Client response module.
The downstream response module contains a set of functions for producing and manipulating responses sent back to the client (downstream). Responses can be produced by Kong (for example, an authentication plugin rejecting a request), or proxied back from an Service’s response body.
Unlike kong.service.response, this module allows mutating the response
before sending it back to the client.
Returns the HTTP status code currently set for the downstream response (as a Lua number).
If the request was proxied (as per kong.response.get_source()), the
return value is the response from the Service (identical to
kong.service.response.get_status()).
If the request was not proxied and the response was produced by Kong
itself (i.e. via kong.response.exit()), the return value is
returned as-is.
Phases
Returns
number: status The HTTP status code currently set for the
downstream response.Usage
kong.response.get_status() -- 200
Returns the value of the specified response header, as would be seen by the client once received.
The list of headers returned by this function can consist of both response
headers from the proxied Service and headers added by Kong (e.g. via
kong.response.add_header()).
The return value is either a string, or can be nil if a header with
name is not found in the response. If a header with the same name is
present multiple times in the request, this function returns the value
of the first occurrence of this header.
Phases
Parameters
string): The name of the header.Header names are case-insensitive and dashes (-) can be written as
underscores (_). For example, the header X-Custom-Header can also be
retrieved as x_custom_header.
Returns
string|nil: The value of the header.Usage
-- Given a response with the following headers:
-- X-Custom-Header: bla
-- X-Another: foo bar
-- X-Another: baz
kong.response.get_header("x-custom-header") -- "bla"
kong.response.get_header("X-Another") -- "foo bar"
kong.response.get_header("X-None") -- nil
Returns a Lua table holding the response headers. Keys are header names.
Values are either a string with the header value, or an array of strings
if a header was sent multiple times. Header names in this table are
case-insensitive and are normalized to lowercase, and dashes (-) can be
written as underscores (_). For example, the header X-Custom-Header can
also be retrieved as x_custom_header.
A response initially has no headers. Headers are added when a plugin short-circuits the proxying by producing a header (e.g. an authentication plugin rejecting a request), or if the request has been proxied, and one of the latter execution phases is currently running.
Unlike kong.service.response.get_headers(), this function returns all
headers as the client would see them upon reception, including headers
added by Kong itself.
By default, this function returns up to 100 headers (or what has been
configured using lua_max_resp_headers). The optional max_headers argument
can be specified to customize this limit, but must be greater than 1 and
equal to or less than 1000.
Phases
Parameters
number, optional): Limits the number of headers parsed.Returns
table: headers A table representation of the headers in the
response.
string: err If more headers than max_headers were present,
returns a string with the error "truncated".
Usage
-- Given an response from the Service with the following headers:
-- X-Custom-Header: bla
-- X-Another: foo bar
-- X-Another: baz
local headers = kong.response.get_headers()
headers.x_custom_header -- "bla"
headers.x_another[1] -- "foo bar"
headers["X-Another"][2] -- "baz"
This function helps determine where the current response originated from. Since Kong is a reverse proxy, it can short-circuit a request and produce a response of its own, or the response can come from the proxied Service.
Returns a string with three possible values:
"exit" is returned when, at some point during the processing of the
request, there has been a call to kong.response.exit(). This happens
when the request was short-circuited by a plugin or by Kong
itself (e.g. invalid credentials)."error" is returned when an error has happened while processing the
request. For example, a timeout while connecting to the upstream
service."service" is returned when the response was originated by successfully
contacting the proxied Service.Phases
Returns
string: The source.Usage
if kong.response.get_source() == "service" then
kong.log("The response comes from the Service")
elseif kong.response.get_source() == "error" then
kong.log("There was an error while processing the request")
elseif kong.response.get_source() == "exit" then
kong.log("There was an early exit while processing the request")
end
Allows changing the downstream response HTTP status code before sending it to the client.
Phases
Parameters
number): The new status.Returns
Usage
kong.response.set_status(404)
Sets a response header with the given value. This function overrides any existing header with the same name.
