module Http_client

: sig

HTTP 1.1 client

Note for beginners: There is a simplified interface called Http_client.Convenience.

Thread safety

The module can be compiled such that it is thread-safe. In particular, one has to link the http_client_mt.cmxo object, and thread-safety is restricted to the following kinds of usage:

  • The golden rule is that threads must not share pipeline objects. If every thread uses its own pipeline, every thread will have its own set of state variables. It is not detected if two threads errornously share a pipeline, neither by an error message nor by implicit serialization. Strange things may happen.
  • The same applies to the other objects, e.g. http_call objects
  • The Convenience module even serializes; see below.

Types and Exceptions

exception Bad_message of string

The server sent a message which cannot be interpreted. The string indicates the reason.

exception No_reply

There was no response to the request because some other request failed earlier and it was not allowed to send the request again.

exception Too_many_redirections

While following redirections the limit has been reached

exception Name_resolution_error of string

Could not resolve this name - same as Uq_engines.Host_not_found

exception URL_syntax_error of string

This URL cannot be parsed after a redirection has been followed.

exception Timeout of string

A timeout. The string explains which connection is affected. New since Ocamlnet-3.3.

exception Proxy_error of int

An error status from a proxy. This is only used when extra proxy messages are used to configure the proxy (e.g. the CONNECT message).

exception Response_too_large

The length of the response exceeds the configured maximum

exception Http_protocol of exn

The request could not be processed because the exception condition was raised. The inner exception is one of the above defined.

exception Http_error of (int * string)

Deprecated. The server sent an error message. The left component of the pair is the error code, the right component is the error text. This exception is only used by get_resp_body, and by the Http_client.Convenience module.

type status = [
| `Unserved
| `Http_protocol_error of exn
| `Successful
| `Redirection
| `Client_error
| `Server_error

Condensed status information of a HTTP call:

  • `Unserved: The call has not yet been finished
  • `HTTP_protocol_error e: An error on HTTP level occurred. Corresponds to the exception Http_protocol.
  • `Successful: The call is successful, and the response code is between 200 and 299.
  • `Redirection: The call is successful, and the response code is between 300 and 399.
  • `Client_error: The call failed with a response code between 400 and 499.
  • `Server_error: The call failed for any other reason.
type 'message_class how_to_reconnect =
# | Send_again
(*Send the request automatically again*)
# | Request_fails
(*Drop the request*)
# | Inquire of 'message_class -> bool
(*If the function return true send again, otherwise drop the request.*)
# | Send_again_if_idem
(*Default behaviour: Send_again for idempotent methods (GET, HEAD), Request_fails for the rest*)

How to deal with automatic reconnections, especially when the connection crashes.

type 'message_class how_to_redirect =
# | Redirect
(*Perform the redirection*)
# | Do_not_redirect
(*No redirection*)
# | Redirect_inquire of 'message_class -> bool
(*If the function return true redirect, otherwise do not redirect. It is legal to set the Location header as part of the action performed by the function. (Should be an absolute http URL.)*)
# | Redirect_if_idem
(*Default behaviour: Redirect for idempotent methods (GET, HEAD), Do_not_redirect for the rest*)
type private_api

The private part of the http_call class type

type response_body_storage = [
| `Memory
| `File of unit -> string
| `Body of unit -> Netmime.mime_body
| `Device of unit -> Uq_io.out_device

How to create the response body:

  • `Memory: The response body is in-memory
  • `File f: The response body is stored into the file whose name is returned by f()
  • `Body f: The response body is stored into the object returned by f()
  • `Device f: The response is directly forwarded to the device obtained by f() (new since Ocamlnet-3.3)

When the function f is called in the latter cases the response header has already been received, and can be retrieved with the response_header method of the call object. Also, response_status_text, response_status_code, and response_status return meaningful values.

type synchronization =
# | Sync
(*The next request begins after the response of the last request has been received.*)
# | Pipeline of int
(*The client is allowed to send several requests without waiting for responses. The number is the maximum number of unreplied requests that are allowed. A typical value: 5. If you increase this value, the risk becomes higher that requests must be repeatedly sent to the server in the case the connection crashes. Increasing is recommended if you send a bigger number of GET or HEAD requests to the server. Decreasing is recommended if you send large POST or PUT requests to the server.
Values > 8 are interpreted as 8.

This type determines whether to keep requests and responses synchronized or not.

The first request/response round is always done in Sync mode, because the protocol version of the other side is not known at that moment. Pipeline requires HTTP/1.1.

