template-functions.md

Template Functions

Runway templates use Go text/template syntax with the full Sprig v3 function library (70+ functions) plus Runway-specific helpers.

Runway-Specific Functions

Function	Signature	Description	Example
json	json(v any) string	Marshal a value to a JSON string	{{json .PathParams}}
first	first(vals []string) string	Return the first element of a string slice, or "" if empty	{{first (.Query "tags")}}

Sprig Functions by Category

The tables below highlight the most useful Sprig functions for gateway templates. For the complete list, see the Sprig documentation.

String Functions

Function	Description	Example
trim	Remove leading/trailing whitespace	{{trim .Headers.Get "X-Name"}}
upper / lower	Change case	{{upper .Method}}
replace	Replace substring	{{replace "-" "_" .RouteID}}
contains	Test if string contains substring	{{if contains "admin" .Path}}...{{end}}
hasPrefix / hasSuffix	Test string prefix/suffix	{{if hasPrefix "/api" .Path}}...{{end}}
trunc	Truncate to length	{{trunc 64 .Body}}
nospace	Remove all whitespace	{{nospace .Body}}
quote	Wrap in double quotes	{{quote .ClientIP}}
substr	Extract substring	{{substr 0 8 .RequestID}}

String List Functions

Function	Description	Example
join	Join list with separator	{{join "," .Tags}}
split	Split string into map	{{split "/" .Path}}
splitList	Split string into list	{{splitList "," .Headers.Get "Accept"}}
sortAlpha	Sort string list alphabetically	{{sortAlpha .Items}}

Math Functions

Function	Description	Example
add	Addition	{{add .StatusCode 1000}}
sub	Subtraction	{{sub .Total .Used}}
mul / div	Multiply / divide	{{mul .Count 100}}
max / min	Maximum / minimum	{{max .Retries 1}}
ceil / floor / round	Rounding	{{round .Score 2}}

Type Conversion Functions

Function	Description	Example
atoi	String to int	{{atoi (.Headers.Get "X-Count")}}
int64	Convert to int64	{{int64 .Port}}
float64	Convert to float64	{{float64 .Score}}
toString	Convert to string	{{toString .StatusCode}}

Date Functions

Function	Description	Example
now	Current time	{{now}}
date	Format time	{{now | date "2006-01-02"}}
dateInZone	Format time in timezone	{{dateInZone "15:04" (now) "UTC"}}
unixEpoch	Time to Unix timestamp	{{now | unixEpoch}}

Default and Conditional Functions

Function	Description	Example
default	Default value if empty	{{default "unknown" .ClientIP}}
empty	Test if value is empty	{{if empty .Body}}...{{end}}
coalesce	First non-empty value	{{coalesce .Host .Headers.Get "X-Forwarded-Host"}}
ternary	Conditional value	{{ternary "yes" "no" .Enabled}}

Encoding Functions

Function	Description	Example
b64enc	Base64 encode	{{b64enc .Body}}
b64dec	Base64 decode	{{b64dec .EncodedData}}

Dict (Map) Functions

Function	Description	Example
dict	Create a dictionary	{{json (dict "ip" .ClientIP "path" .Path)}}
get	Get value from dict	{{get .Parsed "name"}}
set	Set value in dict	{{set .Parsed "timestamp" (now | unixEpoch)}}
hasKey	Test if key exists	{{if hasKey .Parsed "error"}}...{{end}}
keys / values	Get dict keys/values	{{keys .PathParams}}
pick / omit	Include/exclude keys	{{json (pick .Parsed "id" "name")}}

List Functions

Function	Description	Example
list	Create a list	{{list "a" "b" "c"}}
last	Last element	{{last .Items}}
append	Append to list	{{append .Items "new"}}
has	Test if list contains value	{{if has "admin" .Roles}}...{{end}}
without	Remove elements	{{without .Items "deprecated"}}
uniq	Deduplicate	{{uniq .Tags}}

Regex Functions

Function	Description	Example
regexMatch	Test regex match	{{if regexMatch "^/api/v[0-9]+" .Path}}...{{end}}
regexFind	Find first match	{{regexFind "[0-9]+" .Path}}
regexReplaceAll	Replace all matches	{{regexReplaceAll "[^a-z]" .Input ""}}

Crypto Functions

Function	Description	Example
sha256sum	SHA-256 hash	{{sha256sum .Body}}
sha1sum	SHA-1 hash	{{sha1sum .RequestID}}

Other Functions

Function	Description	Example
uuidv4	Generate a UUID v4	{{uuidv4}}
urlquery	URL-encode a string	{{urlquery .Path}}
env	Read environment variable	{{env "REGION"}}
toJson / fromJson	Sprig JSON encode/decode	{{toJson .Parsed}}

Features Using Templates

The full Sprig + Runway function set is available in these features:

• Body Generator — generate request bodies from templates
• Response Body Generator — generate response bodies from templates
• Body Transform — transform request/response bodies with templates
• Sequential Proxy — chain backend calls with templated URLs and bodies
• Response Aggregation — templated backend URLs
• GraphQL Protocol — GraphQL query templates

Exception: Error Pages

Error page templates use standard Go text/template only. Sprig functions are not available in error page templates.

Go Template Syntax Quick Reference

Syntax	Description
{{.Field}}	Access a field
{{.Nested.Field}}	Access nested field
{{index .Map "key"}}	Access map value by key
{{if .Cond}}...{{else}}...{{end}}	Conditional
{{range .List}}...{{end}}	Iterate
{{.Value | func}}	Pipeline
{{- ... -}}	Trim whitespace

See the Go template documentation for complete syntax details.