Lua

Attention

By default Envoy is built without exporting symbols that you may need when interacting with Lua modules installed as shared objects. Envoy may need to be built with support for exported symbols. Please see the Bazel docs for more information.

Overview

The HTTP Lua filter allows Lua scripts to be run during both the request and response flows. LuaJIT is used as the runtime. Because of this, the supported Lua version is mostly 5.1 with some 5.2 features. See the LuaJIT documentation for more details.

Note

moonjit is a continuation of LuaJIT development, which supports more 5.2 features and additional architectures. Envoy can be built with moonjit support by using the following bazel option: --//source/extensions/filters/common/lua:moonjit=1.

The design of the filter and Lua support at a high level is as follows:

• All Lua environments are per worker thread. This means that there is no truly global data. Any globals created and populated at load time will be visible from each worker thread in isolation. True global support may be added via an API in the future.

• All scripts are run as coroutines. This means that they are written in a synchronous style even though they may perform complex asynchronous tasks. This makes the scripts substantially easier to write. All network/async processing is performed by Envoy via a set of APIs. Envoy will suspend execution of the script as appropriate and resume it when async tasks are complete.

• Do not perform blocking operations from scripts. It is critical for performance that Envoy APIs are used for all IO.

Currently supported high level features

NOTE: It is expected that this list will expand over time as the filter is used in production. The API surface has been kept small on purpose. The goal is to make scripts extremely simple and safe to write. Very complex or high performance use cases are assumed to use the native C++ filter API.

• Inspection of headers, body, and trailers while streaming in either the request flow, response flow, or both.

• Modification of headers and trailers.

• Blocking and buffering the full request/response body for inspection.

• Performing an outbound async HTTP call to an upstream host. Such a call can be performed while buffering body data so that when the call completes upstream headers can be modified.

• Performing a direct response and skipping further filter iteration. For example, a script could make an upstream HTTP call for authentication, and then directly respond with a 403 response code.

Configuration

• v3 API reference

• This filter should be configured with the name envoy.filters.http.lua.

A simple example of configuring Lua HTTP filter that contains only inline_code is as follow:

name: envoy.filters.http.lua
typed_config:
  "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua
  inline_code: |
    -- Called on the request path.
    function envoy_on_request(request_handle)
      -- Do something.
    end
    -- Called on the response path.
    function envoy_on_response(response_handle)
      -- Do something.
    end

By default, Lua script defined in inline_code will be treated as a GLOBAL script. Envoy will execute it for every HTTP request.

Per-Route Configuration

The Lua HTTP filter also can be disabled or overridden on a per-route basis by providing a LuaPerRoute configuration on the virtual host, route, or weighted cluster.

LuaPerRoute provides two ways of overriding the GLOBAL Lua script:

• By providing a name reference to the defined named Lua source codes map.

• By providing inline source code (This allows the code to be sent through RDS).

As a concrete example, given the following Lua filter configuration:

name: envoy.filters.http.lua
typed_config:
  "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua
  inline_code: |
    function envoy_on_request(request_handle)
      -- do something
    end
  source_codes:
    hello.lua:
      inline_string: |
        function envoy_on_request(request_handle)
          request_handle:logInfo("Hello World.")
        end
    bye.lua:
      inline_string: |
        function envoy_on_response(response_handle)
          response_handle:logInfo("Bye Bye.")
        end

The HTTP Lua filter can be disabled on some virtual host, route, or weighted cluster by the LuaPerRoute configuration as follow:

typed_per_filter_config:
  envoy.filters.http.lua:
    "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.LuaPerRoute
    disabled: true

We can also refer to a Lua script in the filter configuration by specifying a name in LuaPerRoute. The GLOBAL Lua script will be overridden by the referenced script:

typed_per_filter_config:
  envoy.filters.http.lua:
    "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.LuaPerRoute
    name: hello.lua

Attention

The name GLOBAL is reserved for Lua.inline_code. Therefore, do not use GLOBAL as name for other Lua scripts.

Or we can define a new Lua script in the LuaPerRoute configuration directly to override the GLOBAL Lua script as follows:

typed_per_filter_config:
  envoy.filters.http.lua:
    "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.LuaPerRoute
    source_code:
      inline_string: |
        function envoy_on_response(response_handle)
          response_handle:logInfo("Goodbye.")
        end

Script examples

This section provides some concrete examples of Lua scripts as a more gentle introduction and quick start. Please refer to the stream handle API for more details on the supported API.

