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The Charity Engine Distributed Proxy uses the power and unique, geographically-dispersed nature of volunteer computing to allow web requests to originate from locations all around the world. Once a browser or other comparable web platform is configured to use the Distributed Proxy, any requests made from that interface to a target website will be routed by the request distribution service to ensure that origination is from the proper geographic location and that other options are applied.


Connecting to the proxy

The interface to this service is just like any standard HTTP proxy. Systems using this proxy should be configured to route web traffic through Charity Engine as detailed below and any request that goes out will be made by one of the computers in the Charity Engine network:

Proxy configuration
Port: 20000

Once requests are fulfilled by Charity Engine computers, the responses are returned as though the request was made directly.

It is possible and recommended to submit requests to the proxy in parallel. Even though a single request can take up to 20 seconds (and, in rare events, up to 40 seconds), there are enough nodes in the network to handle parallel loads. It is often a good practice to run up to 500 parallel requests.

IP addresses

If your network requires configuration using IP addresses to allow access to external services (such as a firewall or internal proxy configuration), the following is the full list of IP addresses that the Distributed Proxy service uses:

Though not common, the IP addresses in the list can be changed or become temporarily unavailable due to system maintenance. For this reason, the best approach will typically be to use the hostname to access the proxy service, unless your internal implementation will handle switching IPs to maintain connectivity.

Configuring requests

Each request sent through the Distributed Proxy should be configured according to requirements. Special HTTP headers are included in the request to authenticate with the proxy and also to ensure that the request is processed by a computer in the appropriate geographic location or even by one specific computer on the network.


The Distributed Proxy uses standard proxy authorization. Each authorized request must contain a Proxy-Authorization header. Many of the tools that support HTTP proxies (such as CURL, wget, or web browsers) automatically generate the header (see section "Examples" for details). If the tools in use cannot generate the Proxy-Authorization header automatically, it should be generated manually.

Manual generation of the Proxy-Authorization header

To generate the header manually, encode your authenticator, a colon character (":"), and JSON-based configuration data (only if used - see section "Special use of the password field" for details) in base64. You can use tools like Base64Encode to do the encoding. Once encoded, add "Basic " as a prefix to the base64 encoded string. For example, if the username is "example" and JSON-based configuration is not used, the string to encode in base64 would be "example:" and the final header would be as follows:

Proxy-Authorization: Basic ZXhhbXBsZTo=

When a request is submitted without authorization, HTTP status code "407 Proxy authentication required " will be returned and the request will not be processed.

Special use of the password field

While the password field is unused and can be left blank, any JSON data that is passed in this field will be interpreted as request configuration; for example, using the following password will act as if X-Proxy-Country and X-Proxy-Timeout-Soft headers were configured and will only use nodes in Israel with a timeout of 10 seconds:

{"X-Proxy-Country":"IL","X-Proxy-Timeout-Soft": 10}



Distributed Proxy allows one to request proxy nodes in a specific geographic location.

All geolocation features may be subject to surcharges.

Use of these headers will limit the number of Charity Engine computers available to meet a given request; for best performance, they should only be used when specific geographic origination is required.

By country

When either of the X-Proxy-Country and X-Proxy-CountryExclude headers are included in the request, the proxy will perform geolocation and then include or exclude computers in the Charity Engine network based on the countries specified.

X-Proxy-Country will only use computers in the listed countries. For instance, to use only computers in the United States or United Kingdom, the following header should be specified (note that when designating multiple countries, country codes must be comma separated):

X-Proxy-Country: US,GB

To take the opposite approach, the X-Proxy-CountryExclude header is the reverse of X-Proxy-Country and will exclude any specified countries. For example, if a request can originate from anywhere except Argentina, the header would look like this:

X-Proxy-CountryExclude: AR

Country codes are defined in ISO 3166.

Geolocation headers are mutually-exclusive; if both X-Proxy-Country and X-Proxy-CountryExclude headers are used in the same request, only X-Proxy-Country will be used.

