debug: add a 'debugdownload' command

This command resolve and fetch and URL through the Mercurial logic. Mercurial
logic add various headers (including authentication) while resolving an URL so
the commands helps with building the same request Mercurial would be doing.

A new test file is created because we'll add more logic regarding Mercurial
download logic and it will grow to a reasonable size.

tests/test-url-download.t

@@ -0,0 +1,36 b''
+#require serve
+
+  $ hg init server
+  $ hg serve -R server -p $HGPORT -d --pid-file=hg1.pid -E ../error.log
+  $ cat hg1.pid >> $DAEMON_PIDS
+
+Check basic fetching
+
+  $ hg debugdownload "http://localhost:$HGPORT/?cmd=lookup&key=tip"
+  1 0000000000000000000000000000000000000000
+  $ hg debugdownload  -o null.txt "http://localhost:$HGPORT/?cmd=lookup&key=null"
+  $ cat null.txt
+  1 0000000000000000000000000000000000000000
+
+Check the request is made from the usual Mercurial logic
+(rev details, give different content if the request has a Mercurial user agent)
+
+  $ get-with-headers.py --headeronly "localhost:$HGPORT" "rev/tip" content-type
+  200 Script output follows
+  content-type: text/html; charset=ascii
+  $ hg debugdownload "http://localhost:$HGPORT/rev/tip"
+  
+  # HG changeset patch
+  # User 
+  # Date 0 0
+  # Node ID 0000000000000000000000000000000000000000
+  
+  
+  
+  
+
+Check other kind of compatible url
+
+  $ hg debugdownload ./null.txt
+  1 0000000000000000000000000000000000000000
+

mercurial/debugcommands.py

@@ -69,6 +69,7 b' from . import ('
     templater,
     treediscovery,
     upgrade,
+    url as urlmod,
     util,
     vfs as vfsmod,
 )
@@ -786,6 +787,30 b' def debugdiscovery(ui, repo, remoteurl="'
     localrevs = opts['rev']
     doit(localrevs, remoterevs)
 
+_chunksize = 4 << 10
+
+@command('debugdownload',
+    [
+        ('o', 'output', '', _('path')),
+    ],
+    norepo=True)
+def debugdownload(ui, url, output=None, **opts):
+    """download a resource using Mercurial logic and config
+    """
+    fh = urlmod.open(ui, url, output)
+
+    dest = ui
+    if output:
+        dest = open(output, "wb", _chunksize)
+    try:
+        data = fh.read(_chunksize)
+        while data:
+            dest.write(data)
+            data = fh.read(_chunksize)
+    finally:
+        if output:
+            dest.close()
+
 @command('debugextensions', cmdutil.formatteropts, [], norepo=True)
 def debugextensions(ui, **opts):
     '''show information about active extensions'''

tests/test-completion.t

@@ -85,6 +85,7 b' Show debug commands if there are no othe'
   debugdeltachain
   debugdirstate
   debugdiscovery
+  debugdownload
   debugextensions
   debugfileset
   debugformat
@@ -263,6 +264,7 b' Show all commands + options'
   debugdeltachain: changelog, manifest, dir, template
   debugdirstate: nodates, datesort
   debugdiscovery: old, nonheads, rev, ssh, remotecmd, insecure
+  debugdownload: output
   debugextensions: template
   debugfileset: rev
   debugformat: template

tests/test-help.t

@@ -919,6 +919,8 b' Test list of internal help commands'
                  show the contents of the current dirstate
    debugdiscovery
                  runs the changeset discovery protocol in isolation
+   debugdownload
+                 download a resource using Mercurial logic and config
    debugextensions
                  show information about active extensions
    debugfileset  parse and apply a fileset specification