-- Called on the request path.
function envoy_on_request(request_handle)
  -- Wait for the entire request body and add a request header with the body size.
  request_handle:headers():add("request_body_size", request_handle:body():length())
end
-- Called on the response path.
function envoy_on_response(response_handle)
  -- Wait for the entire response body and add a response header with the body size.
  response_handle:headers():add("response_body_size", response_handle:body():length())
  -- Remove a response header named 'foo'
  response_handle:headers():remove("foo")
end

function envoy_on_request(request_handle)
  -- Make an HTTP call to an upstream host with the following headers, body, and timeout.
  local headers, body = request_handle:httpCall(
  "lua_cluster",
  {
    [":method"] = "POST",
    [":path"] = "/",
    [":authority"] = "lua_cluster"
  },
  "hello world",
  5000)
  -- Add information from the HTTP call into the headers that are about to be sent to the next
  -- filter in the filter chain.
  request_handle:headers():add("upstream_foo", headers["foo"])
  request_handle:headers():add("upstream_body_size", #body)
end

function envoy_on_request(request_handle)
  -- Make an HTTP call.
  local headers, body = request_handle:httpCall(
  "lua_cluster",
  {
    [":method"] = "POST",
    [":path"] = "/",
    [":authority"] = "lua_cluster",
    ["set-cookie"] = { "lang=lua; Path=/", "type=binding; Path=/" }
  },
  "hello world",
  5000)
  -- Response directly and set a header from the HTTP call. No further filter iteration
  -- occurs.
  request_handle:respond(
    {[":status"] = "403",
     ["upstream_foo"] = headers["foo"]},
    "nope")
end

function envoy_on_request(request_handle)
  -- Log information about the request
  request_handle:logInfo("Authority: "..request_handle:headers():get(":authority"))
  request_handle:logInfo("Method: "..request_handle:headers():get(":method"))
  request_handle:logInfo("Path: "..request_handle:headers():get(":path"))
end
function envoy_on_response(response_handle)
  -- Log response status code
  response_handle:logInfo("Status: "..response_handle:headers():get(":status"))
end

A common use-case is to rewrite upstream response body, for example: an upstream sends non-2xx response with JSON data, but the application requires HTML page to be sent to browsers.

There are two ways of doing this, the first one is via the body() API.

function envoy_on_response(response_handle)
  response_handle:body():setBytes("<html><b>Not Found<b></html>")
  response_handle:headers():replace("content-type", "text/html")
end

Or, through bodyChunks() API, which let Envoy to skip buffering the upstream response data.

function envoy_on_response(response_handle)
  -- Sets the content-type.
  response_handle:headers():replace("content-type", "text/html")
  local last
  for chunk in response_handle:bodyChunks() do
    -- Clears each received chunk.
    chunk:setBytes("")
    last = chunk
  end
  last:setBytes("<html><b>Not Found<b></html>")
end

Complete example

A complete example using Docker is available in /examples/lua.

Stream handle API

When Envoy loads the script in the configuration, it looks for two global functions that the script defines:

function envoy_on_request(request_handle)
end
function envoy_on_response(response_handle)
end

A script can define either or both of these functions. During the request path, Envoy will run envoy_on_request as a coroutine, passing a handle to the request API. During the response path, Envoy will run envoy_on_response as a coroutine, passing handle to the response API.

Attention

It is critical that all interaction with Envoy occur through the passed stream handle. The stream handle should not be assigned to any global variable and should not be used outside of the coroutine. Envoy will fail your script if the handle is used incorrectly.

The following methods on the stream handle are supported:

headers()

local headers = handle:headers()

Returns the stream’s headers. The headers can be modified as long as they have not been sent to the next filter in the header chain. For example, they can be modified after an httpCall() or after a body() call returns. The script will fail if the headers are modified in any other situation.

Returns a header object.

body()

local body = handle:body(always_wrap_body)

Returns the stream’s body. This call will cause Envoy to suspend execution of the script until the entire body has been received in a buffer. Note that all buffering must adhere to the flow-control policies in place. Envoy will not buffer more data than is allowed by the connection manager.

An optional boolean argument always_wrap_body can be used to require Envoy always returns a body object even if the body is empty. Therefore we can modify the body regardless of whether the original body exists or not.