By location (local targeting)

A more exact geographic location (such as a city) can be requested by using X-Proxy-LatLon header. It takes a list of requested latitude, longitude, and search radius in meters, all separated with semicolons. For example, to target 50km around New York, the header would look as follows:

X-Proxy-LatLon: 40.730610;-73.935242;50000

Values for latitude are positive for north and negative for south; values for longitude are positive for east and negative for west.

Geolocation headers are mutually-exclusive; if either of the X-Proxy-Country headers are used with X-Proxy-LatLon in the same request, X-Proxy-LatLon will be ignored.

Geolocation accuracy

Geolocation functions are not perfectly accurate: ie, a portion of nodes accessed via these features will not be in the designated regions. 

As a rule, the error rate increases with the specificity of the targeting.  For instance, geolocation using X-Proxy-Country will be more accurate than geolocation via X-Proxy-LatLon.  And X-Proxy-LatLon with radius set to 50000 will be more accurate than X-Proxy-LatLon with radius set to 25000. 

Additionally, geolocation accuracy may differ in various parts of the world, and is capped to a minimum of 25000 meters (25km, 15.5 miles).

By way of guidance, for country-level targeting, we estimate 99.8% accuracy. For LatLon targeting, at 50km radius, in the USA, we estimate 80-90% accuracy (*lower outside the USA)

Session persistence

When needed, it is possible for multiple requests to be served by the same computer on the Charity Engine network (e.g. for sessions to be maintained). This is accomplished by use of the X-Proxy-Session header in the request. We recommend using a V4 (random) UUID (the ID in this example is "b4b6ea85-b4bc-461f-bc14-63b7d37206e6"):

X-Proxy-Session: b4b6ea85-b4bc-461f-bc14-63b7d37206e6

Subsequent requests can then include the same header to ensure that they are handled by the same computer as the first request. 

The session identifier will usually remain active for at least 10 minutes following the last request made using that identifier. If no additional requests are received in that time, the ID may expire and will no longer be useful. Note that even if the ID has not yet expired, it is still possible that the computer referenced by that ID will shut down or otherwise disconnect from the Charity Engine network. If this occurs, the request will return HTTP status code 503 Service unavailable.

If a 503 Service unavailable response is received while using the X-Proxy-Session header, in most cases a new request should be made with a new ID in the X-Proxy-Session header and that new ID should be used for subsequent requests.

Please note:

  • Session IDs are not aliases for IP addresses; session IDs expire after a short period of time. The design assumption is that a session ID will be used to load all the elements of a single page, e.g. for a single transaction with multiple parts. (*Re-using a session ID for a series of pages will impair performance, as the pages will be read serially instead of in parallel.)
  • Though unlikely, a single node may serve more than one session at a time.

Note: the legacy name for this feature was "Connection Groups". The older HTTP header, X-Proxy-ConnectionGroup, is currently deprecated but still supported.

Special considerations regarding HTTPS requests

Due to the nature of HTTPS proxying, the X-Proxy-Session header must be included either in the initial proxy CONNECT request, or in the password field as described in the "Special use of the password field" section of this document. Headers included in the HTTPS request itself may be ignored.

The method used to submit headers properly over HTTPS will depend on the software that is in use. For example, CURL requires the use of the --proxy-header parameter, e.g.: --proxy-header "X-Proxy-Session: b4b6ea85-b4bc-461f-bc14-63b7d37206e6"

See the "HTTPS requests" section for further details on how HTTPS proxying is handled.


The default behavior of the system is to run the request on a node and resend the request to another if the first one fails to respond within 20 seconds. If the second node also fails to respond, the request is expired (see section "Request expiration") after a total of 40 seconds.

It is possible to configure proxy timeouts for non-standard workloads such as crawling of pages that are slow to respond or generate large amounts of data. Specifying a "soft" timeout header X-Proxy-Timeout-Soft will change when work is reassigned to another host; specifying "hard" timeout header X-Proxy-Timeout-Hard will change when the request is expired.

