simplegoproxy

simplegoproxy

Simplegoproxy is a http / API proxy that can, and is designed and intended to be used to modify the http request headers, response headers and / or response body on the fly, based on custom rules per request, and then return the modified response to the user.

Simply put, Simplegoproxy generates an "entrypoint url", which can be accessed (GET) to make an arbitrary request to the "target url" (All aspects of the Request or Response can be set or modified), and returns the final result (modified Response) to the user.

Basically, the "target url" is a http(s) url, but it also supports some special customary scheme urls. E.g. the exec:// urls, which execute a local program and send it's output back to the client as http response.

Use cases:

• Remove CORS restrictions.
• Add "Authorization" or other headers to the request.
• Apply string replacements on the response body.

TOC

• simplegoproxy
• Run
• Usage
• Modification parameters
• Other features
  • Modification parameters fronting
  • Impersonate the Browser
  • Response template
  • Admin UI
  • "data:" urls
  • unix://, file://, rclone://, curl+*//, exec:// urls
• Security features
  • Set the rootpath
  • Request signing
  • Admin UI Authorization
  • Env substitutions
  • Signing key type
  • Scope signing
  • Open scopes
  • URL encryption
  • Response authorization
  • Response body encrpytion
  • Referer restrictions
  • Origin restrictions
  • Error Suppressions and Logging

Run

Simplegoproxy is written in Go and published as a single executable file which requires no mandatory argument.

You can also run it using Docker:

docker run --name sgp -p 8380:8380 -d \
  ghcr.io/sagan/simplegoproxy

Command-line flag arguments:

  -addr string
        Http listening addr, e.g. "127.0.0.1:8380" or ":8380". If not set, will listen on "0.0.0.0:8380" (default "0.0.0.0:8380")
  -cors
        Set "Access-Control-Allow-Origin: *" header for admin API
  -curl-binary string
        Curl binary path (default "curl")
  -decrypt
        Decrypt the encrypted url(s)
  -eid string
        Used with "-sign -encrypt". Encrypted url id, it will appear at the start of generated encrypted entrypoint utl
  -enable-all
        Enable all schemes url: unix & file & rclone & curl & exec
  -enable-curl
        Enable "curl+*" scheme url: "curl+https://ipinfo.io"
  -enable-exec
        Enable exec scheme url: "exec:///path/to/bin?arg=foo&arg=bar"
  -enable-file
        Enable file scheme url: "file:///path/to/file"
  -enable-rclone
        Enable rclone scheme url: "rclone://remote/path/to/file"
  -enable-unix
        Enable unix domain socket url: "unix:///path/to/socket:http://server/path"
  -encrypt
        Used with "-sign", encrypt generated entrypoint url
  -key string
        The sign key. If set, all requests must be signed using HMAC(key, 'sha-256', payload=url), providing calculated MAC (hex string) in _sgp_sign
  -keytype string
        The sign keytype. Used with "-sign"
  -keytypebl string
        Comma-separated list of blacklisted keytypes
  -log
        Log every request urls
  -open-http
        Used with request signing, make all http(s) urls do not require signing
  -open-scope value
        Used with request signing. Array list. Public scopes that urls of these scopes do not require signing. E.g. "http://example.com/*"
  -pass string
        Password of admin UI. If not set, the "key" will be used
  -prefix string
        Prefix of settings in query parameters (default "_sgp_")
  -publicurl string
        Public url of this service. Used with "-sign". E.g. "https://sgp.example.com/". If set, will output the full generated entrypoint url instead of sign
  -rclone-binary string
        Rclone binary path (default "rclone")
  -rclone-config string
        Manually specify rclone config file path
  -rootpath string
        Root path (with leading and trailing slash) (default "/")
  -sign
        Calculate the sign of target url and output result. The "key" flag need to be set. Args are url(s)
  -supress-error
        Supress error display, send a 404 to client instead
  -user string
        Username of admin UI (Admin UI is available at "/admin" path) (default "root")

All arguments are optional, and can also be set by environment variable. The environment variable name is the SGP_ prefix concating flag name in uppercase and replacing - with _. E.g.: enable-file flag can be set by setting SGP_ENABLE_FILE=true env.