Returns a buffer object.

bodyChunks()

local iterator = handle:bodyChunks()

Returns an iterator that can be used to iterate through all received body chunks as they arrive. Envoy will suspend executing the script in between chunks, but will not buffer them. This can be used by a script to inspect data as it is streaming by.

for chunk in request_handle:bodyChunks() do
  request_handle:log(0, chunk:length())
end

Each chunk the iterator returns is a buffer object.

trailers()

local trailers = handle:trailers()

Returns the stream’s trailers. May return nil if there are no trailers. The trailers may be modified before they are sent to the next filter.

Returns a header object.

log*()

handle:logTrace(message)
handle:logDebug(message)
handle:logInfo(message)
handle:logWarn(message)
handle:logErr(message)
handle:logCritical(message)

Logs a message using Envoy’s application logging. message is a string to log.

httpCall()

local headers, body = handle:httpCall(cluster, headers, body, timeout, asynchronous)

Makes an HTTP call to an upstream host. cluster is a string which maps to a configured cluster manager cluster. headers is a table of key/value pairs to send (the value can be a string or table of strings). Note that the :method, :path, and :authority headers must be set. body is an optional string of body data to send. timeout is an integer that specifies the call timeout in milliseconds.

asynchronous is a boolean flag. If asynchronous is set to true, Envoy will make the HTTP request and continue, regardless of the response success or failure. If this is set to false, or not set, Envoy will suspend executing the script until the call completes or has an error.

Returns headers which is a table of response headers. Returns body which is the string response body. May be nil if there is no body.

respond()

handle:respond(headers, body)

Respond immediately and do not continue further filter iteration. This call is only valid in the request flow. Additionally, a response is only possible if the request headers have not yet been passed to subsequent filters. Meaning, the following Lua code is invalid:

function envoy_on_request(request_handle)
  for chunk in request_handle:bodyChunks() do
    request_handle:respond(
      {[":status"] = "100"},
      "nope")
  end
end

headers is a table of key/value pairs to send (the value can be a string or table of strings). Note that the :status header must be set. body is a string and supplies the optional response body. May be nil.

metadata()

local metadata = handle:metadata()

Returns the current route entry metadata. Note that the metadata should be specified under the filter name i.e. envoy.filters.http.lua. Below is an example of a metadata in a route entry.

metadata:
  filter_metadata:
    envoy.filters.http.lua:
      foo: bar
      baz:
        - bad
        - baz

Returns a metadata object.

streamInfo()

local streamInfo = handle:streamInfo()

Returns information related to the current request.

Returns a stream info object.

connection()

local connection = handle:connection()

Returns the current request’s underlying connection.

Returns a connection object.

importPublicKey()

local pubkey = handle:importPublicKey(keyder, keyderLength)

Returns public key which is used by verifySignature to verify digital signature.

verifySignature()

local ok, error = handle:verifySignature(hashFunction, pubkey, signature, signatureLength, data, dataLength)

Verify signature using provided parameters. hashFunction is the variable for the hash function which be used for verifying signature. SHA1, SHA224, SHA256, SHA384 and SHA512 are supported. pubkey is the public key. signature is the signature to be verified. signatureLength is the length of the signature. data is the content which will be hashed. dataLength is the length of data.

The function returns a pair. If the first element is true, the second element will be empty which means signature is verified; otherwise, the second element will store the error message.

base64Escape()

local base64_encoded = handle:base64Escape("input string")

Encodes the input string as base64. This can be useful for escaping binary data.

timestamp()

timestamp = handle:timestamp(format)

High resolution timestamp function. format is an optional enum parameter to indicate the format of the timestamp. EnvoyTimestampResolution.MILLISECOND is supported The function returns timestamp in milliseconds since epoch by default if format is not set.

Header object API

add()

headers:add(key, value)

Adds a header. key is a string that supplies the header key. value is a string that supplies the header value.

get()

headers:get(key)

Gets a header. key is a string that supplies the header key. Returns a string that is the header value or nil if there is no such header.

getAtIndex()

headers:getAtIndex(key, index)

Gets the header value at the given index. It can be used to fetch a specific value in case the given header has multiple values. key is a string that supplies the header key and index is an integer that supplies the position. It returns a string that is the header value or nil if there is no such header or if there is no value at the specified index.

getNumValues()

headers:getNumValues(key)

Gets the number of values of a given header. It can be used to fetch the total number of values in case the given header has multiple values. key is a string that supplies the header key. It returns an integer with the value size for the given header or 0 if there is no such header.