The "soft" timeout is limited to a minimum of 5 seconds and a maximum of 120 seconds and defaults to 20 seconds; "hard" timeout is limited to a minimum of 10 seconds and a maximum of 120 seconds and defaults to 40 seconds. "Soft" timeout cannot be larger than "hard" timeout.

In the typical case where the "hard" timeout is larger than the "soft" timeout, more than 1 node can be dispatched to serve the same request; to prevent retries on a different node, set the "hard" limit equal to the "soft" limit.

Setting the soft timeout to the same value as the hard timeout will disable automatic request retries and may degrade your performance.

Restrictions of the system

Request expiration

Requests that cannot be resolved within 40 seconds will expire and return HTTP status code 503 Service unavailable. In order to distinguish 503 codes from the Distributed Proxy with 503 codes returned from the target of the request, 503 codes coming from the Distributed Proxy will also include an extra header:

X-Generated-By: CharityEngine

It is also possible to configure the expiration limits, see section "X-Proxy-Timeout-Hard and X-Proxy-Timeout-Soft".

HTTPS requests

HTTPS (SSL) requests are accepted using the HTTP CONNECT method where the initial request will open a tunnel and subsequent requests will load data. Most software will automatically handle this when the HTTPS protocol is specified for the request.

The SSL request will be decrypted at the proxy server and will be reissued as a separate request by the proxy node. Depending on the software you use, you may receive certificate warnings or information about a man-in-the-middle attack. You should disregard this warning as long as the certificate used in the response is for *

Special considerations for HSTS enabled sites

If an HSTS enabled site is visited through a web browser, the site will set a persistent HSTS cookie which normally cannot be removed. The cookie tells the browser to never allow certificate exceptions. Distributed Proxy will automatically remove HSTS headers, allowing the user to set certificate exceptions through the browser. However, if the target site is ever visited without Distributed Proxy, the persistent cookie will be set and the certificate error cannot be worked around. Therefore, it is critical that you do not visit HSTS enabled target sites without Distributed Proxy.

Example sites sending HSTS headers: Google; Reddit.

Error messages

Occasionally, the proxy cannot handle a request and an HTTP error code is returned along with one or more special HTTP headers. In order to be able to distinguish the error code from errors generated by remote servers, we will always include the header X-Generated-By: CharityEngine. There may be other HTTP headers that describe the problem. The following table lists all headers that may be encountered.

HTTP status codeHTTP headerDescriptionSuggested action
429 Too Many Requests
Number of requests per minute allowed for this domain has been exceeded.Decrease the amount of connections made per minute.
503X-Proxy-Error: Host blacklisted by remote serverWe have detected that the host that has been assigned to this session has been blacklisted by the remote server and this session will no longer return valid results for this hostname. Only applies if session feature is used.Resubmit the request with a new session ID, or use a different hostname.
503X-Proxy-Error: Host has reached daily request limitThe host that has been assigned to this session has executed the maximum number of requests to this hostname and this session will no longer return valid results for this hostname. Only applies if session feature is used.Resubmit the request with a new session ID, or use a different hostname.
503X-Proxy-Error: Host has reached transfer limitThe host that has been assigned to this session has transferred the maximum amount of data it is allowed and this session will no longer return valid results for any hostname. Only applies if session feature is used.Resubmit the request with a new session ID.
503X-Proxy-Error: Out of nodesThe request could not be resolved within allocated time because we ran out of available nodes.Decrease the amount of concurrent requests; remove host restrictions if any.
503X-Proxy-Error: TimeoutThe request could not be resolved within allocated time, possibly because the remote server is slow to respond.Verify that the remote server is responsive.


Blacklisting nodes

API endpoint
HTTP methodGET
Parametershostname (string)hostname to blacklist node on
nodeid (string)node ID as specified within any previous response headers
ResponseJSON/HTMLJSON message {"success":true} if successful, otherwise a HTML page explaining the error

Blacklists a node for the specified hostname, preventing any crawls done on that hostname from the specified node for a period of at least 24 hours. Useful having detected an issue with the results returned by the host, e.g. invalid data.

