Try a named GNU mirror before the redirector (#183)

Two hosts turned out to be too few, for a different reason from one being too
few. ftpmirror.gnu.org is a redirector to whichever mirror is near, and the
one it picked answered with an HTTP error:

  -- Using src='https://ftpmirror.gnu.org/gnu/gdb/gdb-15.2.tar.xz'
     error: downloading ... failed
     status_code: 22
     status_string: "HTTP response code said error"

after which the fallback to ftp.gnu.org timed out the way it has all week.

mirrors.kernel.org goes first: it is the same host every time, so it can be
seen to work rather than hoped about. The redirector stays behind it as the
thing that keeps working when that host does not, and ftp.gnu.org stays last.
Checked: kernel.org returns gdb-15.2.tar.xz with the sha256 pinned here.

The test now asks for three hosts, refuses ftp.gnu.org as the first one, and
requires it as the last.

Author: frangarcj

cmake/Components.cmake

@@ -4,18 +4,24 @@ include_guard(GLOBAL)
 # hashes together so version updates cannot accidentally mix artifacts.
 set(GCC_VERSION 15.2.0)
 set(GCC_HASH SHA256=438fd996826b0c82485a29da03a72d71d6e3541a83ec702df4271f6fe025d24e)
-# Everything below that GNU hosts is named twice: ftpmirror.gnu.org first,
-# which is GNU's own redirector to a nearby mirror, and ftp.gnu.org after it.
-# ExternalProject tries them in order and URL_HASH decides whether what came
-# back is the right bytes, so a mirror serving something else fails the same
-# way a corrupt download does.
+# Everything below that GNU hosts is named three times, tried in order:
+# mirrors.kernel.org, then ftpmirror.gnu.org, then ftp.gnu.org. URL_HASH
+# decides whether what came back is the right bytes, so a mirror serving
+# something else fails the way a corrupt download does.
 #
 # One host was one host too few. ftp.gnu.org refused connections for over two
 # minutes at a time through 26 and 27 August, and each time it took a whole
 # build with it -- six components come from there, and gdb is downloaded by
 # every host.
+#
+# Two was also too few, for a different reason: ftpmirror.gnu.org is a
+# redirector to whichever mirror is near, and the one it picked answered with
+# an HTTP error. A named mirror goes first because it is the same host every
+# time and can be seen to work; the redirector stays behind it as the thing
+# that keeps working when that host does not.
 
 set(GCC_URL
+    https://mirrors.kernel.org/gnu/gcc/gcc-${GCC_VERSION}/gcc-${GCC_VERSION}.tar.xz
     https://ftpmirror.gnu.org/gnu/gcc/gcc-${GCC_VERSION}/gcc-${GCC_VERSION}.tar.xz
     https://ftp.gnu.org/gnu/gcc/gcc-${GCC_VERSION}/gcc-${GCC_VERSION}.tar.xz)
 
@@ -34,18 +40,21 @@ set(LIBYAML_URL https://pyyaml.org/download/libyaml/yaml-${LIBYAML_VERSION}.tar.
 set(GMP_VERSION 6.3.0)
 set(GMP_HASH SHA256=ac28211a7cfb609bae2e2c8d6058d66c8fe96434f740cf6fe2e47b000d1c20cb)
 set(GMP_URL
+    https://mirrors.kernel.org/gnu/gmp/gmp-${GMP_VERSION}.tar.bz2
     https://ftpmirror.gnu.org/gnu/gmp/gmp-${GMP_VERSION}.tar.bz2
     https://ftp.gnu.org/gnu/gmp/gmp-${GMP_VERSION}.tar.bz2)
 
 set(MPFR_VERSION 4.2.2)
 set(MPFR_HASH SHA256=9ad62c7dc910303cd384ff8f1f4767a655124980bb6d8650fe62c815a231bb7b)
 set(MPFR_URL
+    https://mirrors.kernel.org/gnu/mpfr/mpfr-${MPFR_VERSION}.tar.bz2
     https://ftpmirror.gnu.org/gnu/mpfr/mpfr-${MPFR_VERSION}.tar.bz2
     https://ftp.gnu.org/gnu/mpfr/mpfr-${MPFR_VERSION}.tar.bz2)
 
 set(MPC_VERSION 1.3.1)
 set(MPC_HASH SHA256=ab642492f5cf882b74aa0cb730cd410a81edcdbec895183ce930e706c1c759b8)
 set(MPC_URL
+    https://mirrors.kernel.org/gnu/mpc/mpc-${MPC_VERSION}.tar.gz
     https://ftpmirror.gnu.org/gnu/mpc/mpc-${MPC_VERSION}.tar.gz
     https://ftp.gnu.org/gnu/mpc/mpc-${MPC_VERSION}.tar.gz)
 
@@ -61,12 +70,14 @@ set(EXPAT_URL https://github.com/libexpat/libexpat/releases/download/R_2_3_0/exp
 set(BINUTILS_VERSION 2.46.1)
 set(BINUTILS_HASH SHA256=e127a709cba24c76de8936cb7083dd768f28cd37eb010492e2f19b71eb1294e4)
 set(BINUTILS_URL
+    https://mirrors.kernel.org/gnu/binutils/binutils-${BINUTILS_VERSION}.tar.xz
     https://ftpmirror.gnu.org/gnu/binutils/binutils-${BINUTILS_VERSION}.tar.xz
     https://ftp.gnu.org/gnu/binutils/binutils-${BINUTILS_VERSION}.tar.xz)
 
 set(GDB_VERSION 15.2)
 set(GDB_HASH SHA256=83350ccd35b5b5a0cba6b334c41294ea968158c573940904f00b92f76345314d)
 set(GDB_URL
+    https://mirrors.kernel.org/gnu/gdb/gdb-${GDB_VERSION}.tar.xz
     https://ftpmirror.gnu.org/gnu/gdb/gdb-${GDB_VERSION}.tar.xz
     https://ftp.gnu.org/gnu/gdb/gdb-${GDB_VERSION}.tar.xz)
 

tests/cmake/gnu-download-mirror.cmake

@@ -16,14 +16,22 @@ include("${repository_root}/cmake/Components.cmake")
 foreach(component GCC GMP MPFR MPC BINUTILS GDB)
     set(urls "${${component}_URL}")
     list(LENGTH urls count)
-    if(count LESS 2)
+    if(count LESS 3)
         message(SEND_ERROR
-            "FAIL: ${component}_URL names one host; an outage there is a failed build")
+            "FAIL: ${component}_URL names ${count} host(s); two outages in a row is a "
+            "failed build, and both happened on 27 August")
     endif()
+    # ftp.gnu.org is the one that went down, so it is the last resort and not
+    # the first thing tried.
     list(GET urls 0 first)
-    if(NOT first MATCHES "^https://ftpmirror\\.gnu\\.org/")
+    if(first MATCHES "^https://ftp\\.gnu\\.org/")
         message(SEND_ERROR
-            "FAIL: ${component}_URL does not try GNU's mirror redirector first: ${first}")
+            "FAIL: ${component}_URL tries ftp.gnu.org first")
+    endif()
+    list(GET urls -1 last)
+    if(NOT last MATCHES "^https://ftp\\.gnu\\.org/")
+        message(SEND_ERROR
+            "FAIL: ${component}_URL does not keep ftp.gnu.org as the last resort: ${last}")
     endif()
     # And the hash, without which a mirror is somebody else's word for it.
     if(NOT DEFINED ${component}_HASH)