Usage

Append the target url to the root path to generate the "entrypoint url". E.g.: (Assume Simplegoproxy is started with the default "/' root path):

curl -i "localhost:8380/https://ipcfg.co/json"

# The scheme:// part of target url can be omitted, in which case "https://" is assumed
curl -i "localhost:8380/ipcfg.co/json"

The "entrypoint url" accepts GET requests only. By default it will just fetch the "target url" and return the original response, without any modification. Add specic query parameters to set the modification rules. E.g.:

curl -i "localhost:8380/https://ipcfg.co/json?_sgp_cors"

The _sgp_cors modification parameter indicates Simplegoproxy to modify the original response headers to set the CORS-allow-all headers:

Access-Control-Allow-Credentials: true
Access-Control-Allow-Methods: GET, OPTIONS
Access-Control-Allow-Origin: *

Modification parameters

All modification paramaters has the _sgp_ prefix by default, which can be changed via -prefix command-line argument.

• _sgp_cors : (Value ignored) Add the CORS-allow-all headers to original response.
• _sgp_nocsp : (Value ignored) Remove the Content Security Policy (CSP) headers from original response.
• _sgp_insecure : (Value ignored) Ignore any TLS cert error in http request.
• _sgp_norf : (Value ignored) Do not follow redirects.
• _sgp_nocache : (Value ignored) Add the no-cache headers to original response.
• _sgp_debug : (Value ignored) Debug mode.
• _sgp_proxy=socks5://1.2.3.4:1080 : Set the proxy for the http request.
• _sgp_timeout=5 : Set the timeout for the http request (seconds).
• _sgp_method=GET : Set the method for the http request. Default to GET.
• _sgp_header_<any>=<value> : Set the request header. E.g.: _sgp_header_Authorization=Token%20abcdef will set the "Authorization: Token abcdef" request header. If value is empty, will remove the target header from request.
• _sgp_resheader_<any>=<value> : Similar to _sgp_header_, but set or remove the response header.
• _sgp_sub_<string>=<replacement> : Similar to nginx http_sub module, modifiy the response by replacing one specified string by another. By default _sgp_sub_ rules only apply to the response with a "textual" MIME type, which could be any one of the following: "text/*", "application/json", "application/xml", "application/atom+xml", "application/x-sh".
• _sgp_forcesub : (Value ignored) Force apply _sgp_sub_ rules to the response of any MIME type.
• _sgp_cookie=<value> : Set request cookie. Equivalent to _sgp_header_cookie=<value>.
• _sgp_type=<value> : Set the request content type. Equivalent to _sgp_header_Content-Type=<value>. If _sgp_method is set to POST and _sgp_body is also set, the _sgp_type will have a default value application/x-www-form-urlencoded.
• _sgp_restype=<value> : Set the response content type. Equivalent to _sgp_resheader_Content-Type=<value>. Additionally, _sgp_type and _sgp_restype also accept file extension values like txt or .txt (with or without leading dot), in which case it will use the MIME type associated with the file extension ext.
• _sgp_body=<value> : Set the request body (String only. Binary data is not supported).
• _sgp_resbody=<value> : Set the response body template.
• _sgp_resbodytype=<value> : The original response body type, e.g. json, xml, yaml, toml.
• _sgp_fdheaders=<header1>,<header2>,... : Comma-separated forward headers list. For every header in the list, if the http request to the "entrypoint url" itself contains that header, Simplegoproxy will set the request header to the same value when making http request to the "target url". E.g.: _sgp_fdheaders=Referer,Origin. By default some headers will ALWAYS be forwarded, even if not specified, unless the same _sgp_header_* parameter is set: Range, If-*. Some values have special meanings:
  • *: ALL request headers.
  • %0A (\n) : Supresses default forwarding headers and makes sure no headers would be forwarded.
  • :method : Forward the http request method. Use the incoming method to the entrypoint url as the one sent to the target url.
  • :body : Forward the http request body. Use the incoming body to the entrypoint url as the one sent to the target url.
• _sgp_user=username:password : Set the authentication username & password for request. It can also be directly set in target url via "https://user:password@example.com" syntax.
• _sgp_impersonate=<value> : Impersonate itself as Browser when sending http request. See below "Impersonate the Browser" section.
• _sgp_sign=<value> : The sign of request canonical url. See below "Request signing" section.
• _sgp_keytype=<value> : The sign key type. See below "Signing key type" section.
• _sgp_scope=<value> : The scope of sign. Can be used multiple times. See below "Scope signing" section.
• _sgp_eid=<value> : The encryption url id. See below "URL Encryption" section.
• _sgp_resuser=user:pass : The username & password for http response. See below "Response authorization" section.
• _sgp_respass=<value> : The password to encrypt response body. See below "Response body encrpytion" section.
• _sgp_referer=<value> : Set the allowed referer of request to the entrypoint url. Can be used multiple times. See below "Referer restrictions" section.
• _sgp_origin=<value> : Set the allowed origin of request to the entrypoint url. Can be used multiple times. See below "Origin restrictions" section.
• _sgp_validbefore=<value>, _sgp_validafter=<value> : If set, the entrypoint url can only be used before or after this time accordingly. Value can be any of below time formats: 2006-01-02, 2006-01-02T15:04:05 2006-01-02T15:04:05-07:00, 2006-01-02T15:04:05Z. All but the last format are parsed in local timezone. The last one are parsed as UTC time. Note to enforce these restrictions, "Request signing" must be enabled.