Note: Underscores in header names are automatically transformed into dashes
by default. If you want to deactivate this behavior, set the
lua_transform_underscores_in_response_headers Nginx config option to off.
This setting can be set in the Kong Config file:
nginx_http_lua_transform_underscores_in_response_headers = off
Be aware that changing this setting might break any plugins that rely on the automatic underscore conversion. You cannot set Transfer-Encoding header with this function. It will be ignored.
Phases
Parameters
string): The name of the header
of (array): strings |
string | number | boolean value The new value for the header. |
Returns
Usage
kong.response.set_header("X-Foo", "value")
Adds a response header with the given value. Unlike
kong.response.set_header(), this function does not remove any existing
header with the same name. Instead, another header with the same name is
added to the response. If no header with this name already exists on
the response, then it is added with the given value, similarly to
kong.response.set_header().
Phases
Parameters
string): The header name.
of (array): strings |
string | number | boolean value The header value. |
Returns
Usage
kong.response.add_header("Cache-Control", "no-cache")
kong.response.add_header("Cache-Control", "no-store")
Removes all occurrences of the specified header in the response sent to the client.
Phases
Parameters
string): The name of the header to be clearedReturns
Usage
kong.response.set_header("X-Foo", "foo")
kong.response.add_header("X-Foo", "bar")
kong.response.clear_header("X-Foo")
-- from here onwards, no X-Foo headers will exist in the response
Sets the headers for the response. Unlike kong.response.set_header(),
the headers argument must be a table in which each key is a string
corresponding to a header’s name, and each value is a string, or an
array of strings.
The resulting headers are produced in lexicographical order. The order of entries with the same name (when values are given as an array) is retained.
This function overrides any existing header bearing the same name as those
specified in the headers argument. Other headers remain unchanged.
You cannot set Transfer-Encoding header with this function. It will be ignored.
Phases
Parameters
table):Returns
Usage
kong.response.set_headers({
["Bla"] = "boo",
["X-Foo"] = "foo3",
["Cache-Control"] = { "no-store", "no-cache" }
})
-- Will add the following headers to the response, in this order:
-- X-Bar: bar1
-- Bla: boo
-- Cache-Control: no-store
-- Cache-Control: no-cache
-- X-Foo: foo3
Returns the full body when the last chunk has been read.
Calling this function starts buffering the body in
an internal request context variable, and sets the current
chunk (ngx.arg[1]) to nil when the chunk is not the
last one. When it reads the last chunk, the function returns the full
buffered body.
This PDK function works in both response and body_filter phase,
with different mechanisms. When it is used in response phase, it requires
that the request body buffering has been previously enabled by calling
kong.service.request.enable_buffering() in rewrite or access phase
before calling this function in response phase. When it is used in
body_filter phase, it buffers the body chunks as they arrive from the
upstream service.
Phases
response, body_filter
Returns
string: body The full body when the last chunk has been read,
otherwise returns nil.Usage
-- Plugin needs to call kong.service.request.enable_buffering() on `rewrite`
-- or `access` phase prior calling this function in `response` phase.
local body = kong.response.get_raw_body()
if body then
body = transform(body)
kong.response.set_raw_body(body)
end
Sets the body of the response.
The body argument must be a string and is not processed in any way.
This function can’t change the Content-Length header if one was
added. If you decide to use this function, the Content-Length header
should also be cleared, for example in the header_filter phase.
This PDK function works in both response and body_filter phase,
with different mechanisms. When it is used in response phase, it requires
that the request body buffering has been previously enabled by calling
kong.service.request.enable_buffering() in rewrite or access phase
before calling this function in response phase. When it is used in
body_filter phase, it sets the body chunks as they arrive from the
upstream service.
Phases
response, body_filter
Parameters
string): The raw body.Returns
Usage
-- Plugin needs to call kong.service.request.enable_buffering() on `rewrite`
-- or `access` phase prior calling this function in `response` phase.
kong.response.set_raw_body("Hello, world!")
