Add HTTP proxy support.

Add support for using a proxy for HTTP requests. Only used for external
requests, such as downloading files or talking to source sites such as
Pixiv or Twitter, not for internal requests, such as talking to IQDB or
Reportbooru.

app/logical/danbooru/http.rb

@@ -117,6 +117,14 @@ module Danbooru
       use(cache: { expires_in: expires_in })
     end
 
+    def proxy(host: Danbooru.config.http_proxy_host, port: Danbooru.config.http_proxy_port.to_i, username: Danbooru.config.http_proxy_username, password: Danbooru.config.http_proxy_password)
+      return self if host.blank?
+
+      dup.tap do |o|
+        o.http = o.http.via(host, port, username, password)
+      end
+    end
+
     # allow requests only to public IPs, not to local or private networks.
     def public_only
       dup.tap do |o|

app/logical/sources/strategies/base.rb

@@ -231,7 +231,7 @@ module Sources
 
       # A http client for API requests.
       def http
-        Danbooru::Http.new.public_only
+        Danbooru::Http.new.proxy.public_only
       end
       memoize :http
 

app/logical/sources/strategies/pixiv.rb

@@ -269,7 +269,7 @@ module Sources
       end
 
       def api_client
-        PixivAjaxClient.new(Danbooru.config.pixiv_phpsessid)
+        PixivAjaxClient.new(Danbooru.config.pixiv_phpsessid, http: http)
       end
 
       def api_illust

app/logical/twitter_api_client.rb

@@ -3,13 +3,13 @@
 class TwitterApiClient
   extend Memoist
 
-  attr_reader :api_key, :api_secret
+  attr_reader :api_key, :api_secret, :http
 
   # Create a Twitter API client
   # @param api_key [String] the Twitter API key
   # @param api_secret [String] the Twitter API secret
-  def initialize(api_key, api_secret)
-    @api_key, @api_secret = api_key, api_secret
+  def initialize(api_key, api_secret, http: Danbooru::Http.new)
+    @api_key, @api_secret, @http = api_key, api_secret, http
   end
 
   # Authenticate to Twitter with an API key and secret and receive a bearer token in response.
@@ -17,14 +17,13 @@ class TwitterApiClient
   # @return [String] the Twitter bearer token
   # @see https://developer.twitter.com/en/docs/authentication/api-reference/token
   def bearer_token(token_expiry = 24.hours)
-    http = Danbooru::Http.basic_auth(user: api_key, pass: api_secret)
-    response = http.cache(token_expiry).post("https://api.twitter.com/oauth2/token", form: { grant_type: :client_credentials })
+    response = http.basic_auth(user: api_key, pass: api_secret).cache(token_expiry).post("https://api.twitter.com/oauth2/token", form: { grant_type: :client_credentials })
     response.parse["access_token"]
   end
 
   # @return [Danbooru::Http] the HTTP client to connect to Twitter with
   def client
-    Danbooru::Http.auth("Bearer #{bearer_token}")
+    http.auth("Bearer #{bearer_token}")
   end
 
   # Fetch a tweet by id.

config/danbooru_default_config.rb

@@ -494,6 +494,18 @@ module Danbooru
       false
     end
 
+    def http_proxy_host
+    end
+
+    def http_proxy_port
+    end
+
+    def http_proxy_username
+    end
+
+    def http_proxy_password
+    end
+
     # The URL for the Reportbooru server (https://github.com/evazion/reportbooru).
     # Optional. Used for tracking post views, popular searches, and missed searches.
     # Set to http://localhost/mock/reportbooru to enable a fake reportbooru