Modification paramaters are set in Query Variables. All _sgp_* parameters are stripped from the target url when Simplegoproxy fetch it. E.g.: the http://localhost:8380/https://ipcfg.co/json?abc=1&_sgp_cors entry will actually fetch the https://ipcfg.co/json?abc=1 target url.

All "escapable" characters in paramater name & value should be escaped in '%XX' format. (In general, the "escapable" means JavaScript's encodeURIComponent function return a escaped string for the char)

Other features

Modification parameters fronting

Instead of using Query Variables to set modification parameters, You can also put them in the "path", after the root path but before the target url. E.g.:

http://localhost:8380/_sgp_cors/https://ipcfg.co/json

Impersonate the Browser

Simplegoproxy can impersonate itself as Browser when sending http request to target url. It's similar to what curl-impersonate does. To enable this, set the _sgp_impersonate modification parameter to target browser name. E.g.:

http://localhost:8380/_sgp_impersonate=chrome120/https://ipcfg.co/json

Simplegoproxy will print the list of supported targets when starting. Currently supported impersonates:

• chrome120 : Chrome 120 on Windows 11 x64 en-US
• firefox121 : Firefox 121 on Windows 11 x64 en-US

Response template

if _sgp_resbody parameter is set, Simplegoproxy use it as a Go template for renderring response body. E.g.:

{{.res.status}}

{{.res.body}}

Available variables:

• res : The original http response.
  • res.status : http response status code. type: int.
  • res.header: http response header. type: map[string][]string.
  • res.body : http response body. type: string.
  • res.data : http response body parsed data object. type: any.
• req : The http request sent to the target url server.
  • req.header : Http request header.
• err : Error encountered, if any.

The res.data is parsed according to original http response's content-type header. You can also forcibly specify the type using _sgp_resbodytype parameter (json / yaml / xml / toml).

The "content-type" of renderred response is text/html by default, use _sgp_restype parameter to override it.

Admin UI

Simplegoproxy provides a http admin UI at /admin/ path, e.g. http://localhost:8380/admin/ . The admin UI allow users to generate entrypoint url for a target url and view history records of generated entrypoint urls. All data are stored in the browser local storage.

"data:" urls

Simplegoproxy supports data: urls (Data URLs), which will use the provided contents directly as the response body.

