Module Netmime_channels

Decodes the MIME header that begins at the current position of the netstream, and returns the header as class basic_mime_header. After returning, the stream is advanced to the byte following the empty line terminating the header.

Example: To read the header at the beginning of the file "f", use:

 
 let ch = new Netchannels.input_channel (open_in "f") in
 let stream = new Netstream.input_stream ch in
 let h = read_mime_header stream in
 ...
 stream#close_in();    (* no need to close ch *)
 

Note that although the stream position after parsing is exactly known, the position of ch cannot be predicted.

How to parse multipart messages:

• `None: Do not handle multipart messages specially. Multipart bodies are not further decoded, and returned as `Body b where b is the transfer-encoded text representation.
• `Flat: If the top-level message is a multipart message, the parts are separated and returned as list. If the parts are again multipart messages, these inner multipart messages are not furher decoded and returned as `Body b.
• `Deep: Multipart messages are recursively decoded and returned as tree structure.

This value determines how far the complex_mime_message structure is created for a parsed MIME message. `None means that no parts are decoded, and messages have always only a simple `Body b, even if b is in reality a multi-part body. With `Flat, the top-level multi-part bodies are decoded (if found), and messages can have a structured `Parts [_, `Body b1; _, `Body b1; ...] body. Finally, `Deep allows that inner multi-part bodies are recursively decoded, and messages can have an arbitrarily complex form.

let ch' = decode_mime_body hdr ch: According to the value of the Content-transfer-encoding header field in hdr the encoded MIME body written to ch' is decoded and transferred to ch.

Handles 7bit, 8bit, binary, quoted-printable, base64.

Example: The file "f" contains base64-encoded data, and is to be decoded and to be stored in "g":

 
 let ch_f = new Netchannels.input_channel (open_in "f") in
 let ch_g = new Netchannels.output_channel (open_out "g") in
 let hdr = new basic_mime_header ["content-transfer-encoding", "base64" ] in
 let ch = decode_mime_body hdr ch_g in
 ch # output_channel ch_f;
 ch # close_out();
 ch_g # close_out();
 ch_f # close_in();
 

Note: This function is internally used by read_mime_message to decode bodies. There is usually no need to call it directly.

Creates a new storage facility for a mime body according to store. This function can be used to build the storage_style argument of the class read_mime_message (below). For example, this is useful to store large attachments in external files, as in:

 
 let storage_style hdr = 
   let filename = hdr ... (* extract from hdr *) in
   storage (`File filename)
 

Decodes the MIME message that begins at the current position of the passed netstream. It is expected that the message continues until EOF of the netstream.

Multipart messages are decoded as specified by multipart_style (see above).

Message bodies with content-transfer-encodings of 7bit, 8bit, binary, base64, and quoted-printable can be processed. The bodies are stored without content-transfer-encoding (i.e. in decoded form), but the content-transfer-encoding header field is not removed from the header.

The storage_style function determines where every message body is stored. The corresponding header of the body is passed to the function as argument; the result of the function is a pair of a new mime_body and an out_obj_channel writing into this body. You can create such a pair by calling storage (above).

By default, the storage_style is storage ?ro `Memory for every header. Here, the designator `Memory means that the body will be stored in an O'Caml string. The designator `File fn would mean that the body will be stored in the file fn. The file would be created if it did not yet exist, and it would be overwritten if it did already exist.

Note that the storage_style function is called for every non-multipart body part.

Large message bodies (> maximum string length) are supported if the bodies are stored in files. The memory consumption is optimized for this case, and usually only a small constant amount of memory is needed.

Example:

Parse the MIME message stored in the file f:

 let m = read_mime_message 
           (new input_stream (new input_channel (open_in f)))
 

let ch' = encode_mime_body hdr ch: According to the value of the Content-transfer-encoding header field in hdr the unencoded MIME body written to ch' is encoded and transferred to ch.

Handles 7bit, 8bit, binary, quoted-printable, base64.

For an example, see decode_mime_body which works in a similar way but performs decoding instead of encoding.

Writes the MIME message to the output channel. The content-transfer- encoding of the leaves is respected, and their bodies are encoded accordingly. The content-transfer-encoding of multipart messages is always "fixed", i.e. set to "7bit", "8bit", or "binary" depending on the contents.

The function fails if multipart messages do not have a multipart content type field (i.e. the content type does not begin with "multipart"). If only the boundary parameter is missing, a good boundary parameter is added to the content type. "Good" means here that it is impossible that the boundary string occurs in the message body if the content-transfer-encoding is quoted-printable or base64, and that such an occurrence is very unlikely if the body is not encoded. If the whole content type field is missing, a "multipart/mixed" type with a boundary parameter is added to the printed header.

Note that already existing boundaries are used, no matter whether they are of good quality or not.

No other header fields are added, deleted or modified. The mentioned modifications are _not_ written back to the passed MIME message but only added to the generated message text.

It is possible in some cases that the boundary does not work (both the existing boundary, and the added boundary). This causes that a wrong and unparseable MIME message is written. In order to ensure a correct MIME message, it is recommended to parse the written text, and to compare the structure of the message trees. It is, however, very unlikely that a problem arises.

Note that if the passed message is a simple message like (_,`Body _), and if no content-transfer-encoding is set, the written message might not end with a linefeed character.