In previous versions of netclient there was a third option, Sync_with_handshake_before_request_body. This option is no longer necessary because the HTTP specification has been updated in the meantime, and there is a better mechanism now (the Expect header is set).

type resolver = Unixqueue.unix_event_system -> string -> (Unix.inet_addr option -> unit) -> unit

A name resolver is a function r called as r esys name reply. As name the name to resolve is passed. The resolver must finally call reply with either the resolved address or with None, indicating an error in the latter case. The event system esys can be used to carry out the resolution process in an asynchronous way, but this is optional.

Only 1:1 resolution is supported, 1:n resolution not.

type channel_binding_id = int

A channel binding identifies a requirement for the transport channel, especially whether plain HTTP is sufficient, or HTTPS needs to be used, and if so, whether there are further requirements for the SSL context. There are the predefined IDs:

type http_options = {
# synchronization
: synchronization;(*Default: Pipeline 5.*)
# maximum_connection_failures
: int;(*This option limits the number of connection attempts. Default: 2*)
# maximum_message_errors
: int;(*This option limits the number of protocol errors tolerated per request. If a request leads to a protocol error, the connection is shut down, the server is connected again, and the request is tried again (if the kind of the message allows retransmission). If a request repeatedly fails, this option limits the number of retransmissions. Default: 2*)
# inhibit_persistency
: bool;(*This option turns persistent connections off. Default: false It is normally not necessary to change this option.*)
# connection_timeout
: float;(*If there is no network transmission for this period of time, the connection is shut down, and tried again. Default: 300.0 (seconds) It may be necessary to increase this value if HTTP is used for batch applications that contact extremely slow services.*)
# number_of_parallel_connections
: int;(*The client keeps up to this number of parallel connections to a single content server or proxy. Default: 2 You may increase this value if you are mainly connected with an HTTP/1.0 proxy.*)
# maximum_redirections
: int;(*The maximum number of redirections per message*)
# handshake_timeout
: float;(*The timeout when waiting for "100 Continue". Default: 1.0*)
# resolver
: resolver;(*The function for name resolution*)
# configure_socket
: Unix.file_descr -> unit;(*A function to configure socket options*)
# schemes
: (string * Neturl.url_syntax * int option * channel_binding_id) list;(*The list of supported URL schemes. The tuples mean (scheme, syntax, default_port, cb). By default, the schemes "http", "https", and "ipp" are supported.*)
# verbose_status
: bool;
# verbose_request_header
: bool;
# verbose_response_header
: bool;
# verbose_request_contents
: bool;
# verbose_response_contents
: bool;
# verbose_connection
: bool;
# verbose_events
: bool;(*Enable various debugging message types.
  • verbose_status: reports about status of received documents
  • verbose_request_header: prints the header sent to the server
  • verbose_request_contents: prints the document sent to the server
  • verbose_response_header: prints the header of the answer from the server
  • verbose_response_contents: prints the document received from the server
  • verbose_connection: reports many connection events; authentication, too.
  • verbose_events: everything about the interaction with Unixqueue
By default, verbose_status and verbose_connection are enabled. Note that you also have to set Debug.enable to true to see any log message at all!

Options for the whole pipeline. It is recommended to change options the following way:

	     let opts = pipeline # get_options in
             let new_opts = { opts with <field> = <value>; ... } in
             pipeline # set_options new_opts

New fields can be added anytime to this record, and this style of changing options is transparent to field additions.

type header_kind = [
| `Base
| `Effective

The `Base header is set by the user of http_call and is never changed during processing the call. The `Effective header is a copy of the base header at the time the request is sent. The effective header contains additions like Content-length and authentication info.

class type http_call =

http_call is the runtime container for HTTP method calls. It contains the request message, the response message, and the current transmission status.

In previous versions of netclient, this class type was called message. This was quite inexact because this class embraces both messages that are part of a call.

Incompatible changes:

  • using_proxy has been removed. This simply isn't a property of an individual call.
  • get_req_uri has been removed from the public interface for similar reasons.
  • The request and response messages are now primarily stored as Netmime.mime_header and Netmime.mime_body objects. The old style access methods remain in the API for now. The advantage is that it is possible to use external files as body containers.
  • There are two request headers, `Base and `Effective.

Call State

method is_served : bool

true if request/response cycle(s) have been finished, i.e. the call was successful, or a final error state has been reached.

method status : status

The condensed status

Accessing the request message (new style)

method request_method : string

The HTTP method as string

method request_uri : string

The request URI as string. This is always an absolute URI in the form "http://server/path" or "https://server/path".

method set_request_uri : string -> unit

Sets the request URI. This implicitly also sets the channel binding ID (see below).

Changed in Ocamlnet-3.3: The URI is no longer immediately parsed, but first when the call is submitted to a pipeline. This means that parsing errors will first be reported by the add method. The background is that parsing now depends on pipeline options.

method request_header : header_kind -> Netmime.mime_header

The whole header of the request. Users of this class should only modify the `Base header. After the call has been processed, the `Effective header contains the version of the header that has actually been transmitted.

