response optimized byte code and then stored into cache. This byte code is then executed on delivery, efficiently streaming the response to the client using a zero-parse and zero-copy algorithm. JSON is also stored into cache as a fast search index.

Edgestash currently supports the full Mustache spec plus expressions and variables.

To dynamically insert Edgestash tags into content, see XBody.

This API applies to Varnish Enterprise 6.0 and higher.

Edgestash 4.1 API

Examples

VCL Example

Join a template with JSON:

vcl 4.0;

import edgestash;

backend default
{
  .host = "backend.example.com";
  .port = "80";
}

sub vcl_backend_response
{
  if (bereq.url ~ "\.json$") {
    edgestash.index_json();
  } else if (bereq.url ~ "/edgestash/.*\.txt$") {
    edgestash.parse_response();
  }
}

sub vcl_deliver
{
  # Pair /edgestash/template.txt with /edgestash/template.json
  if (req.url ~ "/edgestash/.*\.txt$" && edgestash.is_edgestash()) {
    edgestash.add_json_url(regsub(req.url, "\.txt$", ".json"));
    edgestash.execute();
  }

  if (edgestash.is_edgestash() || edgestash.is_json()) {
    set resp.http.X-edgestash = edgestash.version();
  }
}

Edgestash Examples

Filter a list and produce JSON output:

[
{{#.}}
  "{{value}}"
  {{^$last}},{{/$last}}
{{/}}
]

Print a list with formatting:

{{#.}}
{{# $first}}
  <!-- Print header here -->
{{/}}
{{#($pos % 2f) == 0f}}
  <span class="even">
{{/}}
{{#($pos % 2f) != 0f}}
  <span class="odd">
{{/}}
  {{value}}
    </span>
  {{# $last}}
    <!-- Print footer here -->
  {{/}}
{{/}}
{{^.}}
  No values found
{{/}}

Detect no JSON:

{{#$type}}
JSON detected
...
{{/}}
{{^$type}}
No JSON detected
{{/}}

Mixing Edgestash with another mustache template:

Edgestash variable 1: {{var1}}

{{=${ }=}}

Untouched: {{var}}
Edgestash variable 2: ${var2}

Edgestash Syntax

{{variable}}

Variable or expression. Substitutes in the JSON value of variable. HTML is escaped, JSON is unescaped, E.g.:

• < turns into <
• > turns into >
• \" turns into "

{{ & variable}}

Unescaped variable. Substitutes in the raw JSON value of variable. {{{variable}}} syntax is NOT supported. Variable supports dotted object and array syntax. HTML is untouched, JSON is untouched. E.g.:

• < is left as <
• > is left as >
• \" is left as \"

{{ # section}} {{ / section}}

A section block. This can be either a variable or an expression. If the value of section is not falsy, the section is executed, otherwise it is skipped. If the value is an object, it is used as context for the section. If the value is a non-empty array, the section is repeated once for each element in the array and used as context (if the element is an object). If the value is a root object, all root JSON includes are iterated (E.g.: {{ # . }}). Falsy values:

• [], false, null

Note: Closing section can be left as {{/}}.

{{ ^ section}} {{ / section}}

An inverted section block. If the value of section is falsy, the section is executed, otherwise it is skipped.

Falsy values:

• [], false, null

Note: Closing section can be left as {{/}}.

{{ ! comment}}

Comment, these are ignored and removed. May contain newlines.

{{ > /url}}

Partial, these are includes. The partial is executed back through VCL with an esi_level + 1. If the partial is a template, the current JSON context is used (assuming no JSON was explicitly set for this template).

If a URL contains a scheme and host, the host is passed as req.http.Host when executing back through Varnish.

E.g.:

• {{> http://example.com/site/templates/user.es}}

{{=sd ed=}}

Change the Edgestash command delimiter to the value of sd and ed. Custom delimiter can not contain whitespace or the equal sign.

Notes:

• Preceding and trailing whitespace is allowed inside of all command syntax. E.g.: {{ $ abc }} is equal to {{$abc}}

• If the variable is not found, the variable is substituted with an empty string, unless overridden. If there is a section context, the variable is searched for in each parent until the root is hit. If multiple JSON files are used, files are searched in added order until the variable is found.

• JSON is strictly parsed in full accordance to the official spec (json.org). Invalid JSON is equivalent to a falsy value with $type as null.

• If an Edgestash parsing error is encountered (unterminated variable, unterminated section, etc.), the document is treated as plain text and templating will not happen.

Variables and Expressions

variable

String. A JSON variable. Variables support dotted object and array syntax. E.g.:

• {{ variable }} - The variable value from the current JSON context.
• {{ . }} - The current context.
• {{ [0] }} - The first element of the current array context.
• {{ name.begin }} - The begin value from the name object. If it doesn’t exist, the value name.begin.
• {{ locations[2].country }} - The country value from the 3nd element (0 based index) of the locations array.

$first

Boolean. true if the current section context is the first element of an array, otherwise false. If the current section context is not an array or does not exist, value defaults to true.

$last

Boolean. true if the current section context is the last element of an array, otherwise false. If the current section context is not an array or does not exist, value defaults to true.

