feat: Add proxy-chain plugin to chain multiple upstream service calls

apisix/plugins/proxy-chain.lua

@@ -0,0 +1,177 @@
+--
+-- Licensed to the Apache Software Foundation (ASF) under one or more
+-- contributor license agreements.  See the NOTICE file distributed with
+-- this work for additional information regarding copyright ownership.
+-- The ASF licenses this file to You under the Apache License, Version 2.0
+-- (the "License"); you may not use this file except in compliance with
+-- the License.  You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+--
+
+local core = require("apisix.core")        -- Core APISIX utilities
+local http = require("resty.http")         -- HTTP client for making service calls
+local cjson = require("cjson")             -- JSON encoding/decoding library
+
+local plugin_name = "proxy-chain"
+
+-- Schema definition for plugin configuration
+local schema = {
+    type = "object",
+    properties = {
+        services = {
+            type = "array",
+            items = {
+                type = "object",
+                properties = {
+                    uri = { type = "string", minLength = 1 },          -- URI of the service to call
+                    method = { type = "string", enum = {"GET", "POST", "PUT", "DELETE"}, default = "POST" }  -- HTTP method
+                },
+                required = {"uri"}  -- URI is mandatory
+            },
+            minItems = 1  -- At least one service must be specified
+        },
+        token_header = { type = "string" }  -- Optional header name for passing a token
+    },
+    required = {"services"}  -- Services array is mandatory
+}
+
+-- Plugin metadata
+local _M = {
+    version = 0.1,                    -- Plugin version
+    priority = 1000,                  -- Execution priority (higher runs earlier)
+    name = plugin_name,               -- Plugin name
+    schema = schema,                  -- Configuration schema
+    description = "A plugin to chain multiple service requests and merge their responses."
+}
+
+-- Validate the plugin configuration against the schema
+function _M.check_schema(conf)
+    return core.schema.check(schema, conf)
+end
+
+-- Access phase: Chain service calls and merge responses
+function _M.access(conf, ctx)
+    -- Read the incoming request body
+    ngx.req.read_body()
+    local original_body = ngx.req.get_body_data()
+    local original_data = {}
+
+    -- Log the original request body
+    core.log.info("Original body: ", original_body or "nil")
+    if original_body and original_body ~= "" then
+        local success, decoded = pcall(cjson.decode, original_body)
+        if success then
+            original_data = decoded  -- Parse JSON body if valid
+        else
+            core.log.warn("Invalid JSON in original body: ", original_body)
+        end
+    end
+
+    -- Merge URI arguments into the original data
+    local uri_args = ngx.req.get_uri_args()
+    for k, v in pairs(uri_args) do
+        original_data[k] = v
+    end
+
+    -- Extract authentication token from headers
+    local headers = ngx.req.get_headers()
+    local auth_header
+    if conf.token_header then
+        -- Check custom token header (case-insensitive)
+        local token = headers[conf.token_header] or headers[conf.token_header:lower()] or ""
+        if token == "" then
+            core.log.info("No token found in header: ", conf.token_header, ", falling back to Authorization")
+            token = headers["Authorization"] or headers["authorization"] or ""
+            if token ~= "" then
+                token = token:gsub("^Bearer%s+", "")  -- Remove "Bearer " prefix
+            end
+        end
+        if token ~= "" then
+            core.log.info("Token extracted from ", conf.token_header, ": ", token)
+            auth_header = "Bearer " .. token
+        else
+            core.log.info("No token provided in ", conf.token_header, " or Authorization, proceeding without auth")
+        end
+    else
+        -- Fallback to Authorization header if no token_header is specified
+        local token = headers["Authorization"] or headers["authorization"] or ""
+        if token ~= "" then
+            token = token:gsub("^Bearer%s+", "")
+            core.log.info("Token extracted from Authorization: ", token)
+            auth_header = "Bearer " .. token
+        else
+            core.log.info("No token_header specified and no Authorization provided, proceeding without auth")
+        end
+    end
+
+    -- Initialize merged data with original request data
+    local merged_data = core.table.deepcopy(original_data)
+
+    -- Iterate through each service in the chain
+    for i, service in ipairs(conf.services) do
+        local httpc = http.new()
+        local service_headers = {
+            ["Content-Type"] = "application/json",
+            ["Accept"] = "*/*"
+        }
+        if auth_header then
+            service_headers["Authorization"] = auth_header  -- Add auth token to headers
+        end
+
+        -- Make the HTTP request to the service
+        local res, err = httpc:request_uri(service.uri, {
+            method = service.method,
+            body = cjson.encode(merged_data),
+            headers = service_headers
+        })
+
+        if not res then
+            core.log.error("Failed to call service ", service.uri, ": ", err)
+            return 500, { error = "Failed to call service: " .. service.uri }
+        end
+
+        if res.status ~= 200 then
+            core.log.error("Service ", service.uri, " returned non-200 status: ", res.status, " body: ", res.body or "nil")
+            return res.status, { error = "Service error", body = res.body }
+        end
+
+        core.log.info("Response from ", service.uri, ": ", res.body or "nil")
+
+        -- Parse the service response
+        local service_data = {}
+        if res.body and res.body ~= "" then
+            local success, decoded = pcall(cjson.decode, res.body)
+            if success then
+                service_data = decoded
+            else
+                core.log.error("Invalid JSON in response from ", service.uri, ": ", res.body)
+                return 500, { error = "Invalid JSON in response from " .. service.uri }
+            end
+        end
+
+        -- Merge service response into the cumulative data
+        for k, v in pairs(service_data) do
+            merged_data[k] = v
+        end
+    end
+
+    -- Prepare the final body to send to the upstream
+    local new_body = cjson.encode(merged_data)
+    core.log.info("Merged data sent to upstream: ", new_body)
+
+    -- Store the merged response in context and update the request
+    ctx.proxy_chain_response = merged_data
+    ngx.req.set_body_data(new_body)
+    if auth_header then
+        ngx.req.set_header("Authorization", auth_header)  -- Pass token to upstream
+    end
+end
+
+return _M