The user should set the following headers:

  • Content-length: Set this to the length of the request body if known. (The client falls back to HTTP 1.0 if not set!)
  • Content-type: Set this to the media type of the request body
  • Expect: Set this to "100-continue" to enable a handshake before the body is sent. Recommended for large bodies. (See also set_expect_handshake below.)

The following headers may be set, but there are reasonable defaults:

  • Date
  • User-agent

The following headers must not be set:

  • Connection
method set_request_header : Netmime.mime_header -> unit

Replaces the whole `Base header object

method set_expect_handshake : unit -> unit

Configures that a handshake is done before sending the request body. This is useful when the request body can be large, and authentication or response indirections are possible. New since Ocamlnet-3.3.

method set_chunked_request : unit -> unit

Configures that the request is transmitted using chunked encoding. This has advantages when the size of the request is not known in advance. However, this works only for true HTTP/1.1 servers. New since Ocamlnet-3.3.

method effective_request_uri : string

The URI actually sent to the server in the request line of the protocol.

method request_body : Netmime.mime_body

The whole body of the request. This method fails after set_request_device has been called (no body then).

method set_request_body : Netmime.mime_body -> unit

Replaces the whole body object

method set_request_device : (unit -> Uq_io.in_device) -> unit

Sets that the request data is read from the passed device instead of taking it from a body object. The device must be connected with the same event loop as the HTTP client.

method set_accept_encoding : unit -> unit

Sets the Accept-Encoding field in the request header, and includes all decompression algorithms registered in [root:Netcompression]. Additionally, the automatic decompression of the response body is enabled.

Note that you need to ensure that the algorithms are really registered at [root:Netcompression]. For example, to get gzip support, run


, and include netzip as library.

Accessing the response message (new style)

These methods will fail if the call has not yet been served! If the call has been finished, but a hard error (e.g. socket error) occurred, the exception Http_protocol is raised. When the server only sent an error code, no exception is raised - but the user can manually test for such codes (e.g. with repsonse_status or status).

method response_status_code : int

The three-digit status code

method response_status_text : string

The text transmitted along with the code

method response_status : Nethttp.http_status

The decoded code. Unknown codes are mapped to the generic status values `Ok, `Multiple_choices, `Bad_request, and `Internal_server_error.

method response_protocol : string

The HTTP version indicated in the response

method response_header : Netmime.mime_header

The whole header of the response. If the call has not succeeded, Http_protocol will be raised.

method response_body : Netmime.mime_body

The whole body of the response. If the call has not succeeded, Http_protocol will be raised. If the call has succeeded, but no body has been transmitted, the empty body is substituted.

If the response is directly forwarded to a device (after calling set_response_body_storage (`Device d)), there is no accessible response body, and this method will fail.


method response_body_storage : response_body_storage

How to create the response body. Defaults to `Memory.

method set_response_body_storage : response_body_storage -> unit

Sets how to create the response body

method max_response_body_length : int64

Returns the current maximum length (initially Int64.max_int)

method set_max_response_body_length : int64 -> unit

Sets a new maximum length. When the body exceeds this maximum by more than the size of the internal buffer, the reception of the response is interrupted, and the error is set to Response_too_large.

method get_reconnect_mode : http_call how_to_reconnect

Get what to do if the server needs to be reconnected, i.e. if the request must be sent repeatedly. By default, this is Send_again_if_idem.

method set_reconnect_mode : http_call how_to_reconnect -> unit

Sets the reconnect mode

method get_redirect_mode : http_call how_to_redirect

By default, the redirect mode is Redirect_if_idem.

method set_redirect_mode : http_call how_to_redirect -> unit

Sets the redirect mode

method proxy_enabled : bool

Returns the proxy mode

method set_proxy_enabled : bool -> unit

Sets the proxy mode

method no_proxy : unit -> unit

Same as set_proxy_enabled false

method is_proxy_allowed : unit -> bool

Deprecated. Same as proxy_enabled

Method characteristics

These properties describe the HTTP method

method proxy_use_connect : bool

Whether to use the CONNECT method if the connection is made via a web proxy. This is normally true if the channel binding is Http_client.https_cb_id

method empty_path_replacement : string

The string to substitute in the request line for the empty path. This is usually "/", and for OPTIONS it is "*".

method is_idempotent : bool

Whether the method is to be considered as idempotent ( = repeated invocations have the same result and no side effect). This is true for GET and HEAD.

method has_req_body : bool

Whether the method allows to send a request body

method has_resp_body : bool

Whether the method allows to reply with a body. This is true except for HEAD.