$type

String. The JSON type of the current context. Possible values: object", "array", "string, number", "true", "false", "null. If there is no JSON context, the value is equivalent to null.

$pos

Number. If in an array context, the element position, 0 based. The first element has a value of 0 and the last element element has a value of $size - 1. If there is no JSON context, defaults to 0.

$size

Number. The size of the current context. Only valid for objects and arrays. All other types have a size of 0.

string

String. A string value to be used in an expression.

123.4f

Number. A number value to be used in an expression. d notation is also supported. All numbers are treated as 64bit Javascript doubles.

== !=

Boolean operator. Equality. Types must be equal for an == expression to be true.

&& || !

Logical AND, OR, and NOT operators. Returns a boolean value.

> >= < <=

Relational operators. Do a numeric comparison in an expression.

+ - * /

Arithmetical operators. Common numerical calculations.

%

Modulus operator. Returns the remainder after a division.

( )

Expression. Use parentheses to enforce logic order.

Note: Preceding and trailing whitespace is required around expression operators. E.g.: {{#($pos % 2f) == 0f}} is correct. {{#($pos%2f)==0f}} is incorrect.

API

parse_response

VOID parse_response()

Parse an Edgestash template into bytecode. Can only be used in sub vcl_backend_response.

Arguments: None

Type: Function

Returns: None

Restricted to: vcl_backend_response

index_json

VOID index_json()

Parse a JSON response. Optional. It enables storage of a fast JSON search index. If not invoked, JSON will be parsed on delivery, resulting in slower Edgestash assembly. Can only be used in sub vcl_backend_response.

Arguments: None

Type: Function

Returns: None

Restricted to: vcl_backend_response

add_json_url

VOID add_json_url(STRING json_url, STRING json_host = "", BOOL xbody = 0)

Include a JSON URL for Edgestash templating. Can only be used in sub vcl_deliver. JSON URL will execute back through VCL with one higher (+1) esi_level. Multiple JSON fetches will happen in parallel. Use index_json() on this URL to enable storage of a fast JSON search index. If this URL is JSON generated from an Edgestash template, use parse_response(). JSON will be searched and used in the order they are added, including add_json().

Arguments:

• json_url accepts type STRING

• json_host accepts type STRING with a default value of empty. optional

• xbody accepts type BOOL with a default value of 0 optional

Type: Function

Returns: None

Restricted to: vcl_deliver

add_json_url_csv

VOID add_json_url_csv(STRING json_urls, STRING prefix = "", STRING delimiter = ",", STRING json_host = "", BOOL xbody = 0)

Parse a comma separated list of URLs and call add_json_url() for each. JSONs can be iterated using the following Edgestash syntax: {{ # . }}

Arguments:

• json_urls accepts type STRING

• prefix accepts type STRING with a default value of empty. optional

• delimiter accepts type STRING with a default value of , optional

• json_host accepts type STRING with a default value of empty. optional

• xbody accepts type BOOL with a default value of 0 optional

Type: Function

Returns: None

Restricted to: vcl_deliver

add_json

VOID add_json(STRING json_blob)

Include a JSON string for Edgestash templating. Can only be used in sub vcl_deliver. JSON will be searched and used in the order they are added, including add_json_url().

Arguments:

• json_blob accepts type STRING

Type: Function

Returns: None

Restricted to: vcl_deliver

execute

VOID execute(BOOL do_gzip = 1)

Execute an Edgestash template. Only valid for responses which have been parsed with parse_response(). Partial includes will execute back through VCL with one higher (+1) esi_level. Can only be used in sub vcl_deliver.

Arguments:

• do_gzip accepts type BOOL with a default value of 1 optional

Type: Function

Returns: None

Restricted to: vcl_deliver

set_delimiter

VOID set_delimiter(STRING start, STRING end, STRING quote_char = "")

Set the initial Edgestash command delimiters. Can only be used in sub vcl_backend_response.

Arguments:

• start accepts type STRING

• end accepts type STRING

• quote_char accepts type STRING with a default value of empty. optional

Type: Function

Returns: None

Restricted to: vcl_backend_response

get_sdelimiter

STRING get_sdelimiter(STRING quote_char = "")

Get the starting delimiter.

Arguments:

• quote_char accepts type STRING with a default value of empty. optional

Type: Function

Returns: String

Restricted to: backend

get_edelimiter

STRING get_edelimiter(STRING quote_char = "")

Get the ending delimiter.

Arguments:

• quote_char accepts type STRING with a default value of empty. optional

Type: Function

Returns: String

Restricted to: backend

is_edgestash

BOOL is_edgestash()

Checks to see if parse_response() was called on this object and was successful in generating bytecode.

Arguments: None

Type: Function

Returns: Bool

is_json

BOOL is_json()

Checks to see if index_json() was called on this object and was successful in generating an index.

Arguments: None

Type: Function

Returns: Bool

version

STRING version()

Get the Edgestash implementation version.

Arguments: None

Type: Function

Returns: String

Availability

The edgestash VMOD is available in Varnish Enterprise version 6.0.0r0 and later.