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0c37925642
The options were added to allow developers to fix timeout issues when reading large bodies. It is also a cleaner and easier to extend interface. This commit deprecates the functions init_stream, stream_body and skip_body which are no longer needed. They will be removed in 1.0. The body function can now take an additional argument that is a list of options. The body_qs, part and part_body functions can too and simply pass this argument down to the body call. There are options for disabling the automatic continue reply, setting a maximum length to be returned (soft limit), setting the read length and read timeout, and setting the transfer and content decode functions. The return value of the body and body_qs have changed slightly. The body function now works similarly to the part_body function, in that it returns either an ok or a more tuple depending on whether there is additional data to be read. The body_qs function can return a badlength tuple if the body is too big. The default size has been increased from 16KB to 64KB. The default read length and timeout have been tweaked and vary depending on the function called. The body function will now adequately process chunked bodies, which means that the body_qs function will too. But this means that the behavior has changed slightly and your code should be tested properly when updating your code. The body and body_qs still accept a length as first argument for compatibility purpose with older code. Note that this form is deprecated and will be removed in 1.0. The part and part_body function, being new and never having been in a release yet, have this form completely removed in this commit. Again, while most code should work as-is, you should make sure that it actually does before pushing this to production.
119 lines
3.5 KiB
Markdown
119 lines
3.5 KiB
Markdown
Multipart requests
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==================
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You can read and parse multipart messages using the
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Req object directly.
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Cowboy defines two functions that allows you to get
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information about each part and read their contents.
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Checking the content-type
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-------------------------
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While there is a variety of multipart messages, the
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most common on the Web is `multipart/form-data`. It's
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the type of message being sent when an HTML form
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allows uploading files.
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You can quickly figure out if a multipart message
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has been sent by parsing the `content-type` header.
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``` erlang
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{ok, {<<"multipart">>, <<"form-data">>, _}, Req2}
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= cowboy_req:parse_header(<<"content-type">>, Req).
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```
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Reading a multipart message
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---------------------------
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To read a message you have to iterate over all its
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parts. Then, for each part, you can inspect its headers
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and read its body.
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``` erlang
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multipart(Req) ->
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case cowboy_req:part(Req) of
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{ok, _Headers, Req2} ->
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{ok, _Body, Req3} = cowboy_req:part_body(Req2),
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multipart(Req3);
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{done, Req2} ->
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Req2
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end.
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```
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Parts do not have a size limit. When a part body is
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too big, Cowboy will return what it read so far and
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allow you to continue if you wish to do so.
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The function `cow_multipart:form_data/1` can be used
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to quickly obtain information about a part from a
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`multipart/form-data` message. This function will
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tell you if the part is for a normal field or if it
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is a file being uploaded.
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This can be used for example to allow large part bodies
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for files but crash when a normal field is too large.
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``` erlang
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multipart(Req) ->
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case cowboy_req:part(Req) of
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{ok, Headers, Req2} ->
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Req4 = case cow_multipart:form_data(Headers) of
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{data, _FieldName} ->
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{ok, _Body, Req3} = cowboy_req:part_body(Req2),
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Req3;
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{file, _FieldName, _Filename, _CType, _CTransferEncoding} ->
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stream_file(Req2)
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end,
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multipart(Req4);
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{done, Req2} ->
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Req2
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end.
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stream_file(Req) ->
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case cowboy_req:part_body(Req) of
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{ok, _Body, Req2} ->
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Req2;
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{more, _Body, Req2} ->
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stream_file(Req2)
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end.
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```
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By default the body chunk Cowboy will return is limited
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to 8MB. This can of course be overriden. Both functions
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can take a second argument, the same list of options that
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will be passed to `cowboy_req:body/2` function.
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Skipping unwanted parts
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-----------------------
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If you do not want to read a part's body, you can skip it.
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Skipping is easy. If you do not call the function to read
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the part's body, Cowboy will automatically skip it when
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you request the next part.
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The following snippet reads all part headers and skips
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all bodies:
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``` erlang
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multipart(Req) ->
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case cowboy_req:part(Req) of
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{ok, _Headers, Req2} ->
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multipart(Req2);
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{done, Req2} ->
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Req2
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end.
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```
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Similarly, if you start reading the body and it ends up
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being too big, you can simply continue with the next part,
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Cowboy will automatically skip what remains.
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Note that the skipping rate may not be adequate for your
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application. If you observe poor performance when skipping,
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you might want to consider manually skipping by calling
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the `cowboy_req:part_body/1` function directly.
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And if you started reading the message but decide that you
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do not need the remaining parts, you can simply stop reading
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entirely and Cowboy will automatically figure out what to do.
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