9.1 library(http/mimepack): Create a MIME message
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Availability::- use_module(library(http/mimepack)).
[det]mime_pack(+Inputs, +Out:stream, ?Boundary)
Pack a number of inputs into a MIME package using a specified or generated boundary. The generated boundary consists of the current time in milliseconds since the epoch and 10 random hexadecimal numbers. Inputs is a list of documents that is added to the mime message. Each element is one of:
Name = Value
Name the document. This emits a header of the form below. The filename is present if Value is of the form file(File). Value may be any of remaining value specifications. 
Content-Disposition: form-data; name="Name"[; filename="<File>"
html(Tokens)
Tokens is a list of HTML tokens as produced by html//1. The token list is emitted using print_html/1.
file(File)
Emit the contents of File. The Content-type is derived from the File using file_mime_type/2. If the content-type is text/_, the file data is copied in text mode, which implies that it is read in the default encoding of the system and written using the encoding of the Out stream. Otherwise the file data is copied binary.
stream(In, Len)
Content is the next Len units from In. Data is copied using copy_stream_data/3. Units is bytes for binary streams and characters codes for text streams.
stream(In)
Content of the stream In, copied using copy_stream_data/2. This is often used with memory files (see new_memory_file/1).
mime(Attributes, Value,[])
Create a MIME header from Attributes and add Value, which can be any of remaining values of this list. Attributes may contain type(ContentType) and/or character_set(CharSet). This can be used to give a content-type to values that otherwise do not have a content-type. For example: 
mime([type(text/html)], '<b>Hello World</b>', [])
mime([], , Parts)
Creates a nested multipart MIME message. Parts is passed as Inputs to a recursive call to mime_pack/2.
Atomic
Atomic values are passed to write/1. This embeds simple atoms and numbers.
Out is a stream opened for writing. Typically, it should be opened in text mode using UTF-8 encoding.
bug
Does not validate that the boundary does not appear in any of the input documents.