__pairs()

for key, value in pairs(headers) do
end

Iterates through every header. key is a string that supplies the header key. value is a string that supplies the header value.

Attention

In the current implementation, headers cannot be modified during iteration. Additionally, if it is necessary to modify headers after an iteration, the iteration must first be completed. This means that break or any other way to exit the loop early must not be used. This may be more flexible in the future.

remove()

headers:remove(key)

Removes a header. key supplies the header key to remove.

replace()

headers:replace(key, value)

Replaces a header. key is a string that supplies the header key. value is a string that supplies the header value. If the header does not exist, it is added as per the add() function.

Buffer API

length()

local size = buffer:length()

Gets the size of the buffer in bytes. Returns an integer.

getBytes()

buffer:getBytes(index, length)

Get bytes from the buffer. By default Envoy will not copy all buffer bytes to Lua. This will cause a buffer segment to be copied. index is an integer and supplies the buffer start index to copy. length is an integer and supplies the buffer length to copy. index + length must be less than the buffer length.

setBytes()

buffer:setBytes(string)

Set the content of wrapped buffer with the input string.

Metadata object API

get()

metadata:get(key)

Gets a metadata. key is a string that supplies the metadata key. Returns the corresponding value of the given metadata key. The type of the value can be: nil, boolean, number, string and table.

__pairs()

for key, value in pairs(metadata) do
end

Iterates through every metadata entry. key is a string that supplies a metadata key. value is a metadata entry value.

Stream info object API

protocol()

streamInfo:protocol()

Returns the string representation of HTTP protocol used by the current request. The possible values are: HTTP/1.0, HTTP/1.1, HTTP/2 and HTTP/3*.

downstreamLocalAddress()

streamInfo:downstreamLocalAddress()

Returns the string representation of downstream remote address used by the current request.

downstreamDirectRemoteAddress()

streamInfo:downstreamDirectRemoteAddress()

Returns the string representation of downstream directly connected address used by the current request. This is equivalent to the address of the physical connection.

dynamicMetadata()

streamInfo:dynamicMetadata()

Returns a dynamic metadata object.

downstreamSslConnection()

streamInfo:downstreamSslConnection()

Returns information related to the current SSL connection.

Returns a downstream SSL connection info object.

requestedServerName()

streamInfo:requestedServerName()

Returns the string representation of requested server name (e.g. SNI in TLS) for the current request if present.

Dynamic metadata object API

get()

dynamicMetadata:get(filterName)
-- to get a value from a returned table.
dynamicMetadata:get(filterName)[key]

Gets an entry in dynamic metadata struct. filterName is a string that supplies the filter name, e.g. envoy.lb. Returns the corresponding table of a given filterName.

set()

dynamicMetadata:set(filterName, key, value)

Sets key-value pair of a filterName’s metadata. filterName is a key specifying the target filter name, e.g. envoy.lb. The type of key is string. The type of value is any Lua type that can be mapped to a metadata value: table, numeric, boolean, string or nil. When using a table as an argument, its keys can only be string or numeric.

function envoy_on_request(request_handle)
  local headers = request_handle:headers()
  request_handle:streamInfo():dynamicMetadata():set("envoy.filters.http.lua", "request.info", {
    auth = headers:get("authorization"),
    token = headers:get("x-request-token"),
  })
end
function envoy_on_response(response_handle)
  local meta = response_handle:streamInfo():dynamicMetadata():get("envoy.filters.http.lua")["request.info"]
  response_handle:logInfo("Auth: "..meta.auth..", token: "..meta.token)
end

__pairs()

for key, value in pairs(dynamicMetadata) do
end

Iterates through every dynamicMetadata entry. key is a string that supplies a dynamicMetadata key. value is a dynamicMetadata entry value.

Connection object API

ssl()

if connection:ssl() == nil then
  print("plain")
else
  print("secure")
end

Returns SSL connection object when the connection is secured and nil when it is not.

Returns an SSL connection info object.