E.g.

http://localhost:8380/data:,Hello%2C%20World%21

http://localhost:8380/data:text/html;base64,SGVsbG8sIFdvcmxkIQ==

Both of above entrypoint urls will output "Hello, World!". The later one will also set the Content-Type: text/html response header.

"data:" urls do not require (enforce) signing, but env substitions do not work if a such url is not signed.

unix://, file://, rclone://, curl+*//, exec:// urls

If -enable-unix, -enable-file, -enable-rclone or -enable-exec flag is set, Simplegoproxy will support some additional schemes of urls respectively. If -enable-all flag is set, all these schemes will be enabled.

• -enable-unix : Make Simplegoproxy supports URLs of http(s) over unix domain socket in local file system. Target url example: unix://path/to/socket:http://server/path. Use : to split http resource url with the unix domain socket file path.
• -enable-file : Make Simplegoproxy supports file:// (File URI scheme) urls, which reference to local file system files. Directory Index is also supported. Target url examples:
  • file:///root/foo.txt: The /root/foo.txt file.
  • file:///D:/foo.txt : The D:\foo.txt file. (Windows)
  • file://server/share/foo.txt: The \\server\share\foo.txt file. (Windows UNC path)
  • file:////server/share/foo.txt : Same as above, another form of UNC path.
• -enable-rclone : Make Simplegoproxy supports rclone:// urls, which reference to a file in rclone remote. Target url example: rclone://remote/path/to/file.txt, which will get the contents of remote:path/to/file.txt file using rclone. It lookups rclone from PATH and use default rclone config file location (~/.config/rclone.conf). To use other locations, use -rclone-binary and -rclone-config flags.
  • For a regular file, it will run rclone cat remote:path to get file contents and output it to client.
  • For a dir, it will run rclone lsjson remote:path to get file list of the dir, and output the Directory Index page to client.
• -enable-curl : Make Simplegoproxy supports curl+*:// urls, which will spawn a curl process to fetch the actual url. Target url example: curl+https://ipinfo.io. It lookups curl from PATH. To use other location, use -curl-binary flag.
• -enable-exec : Make Simplegoproxy supports exec:// urls, which spawn a child process and return it's stdout to client. Target url example: exec://curl?args=-i+ipinfo.io, which will execute curl -i ipinfo.io. You can also specify the full path of executable file use the same format as file:// scheme url.

For rclone://, curl+*//, exec:// urls, if _sgp_debug modification parameter is set, it will output the combined stdout and stderr of spawned child process, instead of stdout only.

Note some _sgp_* modification parameters don't work with most of above schemes urls, obviously the ones that modify http request.

Security features

Set the rootpath

If your Simplegoproxy instance will be publicly accessible, you can set the "rootpath" flag to a "confidential" value other than the default "/". It acts like a password.

E.g.: If rootpath is set to "/abc/", then the entrypoint url should be like http://localhost:8380/abc/https://ipcfg.co/json.

Request signing

Additional, if "key" flag is set, all requests to Simplegoproxy (except requests of data: urls) must be signed via HMAC-SHA256 using the key. The message being signed is the "canonical url" of the request. The result MAC (message authentication code) should be provided in _sgp_sign parameter of the request.

The "canonical url" is the target url with all _sgp_* modification parameters (excluding _sgp_sign and _sgp_keytype) in query values. All query values sorted by key.

It's recommended to use the "Admin UI" to sign a target url and get the signed entrypoint url.

You can also calculate the sign of a target url using CLI by running simplegoproxy with -sign flag. E.g.:

#simplegoproxy -sign -key abc "https://ipinfo.io/ip?_sgp_cors"
https://ipinfo.io/ip?_sgp_cors=  e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef

It outputs the canonical url of the request along with calculated sign.