Channel bindings

Channel bindings are used to distinguish between security requirements. There are normally only two types of requirements:

  • The ID Http_client.http_cb_id is used for messages that can only be sent over HTTP connections, i.e. unencrypted TCP. It is automatically set when the URL of the message starts with "http://".
  • The ID Http_client.https_cb_id describes the requirement that the message can only be sent over HTTPS connections, i.e. TLS-protected TCP. It is automatically set when the URL of the message starts with "https://".

It is possible to change the channel binding to establish further types of security requirements (e.g. that certain client certificates are used), or even other details of the transport connection.

The method channel_binding is gone from this object type. It is now available as part of pipeline.

method set_channel_binding : channel_binding_id -> unit

Sets the channel binding. Note that set_request_uri also sets the channel binding, but always to the default for the type of URL.

Repeating calls

method same_call : unit -> http_call

This method returns a new object that will perform the same call as this object (this function is called "reload" in browsers). The new object is initialized as follows:

  • The state is set to `Unserved
  • The request method remains the same (the class of the returned object remains the same)
  • The request URI is the same string as the original URI
  • The channel binding ID is the same
  • The base request header is the same object
  • The request body is the same object
  • Options like reconnect, redirect mode, and proxy mode are copied.

Old style access methods

These method were introduced in previous versions of netclient, but are quite limited. Some questionable methods are now deprecated and will be removed in future versions of netclient.

method get_req_method : unit -> string

Get the name of the request method. Same as request_method.

method get_host : unit -> string

The host name of the content server, extracted from the URI.

Changed in Ocamlnet-3.3: The host can first be extracted after the call is submitted to a pipeline.

method get_port : unit -> int

The port number of the content server, extracted from the URI.

Changed in Ocamlnet-3.3: The port can first be extracted after the call is submitted to a pipeline.

method get_path : unit -> string

The path (incl. query, if any) extracted from the URI.

Changed in Ocamlnet-3.3: The path can first be extracted after the call is submitted to a pipeline.

method get_uri : unit -> string

the full URI of this message: http://server:port/path. If the path is empty, it is omitted. - Same as request_uri.

method get_req_body : unit -> string

What has been sent as body in the (last) request. Same as request_body # value.

method get_req_header : unit -> (string * string) list

Deprecated. What has been sent as header in the (last) request. Returns (key, value) pairs, where the keys are all in lowercase.

In new code, the request_header object should be accessed instead.

method assoc_req_header : string -> string

Query a specific header entry, or raise Not_found

method assoc_multi_req_header : string -> string list

Return all header values for a given field name (header entries which allow several values separated by commas can also be transmitted by several header lines with the same name).

method set_req_header : string -> string -> unit
method get_resp_header : unit -> (string * string) list

Deprecated. Get the header of the last response. The keys are in lowercase characters again.

method assoc_resp_header : string -> string

Query a specific header entry of the response.

method assoc_multi_resp_header : string -> string list

Return all response header values for a given field name (header entries which allow several values separated by commas can also be transmitted by several header lines with the same name).

method get_resp_body : unit -> string

Deprecated. Returns the body of the last response if the response status is OK (i.e. the code is in the range 200 to 299).

Otherwise, Http_error (code, body) is raised where 'code' is the response code and 'body' is the body of the (errorneous) response.

method dest_status : unit -> string * int * string

Returns the status line of the last response (but status lines with code 100 are ignored). The returned triple is (http_string, code, text)


method private_api : private_api

The container for HTTP calls

class type transport_channel_type =
method setup_e : Unix.file_descr -> channel_binding_id -> float -> exn -> string -> int -> Unixqueue.event_system -> (Uq_engines.multiplex_controller * Http_client_conncache.private_data) Uq_engines.engine

setup fd cb tmo tmo_x host port esys: Create or configure a communication circuit over the file descriptor fd that can be driven by the returned multiplex controller object. Since OCamlnet-3.8, the method can also return private data for the connection cache.

tmo is the timeout. After inactivity the exception tmo_x must be raised.

host is the name of the machine to connect to. port is the port number. The descriptor fd is already connected to this port, directly or via a proxy.

method continue : Unix.file_descr -> channel_binding_id -> float -> exn -> string -> int -> Unixqueue.event_system -> Http_client_conncache.private_data -> Uq_engines.multiplex_controller

continue is called when an already established circuit needs to be continued.

Note that the event system can be different now.

If it is not possible to continue, the method may raise Not_found.

method default_port : int option

If set, the Host header omits this port number

HTTP methods

class virtual generic_call :
inherit http_call
method private virtual fixup_request : unit -> unit

This method is called just before sending the request. It can fix up things in the `Effective request header.

method private virtual def_request_method : string

The following methods define the values for the corresponding methods without the def_ prefix:

method private virtual def_empty_path_replacement : string
method private virtual def_is_idempotent : bool
method private virtual def_has_req_body : bool
method private virtual def_has_resp_body : bool

This class is an implementation of http_call. A subclass must define the virtual methods that mostly define the general properties of the HTTP method.