SSL connection object API

peerCertificatePresented()

if downstreamSslConnection:peerCertificatePresented() then
  print("peer certificate is presented")
end

Returns a bool representing whether the peer certificate is presented.

peerCertificateValidated()

if downstreamSslConnection:peerCertificateVaidated() then
  print("peer certificate is valiedated")
end

Returns bool whether the peer certificate was validated.

uriSanLocalCertificate()

-- For example, uriSanLocalCertificate contains {"san1", "san2"}
local certs = downstreamSslConnection:uriSanLocalCertificate()
-- The following prints san1,san2
handle:logTrace(table.concat(certs, ","))

Returns the URIs (as a table) in the SAN field of the local certificate. Returns an empty table if there is no local certificate, or no SAN field, or no URI SAN entries.

sha256PeerCertificateDigest()

downstreamSslConnection:sha256PeerCertificateDigest()

Returns the SHA256 digest of the peer certificate. Returns "" if there is no peer certificate which can happen in TLS (non-mTLS) connections.

serialNumberPeerCertificate()

downstreamSslConnection:serialNumberPeerCertificate()

Returns the serial number field of the peer certificate. Returns "" if there is no peer certificate, or no serial number.

issuerPeerCertificate()

downstreamSslConnection:issuerPeerCertificate()

Returns the issuer field of the peer certificate in RFC 2253 format. Returns "" if there is no peer certificate, or no issuer.

subjectPeerCertificate()

downstreamSslConnection:subjectPeerCertificate()

Return the subject field of the peer certificate in RFC 2253 format. Returns "" if there is no peer certificate, or no subject.

uriSanPeerCertificate()

downstreamSslConnection:uriSanPeerCertificate()

Returns the URIs (as a table) in the SAN field of the peer certificate. Returns an empty table if there is no peer certificate, or no SAN field, or no URI SAN entries.

subjectLocalCertificate()

downstreamSslConnection:subjectLocalCertificate()

Returns the subject field of the local certificate in RFC 2253 format. Returns "" if there is no local certificate, or no subject.

urlEncodedPemEncodedPeerCertificate()

downstreamSslConnection:urlEncodedPemEncodedPeerCertificate()

Returns the URL-encoded PEM-encoded representation of the peer certificate. Returns "" if there is no peer certificate or encoding fails.

urlEncodedPemEncodedPeerCertificateChain()

downstreamSslConnection:urlEncodedPemEncodedPeerCertificateChain()

Returns the URL-encoded PEM-encoded representation of the full peer certificate chain including the leaf certificate. Returns "" if there is no peer certificate or encoding fails.

dnsSansPeerCertificate()

downstreamSslConnection:dnsSansPeerCertificate()

Returns the DNS entries (as a table) in the SAN field of the peer certificate. Returns an empty table if there is no peer certificate, or no SAN field, or no DNS SAN entries.

dnsSansLocalCertificate()

downstreamSslConnection:dnsSansLocalCertificate()

Returns the DNS entries (as a table) in the SAN field of the local certificate. Returns an empty table if there is no local certificate, or no SAN field, or no DNS SAN entries.

validFromPeerCertificate()

downstreamSslConnection:validFromPeerCertificate()

Returns the time (timestamp-since-epoch in seconds) that the peer certificate was issued and should be considered valid from. Returns 0 if there is no peer certificate.

In Lua, we usually use os.time(os.date("!*t")) to get current timestamp-since-epoch in seconds.

expirationPeerCertificate()

downstreamSslConnection:validFromPeerCertificate()

Returns the time (timestamp-since-epoch in seconds) that the peer certificate expires and should not be considered valid after. Returns 0 if there is no peer certificate.

In Lua, we usually use os.time(os.date("!*t")) to get current timestamp-since-epoch in seconds.

sessionId()

downstreamSslConnection:sessionId()

Returns the hex-encoded TLS session ID as defined in RFC 5246.

ciphersuiteId()

downstreamSslConnection:ciphersuiteId()

Returns the standard ID (hex-encoded) for the ciphers used in the established TLS connection. Returns "0xffff" if there is no current negotiated ciphersuite.

ciphersuiteString()

downstreamSslConnection:ciphersuiteString()

Returns the OpenSSL name for the set of ciphers used in the established TLS connection. Returns "" if there is no current negotiated ciphersuite.

tlsVersion()

downstreamSslConnection:tlsVersion()

Returns the TLS version (e.g., TLSv1.2, TLSv1.3) used in the established TLS connection.