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pcp updates: a few more pmwebd patches

To: pcp developers <pcp@xxxxxxxxxxx>
Subject: pcp updates: a few more pmwebd patches
From: "Frank Ch. Eigler" <fche@xxxxxxxxxx>
Date: Sun, 27 Dec 2015 13:34:13 -0500
Delivered-to: pcp@xxxxxxxxxxx
User-agent: Mutt/1.4.2.2i
Hi -

Also on pcpfans.git fche/pmwebd:

commit 8c9ddae0b3ee7ce4cbe7e8c446ea516d6fe7a02a
Author: Frank Ch. Eigler <fche@xxxxxxxxxx>
Date:   Sun Dec 27 13:31:53 2015 -0500

    pmwebd: graphite/png mode: add units/sem to legend
    
    Tweak the graphite/png rendering mode to add metric units, and tweak
    chart dimensions to match closer the javascript-drawn versions.
    Hand-tested, as QA cannot analyze image contents.

commit 2502fe758e8569ccf6762266d88bd8278559d924
Author: Frank Ch. Eigler <fche@xxxxxxxxxx>
Date:   Sun Dec 27 12:12:48 2015 -0500

    pmwebd: enable graphite image-mode caching via redirection
    
    The graphite web-api allows relative time specifications (e.g.,
    from=-2hr until=now).  When rendered into a png, this allows a web
    browser to cache those images for reuse later, by which time the "now"
    is no longer current.  Even emitting various cache-defeating http
    headers has not proven reliable in preventing this.
    
    So now we defeat this unwanted caching by emitting a HTTP 302 redirect
    for PNG rendering requests that are suspected to include relative-time
    coordinates, turning them into absolute (epoch-seconds) requests.
    The PNGs resulting from those requests are more safely cachable.
    
    While testing in the vicitity, it turns out that the %HEX quoting used
    in "pmwebd -X" appears to awaken a latent graphite/graphlot webapp bug
    in terms of buggy urlencoding of metric names.  So we switch to ~HEX,
    since the tilde ~ character is not a "reserved character" in RFC3986,
    so does not need encoding.

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