Then use the following entrypoint url :

http://localhost:8380/https://ipinfo.io/ip?_sgp_cors&_sgp_sign=e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef

# or
http://localhost:8380/_sgp_cors&_sgp_sign=e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef/https://ipinfo.io/ip

# or
http://localhost:8380/_sgp_sign=e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef/https://ipinfo.io/ip?_sgp_cors

If you pass a -publicurl http://localhost:8380 flag when invoking the above command, it outputs the final entry url diretly:

simplegoproxy -sign -key abc -publicurl "http://localhost:8380" "https://ipinfo.io/ip?_sgp_cors"
https://ipinfo.io/ip?_sgp_cors=  http://localhost:8380/_sgp_sign=e9ccc14d94cd952d08bef094d9037c26b624a8bf18e6dc6c223d76224d4196ef/https://ipinfo.io/ip?_sgp_cors=

The data: urls does not need signing, as they do not actually send any network request or have any side effect.

It's also possible to make some urls do not require signing, see below "Open scopes" section.

Admin UI Authorization

If request signing is enabled, the admin UI will require http basic authorization:

• Username: Default is root. Can be changed by -user string flag.
• Password: Default use "key" flag as password. Use -pass string flag to set standalone password.

Env substitutions

If the entrypoint url is signed, all __SGPENV_**__ style substrings in modification parameter value or normal query variable value will be replaced with the value of the corresponding ** environment variable, if it exists, when sending request to the target url. E.g. __SGPENV_PATH__ will be replaced by PATH env value.

The substitutions occur after the url sign verification.

Signing key type

It's possible to provide a optional "key type" value whening signing a url. The "key type" value will be appended to the "key" to derive the effective actual HMAC key.

To sign a url, set a -keytype string flag:

simplegoproxy -key abc -keytype one -sign -publicurl http://localhost:8380 ipinfo.io

Output:

https://ipinfo.io/  http://localhost:8380/_sgp_keytype=one&_sgp_sign=94bb9904ac8975e1dc3617ca49a9ed4481d7db6626859978dddcd29c3999d3f0/https://ipinfo.io/

The generated entrypoint url will have the _sgp_keytype parameter with same value.

The design purpose of "key type" is that, you can selectively "revoke" the entrypoint urls of some "key type(s)" without invalidating other urls. To do this, set the -keytypebl string flag to the comma-separated blacklist of revoked key types:

simplegoproxy -key abc -keytypebl one,two,three

Without "key type", a signed url can only be revoked by changing the "key", which will invalidate all previous generated entrypoint urls.

Scope signing

If any none-empty _sgp_scope parameter is provided, the sign is calculated against the whole scope, which is a Chrome extension style match pattern, instead of against the single target url.

E.g.:

localhost:8380/_sgp_scope=https%3A%2F%2F%2A%2F%2A/ipinfo.io/ip

Here, the _sgp_scope is https://*/* , which matches all https URLs. The payload ("canonical target url") of scope signing is a ? character plus all _sgp_ parameters sorted by key. To calculate it:

simplegoproxy -sign -key abc "?_sgp_scope=https://*/\_"
edb3aaafe81cc42ea94a862bb5b77b4876d39ab3748410716bc9d7041e64c715 ?_sgp_scope=https%3A%2F%2F%2A%2F%2A

Then use the following entrypoint url:

curl -i "localhost:8380/_sgp_sign=edb3aaafe81cc42ea94a862bb5b77b4876d39ab3748410716bc9d7041e64c715&_sgp_scope=https%3A%2F%2F%2A%2F%2A/ipinfo.io/ip"

Notes:

• The _sgp_scope parameter can be set multiple times. The sign can be used to access any target URL which matches with at least one provided scope.
• A * scheme in scope parameter means "http" or "https". E.g. the *://*/* scope matches with all "http://" or "https://" urls. If you want to target other schemes like "file" ("file://" url) as well, you must put it in explicitly.

Open scopes

When request signing is used, you can define some "open scopes" using -open-scope string flags. E.g.:

-open-scope "http://example.com/*"

This flag can be set multiple times. Target urls of these scopes do not require (enforce) signing. However, env substitutions do not work if a such scope url is not signed. For convenience, -open-http flag can be used to make all http(s) urls do not require signing, equivalent to -open-scope "*://*".