The following classes are implementations for the various HTTP methods. These classes do not initialize the call object.

class get_call : http_call
class trace_call : http_call
class options_call : http_call
class head_call : http_call
class post_call : http_call
class put_call : http_call
class delete_call : http_call

The following classes initialize the request message of the call (header and body). These classes are also backward compatible to the classes found in earlier versions of netclient.

class get : string -> http_call

Argument: URI

class trace : string -> int -> http_call

Arguments: URI, maximum number of hops

class options : string -> http_call

Argument: URI or "*"

class head : string -> http_call

Argument: URI

class post : string -> (string * string) list -> http_call

Arguments: URI, parameter list to be transferred as application/x-www-form-urlencoded body

class post_raw : string -> string -> http_call

Arguments: URI, body

class put : string -> string -> http_call

Arguments: URI, body

class delete : string -> http_call

Argument: URI


class type key =
method user : string

The user name

method password : string

The password in cleartext

method realm : string

The realm

method domain : string list

The domain URIs defining the protection space. The domain URIs are absolute URIs. The list must not be empty for content accesses. For proxy keys the list must be empty.

Normally, this is just a list with one element. The URI must include the protocol scheme, the host name, and "/" as path. The port number is optional. Example: "http://localhost/". If the key is applicable to all domains, set this to "*".

A key is a user/password combination for a certain realm

val key : user:string -> password:string -> realm:string -> domain:string list -> key

Create a key object

class type key_handler =
method inquire_key : domain:string list -> realms:string list -> auth:string -> key

The method is called when a new session must be authenticated. The domain is the URI list describing the protection space. URIs currently have the form "http://host:port/path", i.e. the port is always written out. The realms parameter is a list of realm identifiers. In auth the name of the authentication method is passed (lowercase characters). The method must search (or query for) a key, and return it. The key must refer to one of the passed realms. The domain of the key must be exactly the same as the passed domain (unless domain=["*"]). If the method raises Not_found, authentication will fail.

method invalidate_key : key -> unit

The handler is notified that authentication failed for this key

class key_ring : ?uplink:key_handler option -> unit ->
inherit key_handler
method clear : unit -> unit

Deletes all keys from this key ring

method add_key : key -> unit

Adds a key to the ring

method keys : key list

List of all known keys

The key_ring is a cache for keys. The optional uplink handler is invoked when no matching key is found in the cache.

class type auth_session =
method auth_scheme : string

The authentication scheme, e.g. "basic"

method auth_domain : Neturl.url list

The list of domain URIs defines the protection space.

Change: Since Ocamlnet-3.3, this is a list of Neturl.url, and no longer a list of strings.

method auth_realm : string

The realm

method auth_user : string

The user identifier

method auth_in_advance : bool

Whether "authentication in advance" is enabled

method authenticate : http_call -> (string * string) list

Returns a list of additional headers that will authenticate the passed call for this session. (This is usually only one header, authorization.)

If the call is authenticated in advance, it does not contain any authentication information. If the call is authenticated in reaction to a 401 status, the response header contains the www-authenticate field(s).

method invalidate : http_call -> bool

The session is notified that authentication failed. (This method is not called for authentication-in-advance, but only if an authentication attempt after a 401 status failed.) The method can return true if another authentication should be started immediately.

Note: By returning true the session can indicate a "stale" condition in the sense of RFC 2617.

An auth_session represents an authenticated session

class type auth_handler =
method create_session : http_call -> http_options Pervasives.ref -> auth_session option

Create a new authentication session. The passed call has status 401.

method create_proxy_session : http_call -> http_options Pervasives.ref -> auth_session option

Same for proxy authentication

method skip_challenge : string option

If non-None, this method allows to skip the challenge entirely for authentication. This means that the credentials are added to the HTTP request before any previous response was seen from the server. This adds additional security risks, and may cause that credentials are sent to servers that forge their identity. This is only supported for basic authentication. The string describes the URL space to which this applies (e.g. "http://the-server/subdir"). Set the string to "*" to enable everywhere. As no challenge is known, the realm string is simply assumed to be "anywhere".

method skip_challenge_session : http_call -> http_options Pervasives.ref -> auth_session option

Create a session for the case that the challenge was skipped

An authentication handler has the capability of adding the necessary headers to messages.

class basic_auth_handler : ?enable_auth_in_advance:bool option -> ?skip_challenge:string option option -> key_handler -> auth_handler

