Send file

18.4.0 released Sep 25, 2023

Send file

Purpose: Send file to client.

send-file <file> [ headers \
    [ content-type <content type> ] \
    [ download [ <download> ] ] \
    [ etag [ <etag> ] ] \
    [ file-name <file name> ] \
    [ ( cache-control <cache control> ) | no-cache ] \
    [ status-id <status id> ] \
    [ status-text <status text> ] \
    [ custom <header name>=<header value> [ , ... ] ]
    ]

When a client requests download of a file, you can use send-file to provide <file>, which is its location on the server, and is either a full path or relative to the application home directory (see vv). Note however that you can never use dot-dot (i.e. "..") in <file> - this is a security measure to avoid path-traversal attacks. Thus the file name should never have ".." in it, and if it does, the program will error out and stop.

Headers

The following are subclauses that allow setting any custom header:

<content type> is content type (such as "text/html" or "image/jpg" etc.) If you are sending a file to a client for download and you don't know its content type, you can use "application/octet-stream" for a generic binary file.
If "download" is used without optional boolean expression <download>, or if <download> evaluates to true, then the file is sent to a client for downloading - otherwise the default is to display file in client.
<file name> is the name of the file being sent to a client. This is not the local file name - it is the file name that client will use for its own purposes.
<cache control> is the cache control HTTP header. "no-cache" instructs the client not to cache. Only one of "cache-control" and "no-cache" can be used. An example of <cache control>:
```
send-file "somepic.jpg" headers cache-control "max-age: 3600"
```
If "etag" is used without optional boolean expression <etag>, or if <etag> evaluates to true, then "ETAG" header will be generated (a timestamp) and included, otherwise it is not. The time stamp is of last modification date of the file (and typically used to cache a file on client if it hasn't changed on the server). "etag" is useful to let the client know to download the file only once if it hasn't changed, thus saving network and computing resources.
<status id> and <status text> are status settings for the response (such as "425" for "status-id" and "Too early" for "status-text").
To set any type of generic HTTP header, use "custom" subclause, where <header name> and <header value> represent the name and value of a single header. Multiple headers are separated by a comma. There is no limit on the maximum number of such headers, other than of the underyling HTTP protocol. You must not use "custom" to set headers already set elsewhere (such as "etag" for instance), as that may cause unpredictable behavior. For instance this sets two custom headers:
```
out-header use custom "CustomOption3"="CustomValue3", "Status"="418 I'm a teapot"
```
"custom" subclause lets you use any custom headers that exist today or may be added in the future, as well as any headers of your own design.

Any cookies set prior to send-file (see set-cookie and delete-cookie) will be sent along with the file to the web client.

Examples

To send a document back to the browser and show it, use send-file with the "show" clause:

send-file "/home/vely/files/myfile.jpg" headers content-type "image/jpg"

An example to display a PDF document:

char *pdf_doc="/home/mydir/myfile.pdf";
send-file pdf_doc headers content-type "application/pdf"

If you want to send a file to the client for download (with the dialog), use "download" clause. This way the document is not displayed but the "Save As" (or similar) window shows up, for example to download a "PDF" document:

send-file "/home/user/file.pdf" headers download content-type "application/pdf"