Example:

simplegoproxy -enable-all -key abc -open-http

URL encryption

Instead of putting the plain text target url inside the entrypoint url. If request signing is enabled, Simplegoproxy also accepts the "encrypted form entrypoint url" in which the target url exists as cipher text.

To get the encrypted form entrypoint url, use the -encrypt flag with -sign when signing an url using CLI; Or check the "Encrypt" checkbox in Admin UI.

Note the "Modification parameters fronting" does not work with URL encryption -- the whole target url with all query parameters will be encrypted. The encrypted entrypoint url contains only one path segment, e.g.: http://localhost:8380/abcdefghijklmnopqrstuvwxyz.

It's possible to prepand a fixed eid (encrypted url id) string to the beginning of the generated url to help you identify a encrypted url. To do it, input the "eid" in admin UI or use the -eid <value> CLI flag. The encrypted entrypoint url will have format http://localhost:8380/myeid_abcdefghijklmnopqrstuvwxyz. Only [_a-zA-Z0-9] (regexp) charasters is allowed in eid.

The target urls are encrypted using "key" flag value as the cryptographic key. If you change the key, all previously generated entrypoint urls will be inaccessible.

Response authorization

If "URL encryption" is used and the _sgp_respass=uass:pass parameter is set. The returned http response of Simplegoproxy will require http basic authorization using specified username & password.

Response body encrpytion

If "URL encryption" is used and the _sgp_respass=<value> parameter is set, Simplegoproxy will encrypt the response body sent back to client using the parameter's value as password. The encryption uses AES256-GCM with the cryptographic key derived from password via PBKDF2 + SHA-256 of 1000000 iterations (no salt). The response body sent back to client is the base64 string of iv (12 bytes) + ciphertext.

To decrypt the encrypted response body, see below examples.

JavaScript (Browser & Node.js):

/**
 * Decrypt the encrypted response body sent by Simplegoproxy. Works in browser and node.js.
 * @param string ciphertext base64 encoded ciphertext(with iv as prefix)
 * @param string password
 * @return Promise<string> plaintext
 */
async function aesGcmDecrypt(ciphertext, password) {
  const keymaterial = await crypto.subtle.importKey(
    "raw",
    new TextEncoder().encode(password),
    { name: "PBKDF2" },
    false,
    ["deriveBits", "deriveKey"]
  );
  const key = await crypto.subtle.deriveKey(
    {
      name: "PBKDF2",
      salt: new Uint8Array(),
      iterations: 1000000,
      hash: "SHA-256",
    },
    keymaterial,
    { name: "AES-GCM", length: 256 },
    true,
    ["encrypt", "decrypt"]
  );
  const cipherdata = Uint8Array.from(atob(ciphertext), (m) => m.codePointAt(0));
  const alg = { name: "AES-GCM", iv: cipherdata.slice(0, 12) };
  const plaindata = await crypto.subtle.decrypt(alg, key, cipherdata.slice(12));
  return new TextDecoder().decode(plaindata);
}

Referer restrictions

If any _sgp_referer parameter is provided. Simplegoproxy will validate the Referer header of the request to the entrypoint url and only allow theses requests which referer match with at lease one provided _sgp_referer value.

The format of _sgp_referer should be a Chrome extension style match pattern (same as _sgp_scope). Additionaly, an empty value matches with the "Direct" request, in which case no Referer header is present.

Referer restrictions works even if request signing is not enabled.

Origin restrictions

It works in the same way as the above "Referer restrictions" feature except that the parameter name is _sgp_origin and is verified against the Origin request header.

Error Suppressions and Logging

By default, when Simplegoproxy web server encounters an error handling a request (e.g. signing verification failed), it displays the error to the client. If -supress-error flag is set, it will supress the error display, always sending a standard "404 Not Found" page to client if any error happens.

Also, by default Simplegoproxy does not log incoming requests and / or errors. To do the logging, set the -log flag, the log will outputted to stdout.