Basic authentication. Authentication information is obtained by the passed key_handler.

enable_auth_in_advance: If set to true, a quicker authentication mode is enabled: when a request is sent out, it is checked whether a previous request/response cycle exists that needed authentication. If so, the same credentials are added to the request. Normally, the request would be sent without credentials first, and only after getting the authentication challenge the request is resent with the credentials.

skip_challenge: This option enables a mode so that the credentials are added to HTTP requests even before any response has been seen by the server. This adds additional security risks, and may cause that credentials are sent to servers that forge their identity. The string describes the URL space to which this applies (e.g. "http://the-server/subdir"). Set the string to "*" to enable everywhere. As no challenge is known, the realm string is simply assumed to be "anywhere".

class digest_auth_handler : ?enable_auth_in_advance:bool option -> key_handler -> auth_handler

Digest authentication. Authentication information is obtained by the passed key_handler.

This handler is compatible with RFC 2069 and RFC 2617. In particular, the following protocol options are available:

  • The algorithms MD5 and MD5-sess are implemented
  • The quality of protection mode "auth" is implemented. The optional mode "auth-int" has been omitted.
  • The information of the Authentication-Info header is completely ignored

enable_auth_in_advance: If set to true, authentication can be done in advance, i.e. before the server requests authentication. This reduces the number of messages exchanged with the server, but may be an additional security risk.

class unified_auth_handler : key_handler -> auth_handler

Support both digest and basic authentication, with preference to digest.

Note that there is no way of authenticating in advance, as it is not known in advance which mechanism is used.

class basic_auth_method :
method name : string
method set_realm : string -> string -> string -> unit
method as_auth_handler : auth_handler

Deprecated. For (limited) backwards compatibility:

class digest_auth_method : basic_auth_method

Deprecated. For (limited) backwards compatibility:


A connection cache is an object that keeps connections open that are currently unused. A connection cache can be shared by several pipelines.

type connection_cache = Http_client_conncache.connection_cache
val close_connection_cache : connection_cache -> unit

Closes all descriptors known to the cache

val create_restrictive_cache : unit -> connection_cache

A restrictive cache closes connections as soon as there are no pending requests.

val create_aggressive_cache : unit -> connection_cache

This type of cache tries to keep connections as long open as possible. The consequence is that users are responsible for closing the descriptors (by calling close_connection_cache) when the cache is no longer in use.

val http_cb_id : channel_binding_id

Identifies a channel binding to pure HTTP (without SSL), with or without web proxies

val https_cb_id : channel_binding_id

Identifies a channel binding to anonymous HTTPS (i.e. no client certificates), with or without web proxies.

val proxy_only_cb_id : channel_binding_id

Identifies a channel binding to web proxy connections. Use this to e.g. send an FTP URL to a web proxy via HTTP

val new_cb_id : unit -> channel_binding_id

Allocates and returns a new ID

val http_transport_channel_type : transport_channel_type

Transport via HTTP

type proxy_type = [
| `Http_proxy
| `Socks5


class pipeline :

A pipeline object is a FIFO queue of HTTP calls. It is called "pipeline" because it is processed asynchronously: Requests may be sent to the HTTP server independently of whether responses of the previous requests already arrived or not.

Furthermore, a pipeline object may keep connections to several servers at once. (More exactly, it has a FIFO queue for every server it is connected with.)

The pipeline object keeps track what is happening, so you need not to care about the details of communications. The API is simple: Create a pipeline object, do some setup (add authentication methods; configure the proxy to use), add the requests, and run the pipeline. The rest is done automatically. To get the results, you can either memorize the requests you wanted to know yourself and ask every request object about the reply of the server; or you can specify that a callback function should be called once the request is processed (with positive or negative result). It is possible to add further requests to the pipeline from within these callback functions.

If you want to have several pipelines, or some cooperation with other network services, you may specify a Unixqueue.event_system. For example, to have two pipelines working concurrently:

       let ues = Unixqueue.create_unix_event_system() in
       let p1 = new pipeline in
       let p2 = new pipeline in
       p1 # set_event_system ues;
       p2 # set_event_system ues;
       Unixqueue.run ues             (* run p1 and p2 in parallel *)

This works not only with pipelines, but with every network client or server which is compatible with the Unixqueue design.

