redirect patch for libdap-3.7.6/HTTPConnect.cc

[Rob Cermak]

Here is the small patch that allows for server redirection.

1. Use at your own risk!  This is alpha code.
2. It needs a safety belt.  Does not handle infinite redirection!

http://ak.aoos.org/data/patch/hyrax_redirect.patch

Notes: Feel free to ask Steve any questions about this patch.  As always,
if there is a better way to implement it, please do so.   We are just
glad to help.

_From the 30,000 ft view:

Looks like we hunt for the 'location:' string.  We do not check for 301
or 302 responses.  This string is stored for later and accessible via
get_location method.

Later in the call once all the headers come in, we check if there was a
location passed in the headers and calls fetch_url again (recursively)?.
I get lost in the if statement :)

The result is that GDAL and getdap can find data again with just a few
lines in Apache to perform the redirect.

[cermak at penguin sync]$ curl -I
http://ak.aoos.org/dap/data/FNMOC/sst/latest.nc.bz2.html
HTTP/1.1 302 Found
Date: Thu, 03 May 2007 06:18:19 GMT
Server: Apache/2.2.3 (Mandriva Linux/PREFORK-1mdv2007.0)
Location: http://ak.aoos.org:8080/opendap/FNMOC/sst/latest.nc.bz2.html
Content-Type: text/html; charset=iso-8859-1

[cermak at penguin sync]$ getdap -v -d
http://ak.aoos.org/dap/data/FNMOC/sst/latest.nc.bz2
Fetching: http://ak.aoos.org/dap/data/FNMOC/sst/latest.nc.bz2
DAP version: 3.2, Server version: bes/3.4.1
DDS:
Dataset {
    Float64 lon[lon = 3600];
    Float64 lat[lat = 1586];
    Float64 time[time = 1];
    String ob[time = 1][nob = 19];
    Grid {
      Array:
        Float32 sst[time = 1][lat = 1586][lon = 3600];
      Maps:
        Float64 time[time = 1];
        Float64 lat[lat = 1586];
        Float64 lon[lon = 3600];
    } sst;
} latest.nc;

[cermak at penguin sync]$ gdalinfo
"http://ak.aoos.org/dap/data/FNMOC/sst/latest.nc.bz2?sst[0][y][x]"
Warning 1: I connected to the URL but could not get a DAP 3.x version
string from the server.  I will continue to connect but access may fail.
Driver: DODS/DAP 3.x servers
Size is 3600, 1586
Coordinate System is `'
Origin = (-179.950000000000017,-0.025000000000000)
Pixel Size = (0.100000000000000,0.050000000000000)
Corner Coordinates:
Upper Left  (-179.9500000,  -0.0250000)
Lower Left  (-179.9500000,  79.2750000)
Upper Right ( 180.0500000,  -0.0250000)
Lower Right ( 180.0500000,  79.2750000)
Center      (   0.0500000,  39.6250000)
Band 1 Block=512x128 Type=Float32, ColorInterp=Undefined
  NoData Value=-99999
  Overviews: 1800x793, 900x396, 450x198, 225x99

BES and topcat are setup as per wiki instructions no serious modifications.

The only things needed in Apache are:

RewriteEngine On
RewriteRule ^/dap/data(.*) "http://ak.aoos.org:8080/opendap$1"
RewriteRule ^/opendap/nph-dods/data(.*) "http://ak.aoos.org:8080/opendap$1"

This is the good news.

Rob
-- 
Alaska Ocean Observing System
Data Manager
907-474-7948


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