Nodes are guaranteed to be blacklisted within 30 seconds, but are usually blacklisted immediately after issuing a call to the API endpoint.

Headless Browsers

The Charity Engine "Smart Proxy" service allows running of JavaScript applications within fully-featured web browsers on our network.



Flag -k has to be used if using HTTPS.

Flag -v can be omitted, but is useful for debugging (gives back verbose request details).

Flag -A sets a user agent to the specified string (Google Chrome in the example below). Websites often block CURL user agents, so it is often beneficial to act as a browser.

curl -v -k -x -A "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.167 Safari/537.36" --proxy-user "authenticator:" ""

Additional HTTP headers can be sent to use proxy service configuration options. For example, add --header "X-Proxy-Country: US" (including quotes) to only use nodes from the United States.


$url = '';
$authenticator = 'Your authenticator';
$ch = curl_init();
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false); // Only needed if using HTTPS
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); // Only needed if using HTTPS
curl_setopt($ch, CURLOPT_PROXY, '');
curl_setopt($ch, CURLOPT_PROXYUSERPWD, $authenticator.':');
$result = curl_exec($ch);
$curl_info = curl_getinfo($ch);



import requests
proxies = {
  'http': '',
  'https': ''
r = requests.get('', proxies=proxies, verify=False)

JAVA (with Apache Commons HttpClient)

HttpMethod getMethod = new GetMethod(url);
httpClient = new HttpClient();
httpClient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, "");

HostConfiguration hostConfiguration = httpClient.getHostConfiguration();
hostConfiguration.setProxy("", 20000);
getMethod.addRequestHeader("Proxy-Authorization", "Basic <Base64 key>");
statusCode = httpClient.executeMethod(getMethod);bufferedReader = new BufferedReader(
    new InputStreamReader(

String line;
while ((line = bufferedReader.readLine()) != null) {


var request = require('request');
var options = {
    proxy: 'http://<Base64 key>',
    strictSSL: false, // Ignore certificate errors for HTTPS
    followRedirect: false,
    proxyHeaderWhiteList: ['x-proxy-session'], // Add any other custom headers you are using
    gzip: true,
    uri: '',
    headers: {
        'user-agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.167 Safari/537.36',
        host: '',
        // Add additional headers if needed
request(options, function(error, response, body) {
    console.log('Done with request; status code ' + response.statusCode);

Account Dashboard

Activity and billing data for proxy service (and for computing and storage services) can be viewed via the account dashboard, accessible at  (Reports may also be exported as .csv files.)

The amount of data transfer that is billed is equivalent to the size in bytes of the response body that is received from the remote system. If compression is used by the remote system, billing is based on the compressed size, not the size of the data when unpacked.

Please note: Data is reported in binary units (MiB, GiB, and TiB - i.e. multiples of 1024) rather than decimal (MB, GB, and TB - i.e. multiples of 1000).  For more information, see Units of measurement for storage data.

Additional billing elements:

  • Tasks - Proxy requests are reported in the dashboard as "tasks"
  • Data surcharge for small requests -  minimum charge per proxy request task (any request with a response smaller than the minimum size of 15 KiB carries a "small request" surcharge to bring it up to the minimum)
  • Geolocation - use of geotargeted nodes (See 2.2 “Geolocation”, above) may incur additional charges, on a per-request basis. Contact us for details.
  • Domain surcharge - some domains incur additional charges, on a per-request basis. Contact us for details.
  • (The runtime and cost per hour of tasks are used for billing compute and storage services and are not relevant for proxy services.

Future enhancements

New features will be added to the Distributed Proxy system as they are developed and tested. If a specific capability is desired in order to use the Distributed Proxy for a given task, a new feature can be requested (these will be reviewed and implemented on a case by case basis).

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