scripts/functions: add aria2, a powerfull downloader

aria2 is a powerfull downloader that is capable of chunking and
parallel retrieval.

Due to li;itations in crosstool-NG retrieval facilities, it's not possible
to take fully advantage of aria2. It might happen that, in the future,
those limitations get lifted away, so we can take use features such as
parallel downloading from more than one server at the same time. For now,
it should still speed up downloads thanks to parallel downloading of chunks.

config/global/download.in

@@ -89,7 +89,7 @@ endif # USE_MIRROR
 
 config CONNECT_TIMEOUT
     int
-    prompt "connection timeout"
+    prompt "Connection timeout"
     default 10
     help
       From the curl manual:
@@ -109,6 +109,21 @@ config CONNECT_TIMEOUT
       
       Note that this value applies equally to wget if you have that installed.
 
+config DOWNLOAD_MAX_CHUNKS
+    int
+    prompt "Maximum number of // chunks"
+    default 5
+    range 1 10
+    help
+      If you have aria2 installed, then it will be used to download files.
+      Aria2 can split the download in chunks, and download those chunks in //
+      which can be interesting to speed up the download.
+      
+      On the other hand, using many chunks, or even chunking in general, may
+      be seen by some site admins as being kind of unfair, or even as a DoS.
+      That's why the range of acceptable values is [1..10], and the default
+      is 5 (aria2's default).
+
 config ONLY_DOWNLOAD
     bool
     prompt "Stop after downloading tarballs"

configure

@@ -354,7 +354,7 @@ has_or_abort prog=libtool
              ver='\(GNU libtool.*\) (2[[:digit:]]*\.|1\.6[[:digit:]]*\.|1\.5\.[2-9][[:digit:]]+)'   \
              err="'libtool' 1.5.26 or above was not found"
 has_or_abort prog=stat ver='GNU coreutils'
-has_or_abort prog="curl wget"
+has_or_abort prog="aria2c curl wget"
 has_or_abort prog=cvs
 has_or_abort prog=patch
 has_or_abort prog=tar

scripts/functions

@@ -348,12 +348,31 @@ CT_DoGetFileCurl() {
     || true
 }
 
+# Download using aria2
+# Usage: CT_DoGetFileAria2 <URL>
+CT_DoGetFileAria2() {
+    # Note: comments about curl method (above) are also valid here
+    # Plus: default progress indicator is a single line, so use verbose log
+    #       so that the CT-NG's ouput is 'live'.
+    CT_DoExecLog ALL aria2c -l - -s ${CT_DOWNLOAD_MAX_CHUNKS} -m 3 --retry-wait 5 -t ${CT_CONNECT_TIMEOUT} -p "$1" \
+    || CT_DoExecLog ALL aria2c -l - -s ${CT_DOWNLOAD_MAX_CHUNKS} -m 3 --retry-wait 5 -t ${CT_CONNECT_TIMEOUT} "$1" \
+    || true
+}
+
+# OK, just look if we have them...
+_aria2c=$(CT_Which aria2c)
 _wget=$(CT_Which wget)
 _curl=$(CT_Which curl)
-# Wrapper function to call one of curl or wget
+
+# Wrapper function to call one of, in order of preference:
+#   aria2
+#   curl
+#   wget
 # Usage: CT_DoGetFile <URL>
 CT_DoGetFile() {
-    if   [ -n "${_curl}" ]; then
+    if   [ -n "${_aria2c}" ]; then
+        CT_DoGetFileAria2 "$1"
+    elif [ -n "${_curl}" ]; then
         CT_DoGetFileCurl "$1"
     elif [ -n "${_wget}" ]; then
         CT_DoGetFileWget "$1"