-- or
local body = kong.response.get_raw_body()
if body then
body = transform(body)
kong.response.set_raw_body(body)
end
This function interrupts the current processing and produces a response. It is typical to see plugins using it to produce a response before Kong has a chance to proxy the request (e.g. an authentication plugin rejecting a request, or a caching plugin serving a cached response).
It is recommended to use this function in conjunction with the return
operator, to better reflect its meaning:
return kong.response.exit(200, "Success")
Calling kong.response.exit() interrupts the execution flow of
plugins in the current phase. Subsequent phases will still be invoked.
For example, if a plugin calls kong.response.exit() in the access
phase, no other plugin is executed in that phase, but the
header_filter, body_filter, and log phases are still executed,
along with their plugins. Plugins should be programmed defensively
against cases when a request is not proxied to the Service, but
instead is produced by Kong itself. If you want to interrupt the
execution flow of plugins in the header_filter phase,
set the pdk_response_exit_header_filter_early_exit configuration to on.
The first argument status sets the status code of the response that
is seen by the client.
In L4 proxy mode, the status code provided is primarily for logging
and statistical purposes, and is not visible to the client directly.
In this mode, only the following status codes are supported:
The second, optional, body argument sets the response body. If it is
a string, no special processing is done, and the body is sent
as-is. It is the caller’s responsibility to set the appropriate
Content-Type header via the third argument.
As a convenience, body can be specified as a table. In that case,
the body is JSON-encoded and has the application/json Content-Type
header set.
On gRPC, we cannot send the body with this function, so
it sends "body" in the grpc-message header instead.
message field in the body,
and uses that as a grpc-message header.application/grpc in the Content-Type header, the
body is sent without needing the grpc-message header.In L4 proxy mode, body can only be nil or a string. Automatic JSON
encoding is not available. When body is provided, depending on the
value of status, the following happens:
status is 500, 502 or 503, then body is logged in the Kong
error log file.status is anything else, body is sent back to the L4 client.The third, optional, headers argument can be a table specifying
response headers to send. If specified, its behavior is similar to
kong.response.set_headers(). This argument is ignored in L4 proxy mode.
Unless manually specified, this method automatically sets the
Content-Length header in the produced response for convenience.
Phases
body is nil)Parameters
number): The status to be used.table|string, optional): The body to be used.table, optional): The headers to be used.Returns
Usage
return kong.response.exit(403, "Access Forbidden", {
["Content-Type"] = "text/plain",
["WWW-Authenticate"] = "Basic"
})
---
return kong.response.exit(403, [[{"message":"Access Forbidden"}]], {
["Content-Type"] = "application/json",
["WWW-Authenticate"] = "Basic"
})
---
return kong.response.exit(403, { message = "Access Forbidden" }, {
["WWW-Authenticate"] = "Basic"
})
---
-- In L4 proxy mode
return kong.response.exit(200, "Success")
This function interrupts the current processing and produces an error response.
It is recommended to use this function in conjunction with the return
operator, to better reflect its meaning:
return kong.response.error(500, "Error", {["Content-Type"] = "text/html"})
The status argument sets the status code of the response that
is seen by the client. The status code must an error code, that is,
greater than 399.
The optional message argument sets the message describing
the error, which is written in the body.
The optional headers argument can be a table specifying response
headers to send. If specified, its behavior is similar to
kong.response.set_headers().
This method sends the response formatted in JSON, XML, HTML or plaintext. The actual format is determined using one of the following options, in this order:
headers argument using the Content-Type
header.Accept header from the request.Content-Type or Accept header, the
response defaults to JSON format. Also see the Content-Length
header in the produced response for convenience.Phases
body is nil)Parameters
number): The status to be used (>399).string, optional): The error message to be used.table, optional): The headers to be used.Returns
Usage
return kong.response.error(403, "Access Forbidden", {
["Content-Type"] = "text/plain",
["WWW-Authenticate"] = "Basic"
})
---
return kong.response.error(403, "Access Forbidden")
---
return kong.response.error(403)