By default, the pipeline only supports "http" URLs. You can configure "https" support via [root:Https_client].

method event_system : Unixqueue.event_system

Returns the event system

method set_event_system : Unixqueue.event_system -> unit

Sets the event system. Must be called before the first call is added

method connection_cache : connection_cache

The current connection cache. By default, a private restrictive cache is used.

method set_connection_cache : connection_cache -> unit

Set the connection cache. This must happen before the first call is added.

method add_authentication_method : basic_auth_method -> unit

adds an old-style authentication method

method add_auth_handler : auth_handler -> unit

adds a new-style authentication handler

method set_proxy : string -> int -> unit

set_proxy name port: sets that an HTTP proxy name listening on port is to be used

method set_proxy_auth : string -> string -> unit

sets user and password for the proxy. Works for both "digest" and "basic" mechanisms. Any realm is acceptable.

method avoid_proxy_for : string list -> unit

sets a list of host names or domain suffixes for which no proxy should be used. e.g. "localhost"; ".our.net"

method set_proxy_from_environment : unit -> unit

Inspect the environment variables http_proxy and no_proxy and set the proxy options from them.

method set_socks5_proxy : string -> int -> unit

Sets that a SOCKS version 5 proxy is used at this host and port. There is no authentication. The avoid_proxy_for setting is honoured.

method configure_transport : channel_binding_id -> transport_channel_type -> unit

configure_transport id transport: Configures that messages with channel binding ID id are exchanged on transport.

By default, there is only a configuration for Http_client.http_cb_id, i.e. for normal unencrypted channels.

method set_transport_proxy : channel_binding_id -> string -> int -> (string * string) option -> proxy_type -> unit

set_transport_proxy id host port auth ptype: Sets a special proxy for the transport identified by id. This overrides set_proxy, set_proxy_auth, and set_socks5_proxy for the given transport.

method set_transport_proxy_from_environment : (string * channel_binding_id) list -> unit

Like set_proxy_from_environment, this method inspects environment variables and configures the proxy settings. This function, however, is more flexible, and can use different environment variables for different transports.

The argument list has pairs (var_name, id) meaning that the environment variable var_name configures the proxy for id. For instance,

[("http_proxy", http_cb_id); ("https_proxy", https_cb_id)]

means that these two variables are used for the respective transports.

The variable "no_proxy" is interpreted anyway.

method reset : unit -> unit

Empties the pipeline and inactivates any open connection. The currently active operation is interrupted, and every request with response is set to No_reply (i.e. you get the exception No_reply if you try to access the response). If there are callbacks for these requests, the callback functions are invoked. The queues of open requests and replies are cleared. All connections to all servers are inactivated.

Inactivation means that open connections are given back to the connection cache for further reuse if the state of the connection allows this; otherwise the connections are closed.

method add : http_call -> unit

Adds the call to the end of the pipeline. One must not add calls that have already been served.

method add_with_callback : http_call -> (http_call -> unit) -> unit

Adds the call to the end of the pipeline.

After the call has been processed, the callback function is called. This function is called for every call that leaves the pipeline, it does not matter whether processing was successful or not. Invoke status on the message to get what happened; either some status information from the server is available (perhaps OK status), or an exception is indicated.

method add_e : http_call -> http_call Uq_engines.engine

The same as engine: The call c is added to the pipeline, and when it is processed, the returned engine transitions to the state `Done c.

method proxy_type : string -> proxy_type option

proxy_type url returns Some pt if a proxy would be used for this url, and None if a direct connection would be made.

method proxy_type_of_call : http_call -> proxy_type option

Same for an already created call object

method channel_binding : http_call -> channel_binding_id

Reports the current channel binding of this call

method run : unit -> unit

Runs through the requests in the pipeline. If a request can be fulfilled, i.e. the server sends a response, the state of the request is set and the request is removed from the pipeline. If a request cannot be fulfilled (no response, bad response, network error), the exception is stored in the http_call object and will be raised once the state of the object is queried.

Under certain conditions (serious network errors) run does not catch the exception; it simply cleans its own state up (aborting the errorneous network connection). In this case, simply invoke run again to continue. run terminates normally if the pipeline becomes empty.

The engine handles the following HTTP return codes itself:

  • 100: This is an intermediate return code
  • 301: The redirection is followed if configured
  • 302: The redirection is followed if configured
  • 401: Content server authentication
  • 407: Proxy server authentication

All other return codes remain uninterpreted, it is up to the caller of this function to react on them.

method get_options : http_options
method set_options : http_options -> unit

Get/Set the available options for the HTTP engine. The new options will take into effect immediately.

method number_of_open_messages : int

Returns the number of messages which are still in the pipeline.

method number_of_open_connections : int

Returns the number of connections which are open at the same time and currently being used by this object (i.e. connections returned to the cache do not count)

method connections : (string * int * int) list

Reports which connections exist: (host, port, queue_length)

method cnt_new_connections : int

Counts new connections (or better: attempts to establish connections)

method cnt_timed_out_connections : int

Counts connections given up because of timeouts

method cnt_crashed_connections : int

Counts connections with network or protocol errors

method cnt_server_eof_connections : int

Counts connections the server terminated with EOF

method cnt_successful_connections : int

Counts connections closed because pipelines become empty

method cnt_failed_connections : int

Counts totally failed connections (no more reconnects allowed)

method reset_counters : unit -> unit

Notes on counters:

  • cnt_new_connections: Is increased when a new connection attempt is started (that may fail or timeout in the future). Reconnects do not count.
  • cnt_timed_out_connections: Is increased whenever an established connection times out. Usually, it is immediately reconnected.
  • cnt_crashed_connections: Is increased whenever an established connection crashes. Usually, it is immediately reconnected.
  • cnt_failed_connections: Is increased when a timed out or crashed connection exceeds the maximum number of errors, and it is not tried to reconnect.
  • cnt_successful_connections: Is increased when all HTTP calls have been replied.

When the client has done all of its jobs, we have

cnt_new_connections = cnt_failed_connections + cnt_successful_connections

A pipeline is a queue of HTTP calls to perform

Example using the pipeline:

    let call = new get "http://server/path" in
    let pipeline = new pipeline in
    pipeline # add call;
    pipeline # run();    (* Now the HTTP client is working... *)
    match call # status with
    | `Successful -> ...
    | ...

Auxiliary pipeline functions

val parse_proxy_setting : string -> string * int * (string * string) option

Parses the value of an environment variable like http_proxy, i.e. an HTTP URL. The argument is the URL. Returns (host,port,auth) where auth may include user name and password.

val parse_no_proxy : string -> string list

Parses the value of an environment variable like no_proxy. Returns the list of domains.

Convenience module for simple applications

Do open Http_client.Convenience for simple applications.

module Convenience : sig

Convenience module for simple applications

Do open Http_client.Convenience for simple applications.

The functions of this module share the following behaviour:

The environment variables http_proxy and no_proxy determine the proxy settings. http_proxy must be an http-URL that contains the proxy's name, its port, and optionally user and password. E.g. "http://eric:ericspassword@proxy:8080/". The variable no_proxy is a comma-separated list of hosts and domains for which no proxy must be used. E.g. "localhost, sun, moon, .intra.net"

There is a default behaviour for authentication. Both "basic" and "digest" methods are enabled. Two global variables, http_user and http_password set the user and password if the URL does not specify them. In the case that user and password are included in the URL, these values are always used.

There is a default error behaviour. If a request fails, it is automatically repeated. The variable http_trials specifies the number of times a request is submitted at most. Requests are not repeated if there is a HTTP return code that indicates a normal operating condition. POST and DELETE requests are never repeated.

Error codes are reported as Http_client.Http_error. Note that this is different than what the pipeline core does.

"https" support can be additionally configured via [root:Https_client].

Thread safety

The Convenience module is fully thread-safe with the exception of the exported variables (http_trials, http_user, and http_password). Note that all threads share the same pipeline, and access to the pipeline is serialized. The latter simply means that it always works, but that threads may block each other (i.e. the program slows down if more than one thread wants to open http connections at the same time).

val http_trials : int Pervasives.ref

number of times every request is tried. Default: 3

val http_user : string Pervasives.ref

The default user if authentication is required

val http_password : string Pervasives.ref

The default password if authentication is required

val configure_pipeline : (pipeline -> unit) -> unit

This function will be called before the pipeline is used. This is intended for fine-grained configuration.

val http_get_message : string -> http_call

Does a "GET" request with the given URL and returns the message

val http_head_message : string -> http_call

Does a "HEAD" request with the given URL and returns the reply.

val http_post_message : string -> (string * string) list -> http_call

Does a "POST" request with the given URL and returns the reply. The list contains the parameters sent with the POST request.

val http_put_message : string -> string -> http_call

Does a "PUT" request with the given URL and returns the reply. The second argument contains the contents to be put.

val http_delete_message : string -> http_call

Does a "DELETE" request with the given URL and returns the reply.

val http_get : string -> string

Does a "GET" request with the given URL and returns the message body

val http_post : string -> (string * string) list -> string

Does a "POST" request with the given URL and returns the response body. The list contains the parameters send with the POST request.

val http_put : string -> string -> string

Does a "PUT" request with the given URL and returns the response body. The second argument contains the contents to be put.

val http_delete : string -> string

Does a "DELETE" request with the given URL and returns the response body.

val http_verbose : ?verbose_status:bool -> ?verbose_request_header:bool -> ?verbose_response_header:bool -> ?verbose_request_contents:bool -> ?verbose_response_contents:bool -> ?verbose_connection:bool -> ?verbose_events:bool -> unit -> unit

Turns on debug messages on stderr. By default, all options are turned on.



module Debug : sig
val enable : bool Pervasives.ref

Enables [root:Netlog]-style debugging of this module